[AArch64] Allow unrolling of scalar epilogue loops (#151164)

#147420 changed the unrolling preferences to permit unrolling of
non-auto vectorized loops by checking for the isvectorized attribute,
however when a loop is vectorized this attribute is put on both the
vector loop and the scalar epilogue, so this change prevented the scalar
epilogue from being unrolled.

Restore the previous behaviour of unrolling the scalar epilogue by
checking both for the isvectorized attribute and vector instructions in
the loop.

1 files changed, 8 insertions, 5 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
index 40f49da..18ca22f 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -4905,14 +4905,17 @@ void AArch64TTIImpl::getUnrollingPreferences(
   // Disable partial & runtime unrolling on -Os.
   UP.PartialOptSizeThreshold = 0;
 
-  // No need to unroll auto-vectorized loops
-  if (findStringMetadataForLoop(L, "llvm.loop.isvectorized"))
-    return;
-
   // Scan the loop: don't unroll loops with calls as this could prevent
-  // inlining.
+  // inlining. Don't unroll auto-vectorized loops either, though do allow
+  // unrolling of the scalar remainder.
+  bool IsVectorized = getBooleanLoopAttribute(L, "llvm.loop.isvectorized");
   for (auto *BB : L->getBlocks()) {
     for (auto &I : *BB) {
+      // Both auto-vectorized loops and the scalar remainder have the
+      // isvectorized attribute, so differentiate between them by the presence
+      // of vector instructions.
+      if (IsVectorized && I.getType()->isVectorTy())
+        return;
       if (isa<CallBase>(I)) {
         if (isa<CallInst>(I) || isa<InvokeInst>(I))
           if (const Function *F = cast<CallBase>(I).getCalledFunction())