[PIX] Select callable and node shader debug invocations - #8854
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Damyan Pepper (damyanp) wants to merge 1 commit into
Open
Damyan Pepper (damyanp) wants to merge 1 commit into
Damyan Pepper (damyanp) wants to merge 1 commit into
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Damyan Pepper (damyanp)
requested a review
from Austin Kinross (austinkinross)
August 28, 2026 03:58
Damyan Pepper (damyanp)
marked this pull request as ready for review
August 28, 2026 04:00
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Pull request overview
Extends PIX debug instrumentation to select callable and node shader invocations appropriately.
Changes:
- Selects callable shaders using ray dispatch indices.
- Selects node shaders according to launch type.
- Adds unit and FileCheck coverage for each selection mode.
Reviewed changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.
Show a summary per file
| File | Description |
|---|---|
lib/DxilPIXPasses/DxilDebugInstrumentation.cpp |
Implements callable and node invocation selection. |
tools/clang/unittests/HLSL/PixTest.cpp |
Adds validation tests and parameterized pass execution. |
tools/clang/test/HLSLFileCheck/pix/DebugCallableShader.hlsl |
Checks callable instrumentation. |
tools/clang/test/HLSLFileCheck/pix/DebugNodeBroadcasting.hlsl |
Checks broadcasting-node selection. |
tools/clang/test/HLSLFileCheck/pix/DebugNodeCoalescing.hlsl |
Checks coalescing-node selection. |
tools/clang/test/HLSLFileCheck/pix/DebugNodeThreadLaunch.hlsl |
Checks thread-launch fallback selection. |
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| case DXIL::ShaderKind::AnyHit: | ||
| case DXIL::ShaderKind::ClosestHit: | ||
| case DXIL::ShaderKind::Miss: | ||
| case DXIL::ShaderKind::Callable: |
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| // CHECK: NodeInvocationSelection:GroupThreadId | ||
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| // CHECK: %ThreadIdX = call i32 @dx.op.threadIdInGroup.i32(i32 95, i32 0) | ||
| // CHECK: %ThreadIdY = call i32 @dx.op.threadIdInGroup.i32(i32 95, i32 1) | ||
| // CHECK: %ThreadIdZ = call i32 @dx.op.threadIdInGroup.i32(i32 95, i32 2) | ||
| // CHECK: %CompareToThreadIdX = icmp eq i32 %ThreadIdX, 3 | ||
| // CHECK: %CompareToThreadIdY = icmp eq i32 %ThreadIdY, 1 | ||
| // CHECK: %CompareToThreadIdZ = icmp eq i32 %ThreadIdZ, 0 | ||
| // CHECK: %CompareAll = and i1 %CompareXAndY, %CompareToThreadIdZ | ||
| // CHECK: br i1 %CompareAll, label %PIXInterestingBlock, label %PIXNonInterestingBlock | ||
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| // The requested thread must lie inside the declared thread group, or the pass | ||
| // discriminates nothing. The parameters above lie inside [NumThreads(4, 2, 1)]. | ||
| // CHECK-NOT: NodeInvocationSelection:None |
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| // GroupId for a broadcasting launch only. The thread group ID is legal, so the | ||
| // debugger discriminates invocations within a group by SV_GroupThreadID. |
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| // it. The thread group ID is legal, and discriminates invocations within one | ||
| // group. |
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| PassOutput RunDebugPassWithParameters(IDxcBlob *dxil, unsigned parameter0, | ||
| unsigned parameter1, | ||
| unsigned parameter2) { |
Austin Kinross (austinkinross)
approved these changes
Aug 28, 2026
Copilot started reviewing on behalf of
Damyan Pepper (damyanp)
September 29, 2026 04:29
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Copilot review overview
🟢 Approval recommended
The implementation and coverage are sound; remaining feedback concerns non-blocking wording and style corrections.
Review effort: Balanced
Findings: 1
Open (6)
CHECK-NOTis evaluated only after the branch check, but the pass report is emitted before…RunDebugPass, so any future pass-order or option…SV_GroupThreadID), not the thread-group ID…GroupIdis rejected for coalescing nodes; the legal value used here is…
| })x"; | ||
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| auto compiled = Compile(m_dllSupport, source, L"lib_6_3", {L"-Od"}); | ||
| auto output = RunDebugPass(compiled); |
Copilot started reviewing on behalf of
Damyan Pepper (damyanp)
September 29, 2026 16:36
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Copilot review overview
🔵 Needs a closer look
Newly added tests need minor repository-style and terminology corrections.
Review effort: Balanced
Findings: 1
Open (6)
CHECK-NOTis evaluated only after the branch check, but the pass report is emitted before…RunDebugPass, so any future pass-order or option…SV_GroupThreadID), not the thread-group ID…GroupIdis rejected for coalescing nodes; the legal value used here is…
Copilot started reviewing on behalf of
Damyan Pepper (damyanp)
September 29, 2026 19:01
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Copilot review overview
🟡 Changes recommended
Mixed-launch node libraries produce ambiguous selection-report records, and the new tests also violate the explicit-type convention.
Review effort: Balanced
Findings: 2
Open (7)
CHECK-NOTis evaluated only after the branch check, but the pass report is emitted before…RunDebugPass, so any future pass-order or option…SV_GroupThreadID), not the thread-group ID…GroupIdis rejected for coalescing nodes; the legal value used here is…
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| switch (props.Node.LaunchType) { | ||
| case DXIL::NodeLaunchType::Broadcasting: | ||
| *OSOverride << "NodeInvocationSelection:DispatchThreadId\n"; |
Copilot started reviewing on behalf of
Damyan Pepper (damyanp)
September 29, 2026 21:25
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Copilot review overview
🟢 Approval recommended
The core behavior is coherent and well tested; remaining feedback concerns nonblocking maintainability, conventions, and documentation.
Review effort: Balanced
Findings: 2
Open (8)
CHECK-NOTis evaluated only after the branch check, but the pass report is emitted before…RunDebugPass, so any future pass-order or option…SV_GroupThreadID), not the thread-group ID…GroupIdis rejected for coalescing nodes; the legal value used here is…
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| PassOutput runDebugPassWithParameters(IDxcBlob *dxil, unsigned parameter0, | ||
| unsigned parameter1, | ||
| unsigned parameter2) { |
Copilot started reviewing on behalf of
Damyan Pepper (damyanp)
September 29, 2026 23:52
View session
Contributor
There was a problem hiding this comment.
Copilot review overview
🟢 Approval recommended
The implementation has focused validation coverage, and the remaining maintainability and documentation findings are non-blocking.
Review effort: Balanced
Findings: 2
Open (8)
CHECK-NOTis evaluated only after the branch check, but the pass report is emitted before…RunDebugPass, so any future pass-order or option…SV_GroupThreadID), not the thread-group ID…GroupIdis rejected for coalescing nodes; the legal value used here is…
Copilot started reviewing on behalf of
Damyan Pepper (damyanp)
September 30, 2026 00:15
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Copilot review overview
🔵 Needs a closer look
The test helper duplicates the instrumentation pipeline, and the added tests violate the repository’s explicit-type convention.
Review effort: Balanced
Findings: 2
Open (8)
CHECK-NOTis evaluated only after the branch check, but the pass report is emitted before…RunDebugPass, so any future pass-order or option…SV_GroupThreadID), not the thread-group ID…GroupIdis rejected for coalescing nodes; the legal value used here is…
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Instrument callable shaders, selecting invocations by dispatchRaysIndex, and select node shader invocations according to launch type, reporting whether the selection is exact or approximate. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: 40dc9de3-617e-4caf-ab0d-fba0a033ed93
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The debug instrumentation pass numbers the instructions of a callable shader and advertises them to PIX, but it emits no instrumentation for it. PIX offers a callable shader that it can never step into.
Every node shader uses a selection criterion that is always true. Every invocation matches, so the debugger shows whichever invocation reaches the UAV first, and that differs between runs.
A callable shader has neither a ray nor a thread of its own. dx.op.dispatchRaysIndex is legal in it, and it reports the ray generation index responsible for the call. PIX selects a ray generation, any-hit, closest-hit, or miss invocation on that same identity, so a callable invocation uses it too.
For a node shader, the pass selects by launch type. A broadcasting node is dispatched over a grid, so SV_DispatchThreadID names one invocation, as it does for a compute shader. A coalescing node has only the position of a thread within its group, so the selection narrows to the group size. A thread launch node has no thread identity at all, so every invocation stays of interest.
The pass report names which case applies, so the caller can present the selection as exact or approximate.
Assisted-by: Copilot
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