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
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 1dbc06d..aabedbd 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -705,7 +705,7 @@
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.
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index a3dfbfa..dd2907a 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3414,8 +3414,7 @@
if (isInstructionTriviallyDead(Inst, TLI)) {
++NumDeadInst;
LLVM_DEBUG(dbgs() << "IC: DCE: " << *Inst << '\n');
- if (!salvageDebugInfo(*Inst))
- replaceDbgUsesWithUndef(Inst);
+ salvageDebugInfoOrMarkUndef(*Inst);
Inst->eraseFromParent();
MadeIRChange = true;
continue;
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 5bcd057..d5ae13a 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1611,6 +1611,11 @@
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();