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

[Alex Sepkowski 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)) {
+    FixedOffset += ConstOffset->getZExtValue();
+    Offset = nullptr;
+  }
+
+  Value *CurrentRow = ConstantInt::get(
+      Builder.getInt32Ty(), FixedOffset / hlsl::CBufferRowSizeInBytes);
+  unsigned int CurrentIndex =
+      (FixedOffset % hlsl::CBufferRowSizeInBytes) / Intrin.EltSize;
+
+  assert(!(CurrentIndex && Offset) &&
+         "Dynamic indexing into elements of cbuffer rows is not supported");
+  if (Offset)
+    CurrentRow = FixedOffset ? Builder.CreateAdd(CurrentRow, Offset) : Offset;
+
+  auto *CBufLoad = Builder.CreateIntrinsic(
+      Intrin.RetTy, Intrin.IID, {Handle, CurrentRow}, nullptr, Name + ".load");
+  auto *Elt =
+      Builder.CreateExtractValue(CBufLoad, {CurrentIndex++}, Name + ".extract");
+
+  unsigned int Remaining =
----------------
alsepkow wrote:

I'm assuming the only valid return values for Dl.getTypeSizeInBits(Ty) are 64,32, and 16. It looks like all possible values of Remaining are going to be zero. 

Was there something else causing this check to be here? 

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