[llvm] [AArch64] Add flag to control unrolling for small multi-exit loops (PR #131998)

[David Sherwood via llvm-commits]

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@@ -4389,43 +4475,15 @@ getAppleRuntimeUnrollPreferences(Loop *L, ScalarEvolution &SE,
   if (!L->isInnermost() || L->getNumBlocks() > 8)
     return;
 
+  // This is handled by common code.
+  if (!L->getExitBlock())
+    return;
+
   const SCEV *BTC = SE.getSymbolicMaxBackedgeTakenCount(L);
   if (isa<SCEVConstant>(BTC) || isa<SCEVCouldNotCompute>(BTC) ||
       (SE.getSmallConstantMaxTripCount(L) > 0 &&
        SE.getSmallConstantMaxTripCount(L) <= 32))
     return;
-  if (findStringMetadataForLoop(L, "llvm.loop.isvectorized"))
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david-arm wrote:

Hmm, you're right I was too aggressive in removing it. I've re-added it after the check for early exits.

https://github.com/llvm/llvm-project/pull/131998