[llvm] [LoopVectorize] Enable vectorisation of early exit loops with live-outs (PR #120567)

[Florian Hahn via llvm-commits]

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@@ -501,7 +501,15 @@ void VPBasicBlock::execute(VPTransformState *State) {
     UnreachableInst *Terminator = State->Builder.CreateUnreachable();
     // Register NewBB in its loop. In innermost loops its the same for all
     // BB's.
-    if (State->CurrentParentLoop)
+    if (this == State->Plan->getEarlyExit()) {
+      // If this is the vector early exit block then it has a single successor,
+      // which is the uncountable early exit block of the original loop. The
+      // parent loop for the exit block may not be the same as the parent loop
+      // of the vectorised loop, so we have to treat this differently.
+      Loop *EEL = State->LI->getLoopFor(State->CFG.UncountableEarlyExitBB);
+      if (EEL)
+        EEL->addBasicBlockToLoop(NewBB, *State->LI);
+    } else if (State->CurrentParentLoop)
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fhahn wrote:

It might be good to frame this more generally if possible.

IIUC the problem here is that now we introduce a VPBB which may be outside the enclosing loop (and in the same loop as the destination VPIRBB.

This is the case when we have a VPBB that only branches to a single exit block and then it must be in the same loop as this VPIRBB. Can we check for that instead?

https://github.com/llvm/llvm-project/pull/120567