We don't need `NonNull::as_ptr` debuginfo

Stop pessimizing the use of local variables in core by skipping debug info for MIR temporaries in tiny (single-BB) functions.

For functions as simple as this -- `Pin::new`, etc -- nobody every actually wants debuginfo for them in the first place.  They're more like intrinsics than real functions, and stepping over them is good.

11 files changed, 170 insertions, 106 deletions

diff --git a/compiler/rustc_mir_transform/src/lib.rs b/compiler/rustc_mir_transform/src/lib.rs
index f0fcb44603b..5c090bf7cad 100644
--- a/compiler/rustc_mir_transform/src/lib.rs
+++ b/compiler/rustc_mir_transform/src/lib.rs
@@ -189,6 +189,7 @@ declare_passes! {
     mod simplify_comparison_integral : SimplifyComparisonIntegral;
     mod single_use_consts : SingleUseConsts;
     mod sroa : ScalarReplacementOfAggregates;
+    mod strip_debuginfo : StripDebugInfo;
     mod unreachable_enum_branching : UnreachableEnumBranching;
     mod unreachable_prop : UnreachablePropagation;
     mod validate : Validator;
@@ -699,6 +700,8 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
             &o1(simplify_branches::SimplifyConstCondition::Final),
             &o1(remove_noop_landing_pads::RemoveNoopLandingPads),
             &o1(simplify::SimplifyCfg::Final),
+            // After the last SimplifyCfg, because this wants one-block functions.
+            &strip_debuginfo::StripDebugInfo,
             &copy_prop::CopyProp,
             &dead_store_elimination::DeadStoreElimination::Final,
             &nrvo::RenameReturnPlace,
diff --git a/compiler/rustc_mir_transform/src/strip_debuginfo.rs b/compiler/rustc_mir_transform/src/strip_debuginfo.rs
new file mode 100644
index 00000000000..438c75726bb
--- /dev/null
+++ b/compiler/rustc_mir_transform/src/strip_debuginfo.rs
@@ -0,0 +1,34 @@
+use rustc_middle::mir::*;
+use rustc_middle::ty::TyCtxt;
+use rustc_session::config::MirStripDebugInfo;
+
+/// Conditionally remove some of the VarDebugInfo in MIR.
+///
+/// In particular, stripping non-parameter debug info for tiny, primitive-like
+/// methods in core saves work later, and nobody ever wanted to use it anyway.
+pub(super) struct StripDebugInfo;
+
+impl<'tcx> crate::MirPass<'tcx> for StripDebugInfo {
+    fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
+        sess.opts.unstable_opts.mir_strip_debuginfo != MirStripDebugInfo::None
+    }
+
+    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        match tcx.sess.opts.unstable_opts.mir_strip_debuginfo {
+            MirStripDebugInfo::None => return,
+            MirStripDebugInfo::AllLocals => {}
+            MirStripDebugInfo::LocalsInTinyFunctions
+                if let TerminatorKind::Return { .. } =
+                    body.basic_blocks[START_BLOCK].terminator().kind => {}
+            MirStripDebugInfo::LocalsInTinyFunctions => return,
+        }
+
+        body.var_debug_info.retain(|vdi| {
+            matches!(
+                vdi.value,
+                VarDebugInfoContents::Place(place)
+                    if place.local.as_usize() <= body.arg_count && place.local != RETURN_PLACE,
+            )
+        });
+    }
+}
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index cb6d539cdf9..936c2ca87d6 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -472,6 +472,13 @@ impl ToString for DebugInfoCompression {
     }
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Hash)]
+pub enum MirStripDebugInfo {
+    None,
+    LocalsInTinyFunctions,
+    AllLocals,
+}
+
 /// Split debug-information is enabled by `-C split-debuginfo`, this enum is only used if split
 /// debug-information is enabled (in either `Packed` or `Unpacked` modes), and the platform
 /// uses DWARF for debug-information.
@@ -2900,10 +2907,10 @@ pub(crate) mod dep_tracking {
         BranchProtection, CFGuard, CFProtection, CollapseMacroDebuginfo, CoverageOptions,
         CrateType, DebugInfo, DebugInfoCompression, ErrorOutputType, FmtDebug, FunctionReturn,
         InliningThreshold, InstrumentCoverage, InstrumentXRay, LinkerPluginLto, LocationDetail,
-        LtoCli, NextSolverConfig, OomStrategy, OptLevel, OutFileName, OutputType, OutputTypes,
-        PatchableFunctionEntry, Polonius, RemapPathScopeComponents, ResolveDocLinks,
-        SourceFileHashAlgorithm, SplitDwarfKind, SwitchWithOptPath, SymbolManglingVersion,
-        WasiExecModel,
+        LtoCli, MirStripDebugInfo, NextSolverConfig, OomStrategy, OptLevel, OutFileName,
+        OutputType, OutputTypes, PatchableFunctionEntry, Polonius, RemapPathScopeComponents,
+        ResolveDocLinks, SourceFileHashAlgorithm, SplitDwarfKind, SwitchWithOptPath,
+        SymbolManglingVersion, WasiExecModel,
     };
     use crate::lint;
     use crate::utils::NativeLib;
@@ -2971,6 +2978,7 @@ pub(crate) mod dep_tracking {
         LtoCli,
         DebugInfo,
         DebugInfoCompression,
+        MirStripDebugInfo,
         CollapseMacroDebuginfo,
         UnstableFeatures,
         NativeLib,
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 9e95e278325..124f0a2525f 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -391,6 +391,8 @@ mod desc {
     pub(crate) const parse_cfprotection: &str = "`none`|`no`|`n` (default), `branch`, `return`, or `full`|`yes`|`y` (equivalent to `branch` and `return`)";
     pub(crate) const parse_debuginfo: &str = "either an integer (0, 1, 2), `none`, `line-directives-only`, `line-tables-only`, `limited`, or `full`";
     pub(crate) const parse_debuginfo_compression: &str = "one of `none`, `zlib`, or `zstd`";
+    pub(crate) const parse_mir_strip_debuginfo: &str =
+        "one of `none`, `locals-in-tiny-functions`, or `all-locals`";
     pub(crate) const parse_collapse_macro_debuginfo: &str = "one of `no`, `external`, or `yes`";
     pub(crate) const parse_strip: &str = "either `none`, `debuginfo`, or `symbols`";
     pub(crate) const parse_linker_flavor: &str = ::rustc_target::spec::LinkerFlavorCli::one_of();
@@ -925,6 +927,16 @@ pub mod parse {
         true
     }
 
+    pub(crate) fn parse_mir_strip_debuginfo(slot: &mut MirStripDebugInfo, v: Option<&str>) -> bool {
+        match v {
+            Some("none") => *slot = MirStripDebugInfo::None,
+            Some("locals-in-tiny-functions") => *slot = MirStripDebugInfo::LocalsInTinyFunctions,
+            Some("all-locals") => *slot = MirStripDebugInfo::AllLocals,
+            _ => return false,
+        };
+        true
+    }
+
     pub(crate) fn parse_linker_flavor(slot: &mut Option<LinkerFlavorCli>, v: Option<&str>) -> bool {
         match v.and_then(LinkerFlavorCli::from_str) {
             Some(lf) => *slot = Some(lf),
@@ -1893,6 +1905,8 @@ options! {
     #[rustc_lint_opt_deny_field_access("use `Session::mir_opt_level` instead of this field")]
     mir_opt_level: Option<usize> = (None, parse_opt_number, [TRACKED],
         "MIR optimization level (0-4; default: 1 in non optimized builds and 2 in optimized builds)"),
+    mir_strip_debuginfo: MirStripDebugInfo = (MirStripDebugInfo::None, parse_mir_strip_debuginfo, [TRACKED],
+        "Whether to remove some of the MIR debug info from methods.  Default: None"),
     move_size_limit: Option<usize> = (None, parse_opt_number, [TRACKED],
         "the size at which the `large_assignments` lint starts to be emitted"),
     mutable_noalias: bool = (true, parse_bool, [TRACKED],
diff --git a/src/bootstrap/src/core/builder/cargo.rs b/src/bootstrap/src/core/builder/cargo.rs
index 38abca8b8da..a3c305997c1 100644
--- a/src/bootstrap/src/core/builder/cargo.rs
+++ b/src/bootstrap/src/core/builder/cargo.rs
@@ -1208,6 +1208,11 @@ impl Builder<'_> {
             // even if we're not going to output debuginfo for the crate we're currently building,
             // so that it'll be available when downstream consumers of std try to use it.
             rustflags.arg("-Zinline-mir-preserve-debug");
+
+            // FIXME: always pass this after the next `#[cfg(bootstrap)]` update.
+            if compiler.stage != 0 {
+                rustflags.arg("-Zmir_strip_debuginfo=locals-in-tiny-functions");
+            }
         }
 
         Cargo {
diff --git a/tests/codegen/mem-replace-big-type.rs b/tests/codegen/mem-replace-big-type.rs
index e62adfa0ba6..0b2229ba7d1 100644
--- a/tests/codegen/mem-replace-big-type.rs
+++ b/tests/codegen/mem-replace-big-type.rs
@@ -25,9 +25,10 @@ pub fn replace_big(dst: &mut Big, src: Big) -> Big {
 // CHECK-NOT: call void @llvm.memcpy
 
 // For a large type, we expect exactly three `memcpy`s
-// CHECK-LABEL: define internal void @{{.+}}mem{{.+}}replace{{.+}}sret([56 x i8])
+// CHECK-LABEL: define internal void @{{.+}}mem{{.+}}replace{{.+}}(ptr
+// CHECK-SAME: sret([56 x i8]){{.+}}[[RESULT:%.+]], ptr{{.+}}%dest, ptr{{.+}}%src)
 // CHECK-NOT: call void @llvm.memcpy
-// CHECK: call void @llvm.memcpy.{{.+}}(ptr align 8 %result, ptr align 8 %dest, i{{.*}} 56, i1 false)
+// CHECK: call void @llvm.memcpy.{{.+}}(ptr align 8 [[RESULT]], ptr align 8 %dest, i{{.*}} 56, i1 false)
 // CHECK-NOT: call void @llvm.memcpy
 // CHECK: call void @llvm.memcpy.{{.+}}(ptr align 8 %dest, ptr align 8 %src, i{{.*}} 56, i1 false)
 // CHECK-NOT: call void @llvm.memcpy
diff --git a/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-abort.diff b/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-abort.diff
index 94017f028cc..56d4d50e967 100644
--- a/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-abort.diff
+++ b/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-abort.diff
@@ -16,7 +16,6 @@
 +     scope 3 (inlined Pin::<&mut {coroutine@$DIR/inline_coroutine.rs:20:5: 20:8}>::new) {
 +         debug pointer => _3;
 +         scope 4 (inlined Pin::<&mut {coroutine@$DIR/inline_coroutine.rs:20:5: 20:8}>::new_unchecked) {
-+             debug pointer => _3;
 +         }
 +     }
 +     scope 5 (inlined g::{closure#0}) {
diff --git a/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-unwind.diff b/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-unwind.diff
index 858f9ace9b4..751916a00f1 100644
--- a/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-unwind.diff
+++ b/tests/mir-opt/inline/inline_coroutine.main.Inline.panic-unwind.diff
@@ -16,7 +16,6 @@
 +     scope 3 (inlined Pin::<&mut {coroutine@$DIR/inline_coroutine.rs:20:5: 20:8}>::new) {
 +         debug pointer => _3;
 +         scope 4 (inlined Pin::<&mut {coroutine@$DIR/inline_coroutine.rs:20:5: 20:8}>::new_unchecked) {
-+             debug pointer => _3;
 +         }
 +     }
 +     scope 5 (inlined g::{closure#0}) {
diff --git a/tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-abort.mir b/tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-abort.mir
index 2efbb6d9904..3f0d60b46f4 100644
--- a/tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-abort.mir
+++ b/tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-abort.mir
@@ -7,48 +7,36 @@ fn vec_deref_to_slice(_1: &Vec<u8>) -> &[u8] {
         debug self => _1;
         scope 2 (inlined Vec::<u8>::as_slice) {
             debug self => _1;
-            let mut _9: *const u8;
-            let mut _10: usize;
+            let mut _7: *const u8;
+            let mut _8: usize;
             scope 3 (inlined Vec::<u8>::as_ptr) {
                 debug self => _1;
-                let mut _2: &alloc::raw_vec::RawVec<u8>;
-                let mut _8: *mut u8;
+                let mut _6: *mut u8;
                 scope 4 (inlined alloc::raw_vec::RawVec::<u8>::ptr) {
-                    debug self => _2;
-                    let mut _3: &alloc::raw_vec::RawVecInner;
                     scope 5 (inlined alloc::raw_vec::RawVecInner::ptr::<u8>) {
-                        debug self => _3;
-                        let mut _7: std::ptr::NonNull<u8>;
+                        let mut _5: std::ptr::NonNull<u8>;
                         scope 6 (inlined alloc::raw_vec::RawVecInner::non_null::<u8>) {
-                            debug self => _3;
-                            let mut _4: std::ptr::NonNull<u8>;
+                            let mut _2: std::ptr::NonNull<u8>;
                             scope 7 (inlined Unique::<u8>::cast::<u8>) {
-                                debug ((self: Unique<u8>).0: std::ptr::NonNull<u8>) => _4;
-                                debug ((self: Unique<u8>).1: std::marker::PhantomData<u8>) => const PhantomData::<u8>;
                                 scope 8 (inlined NonNull::<u8>::cast::<u8>) {
-                                    debug self => _4;
-                                    let mut _5: *mut u8;
-                                    let mut _6: *const u8;
+                                    let mut _3: *mut u8;
+                                    let mut _4: *const u8;
                                     scope 9 (inlined NonNull::<u8>::as_ptr) {
-                                        debug self => _4;
                                     }
                                 }
                             }
                             scope 10 (inlined Unique::<u8>::as_non_null_ptr) {
-                                debug ((self: Unique<u8>).0: std::ptr::NonNull<u8>) => _7;
-                                debug ((self: Unique<u8>).1: std::marker::PhantomData<u8>) => const PhantomData::<u8>;
                             }
                         }
                         scope 11 (inlined NonNull::<u8>::as_ptr) {
-                            debug self => _7;
                         }
                     }
                 }
             }
             scope 12 (inlined std::slice::from_raw_parts::<'_, u8>) {
-                debug data => _9;
-                debug len => _10;
-                let _11: *const [u8];
+                debug data => _7;
+                debug len => _8;
+                let _9: *const [u8];
                 scope 13 (inlined core::ub_checks::check_language_ub) {
                     scope 14 (inlined core::ub_checks::check_language_ub::runtime) {
                     }
@@ -58,11 +46,10 @@ fn vec_deref_to_slice(_1: &Vec<u8>) -> &[u8] {
                 scope 16 (inlined align_of::<u8>) {
                 }
                 scope 17 (inlined slice_from_raw_parts::<u8>) {
-                    debug data => _9;
-                    debug len => _10;
+                    debug data => _7;
+                    debug len => _8;
                     scope 18 (inlined std::ptr::from_raw_parts::<[u8], u8>) {
-                        debug data_pointer => _9;
-                        debug metadata => _10;
+                        debug data_pointer => _7;
                     }
                 }
             }
@@ -70,37 +57,31 @@ fn vec_deref_to_slice(_1: &Vec<u8>) -> &[u8] {
     }
 
     bb0: {
-        StorageLive(_8);
-        StorageLive(_9);
+        StorageLive(_6);
+        StorageLive(_7);
+        StorageLive(_5);
         StorageLive(_2);
-        _2 = &((*_1).0: alloc::raw_vec::RawVec<u8>);
+        _2 = copy (((((*_1).0: alloc::raw_vec::RawVec<u8>).0: alloc::raw_vec::RawVecInner).0: std::ptr::Unique<u8>).0: std::ptr::NonNull<u8>);
         StorageLive(_3);
-        _3 = &(((*_1).0: alloc::raw_vec::RawVec<u8>).0: alloc::raw_vec::RawVecInner);
-        StorageLive(_7);
         StorageLive(_4);
-        _4 = copy (((((*_1).0: alloc::raw_vec::RawVec<u8>).0: alloc::raw_vec::RawVecInner).0: std::ptr::Unique<u8>).0: std::ptr::NonNull<u8>);
-        StorageLive(_5);
-        StorageLive(_6);
-        _5 = copy _4 as *mut u8 (Transmute);
-        _6 = copy _5 as *const u8 (PtrToPtr);
-        _7 = NonNull::<u8> { pointer: move _6 };
-        StorageDead(_6);
-        StorageDead(_5);
+        _3 = copy _2 as *mut u8 (Transmute);
+        _4 = copy _3 as *const u8 (PtrToPtr);
+        _5 = NonNull::<u8> { pointer: move _4 };
         StorageDead(_4);
-        _8 = copy _7 as *mut u8 (Transmute);
-        StorageDead(_7);
         StorageDead(_3);
-        _9 = copy _8 as *const u8 (PtrToPtr);
         StorageDead(_2);
-        StorageLive(_10);
-        _10 = copy ((*_1).1: usize);
-        StorageLive(_11);
-        _11 = *const [u8] from (copy _9, copy _10);
-        _0 = &(*_11);
-        StorageDead(_11);
-        StorageDead(_10);
+        _6 = copy _5 as *mut u8 (Transmute);
+        StorageDead(_5);
+        _7 = copy _6 as *const u8 (PtrToPtr);
+        StorageLive(_8);
+        _8 = copy ((*_1).1: usize);
+        StorageLive(_9);
+        _9 = *const [u8] from (copy _7, copy _8);
+        _0 = &(*_9);
         StorageDead(_9);
         StorageDead(_8);
+        StorageDead(_7);
+        StorageDead(_6);
         return;
     }
 }
diff --git a/tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-unwind.mir b/tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-unwind.mir
index 2efbb6d9904..3f0d60b46f4 100644
--- a/tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-unwind.mir
+++ b/tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-unwind.mir
@@ -7,48 +7,36 @@ fn vec_deref_to_slice(_1: &Vec<u8>) -> &[u8] {
         debug self => _1;
         scope 2 (inlined Vec::<u8>::as_slice) {
             debug self => _1;
-            let mut _9: *const u8;
-            let mut _10: usize;
+            let mut _7: *const u8;
+            let mut _8: usize;
             scope 3 (inlined Vec::<u8>::as_ptr) {
                 debug self => _1;
-                let mut _2: &alloc::raw_vec::RawVec<u8>;
-                let mut _8: *mut u8;
+                let mut _6: *mut u8;
                 scope 4 (inlined alloc::raw_vec::RawVec::<u8>::ptr) {
-                    debug self => _2;
-                    let mut _3: &alloc::raw_vec::RawVecInner;
                     scope 5 (inlined alloc::raw_vec::RawVecInner::ptr::<u8>) {
-                        debug self => _3;
-                        let mut _7: std::ptr::NonNull<u8>;
+                        let mut _5: std::ptr::NonNull<u8>;
                         scope 6 (inlined alloc::raw_vec::RawVecInner::non_null::<u8>) {
-                            debug self => _3;
-                            let mut _4: std::ptr::NonNull<u8>;
+                            let mut _2: std::ptr::NonNull<u8>;
                             scope 7 (inlined Unique::<u8>::cast::<u8>) {
-                                debug ((self: Unique<u8>).0: std::ptr::NonNull<u8>) => _4;
-                                debug ((self: Unique<u8>).1: std::marker::PhantomData<u8>) => const PhantomData::<u8>;
                                 scope 8 (inlined NonNull::<u8>::cast::<u8>) {
-                                    debug self => _4;
-                                    let mut _5: *mut u8;
-                                    let mut _6: *const u8;
+                                    let mut _3: *mut u8;
+                                    let mut _4: *const u8;
                                     scope 9 (inlined NonNull::<u8>::as_ptr) {
-                                        debug self => _4;
                                     }
                                 }
                             }
                             scope 10 (inlined Unique::<u8>::as_non_null_ptr) {
-                                debug ((self: Unique<u8>).0: std::ptr::NonNull<u8>) => _7;
-                                debug ((self: Unique<u8>).1: std::marker::PhantomData<u8>) => const PhantomData::<u8>;
                             }
                         }
                         scope 11 (inlined NonNull::<u8>::as_ptr) {
-                            debug self => _7;
                         }
                     }
                 }
             }
             scope 12 (inlined std::slice::from_raw_parts::<'_, u8>) {
-                debug data => _9;
-                debug len => _10;
-                let _11: *const [u8];
+                debug data => _7;
+                debug len => _8;
+                let _9: *const [u8];
                 scope 13 (inlined core::ub_checks::check_language_ub) {
                     scope 14 (inlined core::ub_checks::check_language_ub::runtime) {
                     }
@@ -58,11 +46,10 @@ fn vec_deref_to_slice(_1: &Vec<u8>) -> &[u8] {
                 scope 16 (inlined align_of::<u8>) {
                 }
                 scope 17 (inlined slice_from_raw_parts::<u8>) {
-                    debug data => _9;
-                    debug len => _10;
+                    debug data => _7;
+                    debug len => _8;
                     scope 18 (inlined std::ptr::from_raw_parts::<[u8], u8>) {
-                        debug data_pointer => _9;
-                        debug metadata => _10;
+                        debug data_pointer => _7;
                     }
                 }
             }
@@ -70,37 +57,31 @@ fn vec_deref_to_slice(_1: &Vec<u8>) -> &[u8] {
     }
 
     bb0: {
-        StorageLive(_8);
-        StorageLive(_9);
+        StorageLive(_6);
+        StorageLive(_7);
+        StorageLive(_5);
         StorageLive(_2);
-        _2 = &((*_1).0: alloc::raw_vec::RawVec<u8>);
+        _2 = copy (((((*_1).0: alloc::raw_vec::RawVec<u8>).0: alloc::raw_vec::RawVecInner).0: std::ptr::Unique<u8>).0: std::ptr::NonNull<u8>);
         StorageLive(_3);
-        _3 = &(((*_1).0: alloc::raw_vec::RawVec<u8>).0: alloc::raw_vec::RawVecInner);
-        StorageLive(_7);
         StorageLive(_4);
-        _4 = copy (((((*_1).0: alloc::raw_vec::RawVec<u8>).0: alloc::raw_vec::RawVecInner).0: std::ptr::Unique<u8>).0: std::ptr::NonNull<u8>);
-        StorageLive(_5);
-        StorageLive(_6);
-        _5 = copy _4 as *mut u8 (Transmute);
-        _6 = copy _5 as *const u8 (PtrToPtr);
-        _7 = NonNull::<u8> { pointer: move _6 };
-        StorageDead(_6);
-        StorageDead(_5);
+        _3 = copy _2 as *mut u8 (Transmute);
+        _4 = copy _3 as *const u8 (PtrToPtr);
+        _5 = NonNull::<u8> { pointer: move _4 };
         StorageDead(_4);
-        _8 = copy _7 as *mut u8 (Transmute);
-        StorageDead(_7);
         StorageDead(_3);
-        _9 = copy _8 as *const u8 (PtrToPtr);
         StorageDead(_2);
-        StorageLive(_10);
-        _10 = copy ((*_1).1: usize);
-        StorageLive(_11);
-        _11 = *const [u8] from (copy _9, copy _10);
-        _0 = &(*_11);
-        StorageDead(_11);
-        StorageDead(_10);
+        _6 = copy _5 as *mut u8 (Transmute);
+        StorageDead(_5);
+        _7 = copy _6 as *const u8 (PtrToPtr);
+        StorageLive(_8);
+        _8 = copy ((*_1).1: usize);
+        StorageLive(_9);
+        _9 = *const [u8] from (copy _7, copy _8);
+        _0 = &(*_9);
         StorageDead(_9);
         StorageDead(_8);
+        StorageDead(_7);
+        StorageDead(_6);
         return;
     }
 }
diff --git a/tests/mir-opt/strip_debuginfo.rs b/tests/mir-opt/strip_debuginfo.rs
new file mode 100644
index 00000000000..310609e1e9d
--- /dev/null
+++ b/tests/mir-opt/strip_debuginfo.rs
@@ -0,0 +1,39 @@
+//@ revisions: NONE TINY ALL
+//@[NONE] compile-flags: -Zmir_strip_debuginfo=none
+//@[TINY] compile-flags: -Zmir_strip_debuginfo=locals-in-tiny-functions
+//@[ALL] compile-flags: -Zmir_strip_debuginfo=all-locals
+
+// CHECK: fn tiny_function
+fn tiny_function(end: u32) -> u32 {
+    // CHECK: debug end => _1;
+    // NONE: debug a =>
+    // NONE: debug b =>
+    // TINY-NOT: debug a =>
+    // TINY-NOT: debug b =>
+    // ALL-NOT: debug a =>
+    // ALL-NOT: debug b =>
+    let a = !end;
+    let b = a ^ 1;
+    b
+}
+
+#[inline(never)]
+fn opaque(_: u32) {}
+
+// CHECK: fn looping_function
+fn looping_function(end: u32) {
+    // CHECK: debug end => _1;
+    // NONE: debug i =>
+    // NONE: debug x =>
+    // TINY: debug i =>
+    // TINY: debug x =>
+    // ALL-NOT: debug i =>
+    // ALL-NOT: debug x =>
+    let mut i = 0;
+    while i < end {
+        let x = i ^ 1;
+        opaque(x);
+    }
+}
+
+fn main() {}