[llvm] [LAA] Compute pointer bounds for pattern with urem operation (PR #106574)

[David Sherwood via llvm-commits]

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@@ -190,6 +190,32 @@ RuntimeCheckingPtrGroup::RuntimeCheckingPtrGroup(
   Members.push_back(Index);
 }
 
+// Match expression in form of: PtrBase + (Dividend urem Divisor) * ConstStride,
+// where PtrBase and Divisor are loop-invariant and ConstStride is non-negative.
+// In this case Start = PtrBase, End = PtrBase + (Divisor - 1) * ConstStride.
+static std::optional<std::pair<const SCEV *, const SCEV *>>
+getStartAndEndForURemAccess(ScalarEvolution &SE, const SCEV *PtrScev,
+                            const Loop *L) {
+  const SCEV *PtrBase = SE.getPointerBase(PtrScev);
+  if (!SE.isLoopInvariant(PtrBase, L))
+    return std::nullopt;
+  const SCEV *PtrAddend = SE.removePointerBase(PtrScev);
+  auto ConstStride = SE.getConstantMultiple(PtrAddend);
+  if (ConstStride.isNegative())
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david-arm wrote:

Should we call `isStrictlyPositive` here instead so we avoid zero strides?

https://github.com/llvm/llvm-project/pull/106574