[PIX] Fix DXR invocation log bounds

[Damyan Pepper (damyanp)]

Part 4 of 14 in the PIX instrumentation stack. It targets users/damyanp/pix-fixes-03. Its content depends on PR 2 for the shared helpers and PR 1 for the validation helpers.

Each DXR invocation takes one slot in the log with an atomic increment on the counter UAV. If the slot number is too large, the pass limits it to the last slot. Every invocation that overflows therefore writes over the last correct record. PIX sees a full log with a plausible final entry and cannot detect the truncation.

A capacity of zero makes that clamp wrap to a very large value, so a log with no slots accepts writes.

An out-of-range slot must produce no write. The correct records then stay unchanged, and the overflow stays visible, because the claimed count is larger than the capacity.

An invocation that overflows contributes no record. A tool that treats a full log as a complete log must compare the claimed count with the capacity.

Assisted-by: Copilot

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

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[Copilot]

Pull request overview

Fixes PIX DXR invocation logging so out-of-capacity entries do not overwrite valid records.

Changes:

• Replaces index clamping with a guarded write path.
• Disables instrumentation for zero-capacity logs.
• Adds overflow, boundary, and validation tests.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
lib/DxilPIXPasses/DxilPIXDXRInvocationsLog.cpp	Adds bounds-checked record writes.
tools/clang/unittests/HLSL/PixTest.cpp	Adds capacity and validation tests.
tools/clang/test/HLSLFileCheck/pix/InvocationsLog_OverflowIsNotClamped.hlsl	Verifies overflow is guarded rather than clamped.
tools/clang/test/HLSLFileCheck/pix/InvocationsLog_ClosestHit.hlsl	Updates checks to reflect removal of clamping.

Suppressed comments (3)

tools/clang/unittests/HLSL/PixTest.cpp:3671

• These declarations infer straightforward CComPtr<IDxcBlob> and std::vector<std::string> types. Please spell them explicitly per the repository's almost-never-auto convention (PixTest.cpp:1814-1815 and PixTest.cpp:3724 show the established forms).

  auto compiledLib =
      Compile(m_dllSupport, kSingleMissInvocationLogShader, L"lib_6_6", {});
  auto output = RunDxilPIXDXRInvocationsLog(compiledLib, 1);
  auto lines = Tokenize(Disassemble(output), "\n");

tools/clang/unittests/HLSL/PixTest.cpp:3680

• These declarations infer straightforward CComPtr<IDxcBlob> and std::vector<std::string> types. Please spell them explicitly per the repository's almost-never-auto convention (PixTest.cpp:1814-1815 and PixTest.cpp:3724 show the established forms).

  auto compiledLib =
      Compile(m_dllSupport, kSingleMissInvocationLogShader, L"lib_6_6", {});
  auto output = RunDxilPIXDXRInvocationsLog(compiledLib, 24);
  auto lines = Tokenize(Disassemble(output), "\n");

tools/clang/unittests/HLSL/PixTest.cpp:3688

• These declarations infer the short CComPtr<IDxcBlob> type. Please spell it explicitly per the repository's almost-never-auto convention; the same test file uses this explicit form at PixTest.cpp:1814-1815.

  auto compiledLib =
      Compile(m_dllSupport, kSingleMissInvocationLogShader, L"lib_6_6", {});
  auto output = RunDxilPIXDXRInvocationsLog(compiledLib, 1);

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