[SPIR-V] Add descriptor heap -fvk-resource-heap-stride / -fvk-sampler-heap-stride CLI flags by jzakharovnv · Pull Request #8519 · microsoft/DirectXShaderCompiler

Jonathan Zakharov (jzakharovnv) · 2026-06-04T21:54:37Z

Building off of #8518, this PR adds two new command-line flags that override the ArrayStride of the descriptor heap runtime arrays emitted by -fspv-use-descriptor-heap. It is part 3/4 in a series.

-fvk-resource-heap-stride and -fvk-sampler-heap-stride sets the stride for ResourceDescriptorHeap SamplerDescriptorHeap arrays respectively. N and M must be a power of two in [8, 256]. When set, the CLI value takes the highest precedence.

Assisted by an AI agent.

Diego Novillo (@dnovillo)

github-actions · 2026-06-04T21:56:50Z

✅ With the latest revision this PR passed the C/C++ code formatter.

Jonathan Zakharov (jzakharovnv) · 2026-06-04T23:02:39Z

@microsoft-github-policy-service agree company="NVIDIA"

Diego Novillo (dnovillo) · 2026-07-17T17:25:12Z

+can be overridden, in increasing order of precedence:
+
+- ``[[vk::resource_heap_stride_constant_id(id)]]`` and
+  ``[[vk::sampler_heap_stride_constant_id(id)]]`` on a ``uint`` global emit the


These spec constant attributes are actually in #8520, right? Maybe move them there? This way, this PR just handles the flags.

Yes, this was a bit clumsy on my part. Will fix the documentation to remove mention of (now dropped feature) stride spec const attributes.

Diego Novillo (dnovillo) · 2026-07-17T17:34:09Z

+      !handleHeapStride(Args, OPT_fvk_sampler_heap_stride,
+                        &opts.SpirvOptions.samplerHeapStride,
+                        "-fvk-sampler-heap-stride", errors)) {
+    return 1;


If both flags are wrong, this will short-circuit and only give a single error message. Could you make both calls always happen and return the aggregate? Something like this:

bool ok = handleHeapStride(...resource...); ok &= handleHeapStride(...sampler...); if (!ok) return 1;

Diego Novillo (dnovillo)

Thanks for the fixes. LGTM now.

Building off of microsoft#8281, this commit adds a native lowering via SPV_EXT_descriptor_heap and SPV_KHR_untyped_pointers. ResourceDescriptorHeap and SamplerDescriptorHeap are lowered to untyped variables decorated with ResourceHeapEXT and SamplerHeapEXT. Each heap access emits OpUntypedAccessChainKHR into a runtime array of the appropriate descriptor type. Buffer-like resources (StructuredBuffer, ByteAddressBuffer, ConstantBuffer, TextureBuffer) use OpTypeBufferEXT and OpBufferPointerEXT; image and sampler resources use OpLoad. Interlocked operations on RWTexture use OpUntypedImageTexelPointerEXT. Requires -fspv-target-env=vulkan1.3. Assisted-by: Claude.

…TODO

Damyan Pepper (damyanp) · 2026-07-30T16:48:12Z

[Auto-generated note from Damyan Pepper (@damyanp)]

This looks like a user-visible bug fix/feature change. Please add (or point to) the corresponding entry in docs/ReleaseNotes.md.

If release-note coverage is planned in a related PR (including one that hasn’t been submitted yet), please mention that plan/link so we can avoid duplicate notes.

Extends the SPV_EXT_descriptor_heap native heap lowering to cover RaytracingAccelerationStructure resources loaded from ResourceDescriptorHeap. Acceleration structure descriptors are accessed via OpUntypedAccessChainKHR into a runtime array of OpTypeAccelerationStructureKHR, consistent with the image and sampler paths added in the previous commit.

Copilot

Pull request overview

Adds configurable resource and sampler descriptor-heap strides while expanding native SPV_EXT_descriptor_heap lowering.

Changes:

Adds and validates the two stride CLI options.
Supports literal and computed descriptor-array strides, including acceleration structures.
Expands documentation and SPIR-V regression coverage.

Reviewed changes

Copilot reviewed 57 out of 57 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
`tools/clang/unittests/SPIRV/SpirvContextTest.cpp`	Tests runtime-array uniquing.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.typed-formats.hlsl`	Tests typed image formats.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.texturecube.hlsl`	Tests cube textures.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.texture.hlsl`	Tests buffer textures.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.texture-sampler-assignment.hlsl`	Tests texture/sampler reassignment.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.texture-ms.hlsl`	Tests multisampled textures.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.texture-dims.hlsl`	Tests sampled texture dimensions.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.structured-buffer-atomic.hlsl`	Tests structured-buffer atomics.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.stride-cli.hlsl`	Tests literal CLI strides.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.stride-cli-permute.hlsl`	Tests stride values and validation.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.static-global.hlsl`	Tests static resource aliases.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.sampler-comparison.hlsl`	Tests comparison samplers.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.sample-grad-bias.hlsl`	Tests gradient and bias sampling.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.rwtexture-dims.hlsl`	Tests storage texture dimensions.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.rwtexture-atomics.hlsl`	Tests untyped image atomics.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.rwbyteaddressbuffer.hlsl`	Tests writable byte buffers.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.nonuniform.hlsl`	Tests divergent heap indexing.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.mixed-bound.hlsl`	Tests bound/heap coexistence.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.mixed-alias.error.hlsl`	Tests mixed-alias diagnostics.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.load-offset.hlsl`	Tests texture-load offsets.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.groupshared.hlsl`	Tests groupshared interoperability.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.gather.hlsl`	Tests texture gathers.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.function-params.hlsl`	Tests resource parameters.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.discarded.error.hlsl`	Tests discarded-access diagnostics.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.counter-ops.error.hlsl`	Tests unsupported counter diagnostics.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.constant-texture-buffer.hlsl`	Tests constant/texture buffers.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.constant-buffer-assignment.hlsl`	Tests constant-buffer reassignment.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.buffer.hlsl`	Tests buffer heap lowering.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.array-stride.hlsl`	Tests computed default strides.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.array-stride.accelstruct.hlsl`	Tests acceleration-structure strides.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.append-consume.error.hlsl`	Tests append/consume diagnostics.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.acceleration-structure.stride.error.hlsl`	Tests acceleration-stride errors.
`tools/clang/test/CodeGenSPIRV/sm6_6.descriptorheap.ext.acceleration-structure.hlsl`	Tests acceleration-structure loads.
`tools/clang/test/CodeGenSPIRV/resource-heap-ext-texture.hlsl`	Removes superseded coverage.
`tools/clang/lib/SPIRV/SpirvType.cpp`	Includes stride IDs in type equality.
`tools/clang/lib/SPIRV/SpirvInstruction.cpp`	Implements new SPIR-V instructions.
`tools/clang/lib/SPIRV/SpirvEmitter.h`	Declares descriptor-heap helpers/state.
`tools/clang/lib/SPIRV/SpirvEmitter.cpp`	Implements native heap lowering and strides.
`tools/clang/lib/SPIRV/SpirvContext.cpp`	Uniques extended descriptor types.
`tools/clang/lib/SPIRV/SpirvBuilder.cpp`	Builds computed heap strides.
`tools/clang/lib/SPIRV/LowerTypeVisitor.cpp`	Lowers untyped image pointers.
`tools/clang/lib/SPIRV/EmitVisitor.h`	Declares new emission handlers.
`tools/clang/lib/SPIRV/EmitVisitor.cpp`	Emits new types, constants, and decorations.
`tools/clang/lib/SPIRV/DeclResultIdMapper.h`	Declares function alias support.
`tools/clang/lib/SPIRV/DeclResultIdMapper.cpp`	Implements function aliases.
`tools/clang/lib/SPIRV/CapabilityVisitor.cpp`	Requires Vulkan 1.3 for native heaps.
`tools/clang/lib/SPIRV/AstTypeProbe.cpp`	Detects acceleration structures.
`tools/clang/include/clang/SPIRV/SpirvVisitor.h`	Extends visitor dispatch.
`tools/clang/include/clang/SPIRV/SpirvType.h`	Stores runtime-array stride IDs.
`tools/clang/include/clang/SPIRV/SpirvInstruction.h`	Defines new instruction classes.
`tools/clang/include/clang/SPIRV/SpirvContext.h`	Exposes extended type uniquing.
`tools/clang/include/clang/SPIRV/SpirvBuilder.h`	Exposes stride construction APIs.
`tools/clang/include/clang/SPIRV/AstTypeProbe.h`	Declares acceleration-type detection.
`lib/DxcSupport/HLSLOptions.cpp`	Parses and validates stride options.
`include/dxc/Support/SPIRVOptions.h`	Stores stride overrides.
`include/dxc/Support/HLSLOptions.td`	Defines the CLI flags.
`docs/SPIR-V.rst`	Documents native heaps and strides.

+        if (isRaytracingAccelerationStructure(resourceType) &&
+            !spvBuilder.resourceHeapStrideIncludesAccelStruct()) {


+  bool strideOk = true;
+  strideOk &= handleHeapStride(Args, OPT_fvk_resource_heap_stride,
+                               &opts.SpirvOptions.resourceHeapStride,
+                               "-fvk-resource-heap-stride", errors);
+  strideOk &= handleHeapStride(Args, OPT_fvk_sampler_heap_stride,
+                               &opts.SpirvOptions.samplerHeapStride,
+                               "-fvk-sampler-heap-stride", errors);


+// [[RS]] = resource-heap stride, [[SS]] = sampler-heap stride (per-RUN via -D).
+
+// ---- Full 6x6 cross product of {8,16,32,64,128,256} x {8,16,32,64,128,256} ----
+// RUN: %dxc -T cs_6_6 -E main -Od -fspv-use-descriptor-heap -fspv-target-env=vulkan1.3 -fvk-resource-heap-stride 8   -fvk-sampler-heap-stride 8   -spirv %s | FileCheck %s -DRS=8   -DSS=8


+  if (!args.hasArg(OPT_spirv)) {
+    errors << name << " requires -spirv";
+    return false;


+def fvk_resource_heap_stride : Separate<["-"], "fvk-resource-heap-stride">, MetaVarName<"<stride>">, Group<spirv_Group>, Flags<[CoreOption, DriverOption]>,
+  HelpText<"Override the byte ArrayStride of the resource descriptor heap runtime array. Must be a power of 2 in [8, 256].">;
+def fvk_sampler_heap_stride : Separate<["-"], "fvk-sampler-heap-stride">, MetaVarName<"<stride>">, Group<spirv_Group>, Flags<[CoreOption, DriverOption]>,
+  HelpText<"Override the byte ArrayStride of the sampler descriptor heap runtime array. Must be a power of 2 in [8, 256].">;


Diego Novillo (dnovillo) · 2026-08-06T22:37:51Z

Added an analysis on this series: #8517 (comment)

Chris B (llvm-beanz) · 2026-08-10T19:33:18Z


+bool isRaytracingAccelerationStructure(QualType type) {
+  if (const auto *rt = type->getAs<RecordType>()) {
+    return rt->getDecl()->getName() == "RaytracingAccelerationStructure";


This string matching stuff is really gross. I posted a PR to clean this all up across the SPIRV code generator:
#8755

Agreed, thanks! Also I'm looking into addressing your comments for #8518 now.

github-project-automation Bot added this to HLSL Roadmap Jun 4, 2026

github-project-automation Bot moved this to New in HLSL Roadmap Jun 4, 2026

Jonathan Zakharov (jzakharovnv) mentioned this pull request Jun 4, 2026

[SPIR-V] Add descriptor heap stride specialization constant attribute #8520

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Jonathan Zakharov (jzakharovnv) force-pushed the pr3-cli-stride-flags branch 3 times, most recently from 1e2a278 to 5e7b928 Compare June 4, 2026 22:59

Jonathan Zakharov (jzakharovnv) force-pushed the pr3-cli-stride-flags branch 2 times, most recently from 9c5badc to ff7bb88 Compare July 6, 2026 20:08

Damyan Pepper (damyanp) requested review from Diego Novillo (dnovillo) and Chris B (llvm-beanz) July 14, 2026 17:50

Jonathan Zakharov (jzakharovnv) force-pushed the pr3-cli-stride-flags branch 2 times, most recently from d2c47bb to 9f55ccb Compare July 15, 2026 22:16

This was referenced Jul 17, 2026

[SPIR-V] Add SPV_EXT_descriptor_heap + SPV_KHR_untyped_pointers codegen #8517

Open

[SPIR-V] Add descriptor heap RaytracingAccelerationStructure support #8518

Open

Diego Novillo (dnovillo) suggested changes Jul 17, 2026

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github-project-automation Bot moved this from New to In progress in HLSL Roadmap Jul 17, 2026

Diego Novillo (dnovillo) added the spirv Work related to SPIR-V label Jul 17, 2026

Jonathan Zakharov (jzakharovnv) force-pushed the pr3-cli-stride-flags branch 3 times, most recently from 6bc5a9e to c69d8a0 Compare July 23, 2026 19:35

Diego Novillo (dnovillo) approved these changes Jul 24, 2026

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Jonathan Zakharov (jzakharovnv) force-pushed the pr3-cli-stride-flags branch from fcc9b25 to 2feca89 Compare July 24, 2026 17:15

Jonathan Zakharov (jzakharovnv) added 6 commits July 28, 2026 13:51

Added OpConstantSizeOfEXT

c7d2389

clang-format

153e928

Shared max(image,buffer) stride for descriptor heap resource arrays

eb4a9bc

Fixed correct StorageClass for descriptor heap buffer alias pointers …

25c5a0a

…TODO

Ammend keyword usage to follow LLVM Coding Standards

88bd33c

Jonathan Zakharov (jzakharovnv) force-pushed the pr3-cli-stride-flags branch from 2feca89 to 7edda02 Compare July 29, 2026 21:05

Jonathan Zakharov (jzakharovnv) added 8 commits August 3, 2026 11:07

fix stride test

1007865

Cover arrayStrideId uniquing in SpirvContextTest

f502bcf

Diagnose mixed bound/heap aliasing and correct documentation

034f3c5

removed erronous CLI options from test

915356a

Included AccelerationStructure in resource heap stride calculation

dd20201

Added AS reassignment diagnostic, fixed tests and docs

1087a6e

update docs

5783deb

Copilot AI review requested due to automatic review settings August 4, 2026 00:41

Jonathan Zakharov (jzakharovnv) force-pushed the pr3-cli-stride-flags branch from 7edda02 to 5783deb Compare August 4, 2026 00:41

Copilot started reviewing on behalf of Jonathan Zakharov (jzakharovnv) August 4, 2026 00:41 View session

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[SPIR-V] Add descriptor heap -fvk-resource-heap-stride / -fvk-sampler-heap-stride CLI flags - #8519

[SPIR-V] Add descriptor heap -fvk-resource-heap-stride / -fvk-sampler-heap-stride CLI flags#8519
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		if (isRaytracingAccelerationStructure(resourceType) &&
		!spvBuilder.resourceHeapStrideIncludesAccelStruct()) {

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