[llvm] [SeparateConstOffsetFromGEP] Support GEP reordering for different types (PR #90802)

[Matt Arsenault via llvm-commits]

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@@ -1017,6 +1016,54 @@ bool SeparateConstOffsetFromGEP::reorderGEP(GetElementPtrInst *GEP,
       IsChainInBounds &= KnownPtrGEPIdx.isNonNegative();
     }
   }
+  TypeSize GEPSize = DL->getTypeSizeInBits(GEP->getIndexedType(
+      GEP->getSourceElementType(), GEP->indices().begin()->get()));
+  TypeSize PtrGEPSize = DL->getTypeSizeInBits(PtrGEP->getIndexedType(
+      PtrGEP->getSourceElementType(), PtrGEP->indices().begin()->get()));
+
+  IRBuilder<> Builder(GEP);
+  Builder.SetCurrentDebugLocation(GEP->getDebugLoc());
+  if (GEPSize > PtrGEPSize) {
+    if (GEPSize % PtrGEPSize)
+      return false;
+    unsigned Ratio = GEPSize / PtrGEPSize;
+    if (NestedByteOffset % Ratio)
+      return false;
+
+    auto NewGEPOffset = Builder.CreateUDiv(
+        *PtrGEP->indices().begin(),
+        Builder.getIntN(
+            PtrGEP->indices().begin()->get()->getType()->getScalarSizeInBits(),
+            Ratio));
+    auto NewSrc = Builder.CreateGEP(GEPType, PtrGEP->getPointerOperand(),
+                                    SmallVector<Value *, 4>(GEP->indices()));
+    cast<GetElementPtrInst>(NewSrc)->setIsInBounds(IsChainInBounds);
+    auto NewGEP = Builder.CreateGEP(GEPType, NewSrc, NewGEPOffset);
+    cast<GetElementPtrInst>(NewGEP)->setIsInBounds(IsChainInBounds);
+    GEP->replaceAllUsesWith(NewGEP);
+    RecursivelyDeleteTriviallyDeadInstructions(GEP);
+    return true;
+  }
+
+  if (GEPSize < PtrGEPSize) {
+    if (PtrGEPSize % GEPSize)
+      return false;
+    unsigned Ratio = PtrGEPSize / GEPSize;
+
+    auto NewGEPOffset = Builder.CreateMul(
+        *PtrGEP->indices().begin(),
+        Builder.getIntN(
+            PtrGEP->indices().begin()->get()->getType()->getScalarSizeInBits(),
+            Ratio));
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arsenm wrote:

Probably shouldn't be using indices() if you aren't iterating over them. You shouldn't have to do this much work just to get the integer size? 

https://github.com/llvm/llvm-project/pull/90802