[llvm] [Transforms] Speed up SSAUpdater::FindExistingPHI (PR #100281)

[Nikita Popov via llvm-commits]

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@@ -413,26 +414,34 @@ class SSAUpdaterImpl {
   /// FindExistingPHI - Look through the PHI nodes in a block to see if any of
   /// them match what is needed.
   void FindExistingPHI(BlkT *BB, BlockListTy *BlockList) {
+    SmallVector<BBInfo *, 20> TaggedBlocks;
     for (auto &SomePHI : BB->phis()) {
-      if (CheckIfPHIMatches(&SomePHI)) {
+      if (CheckIfPHIMatches(&SomePHI, TaggedBlocks)) {
         RecordMatchingPHIs(BlockList);
         break;
       }
-      // Match failed: clear all the PHITag values.
-      for (typename BlockListTy::iterator I = BlockList->begin(),
-             E = BlockList->end(); I != E; ++I)
-        (*I)->PHITag = nullptr;
     }
   }
 
   /// CheckIfPHIMatches - Check if a PHI node matches the placement and values
   /// in the BBMap.
-  bool CheckIfPHIMatches(PhiT *PHI) {
+  bool CheckIfPHIMatches(PhiT *PHI, SmallVector<BBInfo *, 20> &TaggedBlocks) {
+    // Match failed: clear all the PHITag values. Only need to clear visited
+    // blocks.
+    auto Cleanup = make_scope_exit([&]() {
+      for (BBInfo *TaggedBlock : TaggedBlocks) {
+        TaggedBlock->PHITag = nullptr;
+      }
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nikic wrote:

Drop braces.

https://github.com/llvm/llvm-project/pull/100281