[llvm] [LoopPeel] LCSSA form is destroyed by LoopPeel, preserve it (PR #78696)

[Nikita Popov via llvm-commits]

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@@ -643,10 +644,22 @@ bool SimplifyIndvar::replaceIVUserWithLoopInvariant(Instruction *I) {
   }
 
   auto *Invariant = Rewriter.expandCodeFor(S, I->getType(), IP);
+  bool NeedToEmitLCSSAPhis = false;
+  if (!LI->replacementPreservesLCSSAForm(I, Invariant))
+    NeedToEmitLCSSAPhis = true;
 
   I->replaceAllUsesWith(Invariant);
   LLVM_DEBUG(dbgs() << "INDVARS: Replace IV user: " << *I
                     << " with loop invariant: " << *S << '\n');
+
+  if (NeedToEmitLCSSAPhis) {
+    SmallVector<Instruction *, 1> NeedsLCSSAPhis;
+    NeedsLCSSAPhis.push_back(dyn_cast<Instruction>(Invariant));
+    formLCSSAForInstructions(NeedsLCSSAPhis, *DT, *LI, SE);
+    LLVM_DEBUG(dbgs() << "INDVARS: replacement of IV user: " << *I
+                      << " with loop invariant: " << *S
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nikic wrote:

This part of the message will be duplicated with the debug output above. I'd leave it off.

https://github.com/llvm/llvm-project/pull/78696