Fix vectorized min/max/minmax_element for 64-bit types on x86
#2821
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Co-authored-by: Alex Guteniev <gutenev@gmail.com>
CaseyCarter
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AlexGuteniev
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I want to reaffirm my opinion that @AlexGuteniev is a wizard
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
CaseyCarter
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…osoft#2821) Co-authored-by: Alex Guteniev <gutenev@gmail.com>
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This fixes a regression caused by #2447 that was specific to 64-bit types on x86, reported by internal VSO-1558536 "[RWC][prod/fe][Regression][x86] LLVM one test 'Profile/c-counter-overflows.c' failed".
Thanks to @AlexGuteniev for finding the root cause and providing the fix. The problem is that
_mm_extract_epi32and_mm_cvtsi128_si32both returnint. By directly casting to_Unsigned_t, i.e.uint64_tin_Minmax_traits_8, high-bit values were being sign-extended, but the desired behavior was zero-extension. Adding initial casts ofstatic_cast<uint32_t>fixes this.Then, I'm enhancing the test coverage:
[1, 20]range concealed this bug. Now, integers use the full range, while floating-point values use a large range centered around 0. (Unfortunately,uniform_real_distributionrequiresb - a <= max, so we can't generate a full range without extra work. As floating-point is not yet vectorized, I felt that this was sufficient for now.)Fortunately, this regression has not yet shipped in a Preview.