[llvm-branch-commits] [llvm] [DA] Fix Strong SIV test for symbolic coefficients and deltas (#149977) (PR #157738)

[Sushant Gokhale via llvm-branch-commits]

================
@@ -1293,9 +1316,40 @@ bool DependenceInfo::strongSIVtest(const SCEV *Coeff, const SCEV *SrcConst,
       Result.DV[Level].Distance = Delta; // since X/1 == X
       NewConstraint.setDistance(Delta, CurLoop);
     } else {
-      Result.Consistent = false;
-      NewConstraint.setLine(Coeff, SE->getNegativeSCEV(Coeff),
-                            SE->getNegativeSCEV(Delta), CurLoop);
+      // Try symbolic division: Distance = Delta / Coeff.
+      if (const SCEV *Distance = SE->getUDivExactExpr(Delta, Coeff)) {
+        LLVM_DEBUG(dbgs() << "\t    Symbolic distance = " << *Distance << "\n");
+        Result.DV[Level].Distance = Distance;
+        NewConstraint.setDistance(Distance, CurLoop);
+      } else {
+        // Cannot compute exact division - check if we can add runtime
+        // assumptions.
+        if (isa<SCEVUnknown>(Coeff) && !SE->isKnownNonZero(Coeff)) {
+          // Add runtime assumption that coefficient is non-zero for division.
+          const SCEV *Zero = SE->getZero(Coeff->getType());
+          const SCEVPredicate *NonZeroPred =
+              SE->getComparePredicate(ICmpInst::ICMP_NE, Coeff, Zero);
+          if (UnderRuntimeAssumptions) {
+            SmallVector<const SCEVPredicate *, 4> NewPreds(
+                Assumptions.getPredicates());
+            NewPreds.push_back(NonZeroPred);
+            const_cast<DependenceInfo *>(this)->Assumptions =
+                SCEVUnionPredicate(NewPreds, *SE);
----------------
sushgokh wrote:

why are we adding constraint once again when we have already added below constraint?
```
const SCEVPredicate *BoundPred =
            SE->getComparePredicate(ICmpInst::ICMP_SLE, AbsDelta, Product);
```

https://github.com/llvm/llvm-project/pull/157738