[Bug target/71847] New: powerpc64le: Potential rlwinm optimisation

[anton at samba dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71847

            Bug ID: 71847
           Summary: powerpc64le: Potential rlwinm optimisation
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anton at samba dot org
  Target Milestone: ---

The following code:

unsigned long foo(unsigned long x)
{
        unsigned long y = (x & 0xffffffffUL);

        return y | (y << 32);
}

Results in 3 instructions on gcc:

foo:
        rldicl 3,3,0,32
        sldi 9,3,32
        or 3,9,3
        blr

Clang does it in 1, knowing that rotate32 starts with two 32 bit copies of the
data:

foo:
        rlwinm 3, 3, 0, 1, 0
        blr