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Disable _tzcnt_u64 for ARM64EC #1054

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merged 2 commits into from
Jan 27, 2022
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Disable _tzcnt_u64 for ARM64EC #1054

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Disable _tzcnt_u64 for ARM64EC
mcfi Jan 27, 2022
c2d00cb
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mcfi Jan 27, 2022
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7 changes: 6 additions & 1 deletion lib/lz4.c
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Original file line number Diff line number Diff line change
Expand Up @@ -517,7 +517,12 @@ static unsigned LZ4_NbCommonBytes (reg_t val)
assert(val != 0);
if (LZ4_isLittleEndian()) {
if (sizeof(val) == 8) {
# if defined(_MSC_VER) && (_MSC_VER >= 1800) && defined(_M_AMD64) && !defined(LZ4_FORCE_SW_BITCOUNT)
# if defined(_MSC_VER) && (_MSC_VER >= 1800) && (defined(_M_AMD64) && !defined(_M_ARM64EC)) && !defined(LZ4_FORCE_SW_BITCOUNT)
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Could you please add a one-line comment explaining why _M_ARM64EC must be exclude ?
Essentially a summary of what you already explain in the PR, just hosted directly in the code source.

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Thanks, I just added comments.

/*-*************************************************************************************************
* ARM64EC is a Microsoft-designed ARM64 ABI compatible with AMD64 applications on ARM64 Windows 11.
* The ARM64EC ABI does not support AVX/AVX2/AVX512 instructions, nor their relevant intrinsics
* including _tzcnt_u64. Therefore, we need to neuter the _tzcnt_u64 code path for ARM64EC.
****************************************************************************************************/
# if defined(__clang__) && (__clang_major__ < 10)
/* Avoid undefined clang-cl intrinics issue.
* See https://github.com/lz4/lz4/pull/1017 for details. */
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