[Bug target/79080] New: [7 Regression] ICE: internal consistency failure (error: invalid rtl sharing found in the insn) (error: shared rtx)

["asolokha at gmx dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79080

            Bug ID: 79080
           Summary: [7 Regression] ICE: internal consistency failure
                    (error: invalid rtl sharing found in the insn) (error:
                    shared rtx)
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---
            Target: powerpc-*-linux-gnu*

gcc-7.0.0-alpha20170108 snapshot fails when compiling the following snippet for
32-bit BE powerpc target w/ -O1:

int
gd (char ff)
{
  int mi;

  for (;;)
    {
      ff += 59 /* 197 also works */;
      if (ff != 0)
        mi = 0;
      else
        return 0;
    }
}

% powerpc-e500v2-linux-gnuspe-gcc-7.0.0-alpha20170108 -O1 -c dsmbs5u1.c
dsmbs5u1.c: In function 'gd':
dsmbs5u1.c:14:1: error: invalid rtl sharing found in the insn
 }
 ^
(insn 40 39 41 2 (set (subreg:QI (reg:SI 172) 3)
        (subreg:QI (reg:SI 174) 3)) -1
     (nil))
dsmbs5u1.c:14:1: error: shared rtx
(subreg:QI (reg:SI 172) 3)
dsmbs5u1.c:14:1: internal compiler error: internal consistency failure
0x2e55cd6de9b verify_rtx_sharing
       
/var/tmp/portage/cross-powerpc-e500v2-linux-gnuspe/gcc-7.0.0_alpha20170108/work/gcc-7-20170108/gcc/emit-rtl.c:2774
0x2e55cd6ddd7 verify_rtx_sharing
       
/var/tmp/portage/cross-powerpc-e500v2-linux-gnuspe/gcc-7.0.0_alpha20170108/work/gcc-7-20170108/gcc/emit-rtl.c:2789
0x2e55cd6e30e verify_insn_sharing
       
/var/tmp/portage/cross-powerpc-e500v2-linux-gnuspe/gcc-7.0.0_alpha20170108/work/gcc-7-20170108/gcc/emit-rtl.c:2860
0x2e55cd742f7 verify_rtl_sharing()
       
/var/tmp/portage/cross-powerpc-e500v2-linux-gnuspe/gcc-7.0.0_alpha20170108/work/gcc-7-20170108/gcc/emit-rtl.c:2883
0x2e55d058785 execute_function_todo
       
/var/tmp/portage/cross-powerpc-e500v2-linux-gnuspe/gcc-7.0.0_alpha20170108/work/gcc-7-20170108/gcc/passes.c:1982
0x2e55d0595ab execute_todo
       
/var/tmp/portage/cross-powerpc-e500v2-linux-gnuspe/gcc-7.0.0_alpha20170108/work/gcc-7-20170108/gcc/passes.c:2015

% powerpc-e500v2-linux-gnuspe-gcc-7.0.0-alpha20170108 -O1 -c dsmbs5u1.c
-mcpu=power7
No ICE

% powerpc-e300c3-linux-gnu-gcc-7.0.0-alpha20170108 -O1 -c dsmbs5u1.c
No ICE

% powerpc-e300c3-linux-gnu-gcc-7.0.0-alpha20170108 -O1 -c dsmbs5u1.c -mcpu=8548
ICE

This testcase was originally posted in PR72749.