[SPIR-V] Add support for RWTexture2DMS and RWTexture2DMSArray - #8947
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Diego Novillo (dnovillo) wants to merge 1 commit into
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Diego Novillo (dnovillo) wants to merge 1 commit into
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Lower both types to a multisampled storage image and carry the sample index through every read, write and query path.
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Diego Novillo (dnovillo)
September 22, 2026 18:49
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🟡 Changes recommended
Two expression-evaluation bugs can produce incorrect coordinates, samples, and side effects.
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Review effort: Balanced
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What changed in this PR
Adds SPIR-V support for RWTexture2DMS and RWTexture2DMSArray.
Changes:
- Lowers writable multisampled textures to SPIR-V storage images with required capabilities.
- Supports sample-indexed reads, writes, queries, reflection, and sample-zero subscripting.
- Adds documentation and regression tests.
Required fixes:
- Cache coordinate and sample expressions during component/swizzle read-modify-write operations to avoid duplicate evaluation.
- Evaluate sample expressions before coordinate expressions on writes, matching source order and read behavior.
| File | Description |
|---|---|
tools/clang/test/CodeGenSPIRV/vk.subpass-input.hlsl |
Guards subpass-input capability behavior. |
tools/clang/test/CodeGenSPIRV/type.rwtexture2dmsarray.hlsl |
Tests arrayed type lowering and capabilities. |
tools/clang/test/CodeGenSPIRV/type.rwtexture2dms.hlsl |
Tests non-arrayed type lowering. |
tools/clang/test/CodeGenSPIRV/op.rwtexture2dms.ps.hlsl |
Tests validated pixel-shader output. |
tools/clang/test/CodeGenSPIRV/op.rwtexture2dms.access.hlsl |
Tests access forms and dimension queries. |
tools/clang/test/CodeGenSPIRV/decoration.user-type.hlsl |
Tests reflection metadata. |
tools/clang/lib/SPIRV/SpirvEmitter.cpp |
Implements multisampled access; contains the expression-evaluation issues above. |
tools/clang/lib/SPIRV/SpirvBuilder.cpp |
Adds sample operands to image writes. |
tools/clang/lib/SPIRV/LowerTypeVisitor.cpp |
Lowers writable multisampled texture types. |
tools/clang/lib/SPIRV/DeclResultIdMapper.cpp |
Classifies the resources as UAVs. |
tools/clang/lib/SPIRV/CapabilityVisitor.cpp |
Infers required SPIR-V capabilities. |
tools/clang/lib/SPIRV/AstTypeProbe.cpp |
Recognizes writable multisampled textures. |
tools/clang/include/clang/SPIRV/SpirvBuilder.h |
Updates the image-write API. |
tools/clang/include/clang/SPIRV/AstTypeProbe.h |
Declares the new type probe. |
docs/SPIR-V.rst |
Documents resource lowering and operations. |
docs/ReleaseNotes.md |
Announces the new support. |
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| auto *loc = doExpr(indexExpr, range); | ||
| const QualType imageType = baseExpr->getType(); | ||
| // A plain <object>[coord] write to RWTexture2DMS(Array) targets sample 0, | ||
| // matching the DXIL path. | ||
| SpirvInstruction *sample = nullptr; | ||
| if (isMSWrite) | ||
| sample = doExpr(sampleExpr, range); | ||
| else if (isRWTextureMS(imageType)) | ||
| sample = spvBuilder.getConstantInt(astContext.UnsignedIntTy, | ||
| llvm::APInt(32, 0)); |
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RWTexture2DMS<T>andRWTexture2DMSArray<T>do not compile when targeting SPIR-V.LowerTypeVisitor::lowerResourceTypelists neither name, so the type falls through to generic struct lowering.SPIR-V expresses a writable multisampled image as
OpTypeImagewithMSof 1 andSampledof 2, gated byStorageImageMultisample. Every access to one carries a sample index, and both HLSL access forms have to supply it.This change:
RWTexture2DMSandRWTexture2DMSArrayto a multisampled storage image, and infersStorageImageMultisample, plusImageMSArrayfor the arrayed variant, from the lowered type rather than from the HLSL name.Dim::SubpassDatais excluded, since the validator's requirement does not reach it andStorageImageMultisamplemaps to an optional Vulkan device feature.isRWTextureMS(QualType)toAstTypeProbeand applies it at each emitter dispatch point that has to tell a sample index from a mip level, and adds the two names to the resource lists behind-fspv-reflectand theRelaxedPrecisiondecoration.SpirvBuilder::createImageWriteasampleparameter and composes the image operands mask from it, soOpImageWritecarriesSample.<obj>.sample[idx][coord], and sample 0 on the plain<obj>[coord]subscript. Sample 0 is what the DXIL path emits for the same source, pertools/clang/test/HLSLFileCheck/hlsl/objects/RWTexture/rwtexture2dms.hlsl.Tests:
type.rwtexture2dms.hlslandtype.rwtexture2dmsarray.hlsl: the loweredOpTypeImageoperands and the capabilities. Separate files because capabilities are module-global.op.rwtexture2dms.access.hlsl: every access form, scalar and vector sampled types, and bothGetDimensionsoverloads.op.rwtexture2dms.ps.hlsl: the shader from the issue. The one test without-fcgl, so capability trimming and validation cover its output.decoration.user-type.hlsl: the two-fspv-reflectstrings.vk.subpass-input.hlsl: that aSubpassInputMSdoes not acquireStorageImageMultisample.Fixes #5244