Rollup merge of #123409 - ZhuUx:master, r=oli-obk

Implement Modified Condition/Decision  Coverage

This is an implementation based on llvm backend support (>= 18) by `@evodius96` and branch coverage support by `@Zalathar.`

### Major changes:

* Add -Zcoverage-options=mcdc as switch. Now coverage options accept either `no-branch`, `branch`, or `mcdc`. `mcdc` also enables `branch` because it is essential to work.
* Add coverage mapping for MCDCBranch and MCDCDecision. Note that MCDCParameter evolves from  llvm 18 to llvm 19. The mapping in rust side mainly references to 19 and is casted to 18 types in llvm wrapper.
* Add wrapper for mcdc instrinc functions from llvm. And inject associated statements to mir.
* Add BcbMappingKind::Decision, I'm not sure is it proper but can't find a better way temporarily.
* Let coverage-dump support parsing MCDCBranch and MCDCDecision from llvm ir.
* Add simple tests to check whether mcdc works.
* Same as clang, currently rustc does not generate instrument for decision with more than 6 condtions or only 1 condition due to considerations of resource.

### Implementation Details

1. To get information about conditions and decisions, `MCDCState` in `BranchInfoBuilder` is used during hir lowering to mir. For expressions with logical op we call `Builder::visit_coverage_branch_operation` to record its sub conditions, generate condition ids for them and save their spans (to construct the span of whole decision). This process mainly references to the implementation in clang and is described in comments over `MCDCState::record_conditions`. Also true marks and false marks introduced by branch coverage are used to detect where the decision evaluation ends: the next id  of the condition == 0.
2. Once the `MCDCState::decision_stack` popped all recorded conditions, we can ensure that the decision is checked over and push it into `decision_spans`. We do not manually insert decision span to avoid complexity from then_else_break in nested if scopes.
3. When constructing CoverageSpans, add condition info to BcbMappingKind::Branch and decision info to BcbMappingKind::Decision. If the branch mapping has non-zero condition id it will be transformed to MCDCBranch mapping and insert `CondBitmapUpdate` statements to its evaluated blocks. While decision bcb mapping will insert `TestVectorBitmapUpdate` in all its end blocks.

### Usage
```bash
 echo "[build]\nprofiler=true" >> config.toml
./x build --stage 1
./x test tests/coverage/mcdc_if.rs
```
to build the compiler and run tests.

```shell
export PATH=path/to/llvm-build:$PATH
rustup toolchain link mcdc build/host/stage1
cargo +mcdc rustc --bin foo -- -Cinstrument-coverage -Zcoverage-options=mcdc
cd target/debug
LLVM_PROFILE_FILE="foo.profraw" ./foo
llvm-profdata merge -sparse foo.profraw -o foo.profdata
llvm-cov show ./foo -instr-profile=foo.profdata --show-mcdc
```
to check "foo" code.

### Problems to solve

For now decision mapping will insert statements to its all end blocks, which may be optimized by inserting a final block of the decision. To do this we must also trace the evaluated value at each end of the decision and join them separately.

This implementation is not heavily tested so there should be some unrevealed issues. We are going to check our rust products in the next.  Please let me know if you had any suggestions or comments.

29 files changed, 1642 insertions, 59 deletions

diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index 160f361b9b5..4c2bdb2f5ec 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -17,7 +17,7 @@ use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_hir::def_id::DefId;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
 use rustc_middle::ty::layout::{
-    FnAbiError, FnAbiOfHelpers, FnAbiRequest, LayoutError, LayoutOfHelpers, TyAndLayout,
+    FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasTyCtxt, LayoutError, LayoutOfHelpers, TyAndLayout,
 };
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
 use rustc_sanitizers::{cfi, kcfi};
@@ -1702,4 +1702,128 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
         };
         kcfi_bundle
     }
+
+    pub(crate) fn mcdc_parameters(
+        &mut self,
+        fn_name: &'ll Value,
+        hash: &'ll Value,
+        bitmap_bytes: &'ll Value,
+    ) -> &'ll Value {
+        debug!("mcdc_parameters() with args ({:?}, {:?}, {:?})", fn_name, hash, bitmap_bytes);
+
+        assert!(llvm_util::get_version() >= (18, 0, 0), "MCDC intrinsics require LLVM 18 or later");
+
+        let llfn = unsafe { llvm::LLVMRustGetInstrProfMCDCParametersIntrinsic(self.cx().llmod) };
+        let llty = self.cx.type_func(
+            &[self.cx.type_ptr(), self.cx.type_i64(), self.cx.type_i32()],
+            self.cx.type_void(),
+        );
+        let args = &[fn_name, hash, bitmap_bytes];
+        let args = self.check_call("call", llty, llfn, args);
+
+        unsafe {
+            let _ = llvm::LLVMRustBuildCall(
+                self.llbuilder,
+                llty,
+                llfn,
+                args.as_ptr() as *const &llvm::Value,
+                args.len() as c_uint,
+                [].as_ptr(),
+                0 as c_uint,
+            );
+            // Create condition bitmap named `mcdc.addr`.
+            let mut bx = Builder::with_cx(self.cx);
+            bx.position_at_start(llvm::LLVMGetFirstBasicBlock(self.llfn()));
+            let cond_bitmap = {
+                let alloca =
+                    llvm::LLVMBuildAlloca(bx.llbuilder, bx.cx.type_i32(), c"mcdc.addr".as_ptr());
+                llvm::LLVMSetAlignment(alloca, 4);
+                alloca
+            };
+            bx.store(self.const_i32(0), cond_bitmap, self.tcx().data_layout.i32_align.abi);
+            cond_bitmap
+        }
+    }
+
+    pub(crate) fn mcdc_tvbitmap_update(
+        &mut self,
+        fn_name: &'ll Value,
+        hash: &'ll Value,
+        bitmap_bytes: &'ll Value,
+        bitmap_index: &'ll Value,
+        mcdc_temp: &'ll Value,
+    ) {
+        debug!(
+            "mcdc_tvbitmap_update() with args ({:?}, {:?}, {:?}, {:?}, {:?})",
+            fn_name, hash, bitmap_bytes, bitmap_index, mcdc_temp
+        );
+        assert!(llvm_util::get_version() >= (18, 0, 0), "MCDC intrinsics require LLVM 18 or later");
+
+        let llfn =
+            unsafe { llvm::LLVMRustGetInstrProfMCDCTVBitmapUpdateIntrinsic(self.cx().llmod) };
+        let llty = self.cx.type_func(
+            &[
+                self.cx.type_ptr(),
+                self.cx.type_i64(),
+                self.cx.type_i32(),
+                self.cx.type_i32(),
+                self.cx.type_ptr(),
+            ],
+            self.cx.type_void(),
+        );
+        let args = &[fn_name, hash, bitmap_bytes, bitmap_index, mcdc_temp];
+        let args = self.check_call("call", llty, llfn, args);
+        unsafe {
+            let _ = llvm::LLVMRustBuildCall(
+                self.llbuilder,
+                llty,
+                llfn,
+                args.as_ptr() as *const &llvm::Value,
+                args.len() as c_uint,
+                [].as_ptr(),
+                0 as c_uint,
+            );
+        }
+        let i32_align = self.tcx().data_layout.i32_align.abi;
+        self.store(self.const_i32(0), mcdc_temp, i32_align);
+    }
+
+    pub(crate) fn mcdc_condbitmap_update(
+        &mut self,
+        fn_name: &'ll Value,
+        hash: &'ll Value,
+        cond_loc: &'ll Value,
+        mcdc_temp: &'ll Value,
+        bool_value: &'ll Value,
+    ) {
+        debug!(
+            "mcdc_condbitmap_update() with args ({:?}, {:?}, {:?}, {:?}, {:?})",
+            fn_name, hash, cond_loc, mcdc_temp, bool_value
+        );
+        assert!(llvm_util::get_version() >= (18, 0, 0), "MCDC intrinsics require LLVM 18 or later");
+        let llfn = unsafe { llvm::LLVMRustGetInstrProfMCDCCondBitmapIntrinsic(self.cx().llmod) };
+        let llty = self.cx.type_func(
+            &[
+                self.cx.type_ptr(),
+                self.cx.type_i64(),
+                self.cx.type_i32(),
+                self.cx.type_ptr(),
+                self.cx.type_i1(),
+            ],
+            self.cx.type_void(),
+        );
+        let args = &[fn_name, hash, cond_loc, mcdc_temp, bool_value];
+        self.check_call("call", llty, llfn, args);
+        unsafe {
+            let _ = llvm::LLVMRustBuildCall(
+                self.llbuilder,
+                llty,
+                llfn,
+                args.as_ptr() as *const &llvm::Value,
+                args.len() as c_uint,
+                [].as_ptr(),
+                0 as c_uint,
+            );
+        }
+    }
 }
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs
index 2af28146a51..12a846a49ec 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs
@@ -1,4 +1,6 @@
-use rustc_middle::mir::coverage::{CodeRegion, CounterId, CovTerm, ExpressionId, MappingKind};
+use rustc_middle::mir::coverage::{
+    CodeRegion, ConditionInfo, CounterId, CovTerm, DecisionInfo, ExpressionId, MappingKind,
+};
 
 /// Must match the layout of `LLVMRustCounterKind`.
 #[derive(Copy, Clone, Debug)]
@@ -99,6 +101,86 @@ pub enum RegionKind {
     /// associated with two counters, each representing the number of times the
     /// expression evaluates to true or false.
     BranchRegion = 4,
+
+    /// A DecisionRegion represents a top-level boolean expression and is
+    /// associated with a variable length bitmap index and condition number.
+    MCDCDecisionRegion = 5,
+
+    /// A Branch Region can be extended to include IDs to facilitate MC/DC.
+    MCDCBranchRegion = 6,
+}
+
+pub mod mcdc {
+    use rustc_middle::mir::coverage::{ConditionInfo, DecisionInfo};
+
+    /// Must match the layout of `LLVMRustMCDCDecisionParameters`.
+    #[repr(C)]
+    #[derive(Clone, Copy, Debug, Default)]
+    pub struct DecisionParameters {
+        bitmap_idx: u32,
+        conditions_num: u16,
+    }
+
+    // ConditionId in llvm is `unsigned int` at 18 while `int16_t` at [19](https://github.com/llvm/llvm-project/pull/81257)
+    type LLVMConditionId = i16;
+
+    /// Must match the layout of `LLVMRustMCDCBranchParameters`.
+    #[repr(C)]
+    #[derive(Clone, Copy, Debug, Default)]
+    pub struct BranchParameters {
+        condition_id: LLVMConditionId,
+        condition_ids: [LLVMConditionId; 2],
+    }
+
+    #[repr(C)]
+    #[derive(Clone, Copy, Debug)]
+    pub enum ParameterTag {
+        None = 0,
+        Decision = 1,
+        Branch = 2,
+    }
+    /// Same layout with `LLVMRustMCDCParameters`
+    #[repr(C)]
+    #[derive(Clone, Copy, Debug)]
+    pub struct Parameters {
+        tag: ParameterTag,
+        decision_params: DecisionParameters,
+        branch_params: BranchParameters,
+    }
+
+    impl Parameters {
+        pub fn none() -> Self {
+            Self {
+                tag: ParameterTag::None,
+                decision_params: Default::default(),
+                branch_params: Default::default(),
+            }
+        }
+        pub fn decision(decision_params: DecisionParameters) -> Self {
+            Self { tag: ParameterTag::Decision, decision_params, branch_params: Default::default() }
+        }
+        pub fn branch(branch_params: BranchParameters) -> Self {
+            Self { tag: ParameterTag::Branch, decision_params: Default::default(), branch_params }
+        }
+    }
+
+    impl From<ConditionInfo> for BranchParameters {
+        fn from(value: ConditionInfo) -> Self {
+            Self {
+                condition_id: value.condition_id.as_u32() as LLVMConditionId,
+                condition_ids: [
+                    value.false_next_id.as_u32() as LLVMConditionId,
+                    value.true_next_id.as_u32() as LLVMConditionId,
+                ],
+            }
+        }
+    }
+
+    impl From<DecisionInfo> for DecisionParameters {
+        fn from(value: DecisionInfo) -> Self {
+            Self { bitmap_idx: value.bitmap_idx, conditions_num: value.conditions_num }
+        }
+    }
 }
 
 /// This struct provides LLVM's representation of a "CoverageMappingRegion", encoded into the
@@ -122,6 +204,7 @@ pub struct CounterMappingRegion {
     /// for the false branch of the region.
     false_counter: Counter,
 
+    mcdc_params: mcdc::Parameters,
     /// An indirect reference to the source filename. In the LLVM Coverage Mapping Format, the
     /// file_id is an index into a function-specific `virtual_file_mapping` array of indexes
     /// that, in turn, are used to look up the filename for this region.
@@ -173,6 +256,26 @@ impl CounterMappingRegion {
                 end_line,
                 end_col,
             ),
+            MappingKind::MCDCBranch { true_term, false_term, mcdc_params } => {
+                Self::mcdc_branch_region(
+                    Counter::from_term(true_term),
+                    Counter::from_term(false_term),
+                    mcdc_params,
+                    local_file_id,
+                    start_line,
+                    start_col,
+                    end_line,
+                    end_col,
+                )
+            }
+            MappingKind::MCDCDecision(decision_info) => Self::decision_region(
+                decision_info,
+                local_file_id,
+                start_line,
+                start_col,
+                end_line,
+                end_col,
+            ),
         }
     }
 
@@ -187,6 +290,7 @@ impl CounterMappingRegion {
         Self {
             counter,
             false_counter: Counter::ZERO,
+            mcdc_params: mcdc::Parameters::none(),
             file_id,
             expanded_file_id: 0,
             start_line,
@@ -209,6 +313,7 @@ impl CounterMappingRegion {
         Self {
             counter,
             false_counter,
+            mcdc_params: mcdc::Parameters::none(),
             file_id,
             expanded_file_id: 0,
             start_line,
@@ -219,6 +324,54 @@ impl CounterMappingRegion {
         }
     }
 
+    pub(crate) fn mcdc_branch_region(
+        counter: Counter,
+        false_counter: Counter,
+        condition_info: ConditionInfo,
+        file_id: u32,
+        start_line: u32,
+        start_col: u32,
+        end_line: u32,
+        end_col: u32,
+    ) -> Self {
+        Self {
+            counter,
+            false_counter,
+            mcdc_params: mcdc::Parameters::branch(condition_info.into()),
+            file_id,
+            expanded_file_id: 0,
+            start_line,
+            start_col,
+            end_line,
+            end_col,
+            kind: RegionKind::MCDCBranchRegion,
+        }
+    }
+
+    pub(crate) fn decision_region(
+        decision_info: DecisionInfo,
+        file_id: u32,
+        start_line: u32,
+        start_col: u32,
+        end_line: u32,
+        end_col: u32,
+    ) -> Self {
+        let mcdc_params = mcdc::Parameters::decision(decision_info.into());
+
+        Self {
+            counter: Counter::ZERO,
+            false_counter: Counter::ZERO,
+            mcdc_params,
+            file_id,
+            expanded_file_id: 0,
+            start_line,
+            start_col,
+            end_line,
+            end_col,
+            kind: RegionKind::MCDCDecisionRegion,
+        }
+    }
+
     // This function might be used in the future; the LLVM API is still evolving, as is coverage
     // support.
     #[allow(dead_code)]
@@ -233,6 +386,7 @@ impl CounterMappingRegion {
         Self {
             counter: Counter::ZERO,
             false_counter: Counter::ZERO,
+            mcdc_params: mcdc::Parameters::none(),
             file_id,
             expanded_file_id,
             start_line,
@@ -256,6 +410,7 @@ impl CounterMappingRegion {
         Self {
             counter: Counter::ZERO,
             false_counter: Counter::ZERO,
+            mcdc_params: mcdc::Parameters::none(),
             file_id,
             expanded_file_id: 0,
             start_line,
@@ -280,6 +435,7 @@ impl CounterMappingRegion {
         Self {
             counter,
             false_counter: Counter::ZERO,
+            mcdc_params: mcdc::Parameters::none(),
             file_id,
             expanded_file_id: 0,
             start_line,
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
index 140566e8da9..085ce15d81f 100644
--- a/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs
@@ -13,7 +13,7 @@ use rustc_codegen_ssa::traits::{
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_llvm::RustString;
 use rustc_middle::bug;
-use rustc_middle::mir::coverage::CoverageKind;
+use rustc_middle::mir::coverage::{CoverageKind, FunctionCoverageInfo};
 use rustc_middle::ty::layout::HasTyCtxt;
 use rustc_middle::ty::Instance;
 use rustc_target::abi::Align;
@@ -30,6 +30,7 @@ pub struct CrateCoverageContext<'ll, 'tcx> {
     pub(crate) function_coverage_map:
         RefCell<FxIndexMap<Instance<'tcx>, FunctionCoverageCollector<'tcx>>>,
     pub(crate) pgo_func_name_var_map: RefCell<FxHashMap<Instance<'tcx>, &'ll llvm::Value>>,
+    pub(crate) mcdc_condition_bitmap_map: RefCell<FxHashMap<Instance<'tcx>, &'ll llvm::Value>>,
 }
 
 impl<'ll, 'tcx> CrateCoverageContext<'ll, 'tcx> {
@@ -37,6 +38,7 @@ impl<'ll, 'tcx> CrateCoverageContext<'ll, 'tcx> {
         Self {
             function_coverage_map: Default::default(),
             pgo_func_name_var_map: Default::default(),
+            mcdc_condition_bitmap_map: Default::default(),
         }
     }
 
@@ -45,6 +47,12 @@ impl<'ll, 'tcx> CrateCoverageContext<'ll, 'tcx> {
     ) -> FxIndexMap<Instance<'tcx>, FunctionCoverageCollector<'tcx>> {
         self.function_coverage_map.replace(FxIndexMap::default())
     }
+
+    /// LLVM use a temp value to record evaluated mcdc test vector of each decision, which is called condition bitmap.
+    /// This value is named `mcdc.addr` (same as clang) and is a 32-bit integer.
+    fn try_get_mcdc_condition_bitmap(&self, instance: &Instance<'tcx>) -> Option<&'ll llvm::Value> {
+        self.mcdc_condition_bitmap_map.borrow().get(instance).copied()
+    }
 }
 
 // These methods used to be part of trait `CoverageInfoMethods`, which no longer
@@ -90,6 +98,10 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
             return;
         };
 
+        if function_coverage_info.mcdc_bitmap_bytes > 0 {
+            ensure_mcdc_parameters(bx, instance, function_coverage_info);
+        }
+
         let Some(coverage_context) = bx.coverage_context() else { return };
         let mut coverage_map = coverage_context.function_coverage_map.borrow_mut();
         let func_coverage = coverage_map
@@ -131,10 +143,66 @@ impl<'tcx> CoverageInfoBuilderMethods<'tcx> for Builder<'_, '_, 'tcx> {
             CoverageKind::ExpressionUsed { id } => {
                 func_coverage.mark_expression_id_seen(id);
             }
+            CoverageKind::CondBitmapUpdate { id, value, .. } => {
+                drop(coverage_map);
+                assert_ne!(
+                    id.as_u32(),
+                    0,
+                    "ConditionId of evaluated conditions should never be zero"
+                );
+                let cond_bitmap = coverage_context
+                    .try_get_mcdc_condition_bitmap(&instance)
+                    .expect("mcdc cond bitmap should have been allocated for updating");
+                let cond_loc = bx.const_i32(id.as_u32() as i32 - 1);
+                let bool_value = bx.const_bool(value);
+                let fn_name = bx.get_pgo_func_name_var(instance);
+                let hash = bx.const_u64(function_coverage_info.function_source_hash);
+                bx.mcdc_condbitmap_update(fn_name, hash, cond_loc, cond_bitmap, bool_value);
+            }
+            CoverageKind::TestVectorBitmapUpdate { bitmap_idx } => {
+                drop(coverage_map);
+                let cond_bitmap = coverage_context
+                                    .try_get_mcdc_condition_bitmap(&instance)
+                                    .expect("mcdc cond bitmap should have been allocated for merging into the global bitmap");
+                let bitmap_bytes = bx.tcx().coverage_ids_info(instance.def).mcdc_bitmap_bytes;
+                assert!(bitmap_idx < bitmap_bytes, "bitmap index of the decision out of range");
+                assert!(
+                    bitmap_bytes <= function_coverage_info.mcdc_bitmap_bytes,
+                    "bitmap length disagreement: query says {bitmap_bytes} but function info only has {}",
+                    function_coverage_info.mcdc_bitmap_bytes
+                );
+
+                let fn_name = bx.get_pgo_func_name_var(instance);
+                let hash = bx.const_u64(function_coverage_info.function_source_hash);
+                let bitmap_bytes = bx.const_u32(bitmap_bytes);
+                let bitmap_index = bx.const_u32(bitmap_idx);
+                bx.mcdc_tvbitmap_update(fn_name, hash, bitmap_bytes, bitmap_index, cond_bitmap);
+            }
         }
     }
 }
 
+fn ensure_mcdc_parameters<'ll, 'tcx>(
+    bx: &mut Builder<'_, 'll, 'tcx>,
+    instance: Instance<'tcx>,
+    function_coverage_info: &FunctionCoverageInfo,
+) {
+    let Some(cx) = bx.coverage_context() else { return };
+    if cx.mcdc_condition_bitmap_map.borrow().contains_key(&instance) {
+        return;
+    }
+
+    let fn_name = bx.get_pgo_func_name_var(instance);
+    let hash = bx.const_u64(function_coverage_info.function_source_hash);
+    let bitmap_bytes = bx.const_u32(function_coverage_info.mcdc_bitmap_bytes);
+    let cond_bitmap = bx.mcdc_parameters(fn_name, hash, bitmap_bytes);
+    bx.coverage_context()
+        .expect("already checked above")
+        .mcdc_condition_bitmap_map
+        .borrow_mut()
+        .insert(instance, cond_bitmap);
+}
+
 /// Calls llvm::createPGOFuncNameVar() with the given function instance's
 /// mangled function name. The LLVM API returns an llvm::GlobalVariable
 /// containing the function name, with the specific variable name and linkage
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 83158f6f1d5..a10dc61967e 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -1631,6 +1631,10 @@ extern "C" {
 
     // Miscellaneous instructions
     pub fn LLVMRustGetInstrProfIncrementIntrinsic(M: &Module) -> &Value;
+    pub fn LLVMRustGetInstrProfMCDCParametersIntrinsic(M: &Module) -> &Value;
+    pub fn LLVMRustGetInstrProfMCDCTVBitmapUpdateIntrinsic(M: &Module) -> &Value;
+    pub fn LLVMRustGetInstrProfMCDCCondBitmapIntrinsic(M: &Module) -> &Value;
+
     pub fn LLVMRustBuildCall<'a>(
         B: &Builder<'a>,
         Ty: &'a Type,
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 9d53f0799ea..8d741ef4c1b 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -760,7 +760,7 @@ fn test_unstable_options_tracking_hash() {
     );
     tracked!(codegen_backend, Some("abc".to_string()));
     tracked!(collapse_macro_debuginfo, CollapseMacroDebuginfo::Yes);
-    tracked!(coverage_options, CoverageOptions { branch: true });
+    tracked!(coverage_options, CoverageOptions { branch: true, mcdc: true });
     tracked!(crate_attr, vec!["abc".to_string()]);
     tracked!(cross_crate_inline_threshold, InliningThreshold::Always);
     tracked!(debug_info_for_profiling, true);
diff --git a/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp
index 0998b463a88..e842f47f48c 100644
--- a/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/CoverageMappingWrapper.cpp
@@ -4,8 +4,6 @@
 #include "llvm/ProfileData/Coverage/CoverageMappingWriter.h"
 #include "llvm/ProfileData/InstrProf.h"
 
-#include <iostream>
-
 using namespace llvm;
 
 // FFI equivalent of enum `llvm::coverage::Counter::CounterKind`
@@ -43,6 +41,8 @@ enum class LLVMRustCounterMappingRegionKind {
   SkippedRegion = 2,
   GapRegion = 3,
   BranchRegion = 4,
+  MCDCDecisionRegion = 5,
+  MCDCBranchRegion = 6
 };
 
 static coverage::CounterMappingRegion::RegionKind
@@ -58,15 +58,102 @@ fromRust(LLVMRustCounterMappingRegionKind Kind) {
     return coverage::CounterMappingRegion::GapRegion;
   case LLVMRustCounterMappingRegionKind::BranchRegion:
     return coverage::CounterMappingRegion::BranchRegion;
+#if LLVM_VERSION_GE(18, 0)
+  case LLVMRustCounterMappingRegionKind::MCDCDecisionRegion:
+    return coverage::CounterMappingRegion::MCDCDecisionRegion;
+  case LLVMRustCounterMappingRegionKind::MCDCBranchRegion:
+    return coverage::CounterMappingRegion::MCDCBranchRegion;
+#else
+  case LLVMRustCounterMappingRegionKind::MCDCDecisionRegion:
+    break;
+  case LLVMRustCounterMappingRegionKind::MCDCBranchRegion:
+    break;
+#endif
   }
   report_fatal_error("Bad LLVMRustCounterMappingRegionKind!");
 }
 
+enum LLVMRustMCDCParametersTag {
+  None = 0,
+  Decision = 1,
+  Branch = 2,
+};
+
+struct LLVMRustMCDCDecisionParameters {
+  uint32_t BitmapIdx;
+  uint16_t NumConditions;
+};
+
+struct LLVMRustMCDCBranchParameters {
+  int16_t ConditionID;
+  int16_t ConditionIDs[2];
+};
+
+struct LLVMRustMCDCParameters {
+  LLVMRustMCDCParametersTag Tag;
+  LLVMRustMCDCDecisionParameters DecisionParameters;
+  LLVMRustMCDCBranchParameters BranchParameters;
+};
+
+// LLVM representations for `MCDCParameters` evolved from LLVM 18 to 19.
+// Look at representations in 18
+// https://github.com/rust-lang/llvm-project/blob/66a2881a/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h#L253-L263
+// and representations in 19
+// https://github.com/llvm/llvm-project/blob/843cc474faefad1d639f4c44c1cf3ad7dbda76c8/llvm/include/llvm/ProfileData/Coverage/MCDCTypes.h
+#if LLVM_VERSION_GE(18, 0) && LLVM_VERSION_LT(19, 0)
+static coverage::CounterMappingRegion::MCDCParameters
+fromRust(LLVMRustMCDCParameters Params) {
+  auto parameter = coverage::CounterMappingRegion::MCDCParameters{};
+  switch (Params.Tag) {
+  case LLVMRustMCDCParametersTag::None:
+    return parameter;
+  case LLVMRustMCDCParametersTag::Decision:
+    parameter.BitmapIdx =
+        static_cast<unsigned>(Params.DecisionParameters.BitmapIdx),
+    parameter.NumConditions =
+        static_cast<unsigned>(Params.DecisionParameters.NumConditions);
+    return parameter;
+  case LLVMRustMCDCParametersTag::Branch:
+    parameter.ID = static_cast<coverage::CounterMappingRegion::MCDCConditionID>(
+        Params.BranchParameters.ConditionID),
+    parameter.FalseID =
+        static_cast<coverage::CounterMappingRegion::MCDCConditionID>(
+            Params.BranchParameters.ConditionIDs[0]),
+    parameter.TrueID =
+        static_cast<coverage::CounterMappingRegion::MCDCConditionID>(
+            Params.BranchParameters.ConditionIDs[1]);
+    return parameter;
+  }
+  report_fatal_error("Bad LLVMRustMCDCParametersTag!");
+}
+#elif LLVM_VERSION_GE(19, 0)
+static coverage::mcdc::Parameters fromRust(LLVMRustMCDCParameters Params) {
+  switch (Params.Tag) {
+  case LLVMRustMCDCParametersTag::None:
+    return std::monostate();
+  case LLVMRustMCDCParametersTag::Decision:
+    return coverage::mcdc::DecisionParameters(
+        Params.DecisionParameters.BitmapIdx,
+        Params.DecisionParameters.NumConditions);
+  case LLVMRustMCDCParametersTag::Branch:
+    return coverage::mcdc::BranchParameters(
+        static_cast<coverage::mcdc::ConditionID>(
+            Params.BranchParameters.ConditionID),
+        {static_cast<coverage::mcdc::ConditionID>(
+             Params.BranchParameters.ConditionIDs[0]),
+         static_cast<coverage::mcdc::ConditionID>(
+             Params.BranchParameters.ConditionIDs[1])});
+  }
+  report_fatal_error("Bad LLVMRustMCDCParametersTag!");
+}
+#endif
+
 // FFI equivalent of struct `llvm::coverage::CounterMappingRegion`
 // https://github.com/rust-lang/llvm-project/blob/ea6fa9c2/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h#L211-L304
 struct LLVMRustCounterMappingRegion {
   LLVMRustCounter Count;
   LLVMRustCounter FalseCount;
+  LLVMRustMCDCParameters MCDCParameters;
   uint32_t FileID;
   uint32_t ExpandedFileID;
   uint32_t LineStart;
@@ -135,7 +222,8 @@ extern "C" void LLVMRustCoverageWriteMappingToBuffer(
     MappingRegions.emplace_back(
         fromRust(Region.Count), fromRust(Region.FalseCount),
 #if LLVM_VERSION_GE(18, 0) && LLVM_VERSION_LT(19, 0)
-        coverage::CounterMappingRegion::MCDCParameters{},
+        // LLVM 19 may move this argument to last.
+        fromRust(Region.MCDCParameters),
 #endif
         Region.FileID, Region.ExpandedFileID, // File IDs, then region info.
         Region.LineStart, Region.ColumnStart, Region.LineEnd, Region.ColumnEnd,
diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index 6e11fd629e4..2a9de499622 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
@@ -1546,6 +1546,33 @@ extern "C" LLVMValueRef LLVMRustGetInstrProfIncrementIntrinsic(LLVMModuleRef M)
       unwrap(M), llvm::Intrinsic::instrprof_increment));
 }
 
+extern "C" LLVMValueRef LLVMRustGetInstrProfMCDCParametersIntrinsic(LLVMModuleRef M) {
+#if LLVM_VERSION_GE(18, 0)
+  return wrap(llvm::Intrinsic::getDeclaration(
+      unwrap(M), llvm::Intrinsic::instrprof_mcdc_parameters));
+#else
+  report_fatal_error("LLVM 18.0 is required for mcdc intrinsic functions");
+#endif
+}
+
+extern "C" LLVMValueRef LLVMRustGetInstrProfMCDCTVBitmapUpdateIntrinsic(LLVMModuleRef M) {
+#if LLVM_VERSION_GE(18, 0)
+  return wrap(llvm::Intrinsic::getDeclaration(
+      unwrap(M), llvm::Intrinsic::instrprof_mcdc_tvbitmap_update));
+#else
+  report_fatal_error("LLVM 18.0 is required for mcdc intrinsic functions");
+#endif
+}
+
+extern "C" LLVMValueRef LLVMRustGetInstrProfMCDCCondBitmapIntrinsic(LLVMModuleRef M) {
+#if LLVM_VERSION_GE(18, 0)
+  return wrap(llvm::Intrinsic::getDeclaration(
+      unwrap(M), llvm::Intrinsic::instrprof_mcdc_condbitmap_update));
+#else
+  report_fatal_error("LLVM 18.0 is required for mcdc intrinsic functions");
+#endif
+}
+
 extern "C" LLVMValueRef LLVMRustBuildMemCpy(LLVMBuilderRef B,
                                             LLVMValueRef Dst, unsigned DstAlign,
                                             LLVMValueRef Src, unsigned SrcAlign,
diff --git a/compiler/rustc_middle/src/mir/coverage.rs b/compiler/rustc_middle/src/mir/coverage.rs
index 582a1806688..b1d0c815ae0 100644
--- a/compiler/rustc_middle/src/mir/coverage.rs
+++ b/compiler/rustc_middle/src/mir/coverage.rs
@@ -51,6 +51,25 @@ rustc_index::newtype_index! {
     pub struct ExpressionId {}
 }
 
+rustc_index::newtype_index! {
+    /// ID of a mcdc condition. Used by llvm to check mcdc coverage.
+    ///
+    /// Note for future: the max limit of 0xFFFF is probably too loose. Actually llvm does not
+    /// support decisions with too many conditions (7 and more at LLVM 18 while may be hundreds at 19)
+    /// and represents it with `int16_t`. This max value may be changed once we could
+    /// figure out an accurate limit.
+    #[derive(HashStable)]
+    #[encodable]
+    #[orderable]
+    #[max = 0xFFFF]
+    #[debug_format = "ConditionId({})"]
+    pub struct ConditionId {}
+}
+
+impl ConditionId {
+    pub const NONE: Self = Self::from_u32(0);
+}
+
 /// Enum that can hold a constant zero value, the ID of an physical coverage
 /// counter, or the ID of a coverage-counter expression.
 ///
@@ -106,6 +125,22 @@ pub enum CoverageKind {
     /// mappings. Intermediate expressions with no direct mappings are
     /// retained/zeroed based on whether they are transitively used.)
     ExpressionUsed { id: ExpressionId },
+
+    /// Marks the point in MIR control flow represented by a evaluated condition.
+    ///
+    /// This is eventually lowered to `llvm.instrprof.mcdc.condbitmap.update` in LLVM IR.
+    ///
+    /// If this statement does not survive MIR optimizations, the condition would never be
+    /// taken as evaluated.
+    CondBitmapUpdate { id: ConditionId, value: bool },
+
+    /// Marks the point in MIR control flow represented by a evaluated decision.
+    ///
+    /// This is eventually lowered to `llvm.instrprof.mcdc.tvbitmap.update` in LLVM IR.
+    ///
+    /// If this statement does not survive MIR optimizations, the decision would never be
+    /// taken as evaluated.
+    TestVectorBitmapUpdate { bitmap_idx: u32 },
 }
 
 impl Debug for CoverageKind {
@@ -116,6 +151,12 @@ impl Debug for CoverageKind {
             BlockMarker { id } => write!(fmt, "BlockMarker({:?})", id.index()),
             CounterIncrement { id } => write!(fmt, "CounterIncrement({:?})", id.index()),
             ExpressionUsed { id } => write!(fmt, "ExpressionUsed({:?})", id.index()),
+            CondBitmapUpdate { id, value } => {
+                write!(fmt, "CondBitmapUpdate({:?}, {:?})", id.index(), value)
+            }
+            TestVectorBitmapUpdate { bitmap_idx } => {
+                write!(fmt, "TestVectorUpdate({:?})", bitmap_idx)
+            }
         }
     }
 }
@@ -172,16 +213,23 @@ pub enum MappingKind {
     Code(CovTerm),
     /// Associates a branch region with separate counters for true and false.
     Branch { true_term: CovTerm, false_term: CovTerm },
+    /// Associates a branch region with separate counters for true and false.
+    MCDCBranch { true_term: CovTerm, false_term: CovTerm, mcdc_params: ConditionInfo },
+    /// Associates a decision region with a bitmap and number of conditions.
+    MCDCDecision(DecisionInfo),
 }
 
 impl MappingKind {
     /// Iterator over all coverage terms in this mapping kind.
     pub fn terms(&self) -> impl Iterator<Item = CovTerm> {
-        let one = |a| std::iter::once(a).chain(None);
-        let two = |a, b| std::iter::once(a).chain(Some(b));
+        let zero = || None.into_iter().chain(None);
+        let one = |a| Some(a).into_iter().chain(None);
+        let two = |a, b| Some(a).into_iter().chain(Some(b));
         match *self {
             Self::Code(term) => one(term),
             Self::Branch { true_term, false_term } => two(true_term, false_term),
+            Self::MCDCBranch { true_term, false_term, .. } => two(true_term, false_term),
+            Self::MCDCDecision(_) => zero(),
         }
     }
 
@@ -193,6 +241,12 @@ impl MappingKind {
             Self::Branch { true_term, false_term } => {
                 Self::Branch { true_term: map_fn(true_term), false_term: map_fn(false_term) }
             }
+            Self::MCDCBranch { true_term, false_term, mcdc_params } => Self::MCDCBranch {
+                true_term: map_fn(true_term),
+                false_term: map_fn(false_term),
+                mcdc_params,
+            },
+            Self::MCDCDecision(param) => Self::MCDCDecision(param),
         }
     }
 }
@@ -212,7 +266,7 @@ pub struct Mapping {
 pub struct FunctionCoverageInfo {
     pub function_source_hash: u64,
     pub num_counters: usize,
-
+    pub mcdc_bitmap_bytes: u32,
     pub expressions: IndexVec<ExpressionId, Expression>,
     pub mappings: Vec<Mapping>,
 }
@@ -226,6 +280,8 @@ pub struct BranchInfo {
     /// data structures without having to scan the entire body first.
     pub num_block_markers: usize,
     pub branch_spans: Vec<BranchSpan>,
+    pub mcdc_branch_spans: Vec<MCDCBranchSpan>,
+    pub mcdc_decision_spans: Vec<MCDCDecisionSpan>,
 }
 
 #[derive(Clone, Debug)]
@@ -235,3 +291,45 @@ pub struct BranchSpan {
     pub true_marker: BlockMarkerId,
     pub false_marker: BlockMarkerId,
 }
+
+#[derive(Copy, Clone, Debug)]
+#[derive(TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
+pub struct ConditionInfo {
+    pub condition_id: ConditionId,
+    pub true_next_id: ConditionId,
+    pub false_next_id: ConditionId,
+}
+
+impl Default for ConditionInfo {
+    fn default() -> Self {
+        Self {
+            condition_id: ConditionId::NONE,
+            true_next_id: ConditionId::NONE,
+            false_next_id: ConditionId::NONE,
+        }
+    }
+}
+
+#[derive(Clone, Debug)]
+#[derive(TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
+pub struct MCDCBranchSpan {
+    pub span: Span,
+    pub condition_info: ConditionInfo,
+    pub true_marker: BlockMarkerId,
+    pub false_marker: BlockMarkerId,
+}
+
+#[derive(Copy, Clone, Debug)]
+#[derive(TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
+pub struct DecisionInfo {
+    pub bitmap_idx: u32,
+    pub conditions_num: u16,
+}
+
+#[derive(Clone, Debug)]
+#[derive(TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
+pub struct MCDCDecisionSpan {
+    pub span: Span,
+    pub conditions_num: usize,
+    pub end_markers: Vec<BlockMarkerId>,
+}
diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
index 15bd5c08965..a3cdcec9ec0 100644
--- a/compiler/rustc_middle/src/mir/pretty.rs
+++ b/compiler/rustc_middle/src/mir/pretty.rs
@@ -475,7 +475,8 @@ fn write_coverage_branch_info(
     branch_info: &coverage::BranchInfo,
     w: &mut dyn io::Write,
 ) -> io::Result<()> {
-    let coverage::BranchInfo { branch_spans, .. } = branch_info;
+    let coverage::BranchInfo { branch_spans, mcdc_branch_spans, mcdc_decision_spans, .. } =
+        branch_info;
 
     for coverage::BranchSpan { span, true_marker, false_marker } in branch_spans {
         writeln!(
@@ -483,7 +484,26 @@ fn write_coverage_branch_info(
             "{INDENT}coverage branch {{ true: {true_marker:?}, false: {false_marker:?} }} => {span:?}",
         )?;
     }
-    if !branch_spans.is_empty() {
+
+    for coverage::MCDCBranchSpan { span, condition_info, true_marker, false_marker } in
+        mcdc_branch_spans
+    {
+        writeln!(
+            w,
+            "{INDENT}coverage mcdc branch {{ condition_id: {:?}, true: {true_marker:?}, false: {false_marker:?} }} => {span:?}",
+            condition_info.condition_id
+        )?;
+    }
+
+    for coverage::MCDCDecisionSpan { span, conditions_num, end_markers } in mcdc_decision_spans {
+        writeln!(
+            w,
+            "{INDENT}coverage mcdc decision {{ conditions_num: {conditions_num:?}, end: {end_markers:?} }} => {span:?}"
+        )?;
+    }
+
+    if !branch_spans.is_empty() || !mcdc_branch_spans.is_empty() || !mcdc_decision_spans.is_empty()
+    {
         writeln!(w)?;
     }
 
diff --git a/compiler/rustc_middle/src/mir/query.rs b/compiler/rustc_middle/src/mir/query.rs
index 105f30f1db8..e3f58729fbd 100644
--- a/compiler/rustc_middle/src/mir/query.rs
+++ b/compiler/rustc_middle/src/mir/query.rs
@@ -361,4 +361,8 @@ pub struct CoverageIdsInfo {
     /// InstrumentCoverage MIR pass, if the highest-numbered counter increments
     /// were removed by MIR optimizations.
     pub max_counter_id: mir::coverage::CounterId,
+
+    /// Coverage codegen for mcdc needs to know the size of the global bitmap so that it can
+    /// set the `bytemap-bytes` argument of the `llvm.instrprof.mcdc.tvbitmap.update` intrinsic.
+    pub mcdc_bitmap_bytes: u32,
 }
diff --git a/compiler/rustc_middle/src/ty/structural_impls.rs b/compiler/rustc_middle/src/ty/structural_impls.rs
index 90c68e7ddfc..14a77d4b37e 100644
--- a/compiler/rustc_middle/src/ty/structural_impls.rs
+++ b/compiler/rustc_middle/src/ty/structural_impls.rs
@@ -427,6 +427,7 @@ TrivialTypeTraversalImpls! {
     crate::mir::coverage::BlockMarkerId,
     crate::mir::coverage::CounterId,
     crate::mir::coverage::ExpressionId,
+    crate::mir::coverage::ConditionId,
     crate::mir::Local,
     crate::mir::Promoted,
     crate::traits::Reveal,
diff --git a/compiler/rustc_mir_build/messages.ftl b/compiler/rustc_mir_build/messages.ftl
index 1de691f32a7..34440c60cf3 100644
--- a/compiler/rustc_mir_build/messages.ftl
+++ b/compiler/rustc_mir_build/messages.ftl
@@ -97,6 +97,8 @@ mir_build_deref_raw_pointer_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
     .note = raw pointers may be null, dangling or unaligned; they can violate aliasing rules and cause data races: all of these are undefined behavior
     .label = dereference of raw pointer
 
+mir_build_exceeds_mcdc_condition_num_limit =  Conditions number of the decision ({$conditions_num}) exceeds limit ({$max_conditions_num}). MCDC analysis will not count this expression.
+
 mir_build_extern_static_requires_unsafe =
     use of extern static is unsafe and requires unsafe block
     .note = extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
diff --git a/compiler/rustc_mir_build/src/build/coverageinfo.rs b/compiler/rustc_mir_build/src/build/coverageinfo.rs
index ab0043906b1..57f809ef7cf 100644
--- a/compiler/rustc_mir_build/src/build/coverageinfo.rs
+++ b/compiler/rustc_mir_build/src/build/coverageinfo.rs
@@ -1,14 +1,20 @@
 use std::assert_matches::assert_matches;
 use std::collections::hash_map::Entry;
+use std::collections::VecDeque;
 
 use rustc_data_structures::fx::FxHashMap;
-use rustc_middle::mir::coverage::{BlockMarkerId, BranchSpan, CoverageKind};
+use rustc_middle::mir::coverage::{
+    BlockMarkerId, BranchSpan, ConditionId, ConditionInfo, CoverageKind, MCDCBranchSpan,
+    MCDCDecisionSpan,
+};
 use rustc_middle::mir::{self, BasicBlock, UnOp};
-use rustc_middle::thir::{ExprId, ExprKind, Thir};
+use rustc_middle::thir::{ExprId, ExprKind, LogicalOp, Thir};
 use rustc_middle::ty::TyCtxt;
 use rustc_span::def_id::LocalDefId;
+use rustc_span::Span;
 
 use crate::build::Builder;
+use crate::errors::MCDCExceedsConditionNumLimit;
 
 pub(crate) struct BranchInfoBuilder {
     /// Maps condition expressions to their enclosing `!`, for better instrumentation.
@@ -16,6 +22,9 @@ pub(crate) struct BranchInfoBuilder {
 
     num_block_markers: usize,
     branch_spans: Vec<BranchSpan>,
+    mcdc_branch_spans: Vec<MCDCBranchSpan>,
+    mcdc_decision_spans: Vec<MCDCDecisionSpan>,
+    mcdc_state: Option<MCDCState>,
 }
 
 #[derive(Clone, Copy)]
@@ -33,7 +42,14 @@ impl BranchInfoBuilder {
     /// is enabled and `def_id` represents a function that is eligible for coverage.
     pub(crate) fn new_if_enabled(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<Self> {
         if tcx.sess.instrument_coverage_branch() && tcx.is_eligible_for_coverage(def_id) {
-            Some(Self { nots: FxHashMap::default(), num_block_markers: 0, branch_spans: vec![] })
+            Some(Self {
+                nots: FxHashMap::default(),
+                num_block_markers: 0,
+                branch_spans: vec![],
+                mcdc_branch_spans: vec![],
+                mcdc_decision_spans: vec![],
+                mcdc_state: MCDCState::new_if_enabled(tcx),
+            })
         } else {
             None
         }
@@ -79,6 +95,55 @@ impl BranchInfoBuilder {
         }
     }
 
+    fn record_conditions_operation(&mut self, logical_op: LogicalOp, span: Span) {
+        if let Some(mcdc_state) = self.mcdc_state.as_mut() {
+            mcdc_state.record_conditions(logical_op, span);
+        }
+    }
+
+    fn fetch_condition_info(
+        &mut self,
+        tcx: TyCtxt<'_>,
+        true_marker: BlockMarkerId,
+        false_marker: BlockMarkerId,
+    ) -> Option<ConditionInfo> {
+        let mcdc_state = self.mcdc_state.as_mut()?;
+        let (mut condition_info, decision_result) =
+            mcdc_state.take_condition(true_marker, false_marker);
+        if let Some(decision) = decision_result {
+            match decision.conditions_num {
+                0 => {
+                    unreachable!("Decision with no condition is not expected");
+                }
+                1..=MAX_CONDITIONS_NUM_IN_DECISION => {
+                    self.mcdc_decision_spans.push(decision);
+                }
+                _ => {
+                    // Do not generate mcdc mappings and statements for decisions with too many conditions.
+                    let rebase_idx = self.mcdc_branch_spans.len() - decision.conditions_num + 1;
+                    let to_normal_branches = self.mcdc_branch_spans.split_off(rebase_idx);
+                    self.branch_spans.extend(to_normal_branches.into_iter().map(
+                        |MCDCBranchSpan { span, true_marker, false_marker, .. }| BranchSpan {
+                            span,
+                            true_marker,
+                            false_marker,
+                        },
+                    ));
+
+                    // ConditionInfo of this branch shall also be reset.
+                    condition_info = None;
+
+                    tcx.dcx().emit_warn(MCDCExceedsConditionNumLimit {
+                        span: decision.span,
+                        conditions_num: decision.conditions_num,
+                        max_conditions_num: MAX_CONDITIONS_NUM_IN_DECISION,
+                    });
+                }
+            }
+        }
+        condition_info
+    }
+
     fn next_block_marker_id(&mut self) -> BlockMarkerId {
         let id = BlockMarkerId::from_usize(self.num_block_markers);
         self.num_block_markers += 1;
@@ -86,14 +151,167 @@ impl BranchInfoBuilder {
     }
 
     pub(crate) fn into_done(self) -> Option<Box<mir::coverage::BranchInfo>> {
-        let Self { nots: _, num_block_markers, branch_spans } = self;
+        let Self {
+            nots: _,
+            num_block_markers,
+            branch_spans,
+            mcdc_branch_spans,
+            mcdc_decision_spans,
+            ..
+        } = self;
 
         if num_block_markers == 0 {
             assert!(branch_spans.is_empty());
             return None;
         }
 
-        Some(Box::new(mir::coverage::BranchInfo { num_block_markers, branch_spans }))
+        Some(Box::new(mir::coverage::BranchInfo {
+            num_block_markers,
+            branch_spans,
+            mcdc_branch_spans,
+            mcdc_decision_spans,
+        }))
+    }
+}
+
+/// The MCDC bitmap scales exponentially (2^n) based on the number of conditions seen,
+/// So llvm sets a maximum value prevents the bitmap footprint from growing too large without the user's knowledge.
+/// This limit may be relaxed if the [upstream change](https://github.com/llvm/llvm-project/pull/82448) is merged.
+const MAX_CONDITIONS_NUM_IN_DECISION: usize = 6;
+
+struct MCDCState {
+    /// To construct condition evaluation tree.
+    decision_stack: VecDeque<ConditionInfo>,
+    processing_decision: Option<MCDCDecisionSpan>,
+}
+
+impl MCDCState {
+    fn new_if_enabled(tcx: TyCtxt<'_>) -> Option<Self> {
+        tcx.sess
+            .instrument_coverage_mcdc()
+            .then(|| Self { decision_stack: VecDeque::new(), processing_decision: None })
+    }
+
+    // At first we assign ConditionIds for each sub expression.
+    // If the sub expression is composite, re-assign its ConditionId to its LHS and generate a new ConditionId for its RHS.
+    //
+    // Example: "x = (A && B) || (C && D) || (D && F)"
+    //
+    //      Visit Depth1:
+    //              (A && B) || (C && D) || (D && F)
+    //              ^-------LHS--------^    ^-RHS--^
+    //                      ID=1              ID=2
+    //
+    //      Visit LHS-Depth2:
+    //              (A && B) || (C && D)
+    //              ^-LHS--^    ^-RHS--^
+    //                ID=1        ID=3
+    //
+    //      Visit LHS-Depth3:
+    //               (A && B)
+    //               LHS   RHS
+    //               ID=1  ID=4
+    //
+    //      Visit RHS-Depth3:
+    //                         (C && D)
+    //                         LHS   RHS
+    //                         ID=3  ID=5
+    //
+    //      Visit RHS-Depth2:              (D && F)
+    //                                     LHS   RHS
+    //                                     ID=2  ID=6
+    //
+    //      Visit Depth1:
+    //              (A && B)  || (C && D)  || (D && F)
+    //              ID=1  ID=4   ID=3  ID=5   ID=2  ID=6
+    //
+    // A node ID of '0' always means MC/DC isn't being tracked.
+    //
+    // If a "next" node ID is '0', it means it's the end of the test vector.
+    //
+    // As the compiler tracks expression in pre-order, we can ensure that condition info of parents are always properly assigned when their children are visited.
+    // - If the op is AND, the "false_next" of LHS and RHS should be the parent's "false_next". While "true_next" of the LHS is the RHS, the "true next" of RHS is the parent's "true_next".
+    // - If the op is OR, the "true_next" of LHS and RHS should be the parent's "true_next". While "false_next" of the LHS is the RHS, the "false next" of RHS is the parent's "false_next".
+    fn record_conditions(&mut self, op: LogicalOp, span: Span) {
+        let decision = match self.processing_decision.as_mut() {
+            Some(decision) => {
+                decision.span = decision.span.to(span);
+                decision
+            }
+            None => self.processing_decision.insert(MCDCDecisionSpan {
+                span,
+                conditions_num: 0,
+                end_markers: vec![],
+            }),
+        };
+
+        let parent_condition = self.decision_stack.pop_back().unwrap_or_default();
+        let lhs_id = if parent_condition.condition_id == ConditionId::NONE {
+            decision.conditions_num += 1;
+            ConditionId::from(decision.conditions_num)
+        } else {
+            parent_condition.condition_id
+        };
+
+        decision.conditions_num += 1;
+        let rhs_condition_id = ConditionId::from(decision.conditions_num);
+
+        let (lhs, rhs) = match op {
+            LogicalOp::And => {
+                let lhs = ConditionInfo {
+                    condition_id: lhs_id,
+                    true_next_id: rhs_condition_id,
+                    false_next_id: parent_condition.false_next_id,
+                };
+                let rhs = ConditionInfo {
+                    condition_id: rhs_condition_id,
+                    true_next_id: parent_condition.true_next_id,
+                    false_next_id: parent_condition.false_next_id,
+                };
+                (lhs, rhs)
+            }
+            LogicalOp::Or => {
+                let lhs = ConditionInfo {
+                    condition_id: lhs_id,
+                    true_next_id: parent_condition.true_next_id,
+                    false_next_id: rhs_condition_id,
+                };
+                let rhs = ConditionInfo {
+                    condition_id: rhs_condition_id,
+                    true_next_id: parent_condition.true_next_id,
+                    false_next_id: parent_condition.false_next_id,
+                };
+                (lhs, rhs)
+            }
+        };
+        // We visit expressions tree in pre-order, so place the left-hand side on the top.
+        self.decision_stack.push_back(rhs);
+        self.decision_stack.push_back(lhs);
+    }
+
+    fn take_condition(
+        &mut self,
+        true_marker: BlockMarkerId,
+        false_marker: BlockMarkerId,
+    ) -> (Option<ConditionInfo>, Option<MCDCDecisionSpan>) {
+        let Some(condition_info) = self.decision_stack.pop_back() else {
+            return (None, None);
+        };
+        let Some(decision) = self.processing_decision.as_mut() else {
+            bug!("Processing decision should have been created before any conditions are taken");
+        };
+        if condition_info.true_next_id == ConditionId::NONE {
+            decision.end_markers.push(true_marker);
+        }
+        if condition_info.false_next_id == ConditionId::NONE {
+            decision.end_markers.push(false_marker);
+        }
+
+        if self.decision_stack.is_empty() {
+            (Some(condition_info), self.processing_decision.take())
+        } else {
+            (Some(condition_info), None)
+        }
     }
 }
 
@@ -137,10 +355,27 @@ impl Builder<'_, '_> {
         let true_marker = inject_branch_marker(then_block);
         let false_marker = inject_branch_marker(else_block);
 
-        branch_info.branch_spans.push(BranchSpan {
-            span: source_info.span,
-            true_marker,
-            false_marker,
-        });
+        if let Some(condition_info) =
+            branch_info.fetch_condition_info(self.tcx, true_marker, false_marker)
+        {
+            branch_info.mcdc_branch_spans.push(MCDCBranchSpan {
+                span: source_info.span,
+                condition_info,
+                true_marker,
+                false_marker,
+            });
+        } else {
+            branch_info.branch_spans.push(BranchSpan {
+                span: source_info.span,
+                true_marker,
+                false_marker,
+            });
+        }
+    }
+
+    pub(crate) fn visit_coverage_branch_operation(&mut self, logical_op: LogicalOp, span: Span) {
+        if let Some(branch_info) = self.coverage_branch_info.as_mut() {
+            branch_info.record_conditions_operation(logical_op, span);
+        }
     }
 }
diff --git a/compiler/rustc_mir_build/src/build/matches/mod.rs b/compiler/rustc_mir_build/src/build/matches/mod.rs
index 9730473c428..f46dceeeedf 100644
--- a/compiler/rustc_mir_build/src/build/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/build/matches/mod.rs
@@ -77,11 +77,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
         match expr.kind {
             ExprKind::LogicalOp { op: LogicalOp::And, lhs, rhs } => {
+                this.visit_coverage_branch_operation(LogicalOp::And, expr_span);
                 let lhs_then_block = unpack!(this.then_else_break_inner(block, lhs, args));
                 let rhs_then_block = unpack!(this.then_else_break_inner(lhs_then_block, rhs, args));
                 rhs_then_block.unit()
             }
             ExprKind::LogicalOp { op: LogicalOp::Or, lhs, rhs } => {
+                this.visit_coverage_branch_operation(LogicalOp::Or, expr_span);
                 let local_scope = this.local_scope();
                 let (lhs_success_block, failure_block) =
                     this.in_if_then_scope(local_scope, expr_span, |this| {
diff --git a/compiler/rustc_mir_build/src/errors.rs b/compiler/rustc_mir_build/src/errors.rs
index 26f10fdd333..9ddfb12bf76 100644
--- a/compiler/rustc_mir_build/src/errors.rs
+++ b/compiler/rustc_mir_build/src/errors.rs
@@ -819,6 +819,15 @@ pub struct NontrivialStructuralMatch<'tcx> {
 }
 
 #[derive(Diagnostic)]
+#[diag(mir_build_exceeds_mcdc_condition_num_limit)]
+pub(crate) struct MCDCExceedsConditionNumLimit {
+    #[primary_span]
+    pub span: Span,
+    pub conditions_num: usize,
+    pub max_conditions_num: usize,
+}
+
+#[derive(Diagnostic)]
 #[diag(mir_build_pattern_not_covered, code = E0005)]
 pub(crate) struct PatternNotCovered<'s, 'tcx> {
     #[primary_span]
diff --git a/compiler/rustc_mir_transform/src/coverage/mod.rs b/compiler/rustc_mir_transform/src/coverage/mod.rs
index d382d2c03c2..9e8648b0f93 100644
--- a/compiler/rustc_mir_transform/src/coverage/mod.rs
+++ b/compiler/rustc_mir_transform/src/coverage/mod.rs
@@ -100,9 +100,12 @@ fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir:
         &coverage_counters,
     );
 
+    inject_mcdc_statements(mir_body, &basic_coverage_blocks, &coverage_spans);
+
     mir_body.function_coverage_info = Some(Box::new(FunctionCoverageInfo {
         function_source_hash: hir_info.function_source_hash,
         num_counters: coverage_counters.num_counters(),
+        mcdc_bitmap_bytes: coverage_spans.test_vector_bitmap_bytes(),
         expressions: coverage_counters.into_expressions(),
         mappings,
     }));
@@ -136,20 +139,33 @@ fn create_mappings<'tcx>(
             .as_term()
     };
 
-    coverage_spans
-        .all_bcb_mappings()
-        .filter_map(|&BcbMapping { kind: bcb_mapping_kind, span }| {
-            let kind = match bcb_mapping_kind {
+    let mut mappings = Vec::new();
+
+    mappings.extend(coverage_spans.all_bcb_mappings().filter_map(
+        |BcbMapping { kind: bcb_mapping_kind, span }| {
+            let kind = match *bcb_mapping_kind {
                 BcbMappingKind::Code(bcb) => MappingKind::Code(term_for_bcb(bcb)),
                 BcbMappingKind::Branch { true_bcb, false_bcb } => MappingKind::Branch {
                     true_term: term_for_bcb(true_bcb),
                     false_term: term_for_bcb(false_bcb),
                 },
+                BcbMappingKind::MCDCBranch { true_bcb, false_bcb, condition_info } => {
+                    MappingKind::MCDCBranch {
+                        true_term: term_for_bcb(true_bcb),
+                        false_term: term_for_bcb(false_bcb),
+                        mcdc_params: condition_info,
+                    }
+                }
+                BcbMappingKind::MCDCDecision { bitmap_idx, conditions_num, .. } => {
+                    MappingKind::MCDCDecision(DecisionInfo { bitmap_idx, conditions_num })
+                }
             };
-            let code_region = make_code_region(source_map, file_name, span, body_span)?;
+            let code_region = make_code_region(source_map, file_name, *span, body_span)?;
             Some(Mapping { kind, code_region })
-        })
-        .collect::<Vec<_>>()
+        },
+    ));
+
+    mappings
 }
 
 /// For each BCB node or BCB edge that has an associated coverage counter,
@@ -204,6 +220,55 @@ fn inject_coverage_statements<'tcx>(
     }
 }
 
+/// For each conditions inject statements to update condition bitmap after it has been evaluated.
+/// For each decision inject statements to update test vector bitmap after it has been evaluated.
+fn inject_mcdc_statements<'tcx>(
+    mir_body: &mut mir::Body<'tcx>,
+    basic_coverage_blocks: &CoverageGraph,
+    coverage_spans: &CoverageSpans,
+) {
+    if coverage_spans.test_vector_bitmap_bytes() == 0 {
+        return;
+    }
+
+    // Inject test vector update first because `inject_statement` always insert new statement at head.
+    for (end_bcbs, bitmap_idx) in
+        coverage_spans.all_bcb_mappings().filter_map(|mapping| match &mapping.kind {
+            BcbMappingKind::MCDCDecision { end_bcbs, bitmap_idx, .. } => {
+                Some((end_bcbs, *bitmap_idx))
+            }
+            _ => None,
+        })
+    {
+        for end in end_bcbs {
+            let end_bb = basic_coverage_blocks[*end].leader_bb();
+            inject_statement(mir_body, CoverageKind::TestVectorBitmapUpdate { bitmap_idx }, end_bb);
+        }
+    }
+
+    for (true_bcb, false_bcb, condition_id) in
+        coverage_spans.all_bcb_mappings().filter_map(|mapping| match mapping.kind {
+            BcbMappingKind::MCDCBranch { true_bcb, false_bcb, condition_info } => {
+                Some((true_bcb, false_bcb, condition_info.condition_id))
+            }
+            _ => None,
+        })
+    {
+        let true_bb = basic_coverage_blocks[true_bcb].leader_bb();
+        inject_statement(
+            mir_body,
+            CoverageKind::CondBitmapUpdate { id: condition_id, value: true },
+            true_bb,
+        );
+        let false_bb = basic_coverage_blocks[false_bcb].leader_bb();
+        inject_statement(
+            mir_body,
+            CoverageKind::CondBitmapUpdate { id: condition_id, value: false },
+            false_bb,
+        );
+    }
+}
+
 /// Given two basic blocks that have a control-flow edge between them, creates
 /// and returns a new block that sits between those blocks.
 fn inject_edge_counter_basic_block(
diff --git a/compiler/rustc_mir_transform/src/coverage/query.rs b/compiler/rustc_mir_transform/src/coverage/query.rs
index 65715253647..f77ee63d02c 100644
--- a/compiler/rustc_mir_transform/src/coverage/query.rs
+++ b/compiler/rustc_mir_transform/src/coverage/query.rs
@@ -61,7 +61,17 @@ fn coverage_ids_info<'tcx>(
         .max()
         .unwrap_or(CounterId::ZERO);
 
-    CoverageIdsInfo { max_counter_id }
+    let mcdc_bitmap_bytes = mir_body
+        .coverage_branch_info
+        .as_deref()
+        .map(|info| {
+            info.mcdc_decision_spans
+                .iter()
+                .fold(0, |acc, decision| acc + (1_u32 << decision.conditions_num).div_ceil(8))
+        })
+        .unwrap_or_default();
+
+    CoverageIdsInfo { max_counter_id, mcdc_bitmap_bytes }
 }
 
 fn all_coverage_in_mir_body<'a, 'tcx>(
diff --git a/compiler/rustc_mir_transform/src/coverage/spans.rs b/compiler/rustc_mir_transform/src/coverage/spans.rs
index 03ede886688..a4cd8a38c66 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans.rs
@@ -1,7 +1,9 @@
 use rustc_data_structures::graph::DirectedGraph;
 use rustc_index::bit_set::BitSet;
 use rustc_middle::mir;
+use rustc_middle::mir::coverage::ConditionInfo;
 use rustc_span::{BytePos, Span};
+use std::collections::BTreeSet;
 
 use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph, START_BCB};
 use crate::coverage::spans::from_mir::SpanFromMir;
@@ -9,12 +11,20 @@ use crate::coverage::ExtractedHirInfo;
 
 mod from_mir;
 
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Debug)]
 pub(super) enum BcbMappingKind {
     /// Associates an ordinary executable code span with its corresponding BCB.
     Code(BasicCoverageBlock),
     /// Associates a branch span with BCBs for its true and false arms.
     Branch { true_bcb: BasicCoverageBlock, false_bcb: BasicCoverageBlock },
+    /// Associates a mcdc branch span with condition info besides fields for normal branch.
+    MCDCBranch {
+        true_bcb: BasicCoverageBlock,
+        false_bcb: BasicCoverageBlock,
+        condition_info: ConditionInfo,
+    },
+    /// Associates a mcdc decision with its join BCB.
+    MCDCDecision { end_bcbs: BTreeSet<BasicCoverageBlock>, bitmap_idx: u32, conditions_num: u16 },
 }
 
 #[derive(Debug)]
@@ -26,6 +36,7 @@ pub(super) struct BcbMapping {
 pub(super) struct CoverageSpans {
     bcb_has_mappings: BitSet<BasicCoverageBlock>,
     mappings: Vec<BcbMapping>,
+    test_vector_bitmap_bytes: u32,
 }
 
 impl CoverageSpans {
@@ -36,6 +47,10 @@ impl CoverageSpans {
     pub(super) fn all_bcb_mappings(&self) -> impl Iterator<Item = &BcbMapping> {
         self.mappings.iter()
     }
+
+    pub(super) fn test_vector_bitmap_bytes(&self) -> u32 {
+        self.test_vector_bitmap_bytes
+    }
 }
 
 /// Extracts coverage-relevant spans from MIR, and associates them with
@@ -85,17 +100,26 @@ pub(super) fn generate_coverage_spans(
     let mut insert = |bcb| {
         bcb_has_mappings.insert(bcb);
     };
-    for &BcbMapping { kind, span: _ } in &mappings {
-        match kind {
+    let mut test_vector_bitmap_bytes = 0;
+    for BcbMapping { kind, span: _ } in &mappings {
+        match *kind {
             BcbMappingKind::Code(bcb) => insert(bcb),
-            BcbMappingKind::Branch { true_bcb, false_bcb } => {
+            BcbMappingKind::Branch { true_bcb, false_bcb }
+            | BcbMappingKind::MCDCBranch { true_bcb, false_bcb, .. } => {
                 insert(true_bcb);
                 insert(false_bcb);
             }
+            BcbMappingKind::MCDCDecision { bitmap_idx, conditions_num, .. } => {
+                // `bcb_has_mappings` is used for inject coverage counters
+                // but they are not needed for decision BCBs.
+                // While the length of test vector bitmap should be calculated here.
+                test_vector_bitmap_bytes = test_vector_bitmap_bytes
+                    .max(bitmap_idx + (1_u32 << conditions_num as u32).div_ceil(8));
+            }
         }
     }
 
-    Some(CoverageSpans { bcb_has_mappings, mappings })
+    Some(CoverageSpans { bcb_has_mappings, mappings, test_vector_bitmap_bytes })
 }
 
 #[derive(Debug)]
diff --git a/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs b/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
index adb0c9f1929..b9919a2ae88 100644
--- a/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
+++ b/compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
@@ -1,7 +1,9 @@
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_index::IndexVec;
-use rustc_middle::mir::coverage::{BlockMarkerId, BranchSpan, CoverageKind};
+use rustc_middle::mir::coverage::{
+    BlockMarkerId, BranchSpan, CoverageKind, MCDCBranchSpan, MCDCDecisionSpan,
+};
 use rustc_middle::mir::{
     self, AggregateKind, BasicBlock, FakeReadCause, Rvalue, Statement, StatementKind, Terminator,
     TerminatorKind,
@@ -227,7 +229,10 @@ fn filtered_statement_span(statement: &Statement<'_>) -> Option<Span> {
 
         // These coverage statements should not exist prior to coverage instrumentation.
         StatementKind::Coverage(
-            CoverageKind::CounterIncrement { .. } | CoverageKind::ExpressionUsed { .. },
+            CoverageKind::CounterIncrement { .. }
+            | CoverageKind::ExpressionUsed { .. }
+            | CoverageKind::CondBitmapUpdate { .. }
+            | CoverageKind::TestVectorBitmapUpdate { .. },
         ) => bug!(
             "Unexpected coverage statement found during coverage instrumentation: {statement:?}"
         ),
@@ -384,10 +389,11 @@ pub(super) fn extract_branch_mappings(
         }
     }
 
-    branch_info
-        .branch_spans
-        .iter()
-        .filter_map(|&BranchSpan { span: raw_span, true_marker, false_marker }| {
+    let bcb_from_marker =
+        |marker: BlockMarkerId| basic_coverage_blocks.bcb_from_bb(block_markers[marker]?);
+
+    let check_branch_bcb =
+        |raw_span: Span, true_marker: BlockMarkerId, false_marker: BlockMarkerId| {
             // For now, ignore any branch span that was introduced by
             // expansion. This makes things like assert macros less noisy.
             if !raw_span.ctxt().outer_expn_data().is_root() {
@@ -395,13 +401,56 @@ pub(super) fn extract_branch_mappings(
             }
             let (span, _) = unexpand_into_body_span_with_visible_macro(raw_span, body_span)?;
 
-            let bcb_from_marker =
-                |marker: BlockMarkerId| basic_coverage_blocks.bcb_from_bb(block_markers[marker]?);
-
             let true_bcb = bcb_from_marker(true_marker)?;
             let false_bcb = bcb_from_marker(false_marker)?;
+            Some((span, true_bcb, false_bcb))
+        };
 
-            Some(BcbMapping { kind: BcbMappingKind::Branch { true_bcb, false_bcb }, span })
+    let branch_filter_map = |&BranchSpan { span: raw_span, true_marker, false_marker }| {
+        check_branch_bcb(raw_span, true_marker, false_marker).map(|(span, true_bcb, false_bcb)| {
+            BcbMapping { kind: BcbMappingKind::Branch { true_bcb, false_bcb }, span }
         })
+    };
+
+    let mcdc_branch_filter_map =
+        |&MCDCBranchSpan { span: raw_span, true_marker, false_marker, condition_info }| {
+            check_branch_bcb(raw_span, true_marker, false_marker).map(
+                |(span, true_bcb, false_bcb)| BcbMapping {
+                    kind: BcbMappingKind::MCDCBranch { true_bcb, false_bcb, condition_info },
+                    span,
+                },
+            )
+        };
+
+    let mut next_bitmap_idx = 0;
+
+    let decision_filter_map = |decision: &MCDCDecisionSpan| {
+        let (span, _) = unexpand_into_body_span_with_visible_macro(decision.span, body_span)?;
+
+        let end_bcbs = decision
+            .end_markers
+            .iter()
+            .map(|&marker| bcb_from_marker(marker))
+            .collect::<Option<_>>()?;
+
+        let bitmap_idx = next_bitmap_idx;
+        next_bitmap_idx += (1_u32 << decision.conditions_num).div_ceil(8);
+
+        Some(BcbMapping {
+            kind: BcbMappingKind::MCDCDecision {
+                end_bcbs,
+                bitmap_idx,
+                conditions_num: decision.conditions_num as u16,
+            },
+            span,
+        })
+    };
+
+    branch_info
+        .branch_spans
+        .iter()
+        .filter_map(branch_filter_map)
+        .chain(branch_info.mcdc_branch_spans.iter().filter_map(mcdc_branch_filter_map))
+        .chain(branch_info.mcdc_decision_spans.iter().filter_map(decision_filter_map))
         .collect::<Vec<_>>()
 }
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 8ad64897e83..d5b22f841d2 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -148,6 +148,8 @@ pub enum InstrumentCoverage {
 pub struct CoverageOptions {
     /// Add branch coverage instrumentation.
     pub branch: bool,
+    /// Add mcdc coverage instrumentation.
+    pub mcdc: bool,
 }
 
 /// Settings for `-Z instrument-xray` flag.
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 8567591cbd9..d5108058948 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -398,7 +398,7 @@ mod desc {
     pub const parse_optimization_fuel: &str = "crate=integer";
     pub const parse_dump_mono_stats: &str = "`markdown` (default) or `json`";
     pub const parse_instrument_coverage: &str = parse_bool;
-    pub const parse_coverage_options: &str = "`branch` or `no-branch`";
+    pub const parse_coverage_options: &str = "either  `no-branch`, `branch` or `mcdc`";
     pub const parse_instrument_xray: &str = "either a boolean (`yes`, `no`, `on`, `off`, etc), or a comma separated list of settings: `always` or `never` (mutually exclusive), `ignore-loops`, `instruction-threshold=N`, `skip-entry`, `skip-exit`";
     pub const parse_unpretty: &str = "`string` or `string=string`";
     pub const parse_treat_err_as_bug: &str = "either no value or a non-negative number";
@@ -949,17 +949,19 @@ mod parse {
         let Some(v) = v else { return true };
 
         for option in v.split(',') {
-            let (option, enabled) = match option.strip_prefix("no-") {
-                Some(without_no) => (without_no, false),
-                None => (option, true),
-            };
-            let slot = match option {
-                "branch" => &mut slot.branch,
+            match option {
+                "no-branch" => {
+                    slot.branch = false;
+                    slot.mcdc = false;
+                }
+                "branch" => slot.branch = true,
+                "mcdc" => {
+                    slot.branch = true;
+                    slot.mcdc = true;
+                }
                 _ => return false,
-            };
-            *slot = enabled;
+            }
         }
-
         true
     }
 
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index b63c119eee0..2bc14b43234 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -352,6 +352,10 @@ impl Session {
         self.instrument_coverage() && self.opts.unstable_opts.coverage_options.branch
     }
 
+    pub fn instrument_coverage_mcdc(&self) -> bool {
+        self.instrument_coverage() && self.opts.unstable_opts.coverage_options.mcdc
+    }
+
     pub fn is_sanitizer_cfi_enabled(&self) -> bool {
         self.opts.unstable_opts.sanitizer.contains(SanitizerSet::CFI)
     }
diff --git a/src/doc/rustc/src/instrument-coverage.md b/src/doc/rustc/src/instrument-coverage.md
index 185a3ba5dbd..bbd81e7437c 100644
--- a/src/doc/rustc/src/instrument-coverage.md
+++ b/src/doc/rustc/src/instrument-coverage.md
@@ -351,8 +351,8 @@ $ llvm-cov report \
 This unstable option provides finer control over some aspects of coverage
 instrumentation. Pass one or more of the following values, separated by commas.
 
-- `branch` or `no-branch`
-  - Enables or disables branch coverage instrumentation.
+- Either `no-branch`, `branch` or `mcdc`
+  - `branch` enables branch coverage instrumentation and `mcdc` further enables modified condition/decision coverage instrumentation. `no-branch` disables branch coverage instrumentation, which is same as do not pass `branch` or `mcdc`.
 
 ## Other references
 
diff --git a/src/doc/unstable-book/src/compiler-flags/coverage-options.md b/src/doc/unstable-book/src/compiler-flags/coverage-options.md
index 450573cc6c7..5e192d9aca1 100644
--- a/src/doc/unstable-book/src/compiler-flags/coverage-options.md
+++ b/src/doc/unstable-book/src/compiler-flags/coverage-options.md
@@ -5,4 +5,4 @@ This option controls details of the coverage instrumentation performed by
 
 Multiple options can be passed, separated by commas. Valid options are:
 
-- `branch` or `no-branch`: Enables or disables branch coverage instrumentation.
+- `no-branch`, `branch` or `mcdc`: `branch` enables branch coverage instrumentation and `mcdc` further enables modified condition/decision coverage instrumentation. `no-branch` disables branch coverage instrumentation as well as mcdc instrumentation, which is same as do not pass `branch` or `mcdc`.
diff --git a/tests/coverage/mcdc_if.cov-map b/tests/coverage/mcdc_if.cov-map
new file mode 100644
index 00000000000..35a265684d2
--- /dev/null
+++ b/tests/coverage/mcdc_if.cov-map
@@ -0,0 +1,218 @@
+Function name: mcdc_if::mcdc_check_a
+Raw bytes (64): 0x[01, 01, 04, 01, 05, 09, 02, 0d, 0f, 09, 02, 08, 01, 0f, 01, 01, 09, 28, 00, 02, 01, 08, 00, 0e, 30, 05, 02, 01, 02, 00, 00, 08, 00, 09, 05, 00, 0d, 00, 0e, 30, 0d, 09, 02, 00, 00, 00, 0d, 00, 0e, 0d, 00, 0f, 02, 06, 0f, 02, 0c, 02, 06, 0b, 03, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 4
+- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
+- expression 1 operands: lhs = Counter(2), rhs = Expression(0, Sub)
+- expression 2 operands: lhs = Counter(3), rhs = Expression(3, Add)
+- expression 3 operands: lhs = Counter(2), rhs = Expression(0, Sub)
+Number of file 0 mappings: 8
+- Code(Counter(0)) at (prev + 15, 1) to (start + 1, 9)
+- MCDCDecision { bitmap_idx: 0, conditions_num: 2 } at (prev + 1, 8) to (start + 0, 14)
+- MCDCBranch { true: Counter(1), false: Expression(0, Sub), condition_id: 1, true_next_id: 2, false_next_id: 0 } at (prev + 0, 8) to (start + 0, 9)
+    true  = c1
+    false = (c0 - c1)
+- Code(Counter(1)) at (prev + 0, 13) to (start + 0, 14)
+- MCDCBranch { true: Counter(3), false: Counter(2), condition_id: 2, true_next_id: 0, false_next_id: 0 } at (prev + 0, 13) to (start + 0, 14)
+    true  = c3
+    false = c2
+- Code(Counter(3)) at (prev + 0, 15) to (start + 2, 6)
+- Code(Expression(3, Add)) at (prev + 2, 12) to (start + 2, 6)
+    = (c2 + (c0 - c1))
+- Code(Expression(2, Add)) at (prev + 3, 1) to (start + 0, 2)
+    = (c3 + (c2 + (c0 - c1)))
+
+Function name: mcdc_if::mcdc_check_b
+Raw bytes (64): 0x[01, 01, 04, 01, 05, 09, 02, 0d, 0f, 09, 02, 08, 01, 17, 01, 01, 09, 28, 00, 02, 01, 08, 00, 0e, 30, 05, 02, 01, 02, 00, 00, 08, 00, 09, 05, 00, 0d, 00, 0e, 30, 0d, 09, 02, 00, 00, 00, 0d, 00, 0e, 0d, 00, 0f, 02, 06, 0f, 02, 0c, 02, 06, 0b, 03, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 4
+- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
+- expression 1 operands: lhs = Counter(2), rhs = Expression(0, Sub)
+- expression 2 operands: lhs = Counter(3), rhs = Expression(3, Add)
+- expression 3 operands: lhs = Counter(2), rhs = Expression(0, Sub)
+Number of file 0 mappings: 8
+- Code(Counter(0)) at (prev + 23, 1) to (start + 1, 9)
+- MCDCDecision { bitmap_idx: 0, conditions_num: 2 } at (prev + 1, 8) to (start + 0, 14)
+- MCDCBranch { true: Counter(1), false: Expression(0, Sub), condition_id: 1, true_next_id: 2, false_next_id: 0 } at (prev + 0, 8) to (start + 0, 9)
+    true  = c1
+    false = (c0 - c1)
+- Code(Counter(1)) at (prev + 0, 13) to (start + 0, 14)
+- MCDCBranch { true: Counter(3), false: Counter(2), condition_id: 2, true_next_id: 0, false_next_id: 0 } at (prev + 0, 13) to (start + 0, 14)
+    true  = c3
+    false = c2
+- Code(Counter(3)) at (prev + 0, 15) to (start + 2, 6)
+- Code(Expression(3, Add)) at (prev + 2, 12) to (start + 2, 6)
+    = (c2 + (c0 - c1))
+- Code(Expression(2, Add)) at (prev + 3, 1) to (start + 0, 2)
+    = (c3 + (c2 + (c0 - c1)))
+
+Function name: mcdc_if::mcdc_check_both
+Raw bytes (64): 0x[01, 01, 04, 01, 05, 09, 02, 0d, 0f, 09, 02, 08, 01, 1f, 01, 01, 09, 28, 00, 02, 01, 08, 00, 0e, 30, 05, 02, 01, 02, 00, 00, 08, 00, 09, 05, 00, 0d, 00, 0e, 30, 0d, 09, 02, 00, 00, 00, 0d, 00, 0e, 0d, 00, 0f, 02, 06, 0f, 02, 0c, 02, 06, 0b, 03, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 4
+- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
+- expression 1 operands: lhs = Counter(2), rhs = Expression(0, Sub)
+- expression 2 operands: lhs = Counter(3), rhs = Expression(3, Add)
+- expression 3 operands: lhs = Counter(2), rhs = Expression(0, Sub)
+Number of file 0 mappings: 8
+- Code(Counter(0)) at (prev + 31, 1) to (start + 1, 9)
+- MCDCDecision { bitmap_idx: 0, conditions_num: 2 } at (prev + 1, 8) to (start + 0, 14)
+- MCDCBranch { true: Counter(1), false: Expression(0, Sub), condition_id: 1, true_next_id: 2, false_next_id: 0 } at (prev + 0, 8) to (start + 0, 9)
+    true  = c1
+    false = (c0 - c1)
+- Code(Counter(1)) at (prev + 0, 13) to (start + 0, 14)
+- MCDCBranch { true: Counter(3), false: Counter(2), condition_id: 2, true_next_id: 0, false_next_id: 0 } at (prev + 0, 13) to (start + 0, 14)
+    true  = c3
+    false = c2
+- Code(Counter(3)) at (prev + 0, 15) to (start + 2, 6)
+- Code(Expression(3, Add)) at (prev + 2, 12) to (start + 2, 6)
+    = (c2 + (c0 - c1))
+- Code(Expression(2, Add)) at (prev + 3, 1) to (start + 0, 2)
+    = (c3 + (c2 + (c0 - c1)))
+
+Function name: mcdc_if::mcdc_check_neither
+Raw bytes (64): 0x[01, 01, 04, 01, 05, 09, 02, 0d, 0f, 09, 02, 08, 01, 07, 01, 01, 09, 28, 00, 02, 01, 08, 00, 0e, 30, 05, 02, 01, 02, 00, 00, 08, 00, 09, 05, 00, 0d, 00, 0e, 30, 0d, 09, 02, 00, 00, 00, 0d, 00, 0e, 0d, 00, 0f, 02, 06, 0f, 02, 0c, 02, 06, 0b, 03, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 4
+- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
+- expression 1 operands: lhs = Counter(2), rhs = Expression(0, Sub)
+- expression 2 operands: lhs = Counter(3), rhs = Expression(3, Add)
+- expression 3 operands: lhs = Counter(2), rhs = Expression(0, Sub)
+Number of file 0 mappings: 8
+- Code(Counter(0)) at (prev + 7, 1) to (start + 1, 9)
+- MCDCDecision { bitmap_idx: 0, conditions_num: 2 } at (prev + 1, 8) to (start + 0, 14)
+- MCDCBranch { true: Counter(1), false: Expression(0, Sub), condition_id: 1, true_next_id: 2, false_next_id: 0 } at (prev + 0, 8) to (start + 0, 9)
+    true  = c1
+    false = (c0 - c1)
+- Code(Counter(1)) at (prev + 0, 13) to (start + 0, 14)
+- MCDCBranch { true: Counter(3), false: Counter(2), condition_id: 2, true_next_id: 0, false_next_id: 0 } at (prev + 0, 13) to (start + 0, 14)
+    true  = c3
+    false = c2
+- Code(Counter(3)) at (prev + 0, 15) to (start + 2, 6)
+- Code(Expression(3, Add)) at (prev + 2, 12) to (start + 2, 6)
+    = (c2 + (c0 - c1))
+- Code(Expression(2, Add)) at (prev + 3, 1) to (start + 0, 2)
+    = (c3 + (c2 + (c0 - c1)))
+
+Function name: mcdc_if::mcdc_check_not_tree_decision
+Raw bytes (87): 0x[01, 01, 08, 01, 05, 02, 09, 05, 09, 0d, 1e, 02, 09, 11, 1b, 0d, 1e, 02, 09, 0a, 01, 31, 01, 03, 0a, 28, 00, 03, 03, 08, 00, 15, 30, 05, 02, 01, 02, 03, 00, 09, 00, 0a, 02, 00, 0e, 00, 0f, 30, 09, 1e, 03, 02, 00, 00, 0e, 00, 0f, 0b, 00, 14, 00, 15, 30, 11, 0d, 02, 00, 00, 00, 14, 00, 15, 11, 00, 16, 02, 06, 1b, 02, 0c, 02, 06, 17, 03, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 8
+- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
+- expression 1 operands: lhs = Expression(0, Sub), rhs = Counter(2)
+- expression 2 operands: lhs = Counter(1), rhs = Counter(2)
+- expression 3 operands: lhs = Counter(3), rhs = Expression(7, Sub)
+- expression 4 operands: lhs = Expression(0, Sub), rhs = Counter(2)
+- expression 5 operands: lhs = Counter(4), rhs = Expression(6, Add)
+- expression 6 operands: lhs = Counter(3), rhs = Expression(7, Sub)
+- expression 7 operands: lhs = Expression(0, Sub), rhs = Counter(2)
+Number of file 0 mappings: 10
+- Code(Counter(0)) at (prev + 49, 1) to (start + 3, 10)
+- MCDCDecision { bitmap_idx: 0, conditions_num: 3 } at (prev + 3, 8) to (start + 0, 21)
+- MCDCBranch { true: Counter(1), false: Expression(0, Sub), condition_id: 1, true_next_id: 2, false_next_id: 3 } at (prev + 0, 9) to (start + 0, 10)
+    true  = c1
+    false = (c0 - c1)
+- Code(Expression(0, Sub)) at (prev + 0, 14) to (start + 0, 15)
+    = (c0 - c1)
+- MCDCBranch { true: Counter(2), false: Expression(7, Sub), condition_id: 3, true_next_id: 2, false_next_id: 0 } at (prev + 0, 14) to (start + 0, 15)
+    true  = c2
+    false = ((c0 - c1) - c2)
+- Code(Expression(2, Add)) at (prev + 0, 20) to (start + 0, 21)
+    = (c1 + c2)
+- MCDCBranch { true: Counter(4), false: Counter(3), condition_id: 2, true_next_id: 0, false_next_id: 0 } at (prev + 0, 20) to (start + 0, 21)
+    true  = c4
+    false = c3
+- Code(Counter(4)) at (prev + 0, 22) to (start + 2, 6)
+- Code(Expression(6, Add)) at (prev + 2, 12) to (start + 2, 6)
+    = (c3 + ((c0 - c1) - c2))
+- Code(Expression(5, Add)) at (prev + 3, 1) to (start + 0, 2)
+    = (c4 + (c3 + ((c0 - c1) - c2)))
+
+Function name: mcdc_if::mcdc_check_tree_decision
+Raw bytes (87): 0x[01, 01, 08, 01, 05, 05, 0d, 05, 0d, 0d, 11, 09, 02, 1b, 1f, 0d, 11, 09, 02, 0a, 01, 27, 01, 03, 09, 28, 00, 03, 03, 08, 00, 15, 30, 05, 02, 01, 02, 00, 00, 08, 00, 09, 05, 00, 0e, 00, 0f, 30, 0d, 0a, 02, 00, 03, 00, 0e, 00, 0f, 0a, 00, 13, 00, 14, 30, 11, 09, 03, 00, 00, 00, 13, 00, 14, 1b, 00, 16, 02, 06, 1f, 02, 0c, 02, 06, 17, 03, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 8
+- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
+- expression 1 operands: lhs = Counter(1), rhs = Counter(3)
+- expression 2 operands: lhs = Counter(1), rhs = Counter(3)
+- expression 3 operands: lhs = Counter(3), rhs = Counter(4)
+- expression 4 operands: lhs = Counter(2), rhs = Expression(0, Sub)
+- expression 5 operands: lhs = Expression(6, Add), rhs = Expression(7, Add)
+- expression 6 operands: lhs = Counter(3), rhs = Counter(4)
+- expression 7 operands: lhs = Counter(2), rhs = Expression(0, Sub)
+Number of file 0 mappings: 10
+- Code(Counter(0)) at (prev + 39, 1) to (start + 3, 9)
+- MCDCDecision { bitmap_idx: 0, conditions_num: 3 } at (prev + 3, 8) to (start + 0, 21)
+- MCDCBranch { true: Counter(1), false: Expression(0, Sub), condition_id: 1, true_next_id: 2, false_next_id: 0 } at (prev + 0, 8) to (start + 0, 9)
+    true  = c1
+    false = (c0 - c1)
+- Code(Counter(1)) at (prev + 0, 14) to (start + 0, 15)
+- MCDCBranch { true: Counter(3), false: Expression(2, Sub), condition_id: 2, true_next_id: 0, false_next_id: 3 } at (prev + 0, 14) to (start + 0, 15)
+    true  = c3
+    false = (c1 - c3)
+- Code(Expression(2, Sub)) at (prev + 0, 19) to (start + 0, 20)
+    = (c1 - c3)
+- MCDCBranch { true: Counter(4), false: Counter(2), condition_id: 3, true_next_id: 0, false_next_id: 0 } at (prev + 0, 19) to (start + 0, 20)
+    true  = c4
+    false = c2
+- Code(Expression(6, Add)) at (prev + 0, 22) to (start + 2, 6)
+    = (c3 + c4)
+- Code(Expression(7, Add)) at (prev + 2, 12) to (start + 2, 6)
+    = (c2 + (c0 - c1))
+- Code(Expression(5, Add)) at (prev + 3, 1) to (start + 0, 2)
+    = ((c3 + c4) + (c2 + (c0 - c1)))
+
+Function name: mcdc_if::mcdc_nested_if
+Raw bytes (124): 0x[01, 01, 0d, 01, 05, 02, 09, 05, 09, 1b, 15, 05, 09, 1b, 15, 05, 09, 11, 15, 02, 09, 2b, 32, 0d, 2f, 11, 15, 02, 09, 0e, 01, 3b, 01, 01, 09, 28, 00, 02, 01, 08, 00, 0e, 30, 05, 02, 01, 00, 02, 00, 08, 00, 09, 02, 00, 0d, 00, 0e, 30, 09, 32, 02, 00, 00, 00, 0d, 00, 0e, 1b, 01, 09, 01, 0d, 28, 01, 02, 01, 0c, 00, 12, 30, 16, 15, 01, 02, 00, 00, 0c, 00, 0d, 16, 00, 11, 00, 12, 30, 0d, 11, 02, 00, 00, 00, 11, 00, 12, 0d, 00, 13, 02, 0a, 2f, 02, 0a, 00, 0b, 32, 01, 0c, 02, 06, 27, 03, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 13
+- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
+- expression 1 operands: lhs = Expression(0, Sub), rhs = Counter(2)
+- expression 2 operands: lhs = Counter(1), rhs = Counter(2)
+- expression 3 operands: lhs = Expression(6, Add), rhs = Counter(5)
+- expression 4 operands: lhs = Counter(1), rhs = Counter(2)
+- expression 5 operands: lhs = Expression(6, Add), rhs = Counter(5)
+- expression 6 operands: lhs = Counter(1), rhs = Counter(2)
+- expression 7 operands: lhs = Counter(4), rhs = Counter(5)
+- expression 8 operands: lhs = Expression(0, Sub), rhs = Counter(2)
+- expression 9 operands: lhs = Expression(10, Add), rhs = Expression(12, Sub)
+- expression 10 operands: lhs = Counter(3), rhs = Expression(11, Add)
+- expression 11 operands: lhs = Counter(4), rhs = Counter(5)
+- expression 12 operands: lhs = Expression(0, Sub), rhs = Counter(2)
+Number of file 0 mappings: 14
+- Code(Counter(0)) at (prev + 59, 1) to (start + 1, 9)
+- MCDCDecision { bitmap_idx: 0, conditions_num: 2 } at (prev + 1, 8) to (start + 0, 14)
+- MCDCBranch { true: Counter(1), false: Expression(0, Sub), condition_id: 1, true_next_id: 0, false_next_id: 2 } at (prev + 0, 8) to (start + 0, 9)
+    true  = c1
+    false = (c0 - c1)
+- Code(Expression(0, Sub)) at (prev + 0, 13) to (start + 0, 14)
+    = (c0 - c1)
+- MCDCBranch { true: Counter(2), false: Expression(12, Sub), condition_id: 2, true_next_id: 0, false_next_id: 0 } at (prev + 0, 13) to (start + 0, 14)
+    true  = c2
+    false = ((c0 - c1) - c2)
+- Code(Expression(6, Add)) at (prev + 1, 9) to (start + 1, 13)
+    = (c1 + c2)
+- MCDCDecision { bitmap_idx: 1, conditions_num: 2 } at (prev + 1, 12) to (start + 0, 18)
+- MCDCBranch { true: Expression(5, Sub), false: Counter(5), condition_id: 1, true_next_id: 2, false_next_id: 0 } at (prev + 0, 12) to (start + 0, 13)
+    true  = ((c1 + c2) - c5)
+    false = c5
+- Code(Expression(5, Sub)) at (prev + 0, 17) to (start + 0, 18)
+    = ((c1 + c2) - c5)
+- MCDCBranch { true: Counter(3), false: Counter(4), condition_id: 2, true_next_id: 0, false_next_id: 0 } at (prev + 0, 17) to (start + 0, 18)
+    true  = c3
+    false = c4
+- Code(Counter(3)) at (prev + 0, 19) to (start + 2, 10)
+- Code(Expression(11, Add)) at (prev + 2, 10) to (start + 0, 11)
+    = (c4 + c5)
+- Code(Expression(12, Sub)) at (prev + 1, 12) to (start + 2, 6)
+    = ((c0 - c1) - c2)
+- Code(Expression(9, Add)) at (prev + 3, 1) to (start + 0, 2)
+    = ((c3 + (c4 + c5)) + ((c0 - c1) - c2))
+
diff --git a/tests/coverage/mcdc_if.coverage b/tests/coverage/mcdc_if.coverage
new file mode 100644
index 00000000000..c2ed311a5bc
--- /dev/null
+++ b/tests/coverage/mcdc_if.coverage
@@ -0,0 +1,262 @@
+   LL|       |#![feature(coverage_attribute)]
+   LL|       |//@ edition: 2021
+   LL|       |//@ min-llvm-version: 18
+   LL|       |//@ compile-flags: -Zcoverage-options=mcdc
+   LL|       |//@ llvm-cov-flags: --show-mcdc
+   LL|       |
+   LL|      2|fn mcdc_check_neither(a: bool, b: bool) {
+   LL|      2|    if a && b {
+                          ^0
+  ------------------
+  |---> MC/DC Decision Region (LL:8) to (LL:14)
+  |
+  |  Number of Conditions: 2
+  |     Condition C1 --> (LL:8)
+  |     Condition C2 --> (LL:13)
+  |
+  |  Executed MC/DC Test Vectors:
+  |
+  |     C1, C2    Result
+  |  1 { F,  -  = F      }
+  |
+  |  C1-Pair: not covered
+  |  C2-Pair: not covered
+  |  MC/DC Coverage for Decision: 0.00%
+  |
+  ------------------
+   LL|      0|        say("a and b");
+   LL|      2|    } else {
+   LL|      2|        say("not both");
+   LL|      2|    }
+   LL|      2|}
+   LL|       |
+   LL|      2|fn mcdc_check_a(a: bool, b: bool) {
+   LL|      2|    if a && b {
+                          ^1
+  ------------------
+  |---> MC/DC Decision Region (LL:8) to (LL:14)
+  |
+  |  Number of Conditions: 2
+  |     Condition C1 --> (LL:8)
+  |     Condition C2 --> (LL:13)
+  |
+  |  Executed MC/DC Test Vectors:
+  |
+  |     C1, C2    Result
+  |  1 { F,  -  = F      }
+  |  2 { T,  T  = T      }
+  |
+  |  C1-Pair: covered: (1,2)
+  |  C2-Pair: not covered
+  |  MC/DC Coverage for Decision: 50.00%
+  |
+  ------------------
+   LL|      1|        say("a and b");
+   LL|      1|    } else {
+   LL|      1|        say("not both");
+   LL|      1|    }
+   LL|      2|}
+   LL|       |
+   LL|      2|fn mcdc_check_b(a: bool, b: bool) {
+   LL|      2|    if a && b {
+  ------------------
+  |---> MC/DC Decision Region (LL:8) to (LL:14)
+  |
+  |  Number of Conditions: 2
+  |     Condition C1 --> (LL:8)
+  |     Condition C2 --> (LL:13)
+  |
+  |  Executed MC/DC Test Vectors:
+  |
+  |     C1, C2    Result
+  |  1 { T,  F  = F      }
+  |  2 { T,  T  = T      }
+  |
+  |  C1-Pair: not covered
+  |  C2-Pair: covered: (1,2)
+  |  MC/DC Coverage for Decision: 50.00%
+  |
+  ------------------
+   LL|      1|        say("a and b");
+   LL|      1|    } else {
+   LL|      1|        say("not both");
+   LL|      1|    }
+   LL|      2|}
+   LL|       |
+   LL|      3|fn mcdc_check_both(a: bool, b: bool) {
+   LL|      3|    if a && b {
+                          ^2
+  ------------------
+  |---> MC/DC Decision Region (LL:8) to (LL:14)
+  |
+  |  Number of Conditions: 2
+  |     Condition C1 --> (LL:8)
+  |     Condition C2 --> (LL:13)
+  |
+  |  Executed MC/DC Test Vectors:
+  |
+  |     C1, C2    Result
+  |  1 { F,  -  = F      }
+  |  2 { T,  F  = F      }
+  |  3 { T,  T  = T      }
+  |
+  |  C1-Pair: covered: (1,3)
+  |  C2-Pair: covered: (2,3)
+  |  MC/DC Coverage for Decision: 100.00%
+  |
+  ------------------
+   LL|      1|        say("a and b");
+   LL|      2|    } else {
+   LL|      2|        say("not both");
+   LL|      2|    }
+   LL|      3|}
+   LL|       |
+   LL|      4|fn mcdc_check_tree_decision(a: bool, b: bool, c: bool) {
+   LL|      4|    // This expression is intentionally written in a way
+   LL|      4|    // where 100% branch coverage indicates 100% mcdc coverage.
+   LL|      4|    if a && (b || c) {
+                           ^3   ^2
+  ------------------
+  |---> MC/DC Decision Region (LL:8) to (LL:21)
+  |
+  |  Number of Conditions: 3
+  |     Condition C1 --> (LL:8)
+  |     Condition C2 --> (LL:14)
+  |     Condition C3 --> (LL:19)
+  |
+  |  Executed MC/DC Test Vectors:
+  |
+  |     C1, C2, C3    Result
+  |  1 { F,  -,  -  = F      }
+  |  2 { T,  F,  F  = F      }
+  |  3 { T,  T,  -  = T      }
+  |  4 { T,  F,  T  = T      }
+  |
+  |  C1-Pair: covered: (1,3)
+  |  C2-Pair: covered: (2,3)
+  |  C3-Pair: covered: (2,4)
+  |  MC/DC Coverage for Decision: 100.00%
+  |
+  ------------------
+   LL|      2|        say("pass");
+   LL|      2|    } else {
+   LL|      2|        say("reject");
+   LL|      2|    }
+   LL|      4|}
+   LL|       |
+   LL|      4|fn mcdc_check_not_tree_decision(a: bool, b: bool, c: bool) {
+   LL|      4|    // Contradict to `mcdc_check_tree_decision`,
+   LL|      4|    // 100% branch coverage of this expression does not mean indicates 100% mcdc coverage.
+   LL|      4|    if (a || b) && c {
+                           ^1
+  ------------------
+  |---> MC/DC Decision Region (LL:8) to (LL:21)
+  |
+  |  Number of Conditions: 3
+  |     Condition C1 --> (LL:9)
+  |     Condition C2 --> (LL:14)
+  |     Condition C3 --> (LL:20)
+  |
+  |  Executed MC/DC Test Vectors:
+  |
+  |     C1, C2, C3    Result
+  |  1 { T,  -,  F  = F      }
+  |  2 { T,  -,  T  = T      }
+  |  3 { F,  T,  T  = T      }
+  |
+  |  C1-Pair: not covered
+  |  C2-Pair: not covered
+  |  C3-Pair: covered: (1,2)
+  |  MC/DC Coverage for Decision: 33.33%
+  |
+  ------------------
+   LL|      2|        say("pass");
+   LL|      2|    } else {
+   LL|      2|        say("reject");
+   LL|      2|    }
+   LL|      4|}
+   LL|       |
+   LL|      3|fn mcdc_nested_if(a: bool, b: bool, c: bool) {
+   LL|      3|    if a || b {
+                          ^0
+  ------------------
+  |---> MC/DC Decision Region (LL:8) to (LL:14)
+  |
+  |  Number of Conditions: 2
+  |     Condition C1 --> (LL:8)
+  |     Condition C2 --> (LL:13)
+  |
+  |  Executed MC/DC Test Vectors:
+  |
+  |     C1, C2    Result
+  |  1 { T,  -  = T      }
+  |
+  |  C1-Pair: not covered
+  |  C2-Pair: not covered
+  |  MC/DC Coverage for Decision: 0.00%
+  |
+  ------------------
+   LL|      3|        say("a or b");
+   LL|      3|        if b && c {
+                              ^2
+  ------------------
+  |---> MC/DC Decision Region (LL:12) to (LL:18)
+  |
+  |  Number of Conditions: 2
+  |     Condition C1 --> (LL:12)
+  |     Condition C2 --> (LL:17)
+  |
+  |  Executed MC/DC Test Vectors:
+  |
+  |     C1, C2    Result
+  |  1 { F,  -  = F      }
+  |  2 { T,  F  = F      }
+  |  3 { T,  T  = T      }
+  |
+  |  C1-Pair: covered: (1,3)
+  |  C2-Pair: covered: (2,3)
+  |  MC/DC Coverage for Decision: 100.00%
+  |
+  ------------------
+   LL|      1|            say("b and c");
+   LL|      2|        }
+   LL|      0|    } else {
+   LL|      0|        say("neither a nor b");
+   LL|      0|    }
+   LL|      3|}
+   LL|       |
+   LL|       |#[coverage(off)]
+   LL|       |fn main() {
+   LL|       |    mcdc_check_neither(false, false);
+   LL|       |    mcdc_check_neither(false, true);
+   LL|       |
+   LL|       |    mcdc_check_a(true, true);
+   LL|       |    mcdc_check_a(false, true);
+   LL|       |
+   LL|       |    mcdc_check_b(true, true);
+   LL|       |    mcdc_check_b(true, false);
+   LL|       |
+   LL|       |    mcdc_check_both(false, true);
+   LL|       |    mcdc_check_both(true, true);
+   LL|       |    mcdc_check_both(true, false);
+   LL|       |
+   LL|       |    mcdc_check_tree_decision(false, true, true);
+   LL|       |    mcdc_check_tree_decision(true, true, false);
+   LL|       |    mcdc_check_tree_decision(true, false, false);
+   LL|       |    mcdc_check_tree_decision(true, false, true);
+   LL|       |
+   LL|       |    mcdc_check_not_tree_decision(false, true, true);
+   LL|       |    mcdc_check_not_tree_decision(true, true, false);
+   LL|       |    mcdc_check_not_tree_decision(true, false, false);
+   LL|       |    mcdc_check_not_tree_decision(true, false, true);
+   LL|       |
+   LL|       |    mcdc_nested_if(true, false, true);
+   LL|       |    mcdc_nested_if(true, true, true);
+   LL|       |    mcdc_nested_if(true, true, false);
+   LL|       |}
+   LL|       |
+   LL|       |#[coverage(off)]
+   LL|       |fn say(message: &str) {
+   LL|       |    core::hint::black_box(message);
+   LL|       |}
+
diff --git a/tests/coverage/mcdc_if.rs b/tests/coverage/mcdc_if.rs
new file mode 100644
index 00000000000..a85843721c6
--- /dev/null
+++ b/tests/coverage/mcdc_if.rs
@@ -0,0 +1,103 @@
+#![feature(coverage_attribute)]
+//@ edition: 2021
+//@ min-llvm-version: 18
+//@ compile-flags: -Zcoverage-options=mcdc
+//@ llvm-cov-flags: --show-mcdc
+
+fn mcdc_check_neither(a: bool, b: bool) {
+    if a && b {
+        say("a and b");
+    } else {
+        say("not both");
+    }
+}
+
+fn mcdc_check_a(a: bool, b: bool) {
+    if a && b {
+        say("a and b");
+    } else {
+        say("not both");
+    }
+}
+
+fn mcdc_check_b(a: bool, b: bool) {
+    if a && b {
+        say("a and b");
+    } else {
+        say("not both");
+    }
+}
+
+fn mcdc_check_both(a: bool, b: bool) {
+    if a && b {
+        say("a and b");
+    } else {
+        say("not both");
+    }
+}
+
+fn mcdc_check_tree_decision(a: bool, b: bool, c: bool) {
+    // This expression is intentionally written in a way
+    // where 100% branch coverage indicates 100% mcdc coverage.
+    if a && (b || c) {
+        say("pass");
+    } else {
+        say("reject");
+    }
+}
+
+fn mcdc_check_not_tree_decision(a: bool, b: bool, c: bool) {
+    // Contradict to `mcdc_check_tree_decision`,
+    // 100% branch coverage of this expression does not mean indicates 100% mcdc coverage.
+    if (a || b) && c {
+        say("pass");
+    } else {
+        say("reject");
+    }
+}
+
+fn mcdc_nested_if(a: bool, b: bool, c: bool) {
+    if a || b {
+        say("a or b");
+        if b && c {
+            say("b and c");
+        }
+    } else {
+        say("neither a nor b");
+    }
+}
+
+#[coverage(off)]
+fn main() {
+    mcdc_check_neither(false, false);
+    mcdc_check_neither(false, true);
+
+    mcdc_check_a(true, true);
+    mcdc_check_a(false, true);
+
+    mcdc_check_b(true, true);
+    mcdc_check_b(true, false);
+
+    mcdc_check_both(false, true);
+    mcdc_check_both(true, true);
+    mcdc_check_both(true, false);
+
+    mcdc_check_tree_decision(false, true, true);
+    mcdc_check_tree_decision(true, true, false);
+    mcdc_check_tree_decision(true, false, false);
+    mcdc_check_tree_decision(true, false, true);
+
+    mcdc_check_not_tree_decision(false, true, true);
+    mcdc_check_not_tree_decision(true, true, false);
+    mcdc_check_not_tree_decision(true, false, false);
+    mcdc_check_not_tree_decision(true, false, true);
+
+    mcdc_nested_if(true, false, true);
+    mcdc_nested_if(true, true, true);
+    mcdc_nested_if(true, true, false);
+}
+
+#[coverage(off)]
+fn say(message: &str) {
+    core::hint::black_box(message);
+}
diff --git a/tests/ui/instrument-coverage/coverage-options.bad.stderr b/tests/ui/instrument-coverage/coverage-options.bad.stderr
index ca82dc5bdb9..f6e5421f878 100644
--- a/tests/ui/instrument-coverage/coverage-options.bad.stderr
+++ b/tests/ui/instrument-coverage/coverage-options.bad.stderr
@@ -1,2 +1,2 @@
-error: incorrect value `bad` for unstable option `coverage-options` - `branch` or `no-branch` was expected
+error: incorrect value `bad` for unstable option `coverage-options` - either  `no-branch`, `branch` or `mcdc` was expected
 
diff --git a/tests/ui/instrument-coverage/coverage-options.rs b/tests/ui/instrument-coverage/coverage-options.rs
index a62e0554f76..50c01ed29b5 100644
--- a/tests/ui/instrument-coverage/coverage-options.rs
+++ b/tests/ui/instrument-coverage/coverage-options.rs
@@ -8,7 +8,13 @@
 //@ [no-branch] check-pass
 //@ [no-branch] compile-flags: -Zcoverage-options=no-branch
 
+//@ [mcdc] check-pass
+//@ [mcdc] compile-flags: -Zcoverage-options=mcdc
+
 //@ [bad] check-fail
 //@ [bad] compile-flags: -Zcoverage-options=bad
 
+//@ [conflict] check-fail
+//@ [conflict] compile-flags: -Zcoverage-options=no-branch,mcdc
+
 fn main() {}