[InstCombine] Print a debug message when we constant fold an operand during worklist...

InstCombine tries to constant fold instruction operands during worklist building, but we don't print that we're doing this.

We also set a change flag here that causes us to rebuild and rerun the worklist one more time even if processing the worklist itself created no additional changes. So in the log I saw two inst combine runs that visited all instructions without printing that anything was changed. I may be submitting another patch to remove the change flag unless I can find some reason why we should be doing that.

Differential Revision: https://reviews.llvm.org/D31091

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298264 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index a0b936681289bbe1f02d81a388d95631a89524ca..7586e481028bb21618e34516b26237507b3e28e0 100644 (file)
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3032,6 +3032,8 @@ static bool AddReachableCodeToWorklist(BasicBlock *BB, const DataLayout &DL,
           FoldRes = C;
 
         if (FoldRes != C) {
+          DEBUG(dbgs() << "IC: ConstFold operand of: " << *Inst << "\n    Old = " << *C
+                       << "\n    New = " << *FoldRes << '\n');
           *i = FoldRes;
           MadeIRChange = true;
         }