[clang] [llvm] MSan: poison the default-init allocation before calling constructors (PR #188001)

[Matt Arsenault via cfe-commits]

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@@ -239,11 +239,13 @@ Instruction *InstCombinerImpl::SimplifyAnyMemSet(AnyMemSetInst *MI) {
   // Remove memset with an undef value.
   // FIXME: This is technically incorrect because it might overwrite a poison
   // value. Change to PoisonValue once #52930 is resolved.
-  if (isa<UndefValue>(MI->getValue())) {
-    // Set the size of the copy to 0, it will be deleted on the next iteration.
-    MI->setLength((uint64_t)0);
-    return MI;
-  }
+  // Postponed to SelectionDAG lowering phase.
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arsenm wrote:

The comment doesn't make sense and this shouldn't be in this PR 

https://github.com/llvm/llvm-project/pull/188001