1//===- CBuffer.cpp - HLSL constant buffer handling ------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "llvm/Frontend/HLSL/CBuffer.h"
10#include "llvm/IR/DerivedTypes.h"
11#include "llvm/IR/Metadata.h"
12#include "llvm/IR/Module.h"
13
14using namespace llvm;
15using namespace llvm::hlsl;
16
17static SmallVector<size_t>
18getMemberOffsets(const DataLayout &DL, GlobalVariable *Handle,
19 llvm::function_ref<bool(Type *)> IsPadding) {
20 SmallVector<size_t> Offsets;
21
22 auto *HandleTy = cast<TargetExtType>(Val: Handle->getValueType());
23 assert((HandleTy->getName().ends_with(".CBuffer") ||
24 HandleTy->getName() == "spirv.VulkanBuffer") &&
25 "Not a cbuffer type");
26 assert(HandleTy->getNumTypeParameters() == 1 && "Expected layout type");
27 auto *LayoutTy = cast<StructType>(Val: HandleTy->getTypeParameter(i: 0));
28
29 const StructLayout *SL = DL.getStructLayout(Ty: LayoutTy);
30 for (int I = 0, E = LayoutTy->getNumElements(); I < E; ++I)
31 if (!IsPadding(LayoutTy->getElementType(N: I)))
32 Offsets.push_back(Elt: SL->getElementOffset(Idx: I));
33
34 return Offsets;
35}
36
37std::optional<CBufferMetadata>
38CBufferMetadata::get(Module &M, llvm::function_ref<bool(Type *)> IsPadding) {
39 NamedMDNode *CBufMD = M.getNamedMetadata(Name: "hlsl.cbs");
40 if (!CBufMD)
41 return std::nullopt;
42
43 std::optional<CBufferMetadata> Result({CBufMD});
44
45 for (const MDNode *MD : CBufMD->operands()) {
46 assert(MD->getNumOperands() && "Invalid cbuffer metadata");
47
48 // For an unused cbuffer, the handle may have been optimized out
49 Metadata *OpMD = MD->getOperand(I: 0);
50 if (!OpMD)
51 continue;
52
53 auto *Handle =
54 cast<GlobalVariable>(Val: cast<ValueAsMetadata>(Val: OpMD)->getValue());
55 CBufferMapping &Mapping = Result->Mappings.emplace_back(Args&: Handle);
56
57 SmallVector<size_t> MemberOffsets =
58 getMemberOffsets(DL: M.getDataLayout(), Handle, IsPadding);
59
60 for (int I = 1, E = MD->getNumOperands(); I < E; ++I) {
61 Metadata *OpMD = MD->getOperand(I);
62 // Some members may be null if they've been optimized out.
63 if (!OpMD)
64 continue;
65 auto *V = cast<GlobalVariable>(Val: cast<ValueAsMetadata>(Val: OpMD)->getValue());
66 Mapping.Members.emplace_back(Args&: V, Args&: MemberOffsets[I - 1]);
67 }
68 }
69
70 return Result;
71}
72
73void CBufferMetadata::eraseFromModule() {
74 // Remove the cbs named metadata
75 MD->eraseFromParent();
76}
77