| Issue |
131324
|
| Summary |
[LLD] [X86] Link-time SSE2AVX support
|
| Labels |
lld
|
| Assignees |
|
| Reporter |
Andarwinux
|
`-march=x86-64-v3` is very fashionable now, and GAS and IAS support `-Wa,-msse2avx` to convert old-style SSE to VEX prefix variants to avoid AVX-SSE transition penalties, but this approach has some limitations:
- If the assembly code is built with NASM instead of gcc/clang, there is no sse2avx support
- If the assembly code is hand-coded using .byte, sse2avx does not work, see https://github.com/openssl/openssl/issues/27054
- Some runtime libraries may be built without `-Wa,-msse2avx`, but then used to build x86-64-v3 programs
The result is that old-style SSE code is still present in typical x86-64-v3 builds, leading to potential penalties, so I propose to implement link-time SSE2AVX in LLD for generality and reliability.
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