[llvm] [CloneFunciton] Optimize PHI incoming value removal using reverse iteration (NFC) (PR #171955)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (int-zjt)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/171955.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/Utils/CloneFunction.cpp (+4-5) 


``````````diff
diff --git a/llvm/lib/Transforms/Utils/CloneFunction.cpp b/llvm/lib/Transforms/Utils/CloneFunction.cpp
index 32924e7b69fdc..1d0244c54a282 100644
--- a/llvm/lib/Transforms/Utils/CloneFunction.cpp
+++ b/llvm/lib/Transforms/Utils/CloneFunction.cpp
@@ -35,6 +35,7 @@
 #include "llvm/Transforms/Utils/Cloning.h"
 #include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/ValueMapper.h"
+#include <cstdint>
 #include <map>
 #include <optional>
 using namespace llvm;
@@ -785,7 +786,7 @@ void llvm::CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
          ++phino) {
       OPN = PHIToResolve[phino];
       PHINode *PN = cast<PHINode>(VMap[OPN]);
-      for (unsigned pred = 0, e = NumPreds; pred != e; ++pred) {
+      for (int64_t pred = NumPreds - 1; pred >= 0; --pred) {
         Value *V = VMap.lookup(PN->getIncomingBlock(pred));
         if (BasicBlock *MappedBlock = cast_or_null<BasicBlock>(V)) {
           Value *InVal =
@@ -794,11 +795,9 @@ void llvm::CloneAndPruneIntoFromInst(Function *NewFunc, const Function *OldFunc,
           assert(InVal && "Unknown input value?");
           PN->setIncomingValue(pred, InVal);
           PN->setIncomingBlock(pred, MappedBlock);
-        } else {
-          PN->removeIncomingValue(pred, false);
-          --pred; // Revisit the next entry.
-          --e;
+          continue;
         }
+        PN->removeIncomingValue(pred, false);
       }
     }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/171955