[llvm] [LoopVectorize] In LoopVectorize.cpp start using getSymbolicMaxBackedgeTakenCount (PR #108833)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: David Sherwood (david-arm)

<details>
<summary>Changes</summary>

LoopVectorizationLegality currently only treats a loop as legal to vectorise
if PredicatedScalarEvolution::getBackedgeTakenCount returns a valid SCEV, or
more precisely that the loop must have an exact backedge taken count.
Therefore, in LoopVectorize.cpp we can safely replace all calls to
getBackedgeTakenCount with calls to getSymbolicMaxBackedgeTakenCount, since
the result is the same.

This also helps prepare the loop vectoriser for PR #<!-- -->88385.

---
Full diff: https://github.com/llvm/llvm-project/pull/108833.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/Vectorize/LoopVectorize.cpp (+3-3) 


``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index f726b171969a30..5ab0fd12c538f3 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -907,7 +907,7 @@ Value *getRuntimeVF(IRBuilderBase &B, Type *Ty, ElementCount VF) {
 
 const SCEV *createTripCountSCEV(Type *IdxTy, PredicatedScalarEvolution &PSE,
                                 Loop *OrigLoop) {
-  const SCEV *BackedgeTakenCount = PSE.getBackedgeTakenCount();
+  const SCEV *BackedgeTakenCount = PSE.getSymbolicMaxBackedgeTakenCount();
   assert(!isa<SCEVCouldNotCompute>(BackedgeTakenCount) && "Invalid loop count");
 
   ScalarEvolution &SE = *PSE.getSE();
@@ -4090,7 +4090,7 @@ LoopVectorizationCostModel::computeMaxVF(ElementCount UserVF, unsigned UserIC) {
     unsigned MaxVFtimesIC =
         UserIC ? *MaxPowerOf2RuntimeVF * UserIC : *MaxPowerOf2RuntimeVF;
     ScalarEvolution *SE = PSE.getSE();
-    const SCEV *BackedgeTakenCount = PSE.getBackedgeTakenCount();
+    const SCEV *BackedgeTakenCount = PSE.getSymbolicMaxBackedgeTakenCount();
     const SCEV *ExitCount = SE->getAddExpr(
         BackedgeTakenCount, SE->getOne(BackedgeTakenCount->getType()));
     const SCEV *Rem = SE->getURemExpr(
@@ -9584,7 +9584,7 @@ static bool processLoopInVPlanNativePath(
     ProfileSummaryInfo *PSI, LoopVectorizeHints &Hints,
     LoopVectorizationRequirements &Requirements) {
 
-  if (isa<SCEVCouldNotCompute>(PSE.getBackedgeTakenCount())) {
+  if (isa<SCEVCouldNotCompute>(PSE.getSymbolicMaxBackedgeTakenCount())) {
     LLVM_DEBUG(dbgs() << "LV: cannot compute the outer-loop trip count\n");
     return false;
   }

``````````

</details>


https://github.com/llvm/llvm-project/pull/108833