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.
