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| author | Lasse Collin <lasse.collin@tukaani.org> | 2023-10-20 23:35:10 +0300 |
|---|---|---|
| committer | Lasse Collin <lasse.collin@tukaani.org> | 2024-01-11 14:29:42 +0200 |
| commit | 419f55f9dfc2df8792902b8953d50690121afeea (patch) | |
| tree | aa95af5e4119ab90423c19ad64cfa73df0044f1c /configure.ac | |
| parent | liblzma: crc_clmul.c: Add crc_attr_target macro. (diff) | |
| download | xz-419f55f9dfc2df8792902b8953d50690121afeea.tar.xz | |
liblzma: Avoid extern lzma_crc32_clmul() and lzma_crc64_clmul().
A CLMUL-only build will have the crcxx_clmul() inlined into
lzma_crcxx(). Previously a jump to the extern lzma_crcxx_clmul()
was needed. Notes about shared liblzma on ELF platforms:
- On platforms that support ifunc and -fvisibility=hidden, this
was silly because CLMUL-only build would have that single extra
jump instruction of extra overhead.
- On platforms that support neither -fvisibility=hidden nor linker
version script (liblzma*.map), jumping to lzma_crcxx_clmul()
would go via PLT so a few more instructions of overhead (still
not a big issue but silly nevertheless).
There was a downside with static liblzma too: if an application only
needs lzma_crc64(), static linking would make the linker include the
CLMUL code for both CRC32 and CRC64 from crc_x86_clmul.o even though
the CRC32 code wouldn't be needed, thus increasing code size of the
executable (assuming that -ffunction-sections isn't used).
Also, now compilers are likely to inline crc_simd_body()
even if they don't support the always_inline attribute
(or MSVC's __forceinline). Quite possibly all compilers
that build the code do support such an attribute. But now
it likely isn't a problem even if the attribute wasn't supported.
Now all x86-specific stuff is in crc_x86_clmul.h. If other archs
The other archs can then have their own headers with their own
is_clmul_supported() and crcxx_clmul().
Another bonus is that the build system doesn't need to care if
crc_clmul.c is needed.
is_clmul_supported() stays as inline function as it's not needed
when doing a CLMUL-only build (avoids a warning about unused function).
Diffstat (limited to 'configure.ac')
| -rw-r--r-- | configure.ac | 1 |
1 files changed, 0 insertions, 1 deletions
diff --git a/configure.ac b/configure.ac index a4ef57a5..9584c4ac 100644 --- a/configure.ac +++ b/configure.ac @@ -1086,7 +1086,6 @@ __m128i my_clmul(__m128i a) ]) AC_MSG_RESULT([$enable_clmul_crc]) ]) -AM_CONDITIONAL([COND_CRC_CLMUL], [test "x$enable_clmul_crc" = xyes]) # Check for sandbox support. If one is found, set enable_sandbox=found. # |