[Bug target/107757] New: PPCLE: Inefficient vector constant creation

[jens.seifert at de dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107757

            Bug ID: 107757
           Summary: PPCLE: Inefficient vector constant creation
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jens.seifert at de dot ibm.com
  Target Milestone: ---

Due to the fact that vslw, vsld, vsrd, ... only use the modulo of bit width for
shifting, the combination with 0xFF..FF vector can be used to create vector
constants for:
vec_splats(-0.0) or vec_splats(1ULL << 31) and scalar -0.0
vec_splats(-0.0f) or vec_splats(1U << 31)
vec_splats((short)0x8000)
with only 2 2-cycle vector instructions.

Sample:

vector long long lsb64()
{
   return vec_splats(1LL);
}

creates:

lsb64():
.LCF5:
        addi 2,2,.TOC.-.LCF5@l
        addis 9,2,.LC12@toc@ha
        addi 9,9,.LC12@toc@l
        lvx 2,0,9
        blr
        .long 0
        .byte 0,9,0,0,0,0,0,0

while:

vector long long lsb64_opt()
{
   vector long long a = vec_splats(~0LL);
   __asm__("vsrd %0,%0,%0":"=v"(a):"v"(a),"v"(a));
   return a;
}

creates:
lsb64_opt():
        vspltisw 2,-1
        vsrd 2,2,2
        blr
        .long 0
        .byte 0,9,0,0,0,0,0,0