[llvm] [DirectX] Teach DXILResourceAccess about cbuffers (PR #164554)

[Helena Kotas via llvm-commits]

================
@@ -171,6 +185,123 @@ static void createRawLoad(IntrinsicInst *II, LoadInst *LI, Value *Offset) {
   LI->replaceAllUsesWith(V);
 }
 
+namespace {
+/// Helper for building a `load.cbufferrow` intrinsic given a simple type.
+struct CBufferRowIntrin {
+  Intrinsic::ID IID;
+  Type *RetTy;
+  unsigned int EltSize;
+  unsigned int NumElts;
+
+  CBufferRowIntrin(const DataLayout &DL, Type *Ty) {
+    assert(Ty == Ty->getScalarType() && "Expected scalar type");
+
+    switch (DL.getTypeSizeInBits(Ty)) {
+    case 16:
+      IID = Intrinsic::dx_resource_load_cbufferrow_8;
+      RetTy = StructType::get(Ty, Ty, Ty, Ty, Ty, Ty, Ty, Ty);
+      EltSize = 2;
+      NumElts = 8;
+      break;
+    case 32:
+      IID = Intrinsic::dx_resource_load_cbufferrow_4;
+      RetTy = StructType::get(Ty, Ty, Ty, Ty);
+      EltSize = 4;
+      NumElts = 4;
+      break;
+    case 64:
+      IID = Intrinsic::dx_resource_load_cbufferrow_2;
+      RetTy = StructType::get(Ty, Ty);
+      EltSize = 8;
+      NumElts = 2;
+      break;
+    default:
+      llvm_unreachable("Only 16, 32, and 64 bit types supported");
+    }
+  }
+};
+} // namespace
+
+static void createCBufferLoad(IntrinsicInst *II, LoadInst *LI, Value *Offset,
+                              dxil::ResourceTypeInfo &RTI) {
+  const DataLayout &DL = LI->getDataLayout();
+
+  Type *Ty = LI->getType();
+  assert(!isa<StructType>(Ty) && "Structs not handled yet");
+  CBufferRowIntrin Intrin(DL, Ty->getScalarType());
+
+  StringRef Name = LI->getName();
+  Value *Handle = II->getOperand(0);
+
+  IRBuilder<> Builder(LI);
+
+  ConstantInt *GlobalOffset = dyn_cast<ConstantInt>(II->getOperand(1));
+  assert(GlobalOffset && "CBuffer getpointer index must be constant");
+
+  unsigned int FixedOffset = GlobalOffset->getZExtValue();
+  // If we have a further constant offset we can just fold it in to the fixed
+  // offset.
+  if (auto *ConstOffset = dyn_cast_if_present<ConstantInt>(Offset)) {
----------------
hekota wrote:

Since Offset is not optional would `dyn_cast_or_null` be better here?
```suggestion
  if (auto *ConstOffset = dyn_cast_or_null<ConstantInt>(Offset)) {
```

https://github.com/llvm/llvm-project/pull/164554