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.

2 files changed, 118 insertions, 3 deletions

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,