[llvm] [MemCpyOpt] fix miscompile for non-dominated use of src alloca for stack-move optimization (PR #66618)

[Nikita Popov via llvm-commits]

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@@ -1486,6 +1486,14 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
       Instruction *I = Worklist.back();
       Worklist.pop_back();
       for (const Use &U : I->uses()) {
+        auto *UI = cast<Instruction>(U.getUser());
+        // If any use that isn't dominated by SrcAlloca exists, non-dominating
+        // uses will be produced.
+        if (!DT->dominates(SrcAlloca, UI)) {
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nikic wrote:

Add a TODO that we could move the SrcAlloca up instead.

https://github.com/llvm/llvm-project/pull/66618