Build: x86-64 needs an explicit -msse4.1 for clang/GCC, since the generated code uses SSE4.1 intrinsics

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
88/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
cmake, cpp
Domain
build-system

Research direction

Open the root CMakeLists.txt and find the if(PS2X_IS_ARM_TARGET) block. Add an else that, for Clang or GNU, calls add_compile_options(-msse4.1) as in the issue (do not replace CMAKE_CXX_FLAGS). Rebuild with clang or GCC on x86-64; done when the SSE4.1 intrinsic errors are gone and the project still links.

Written by the indexing model from the issue text.

Description

What happens

The generated runner code emits SSE4.1 intrinsics -- _mm_blendv_ps (442 occurrences in our output), _mm_mullo_epi32, _mm_extract_epi32. The root CMakeLists.txt only sets an architecture flag for ARM targets (the if(PS2X_IS_ARM_TARGET) block); there is no else branch for x86, and no SSE4.1 handling anywhere in the tree at 75d729ce or on main.

MSVC has no notion of target features and accepts these intrinsics unconditionally on x64, so the defect is invisible when building with cl.exe. clang and GCC keep clang's semantics and refuse:

error: always_inline function '_mm_mullo_epi32' requires target feature 'sse4.1',
       but would be inlined into function 'main' that is compiled without
       support for 'sse4.1'

Measured on this host with clang-cl 22.1.3, flag by flag on a neutral file: without -msse4.1 the intrinsic is rejected; with -msse4.1, /clang:-msse4.1 or /arch:AVX it compiles, links and runs. cl.exe accepts it with no flag at all. On Linux with clang the build broke at unity_85_cxx.cxx.o.

Issue #166 shows another user's configure log containing -- x86 target detected, enabling SSE4.1 and -- SSE4.1 compiler flag enabled. Those strings appear nowhere in this repository's history, on any branch, so that was a local fix on their side rather than an upstream one.

Suggested fix

Give the if(PS2X_IS_ARM_TARGET) block an else branch, so the flag is added rather than left to the caller:

else()
    if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES "GNU")
        message(STATUS "x86-64 Clang/GCC detected - adding -msse4.1")
        add_compile_options(-msse4.1)
    endif()
endif()

add_compile_options adds to the flag set. Worth preferring over telling users to pass -DCMAKE_CXX_FLAGS=-msse4.1, because that form replaces CMake's defaults (/DWIN32 /D_WINDOWS /EHsc) and silently disables exceptions -- which then fails ps2xRecomp with "cannot use 'throw' with exceptions disabled". That cost us a build cycle to diagnose.

Found while statically recompiling Ridge Racer V (NTSC-U, SLUS_200.02) with PS2Recomp.
Tested on commit 75d729ce; main was c5a9d02 at the time of writing, one README-only commit ahead.
Host: Windows 11 x64, clang-cl 22.1.3 + Ninja, MSVC toolset 14.51.36231, Windows SDK 10.0.26100.0, CMake 4.2.3.
None of these are specific to this game.

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Getting set up

This project ships no dev container, Dockerfile or contributing guide, so setting up is up to you: start from its README, and see our first-contribution guide for the general steps.

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

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