[llvm] [MemProf][PGO] Prevent dropping of profile metadata during optimization (PR #121359)

[Nikita Popov via llvm-commits]

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@@ -3379,6 +3379,10 @@ void llvm::combineMetadata(Instruction *K, const Instruction *J,
           K->setMetadata(Kind,
             MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
         break;
+      case LLVMContext::MD_memprof:
+      case LLVMContext::MD_callsite:
+        // Preserve !memprof and !callsite metadata on K.
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nikic wrote:

If it's not possible to correctly merge the metadata, we shouldn't include it in combineMetadata, as it will produce an incorrect result for the sink/hoist cases. It sounds like it would be sufficient for your case to only fix what MemCpyOptimizer does (to avoid merging for memprof/callsite in the first place). I'd rather not introduce incorrect merging logic in combineMetadata to cancel out incorrect code in MemCpyOptimizer...

https://github.com/llvm/llvm-project/pull/121359