8000 build-time popcnt test completes successfully when it should fail · Issue #19067 · numpy/numpy · GitHub
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cmichal2 opened this issue May 22, 2021 · 1 comment · Fixed by #19071
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build-time popcnt test completes successfully when it should fail #19067

cmichal2 opened this issue May 22, 2021 · 1 comment · Fixed by #19071
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00 - Bug 36 - Build Build related PR component: numpy.distutils component: SIMD Issues in SIMD (fast instruction sets) code or machinery

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@cmichal2
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Building numpy 1.20 with gcc-9.2 or 10.2 on cpus that don't support the popcnt instruction produces code that fails at run time when numpy is imported. The issue appears to be that the test to see if popcnt functions, in cpu_popcnt.c, succeeds even when it should fail. The code that's there, when compiled with -S (with or without optimization) produces no popcnt instructions in its output. Probably this could be fixed by executing popcnt on a value that is not known at compile time - perhaps a random number, or a pid?

Another alternative might be to use a similar test at compile time as is used at run-time, where it appears that a cpu register is checked to see if popcnt is available.

More details at https://bugs.gentoo.org/788184
@cmichal2 cmichal2 mentioned this issue May 23, 2021
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@seiko2plus seiko2plus added 00 - Bug 36 - Build Build related PR component: numpy.distutils component: SIMD Issues in SIMD (fast instruction sets) code or machinery labels May 23, 2021
@seiko2plus
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Thank you for your report. According to the build log, this bug can be triggered when option native is provided via build arg --cpu-baseline or through passing GCC flag -march=native via the environment variable CFLAGS.

@seiko2plus seiko2plus linked a pull request May 23, 2021 that will close this issue
BUG: Fix compile-time test of POPCNT #19071
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@charris charris mentioned this issue May 23, 2021
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@charris charris closed this as completed May 23, 2021
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BUG: Fix compile-time test of POPCNT cmichal2/numpy
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