SIMD: PURECFMA scalar dispatch causes SIGILL on x86-64-v2 CPUs (Sandy Bridge)

[SwayamInSync]

This issue is to inform maintainers that the quad-precision scalar dispatcher qdispscalar.c compiles FMA-optimized code paths unconditionally on x86-64, which can cause SIGILL (illegal instruction) crashes on CPUs that don't support FMA instructions (x86-64-v2 / Sandy Bridge era processors). We noticed this issue in version 3.9 but it still persists in current in-development source.

Configure.cmake builds PRECFMA_SCALAR with avx and fma flags on x86

sleef/Configure.cmake

Line 192 in 7623d6c

set(CLANG_FLAGS_ENABLE_PURECFMA_SCALAR "-mavx2;-mfma")

Configure.cmake unconditionally enables PURECFMA_SCALAR for all arch

sleef/Configure.cmake

Line 360 in 7623d6c

set(COMPILER_SUPPORTS_PURECFMA_SCALAR True)