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[HLSL] Allow completely unused cbuffers #164557

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Merged
merged 2 commits into from
Oct 23, 2025
Merged

[HLSL] Allow completely unused cbuffers #164557

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9a77087
[HLSL] Allow completely unused cbuffers
bogner Oct 21, 2025
cca4a31
Update llvm/lib/Frontend/HLSL/CBuffer.cpp
bogner Oct 22, 2025
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9 changes: 7 additions & 2 deletions llvm/lib/Frontend/HLSL/CBuffer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -43,8 +43,13 @@ std::optional<CBufferMetadata> CBufferMetadata::get(Module &M) {
for (const MDNode *MD : CBufMD->operands()) {
assert(MD->getNumOperands() && "Invalid cbuffer metadata");

auto *Handle = cast<GlobalVariable>(
cast<ValueAsMetadata>(MD->getOperand(0))->getValue());
// For an unused cbuffer, the handle may have been optimized out
Metadata *OpMD = MD->getOperand(0);
if (!OpMD)
continue;

auto *Handle =
cast<GlobalVariable>(cast<ValueAsMetadata>(OpMD)->getValue());
CBufferMapping &Mapping = Result->Mappings.emplace_back(Handle);

for (int I = 1, E = MD->getNumOperands(); I < E; ++I) {
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13 changes: 13 additions & 0 deletions llvm/test/CodeGen/DirectX/CBufferAccess/unused.ll
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@@ -0,0 +1,13 @@
; RUN: opt -S -dxil-cbuffer-access -mtriple=dxil--shadermodel6.3-library %s | FileCheck %s
; Check that we correctly ignore cbuffers that were nulled out by optimizations.

%__cblayout_CB = type <{ float }>
@CB.cb = local_unnamed_addr global target("dx.CBuffer", %__cblayout_CB) poison
@x = external local_unnamed_addr addrspace(2) global float, align 4

; CHECK-NOT: !hlsl.cbs =
!hlsl.cbs = !{!0, !1, !2}

!0 = !{ptr @CB.cb, ptr addrspace(2) @x}
!1 = !{ptr @CB.cb, null}
!2 = !{null, null}