[Bug target/94687] New: PPC vector fails to optimize shift (used bits)

["shawn at git dot icu" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94687

            Bug ID: 94687
           Summary: PPC vector fails to optimize shift (used bits)
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shawn at git dot icu
  Target Milestone: ---

https://godbolt.org/z/ZyTG9b


#include <altivec.h>

typedef vector unsigned __int128 block;
typedef vector unsigned long long vector2_u64;

block swap_with_shift(block num) {
    return num << 64 | num >> 64;
}

block swap_without_shift(block num) {
    vector unsigned long long ret;
    ret[0] = ((vector2_u64)num)[1];
    ret[1] = ((vector2_u64)num)[0];
    return (block)ret;
}

typedef unsigned __int128 u128;

u128 swap_scalar(u128 in) {
    return in << 64 | in >> 64;
}

swap_with_shift:
        xxpermdi 34,34,34,2
        addi 9,1,-16
        stxvd2x 34,0,9
        ld 8,-8(1)
        ld 9,-16(1)
        mtvsrd 1,8
        mtvsrd 0,9
        xxpermdi 34,0,1,0
        blr
        .long 0
        .byte 0,0,0,0,0,0,0,0
swap_without_shift:
        xxpermdi 34,34,34,2
        blr
        .long 0
        .byte 0,0,0,0,0,0,0,0
swap_scalar:
        mr 9,3
        mr 3,4
        mr 4,9
        blr
        .long 0
        .byte 0,0,0,0,0,0,0,0