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* [Bug target/98495] New: X86 _mm_extract_pi16 incorrectly sign extends result
@ 2021-01-01  4:14 foom at fuhm dot net
  2021-01-01 13:06 ` [Bug target/98495] " hjl.tools at gmail dot com
                   ` (7 more replies)
  0 siblings, 8 replies; 9+ messages in thread
From: foom at fuhm dot net @ 2021-01-01  4:14 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98495

            Bug ID: 98495
           Summary: X86 _mm_extract_pi16 incorrectly sign extends result
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: foom at fuhm dot net
  Target Milestone: ---

#include <xmmintrin.h>
int test(__m64 a) {
    return _mm_extract_pi16 (a, 0);
}

Compiles to (x86_64 gcc, -O2):
        pextrw  $0, %xmm0, %eax
        cwtl
        ret

Which results in the value being sign-extended from 16-bits to 32-bits.

The intel docs for PEXTRW state that the upper bits are zeroed, and state that
_mm_extract_pi16 is supposed to implement PEXTRW.

So, the expected result is no sign extension:
        pextrw  $0, %xmm0, %eax
        ret


I'd note that this is not a regression due to the new MMX with SSE2 changes --
GCC has had this bug as far back as I can see. It is currently present on trunk
both for the MMX and SSE2 implementations.

Both clang and MSVC zero-extend rather than sign-extend. And, for that matter,
GCC's _mm_extract_epi16 function _also_ zero-extends -- it was fixed in PR45336
for GCC 4.6.

^ permalink raw reply	[flat|nested] 9+ messages in thread
end of thread, other threads:[~2023-05-29 10:03 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-01-01  4:14 [Bug target/98495] New: X86 _mm_extract_pi16 incorrectly sign extends result foom at fuhm dot net
2021-01-01 13:06 ` [Bug target/98495] " hjl.tools at gmail dot com
2021-01-01 13:35 ` hjl.tools at gmail dot com
2021-01-05 13:08 ` cvs-commit at gcc dot gnu.org
2021-01-05 19:23 ` cvs-commit at gcc dot gnu.org
2021-04-27 11:39 ` jakub at gcc dot gnu.org
2021-07-28  7:05 ` rguenth at gcc dot gnu.org
2022-04-21  7:48 ` rguenth at gcc dot gnu.org
2023-05-29 10:03 ` jakub at gcc dot gnu.org

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