[SCEV] Enhance SCEVFindUnsafe for division

This patch allows SCEVFindUnsafe algorithm to tread division by any non-positive
value as safe. Previously, it could only recognize non-zero constants.

Differential Revision: https://reviews.llvm.org/D39228

llvm-svn: 316568

1 files changed, 2 insertions, 8 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
index 47bdac00ae1..964a79803fa 100644
--- a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -2250,10 +2250,6 @@ namespace {
 // only needed when the expression includes some subexpression that is not IV
 // derived.
 //
-// Currently, we only allow division by a nonzero constant here. If this is
-// inadequate, we could easily allow division by SCEVUnknown by using
-// ValueTracking to check isKnownNonZero().
-//
 // We cannot generally expand recurrences unless the step dominates the loop
 // header. The expander handles the special case of affine recurrences by
 // scaling the recurrence outside the loop, but this technique isn't generally
@@ -2268,13 +2264,11 @@ struct SCEVFindUnsafe {
 
   bool follow(const SCEV *S) {
     if (const SCEVUDivExpr *D = dyn_cast<SCEVUDivExpr>(S)) {
-      const SCEVConstant *SC = dyn_cast<SCEVConstant>(D->getRHS());
-      if (!SC || SC->getValue()->isZero()) {
+      if (!SE.isKnownNonZero(D->getRHS())) {
         IsUnsafe = true;
         return false;
       }
-    }
-    if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
+    } else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
       const SCEV *Step = AR->getStepRecurrence(SE);
       if (!AR->isAffine() && !SE.dominates(Step, AR->getLoop()->getHeader())) {
         IsUnsafe = true;