[llvm][LowerConstantIntrinsics] add debug statements

[nickdesaulniers]

Summary

These can help us better understand what builtin_constant_p and
builtin_object_size get folded to.

$ clang -mllvm -debug-only=lower-is-constant-intrinsic ...

[void]

These look fine, so accepted. One comment: Would it be good to somehow identify in the message the intrinsic each message is folding?

[nickdesaulniers]

In D143521#4135797, @void wrote:

These look fine, so accepted. One comment: Would it be good to somehow identify in the message the intrinsic each message is folding?

I think that's what II is in the message, right?

[void]

In D143521#4162405, @nickdesaulniers wrote:

In D143521#4135797, @void wrote:

These look fine, so accepted. One comment: Would it be good to somehow identify in the message the intrinsic each message is folding?

I think that's what II is in the message, right?

Doh! Of course. :-)

llvm/lib/Transforms/Scalar/LowerConstantIntrinsics.cpp

 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Pass.h"
+#include "llvm/Support/Debug.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include <optional>
 
 using namespace llvm;
 using namespace llvm::PatternMatch;
 
 #define DEBUG_TYPE "lower-is-constant-intrinsic"
for (WeakTrackingVH &VH: Worklist) {
     if (!II)
       continue;
     Value *NewValue;
     switch (II->getIntrinsicID()) {
     default:
       continue;
     case Intrinsic::is_constant:
       NewValue = lowerIsConstantIntrinsic(II);
+      LLVM_DEBUG(dbgs() << "Folding " << *II << " to " << *NewValue << "\n");
       IsConstantIntrinsicsHandled++;
       break;
     case Intrinsic::objectsize:
       NewValue = lowerObjectSizeCall(II, DL, &TLI, true);
+      LLVM_DEBUG(dbgs() << "Folding " << *II << " to " << *NewValue << "\n");
       ObjectSizeIntrinsicsHandled++;
       break;
     }
     HasDeadBlocks |= replaceConditionalBranchesOnConstant(
         II, NewValue, DTU ? &*DTU : nullptr);
   }
   if (HasDeadBlocks)
     removeUnreachableBlocks(F, DTU ? &*DTU : nullptr);