[llvm] [DirectX] add GEP i8 legalization (PR #142475)

[Sarah Spall via llvm-commits]

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@@ -164,6 +166,36 @@ static void fixI8UseChain(Instruction &I,
     if (AdjustedCast)
       Cast->replaceAllUsesWith(AdjustedCast);
   }
+  if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
+    if (!GEP->getType()->isPointerTy() ||
+        !GEP->getSourceElementType()->isIntegerTy(8))
+      return;
+
+    Value *BasePtr = GEP->getPointerOperand();
+    if (ReplacedValues.count(BasePtr))
+      BasePtr = ReplacedValues[BasePtr];
+
+    Type *ElementType = BasePtr->getType();
+    if (auto *AI = dyn_cast<AllocaInst>(BasePtr))
+      ElementType = AI->getAllocatedType();
+    if (auto *ArrTy = dyn_cast<ArrayType>(ElementType))
+      ElementType = ArrTy->getArrayElementType();
+
+    ConstantInt *Offset = dyn_cast<ConstantInt>(GEP->getOperand(1));
+    // Note: the only way to convert an i8 offset to an i32 offset without
+    // emitting code Would be to emit code. We sould expect this value to be a
+    // ConstantInt since Offsets are very regulalrly converted.
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spall wrote:

regularly

https://github.com/llvm/llvm-project/pull/142475