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liblzma: CLMUL CRC64: Work around a bug in MSVC, second attempt.

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This affects only 32-bit x86 builds. x86-64 is OK as is.

I still cannot easily test this myself. The reporter has tested
this and it passes the tests included in the CMake build and
performance is good: raw CRC64 is 2-3 times faster than the
C version of the slice-by-four method. (Note that liblzma doesn't
include a MSVC-compatible version of the 32-bit x86 assembly code
for the slice-by-four method.)

Thanks to Iouri Kharon for figuring out a fix, testing, and
benchmarking.
This commit is contained in:
Lasse Collin 2023-01-10 22:14:03 +02:00
parent 765354b50c
commit 0b8fa310cf
1 changed files with 18 additions and 0 deletions
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18
src/liblzma/check/crc64_fast.c
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@ -184,6 +184,20 @@ calc_hi(uint64_t poly, uint64_t a)
MASK_H(in, mask, high)
// MSVC (VS2015 - VS2022) produces bad 32-bit x86 code from the CLMUL CRC
// code when optimizations are enabled (release build). According to the bug
// report, the ebx register is corrupted and the calculated result is wrong.
// Trying to workaround the problem with "__asm mov ebx, ebx" didn't help.
// The following pragma works and performance is still good. x86-64 builds
// aren't affected by this problem.
//
// NOTE: Another pragma after the function restores the optimizations.
// If the #if condition here is updated, the other one must be updated too.
#if defined(_MSC_VER) && !defined(__INTEL_COMPILER) && !defined(__clang__) \
&& defined(_M_IX86)
# pragma optimize("g", off)
#endif
// EDG-based compilers (Intel's classic compiler and compiler for E2K) can
// define __GNUC__ but the attribute must not be used with them.
// The new Clang-based ICX needs the attribute.
@ -371,6 +385,10 @@ crc64_clmul(const uint8_t *buf, size_t size, uint64_t crc)
# pragma GCC diagnostic pop
#endif
}
#if defined(_MSC_VER) && !defined(__INTEL_COMPILER) && !defined(__clang__) \
&& defined(_M_IX86)
# pragma optimize("", on)
#endif
#endif