[Bug target/84781] New: [missed optimization] ignore bitmask after movemask

[kretz at kde dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84781

            Bug ID: 84781
           Summary: [missed optimization] ignore bitmask after movemask
           Product: gcc
           Version: 8.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kretz at kde dot org
  Target Milestone: ---

Testcase: https://godbolt.org/g/S3tfrL

#include <x86intrin.h>

int f(__m128  a) { return _mm_movemask_ps(a)    & 0xf; }
int f(__m128d a) { return _mm_movemask_pd(a)    & 0x3; }
int f(__m128i a) { return _mm_movemask_epi8(a)  & 0xffffu; }
int f(__m256  a) { return _mm256_movemask_ps(a) & 0xff; }
int f(__m256d a) { return _mm256_movemask_pd(a) & 0xf; }

In all of these functions, the bitmask is a no-op since the movemask cannot
yield bits in any of the masked-off places. Consequently, the bitwise and
should be dropped.