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, 5 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 5bcd05757ec..d5ae13ad285 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1611,6 +1611,11 @@ bool llvm::salvageDebugInfo(Instruction &I) {
   return salvageDebugInfoForDbgValues(I, DbgUsers);
 }
 
+void llvm::salvageDebugInfoOrMarkUndef(Instruction &I) {
+  if (!salvageDebugInfo(I))
+    replaceDbgUsesWithUndef(&I);
+}
+
 bool llvm::salvageDebugInfoForDbgValues(
     Instruction &I, ArrayRef<DbgVariableIntrinsic *> DbgUsers) {
   auto &Ctx = I.getContext();