[PIX] Fix shared instrumentation resource handling by damyanp · Pull Request #8842 · microsoft/DirectXShaderCompiler

Damyan Pepper (damyanp) · 2026-08-27T22:44:48Z

Part 2 of 14 in the PIX instrumentation stack. It targets users/damyanp/pix-fixes-01, which supplies the validation helpers. Eleven later layers use the helpers this layer changes, so please review it with care.

More than one PIX pass can run on the same module. Each pass adds its own tools UAV, so a pipeline with two passes makes two resources at the same register and space.

The code that adds this UAV to a root signature has three unsafe paths. Root signature serialization can fail and give a null blob, which the code then reads. An empty result can replace a correct root signature. Only the first global root-signature subobject gets the new parameter, so a state object that declares more than one is left in a mixed state.

The tools UAV is a raw buffer, so it changes the shader flags of the module. The code does not compute the flags again. Some passes make a dx.op overload declaration and then find no callers for it. They leave the declaration in the module, and the validator refuses a module that has an unused declaration.

When serialization fails, the helpers keep the original root signature. A valid signature is better than an empty one.

Assisted-by: Copilot

This changes only the PIX instrumentation, so it needs no release note.

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More than one PIX pass can run on the same module. Each pass adds its own tools UAV, so a pipeline with two passes makes two resources at the same register and space. The code that adds this UAV to a root signature has three unsafe paths. Root signature serialization can fail and give a null blob, which the code then reads. An empty result can replace a correct root signature. Only the first global root-signature subobject gets the new parameter, so a state object that declares more than one is left in a mixed state. The tools UAV is a raw buffer, so it changes the shader flags of the module. The code does not compute the flags again. Some passes make a dx.op overload declaration and then find no callers for it. They leave the declaration in the module, and the validator refuses a module that has an unused declaration. When serialization fails, the helpers keep the original root signature. A valid signature is better than an empty one. Assisted-by: Copilot Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 40dc9de3-617e-4caf-ab0d-fba0a033ed93

Damyan Pepper (damyanp) · 2026-08-27T23:27:42Z

/azp run

azure-pipelines · 2026-08-27T23:27:49Z

Azure Pipelines: 1 pipeline(s) were filtered out due to trigger conditions.

Copilot

Pull request overview

Fixes PIX instrumentation resource reuse, root-signature handling, shader flags, and unused DXIL operation declarations.

Changes:

Reuses tools UAVs and safely updates all global root signatures.
Recomputes shader flags and centralizes unused declaration cleanup.
Adds regression and validation coverage for affected PIX passes.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
`tools/clang/unittests/HLSL/PixTest.cpp`	Adds PIX resource, root-signature, flags, cleanup, and validation tests.
`tools/clang/test/HLSLFileCheck/pix/pixelCounterEarlyZ.hlsl`	Updates expected raw-buffer shader flags.
`lib/DxilPIXPasses/PixPassHelpers.h`	Exposes the operation cleanup helper.
`lib/DxilPIXPasses/PixPassHelpers.cpp`	Implements UAV reuse, root-signature updates, flags, and cleanup.
`lib/DxilPIXPasses/DxilRemoveDiscards.cpp`	Removes unused discard declarations.
`lib/DxilPIXPasses/DxilPIXMeshShaderOutputInstrumentation.cpp`	Cleans obsolete mesh operation overloads.
`lib/DxilPIXPasses/DxilPIXAddTidToAmplificationShaderPayload.cpp`	Cleans the replaced dispatch declaration.
`lib/DxilPIXPasses/DxilOutputColorBecomesConstant.cpp`	Cleans unused output overloads.
`lib/DxilPIXPasses/DxilNonUniformResourceIndexInstrumentation.cpp`	Cleans unused instrumentation operations.
`lib/DxilPIXPasses/DxilDebugInstrumentation.cpp`	Removes obsolete UAV-selection logic.
`lib/DxilPIXPasses/DxilDebugBreakInstrumentation.cpp`	Uses centralized operation cleanup.

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+    ExtendRootSig<DxilRootSignatureDesc1, DxilRootParameter1>(rs->Desc_1_1,
+                                                              toolsUAVRegister);
    rs->Desc_1_1.pParameters[rs->Desc_1_1.NumParameters - 1].Descriptor.Flags =
        hlsl::DxilRootDescriptorFlags::None;


Bring the final approved L1 tip, including its formatting follow-up, into this layer while preserving the original L2 commit as the first parent. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

ExtendRootSig returns early, without appending a parameter, when a version 1.1 root signature already holds the requested tools UAV. The caller still unconditionally cleared Descriptor.Flags on the last parameter in that case, which may be an unrelated, pre-existing parameter whose flags the caller must not disturb. Have ExtendRootSig report whether it actually appended a parameter, and only clear flags on that path. Add a regression test: a v1.1 root signature with the tools UAV already present as parameter 0 and an unrelated root descriptor as parameter 1 with DataVolatile flags. Re-requesting the same register leaves parameter 1's flags untouched; appending a genuinely new register still leaves parameter 1 untouched and gives the new parameter None flags. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Replace the stable, nameable auto-deduced types introduced by L2. Retain only the two DxilSubobjects MapVector ranges whose underlying pair type is implementation-dependent and obscures the loop. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot

🟡 Changes recommended

Declaration cleanup mutations must be reflected in pass modification results.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

Suppressed comments (1)

tools/clang/unittests/HLSL/PixTest.cpp:4243

Use the explicit CComPtr<IDxcBlob> type here. Compile results use that type throughout these new tests (for example, line 4224 immediately above), matching the repository's almost-never-auto convention.

  auto compiled = Compile(m_dllSupport, source, L"cs_6_10", {});

Files reviewed: 11/11 changed files
Comments generated: 1
Review effort level: Balanced

+void EraseIfUnused(hlsl::DxilModule &DM, llvm::Function *OpFunction) {
+  if (OpFunction != nullptr && OpFunction->user_empty()) {
+    DM.GetOP()->RemoveFunction(OpFunction);
+    OpFunction->eraseFromParent();
+  }


github-project-automation Bot added this to HLSL Roadmap Aug 27, 2026

github-project-automation Bot moved this to New in HLSL Roadmap Aug 27, 2026

Damyan Pepper (damyanp) requested a review from Austin Kinross (austinkinross) August 27, 2026 22:45

Austin Kinross (austinkinross) approved these changes Aug 27, 2026

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Damyan Pepper (damyanp) marked this pull request as ready for review August 27, 2026 23:31

Copilot AI balanced review requested due to automatic review settings August 27, 2026 23:31

Copilot started reviewing on behalf of Damyan Pepper (damyanp) August 27, 2026 23:31 View session

Copilot AI reviewed Aug 27, 2026

View reviewed changes

Comment thread lib/DxilPIXPasses/PixPassHelpers.cpp Outdated

Comment on lines 246 to 249

ExtendRootSig<DxilRootSignatureDesc1, DxilRootParameter1>(rs->Desc_1_1,

toolsUAVRegister);

rs->Desc_1_1.pParameters[rs->Desc_1_1.NumParameters - 1].Descriptor.Flags =

hlsl::DxilRootDescriptorFlags::None;

Damyan Pepper (damyanp) and others added 3 commits September 2, 2026 19:03

Merge final approved clean L1 into original L2

8c15684

Bring the final approved L1 tip, including its formatting follow-up, into this layer while preserving the original L2 commit as the first parent. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings September 3, 2026 02:13

Copilot started reviewing on behalf of Damyan Pepper (damyanp) September 3, 2026 02:13 View session

Copilot AI reviewed Sep 3, 2026

View reviewed changes

Comment thread lib/DxilPIXPasses/PixPassHelpers.cpp

Comment on lines +389 to +393

void EraseIfUnused(hlsl::DxilModule &DM, llvm::Function *OpFunction) {

if (OpFunction != nullptr && OpFunction->user_empty()) {

DM.GetOP()->RemoveFunction(OpFunction);

OpFunction->eraseFromParent();

}

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[PIX] Fix shared instrumentation resource handling - #8842

[PIX] Fix shared instrumentation resource handling#8842
Damyan Pepper (damyanp) wants to merge 4 commits into
users/damyanp/pix-fixes-01from
users/damyanp/pix-fixes-02

Damyan Pepper (damyanp) commented Aug 27, 2026 •

edited

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Damyan Pepper (damyanp) commented Aug 27, 2026 •

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