[Bug target/88343] New: [7/8/9 Regression] R31 is unconditionally saved/restored on powerpc-darwin even when it's not necessary.

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88343

            Bug ID: 88343
           Summary: [7/8/9 Regression] R31 is unconditionally
                    saved/restored on powerpc-darwin even when it's not
                    necessary.
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: iains at gcc dot gnu.org
  Target Milestone: ---

This was fallout from the fix for PR 71469.

a trivial 

void foo (void) {}

at -O2 produces

$ more t.s
        .machine ppc7400
        .text
        .align  2
        .globl _foo
_foo:
        stw r31,-4(r1)
        lwz r31,-4(r1)
        blr
        .subsections_via_symbols