[llvm] [LoopInterchange] Forbid interchange if load store type wider than element type (PR #77885)

[via llvm-commits]

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@@ -82,6 +82,40 @@ static void printDepMatrix(CharMatrix &DepMatrix) {
 }
 #endif
 
+// Consider the following case, interchange is not valid as the store type(int)
+// is wider than the array element type(char).
+//
+// char p[7];
+// for (int j = 0; j < 2; ++j)
+//   for (int i = 0; i < 2; ++i)
+//     *((int*)&p[2*i+j]) = 2*i+j+1;
+//
+// Return true if the load/store type is wider than the element type.
+static bool isWiderLoadStore(Instruction *I) {
+  Value *Ptr = getLoadStorePointerOperand(I);
+  Type *ITy = getLoadStoreType(I);
+
+  if (!ITy->isSingleValueType())
+    return false;
+
+  if (auto *GEP = dyn_cast<GetElementPtrInst>(Ptr)) {
+    Type *ElementTy = GEP->getSourceElementType();
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ShivaChen wrote:

Thanks for the information. I was mimicking how the delinearization extract the subscripts. I assume we should not increase the dependency to GEP. Thanks.

https://github.com/llvm/llvm-project/pull/77885