[llvm] [LAA] Perform checks for no-wrap separately from getPtrStride. (PR #126971)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -1458,74 +1544,13 @@ llvm::getPtrStride(PredicatedScalarEvolution &PSE, Type *AccessTy, Value *Ptr,
     return std::nullopt;
   }
 
-  // The access function must stride over the innermost loop.
-  if (Lp != AR->getLoop()) {
-    LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not striding over innermost loop "
-                      << *Ptr << " SCEV: " << *AR << "\n");
-    return std::nullopt;
-  }
-
-  // Check the step is constant.
-  const SCEV *Step = AR->getStepRecurrence(*PSE.getSE());
-
-  // Calculate the pointer stride and check if it is constant.
-  const SCEVConstant *C = dyn_cast<SCEVConstant>(Step);
-  if (!C) {
-    LLVM_DEBUG(dbgs() << "LAA: Bad stride - Not a constant strided " << *Ptr
-                      << " SCEV: " << *AR << "\n");
-    return std::nullopt;
-  }
-
-  const auto &DL = Lp->getHeader()->getDataLayout();
-  TypeSize AllocSize = DL.getTypeAllocSize(AccessTy);
-  int64_t Size = AllocSize.getFixedValue();
-  const APInt &APStepVal = C->getAPInt();
-
-  // Huge step value - give up.
-  if (APStepVal.getBitWidth() > 64)
-    return std::nullopt;
-
-  int64_t StepVal = APStepVal.getSExtValue();
-
-  // Strided access.
-  int64_t Stride = StepVal / Size;
-  int64_t Rem = StepVal % Size;
-  if (Rem)
-    return std::nullopt;
-
-  if (!ShouldCheckWrap)
-    return Stride;
-
-  // The address calculation must not wrap. Otherwise, a dependence could be
-  // inverted.
-  if (isNoWrapAddRec(Ptr, AR, PSE, Lp))
-    return Stride;
-
-  // An nusw getelementptr that is an AddRec cannot wrap. If it would wrap,
-  // the distance between the previously accessed location and the wrapped
-  // location will be larger than half the pointer index type space. In that
-  // case, the GEP would be  poison and any memory access dependent on it would
-  // be immediate UB when executed.
-  if (auto *GEP = dyn_cast<GetElementPtrInst>(Ptr);
-      GEP && GEP->hasNoUnsignedSignedWrap())
+  auto Stride = getStrideFromAddRec(AR, Lp, AccessTy, Ptr, PSE);
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artagnon wrote:

s/auto/actual type/ since it's not clear?

https://github.com/llvm/llvm-project/pull/126971