[llvm] [Transforms][Utils] Handle live-outs not defined in the loop in LoopSplitUtils (PR #214453)

[Ramkumar Ramachandra via llvm-commits]

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@@ -364,13 +364,23 @@ void LoopSplitUtils::collectEscapingValues(SplitState &S) {
     assert(LCSSAPhi.getNumIncomingValues() == 1 &&
            "exit block not in LCSSA form");
     Value *LiveOutDef = LCSSAPhi.getIncomingValue(0);
+    LCSSAPhi.replaceAllUsesWith(LiveOutDef);
+    LCSSAPhi.eraseFromParent();
+
+    // A live-out not defined inside the loop (constant or loop-invariant) holds
+    // the same value in every partition, so the replaceAllUsesWith above is
+    // already correct and it needs no per-partition reconstruction. Skipping it
+    // also avoids walking uses() on a constant (which has no use list) and
+    // rewriting any pre-loop uses of an outside definition.
+    auto *DefInst = dyn_cast<Instruction>(LiveOutDef);
+    if (!DefInst || !L->contains(DefInst))
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artagnon wrote:

How can L not contain DefInst?

https://github.com/llvm/llvm-project/pull/214453