Add opt-in /Os for Windows Release builds - #8998
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Alex Sepkowski (alsepkow) wants to merge 1 commit into
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Alex Sepkowski (alsepkow) wants to merge 1 commit into
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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Alex Sepkowski (alsepkow)
marked this pull request as ready for review
October 2, 2026 01:37
Alex Sepkowski (alsepkow)
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Copilot review overview
🟢 Approval recommended
The scoped CMake changes correctly preserve /O2 while adding the requested opt-in size preference.
Review effort: Balanced
Findings: None
What changed in this PR
Adds an optional MSVC size preference for Windows Release builds without changing default behavior.
Changes:
- Adds the
DXC_OPTIMIZE_FOR_SIZECMake option, defaulting toOFF. - Appends
/Osto Release C and C++ flags when enabled.
| File | Description |
|---|---|
CMakeLists.txt |
Defines the opt-in size optimization setting. |
cmake/modules/HandleLLVMOptions.cmake |
Applies /Os to MSVC Release builds. |
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Add an opt-in size preference for Windows Release builds.
Change
DXC_OPTIMIZE_FOR_SIZE, defaulting toOFF./Osto the C and C++ Release flags on MSVC./Osis used alongside/O2: Release builds remain fully optimized, while MSVC favors smaller generated code when an optimization involves a choice between code size and execution speed.Validation
DXC_OPTIMIZE_FOR_SIZE=ON.llvm-tblgen.vcxprojcontainsOptimization=MaxSpeedandFavorSizeOrSpeed=Size, confirming/O2remains enabled while/Ossupplies the size preference.Assisted-By: Copilot