[Bug bootstrap/100373] New: [12 Regression] Darwin, Compare-debug fail after r12-248-gb58dc0b803057

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100373

            Bug ID: 100373
           Summary: [12 Regression] Darwin, Compare-debug fail after
                    r12-248-gb58dc0b803057
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: bootstrap
          Assignee: unassigned at gcc dot gnu.org
          Reporter: iains at gcc dot gnu.org
  Target Milestone: ---

Created attachment 50725
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50725&action=edit
tarball with asm, objects and obj dumps.

Exactly which cases fail seems to depend on the CPU in use and the OS version. 
For modern CPUs (xeon w, core i5 Skylake) the fail seems to be quite reliably
in mpfr (which I build in tree).  For older corei7 machines on Darwin16, I've
seen also gcc/gcc.o as mismatched.

I did a run with -save-temps -dp (asm attached).
this is on x86_64-darwin20, but the problem is seen on x86_64-darwin* AFAICT. 
Backing out r12-248-gb58dc0b803057 allows bootstrap to succeed.

attached:

stage2-mpfr/src/gmp_op.o.stripped
stage2-mpfr/src/gmp_op.o
stage2-mpfr/src/gmp_op.s
s2.txt == objdump -d -r stage2-mpfr/src/gmp_op.o.stripped >s2.txt
stage3-mpfr/src/gmp_op.o.stripped
stage3-mpfr/src/gmp_op.o
stage3-mpfr/src/gmp_op.s
s3.txt == objdump -d -r stage3-mpfr/src/gmp_op.o.stripped >s3.txt