[llvm] [LoopIdiom] Use SCEV for deciding memmove validity (PR #211274)

[Ramkumar Ramachandra via llvm-commits]

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@@ -1290,43 +1290,45 @@ bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(StoreInst *SI,
 namespace {
 class MemmoveVerifier {
 public:
-  explicit MemmoveVerifier(const Value &LoadBasePtr, const Value &StoreBasePtr,
-                           const DataLayout &DL)
-      : DL(DL), BP1(llvm::GetPointerBaseWithConstantOffset(
-                    LoadBasePtr.stripPointerCasts(), LoadOff, DL)),
-        BP2(llvm::GetPointerBaseWithConstantOffset(
-            StoreBasePtr.stripPointerCasts(), StoreOff, DL)),
-        IsSameObject(BP1 == BP2) {}
+  explicit MemmoveVerifier(const SCEV &LoadStart, const SCEV &StoreStart,
+                           ScalarEvolution &SE)
+      : DL(SE.getDataLayout()),
+        Off(dyn_cast<SCEVConstant>(SE.getMinusSCEV(&StoreStart, &LoadStart))),
+        BasePtr(dyn_cast<SCEVUnknown>(SE.getPointerBase(&StoreStart))),
+        IsSameObject(Off != nullptr) {}
 
   bool loadAndStoreMayFormMemmove(unsigned StoreSize, bool IsNegStride,
                                   const Instruction &TheLoad,
                                   bool IsMemCpy) const {
+    // The store must be at a constant offset from the load, and there must be
+    // an underlying pointer.
+    if (!Off || !BasePtr)
+      return false;
+    const APInt &OffVal = Off->getAPInt();
+    // If null is defined then the base pointer can't be null
+    if (TheLoad.getParent()->getParent()->nullPointerIsDefined() &&
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artagnon wrote:

Kindly use llvm::NullPointerIsDefined from Function.h here? I also think the condition is inverted: if null pointer is undefined, and if the BasePtr is null, then return false?

https://github.com/llvm/llvm-project/pull/211274