[llvm] [DA] Add initial support for monotonicity check (PR #162280)

[via llvm-commits]

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@@ -3479,10 +3732,19 @@ bool DependenceInfo::tryDelinearize(Instruction *Src, Instruction *Dst,
   // resize Pair to contain as many pairs of subscripts as the delinearization
   // has found, and then initialize the pairs following the delinearization.
   Pair.resize(Size);
+  SCEVMonotonicityChecker MonChecker(SE);
+  const Loop *OutermostLoop = SrcLoop ? SrcLoop->getOutermostLoop() : nullptr;
   for (int I = 0; I < Size; ++I) {
     Pair[I].Src = SrcSubscripts[I];
     Pair[I].Dst = DstSubscripts[I];
     unifySubscriptType(&Pair[I]);
+
+    if (EnableMonotonicityCheck) {
+      if (MonChecker.checkMonotonicity(Pair[I].Src, OutermostLoop).isUnknown())
+        return false;
+      if (MonChecker.checkMonotonicity(Pair[I].Dst, OutermostLoop).isUnknown())
+        return false;
+    }
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amehsan wrote:

Another question here, otherwise LGTM.

If we have mutliple subscripts and all of them are monotonic, how could the other monotonicity check (line 4083-4) fail? We need to answer this to make sure we are not running the test redundantly.

https://github.com/llvm/llvm-project/pull/162280