[llvm] [LoopVectorize] Allow Early-Exit Loop Vectorization with EVL (PR #130918)

[Shih-Po Hung via llvm-commits]

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@@ -4038,10 +4038,12 @@ LoopVectorizationCostModel::computeMaxVF(ElementCount UserVF, unsigned UserIC) {
   }
 
   // The only loops we can vectorize without a scalar epilogue, are loops with
-  // a bottom-test and a single exiting block. We'd have to handle the fact
-  // that not every instruction executes on the last iteration.  This will
-  // require a lane mask which varies through the vector loop body.  (TODO)
-  if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) {
+  // a bottom-test and a single exiting block or those with early exits. We'd
+  // have to handle the fact that not every instruction executes on the last
+  // iteration. This will require a lane mask which varies through the vector
+  // loop body. (TODO)
+  if ((TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) &&
+      !Legal->hasUncountableEarlyExit()) {
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arcbbb wrote:

I’ve added a test at llvm/test/Transforms/LoopVectorize/AArch64/simple_early_exit_predication.ll.
>From what I observed, the main difference is that vectorization is not considered beneficial when predication is enabled.

I also ran the LLVM test suite with march=rv64gcv_zvl256b, patched to always vectorize regardless of isDereferenceableReadOnlyLoop., All 2041 tests passed under the following flag:
-O3 -mllvm -prefer-predicate-over-epilogue=predicate-dont-vectorize
-O3 -mllvm -prefer-predicate-over-epilogue=predicate-dont-vectorize -mllvm -force-tail-folding-style=data-with-evl



https://github.com/llvm/llvm-project/pull/130918