[llvm] [DA] Set Distance to zero when Direction is EQ (PR #147966)

[Michael Kruse via llvm-commits]

================
@@ -3991,6 +4003,23 @@ DependenceInfo::depends(Instruction *Src, Instruction *Dst,
     if (CompleteLoops[II])
       Result.DV[II - 1].Scalar = false;
 
+  // Set the distance to zero if the direction is EQ.
+  // TODO: Ideally, the distance should be set to 0 immediately simultaneously
+  // with the corresponding direction being set to EQ.
+  for (unsigned II = 1; II <= Result.getLevels(); ++II) {
+    if (Result.getDirection(II) == Dependence::DVEntry::EQ)
+      Result.DV[II - 1].Distance = SE->getZero(SrcSCEV->getType());
+
+    LLVM_DEBUG({
+      // Check that the converse (i.e., if the distance is zero, then the
+      // direction is EQ) holds.
+      const SCEV *Distance = Result.getDistance(II);
+      if (Distance && Distance->isZero())
+        assert(Result.getDirection(II) == Dependence::DVEntry::EQ &&
+               "Distance is zero, but direction is not EQ");
+    });
----------------
Meinersbur wrote:

```suggestion
#ifndef NDEBUG
      // Check that the converse (i.e., if the distance is zero, then the
      // direction is EQ) holds.
      const SCEV *Distance = Result.getDistance(II);
      if (Distance && Distance->isZero())
        assert(Result.getDirection(II) == Dependence::DVEntry::EQ &&
               "Distance is zero, but direction is not EQ");
#endif
```
For multi-line checks, prefer `#ifndef NDEBUG`. LLVM_DEBUG confuses tooling such as clang-format, debuggers, clang-tidy, code completion, refactoring

https://github.com/llvm/llvm-project/pull/147966