[llvm] [DA] Fix zero coeff bug in Strong SIV test with runtime assumptions (#149991) (PR #155037)

[Ryotaro Kasuga via llvm-commits]

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@@ -1368,7 +1369,35 @@ bool DependenceInfo::strongSIVtest(const SCEV *Coeff, const SCEV *SrcConst,
       Result.DV[Level].Direction &= Dependence::DVEntry::EQ;
     ++StrongSIVsuccesses;
   } else if (Delta->isZero()) {
-    // since 0/X == 0
+    // Check if coefficient could be zero. If so, 0/0 is undefined and we
+    // cannot conclude that only same-iteration dependencies exist.
+    // When coeff=0, all iterations access the same location.
+    if (isa<SCEVUnknown>(Coeff)) {
+      // Use both isKnownNonZero and range analysis to prove coefficient != 0.
+      bool CoeffKnownNonZero = SE->isKnownNonZero(Coeff) ||
+                               isKnownPredicate(CmpInst::ICMP_NE, Coeff,
+                                                SE->getZero(Coeff->getType()));
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kasuga-fj wrote:

Is it insufficient to call only `SE->isKnownNonZero`?

https://github.com/llvm/llvm-project/pull/155037