Wrong debug info generated at -O2 (-O0 is correct)

Instcombiner pass was erasing trivially dead instruction without updating dependent llvm.dbg.value.
which was not showing programmer current state of variables while debugging.
As a part of this fix I did following,
Iterate throught all the users (llvm.dbg) of a instruction which is trivially dead and set each if them undef, Before deleting the instruction.
Now user will see optimized out, when try to print those variables.
This fixes
https://bugs.llvm.org/show_bug.cgi?id=43893

This is my first fix to llvm.

Patch by kamlesh kumar!

Differential Revision: https://reviews.llvm.org/D69809

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 1dbc06d92e7..aabedbda7e6 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -705,7 +705,7 @@ public:
   Instruction *eraseInstFromFunction(Instruction &I) {
     LLVM_DEBUG(dbgs() << "IC: ERASE " << I << '\n');
     assert(I.use_empty() && "Cannot erase instruction that is used!");
-    salvageDebugInfo(I);
+    salvageDebugInfoOrMarkUndef(I);
 
     // Make sure that we reprocess all operands now that we reduced their
     // use counts.