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

[Sebastian Pop via llvm-commits]

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@@ -3664,14 +3699,18 @@ DependenceInfo::depends(Instruction *Src, Instruction *Dst,
   } else {
     // On the other hand, if all directions are equal and there's no
     // loop-independent dependence possible, then no dependence exists.
+    // However, if we added runtime assumptions during the dependence tests,
+    // we must return the result to preserve those assumptions for the caller.
     bool AllEqual = true;
     for (unsigned II = 1; II <= CommonLevels; ++II) {
       if (Result.getDirection(II) != Dependence::DVEntry::EQ) {
         AllEqual = false;
         break;
       }
     }
-    if (AllEqual)
+    bool AddedAssumptionsDuringTests =
+        Result.Assumptions.getPredicates().size() > AssumptionsBeforeTests;
+    if (AllEqual && !AddedAssumptionsDuringTests)
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sebpop wrote:

Currently we return nullptr when dependence vector is "AllEqual".
This code is here to guard against returning nullptr when the dependence is conditional to runtime assumptions: if we return nullptr the assumptions would be discarded.
We may need to revisit what we return for "no dependence" because we can't attach assumptions to a "nullptr".


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