[llvm] [DependenceAnalysis] Extending SIV to handle fusable loops (PR #128782)

[via llvm-commits]

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@@ -3686,6 +3775,46 @@ DependenceInfo::depends(Instruction *Src, Instruction *Dst,
     }
   }
 
+  // Establish loop nesting levels considering fusable loops as common
+  establishNestingLevels(Src, Dst);
+
+  LLVM_DEBUG(dbgs() << "    common nesting levels = " << CommonLevels << "\n");
+  LLVM_DEBUG(dbgs() << "    maximum nesting levels = " << MaxLevels << "\n");
+  LLVM_DEBUG(dbgs() << "    fusable nesting levels = " << FusableLevels
+                    << "\n");
+
+  // Modify common levels to consider the fusable levels in the tests
+  CommonLevels += FusableLevels;
+  MaxLevels -= FusableLevels;
+  if (FusableLevels > 0) {
+    // Not all tests are handled yet over fusable loops
+    // Revoke if there are any tests other than ZIV, SIV or RDIV
+    for (unsigned P = 0; P < Pairs; ++P) {
+      SmallBitVector Loops;
+      Subscript::ClassificationKind TestClass =
+          classifyPair(Pair[P].Src, LI->getLoopFor(Src->getParent()),
+                       Pair[P].Dst, LI->getLoopFor(Dst->getParent()), Loops);
+
+      if (TestClass != Subscript::ZIV && TestClass != Subscript::SIV &&
+          TestClass != Subscript::RDIV) {
+        // Revert the levels to not consider the fusable levels
+        CommonLevels -= FusableLevels;
+        MaxLevels += FusableLevels;
+        FusableLevels = 0;
+        break;
+      }
+    }
+  }
+
+  FullDependence Result(Src, Dst, SCEVUnionPredicate(Assume, *SE),
+                        PossiblyLoopIndependent, CommonLevels);
+  ++TotalArrayPairs;
+
+  if (FusableLevels > 0) {
+    Result.Consistent = false;
+    FusableLoopsConsidered++;
+  }
+
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amehsan wrote:

Other fields of Result is updated later in line 4135.  Also there is no use of `FusableLoopsConsidered` between here and there. Is there a reason that this code is separate from the other conditional on `FusableLevels > 0` ?

https://github.com/llvm/llvm-project/pull/128782