[Bug target/88145] New: ICE: unrecognizable insn (mffs) targeting 32-bit BE FPU-less powerpc CPUs

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88145

            Bug ID: 88145
           Summary: ICE: unrecognizable insn (mffs) targeting 32-bit BE
                    FPU-less powerpc CPUs
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          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-9.0.0-alpha20181118 snapshot (r266255) ICEs when compiling
gcc/testsuite/gcc.target/powerpc/test_mffsl.c for 32-bit powerpc cores that
don't include a FPU:

% powerpc-e300c3-linux-gnu-gcc-9.0.0-alpha20181118 -mcpu=e300c2 -c
gcc/testsuite/gcc.target/powerpc/test_mffsl.c -o /dev/null                      
gcc/testsuite/gcc.target/powerpc/test_mffsl.c: In function 'main':
gcc/testsuite/gcc.target/powerpc/test_mffsl.c:20:3: error: impossible
constraint in 'asm'
   20 |   __asm __volatile ("mffs %0" : "=f"(f14));
      |   ^~~~~
gcc/testsuite/gcc.target/powerpc/test_mffsl.c:32:1: error: unrecognizable insn:
   32 | }
      | ^
(insn 9 8 10 2 (set (reg:DF 128)
        (unspec_volatile:DF [
                (const_int 0 [0])
            ] UNSPECV_MFFS))
"gcc/testsuite/gcc.target/powerpc/test_mffsl.c":23:21 -1
     (nil))
during RTL pass: vregs
gcc/testsuite/gcc.target/powerpc/test_mffsl.c:32:1: internal compiler error: in
extract_insn, at recog.c:2305
0x639917 _fatal_insn(char const*, rtx_def const*, char const*, int, char
const*)
       
/var/tmp/portage/cross-powerpc-e300c3-linux-gnu/gcc-9.0.0_alpha20181118/work/gcc-9-20181118/gcc/rtl-error.c:108
0x639935 _fatal_insn_not_found(rtx_def const*, char const*, int, char const*)
       
/var/tmp/portage/cross-powerpc-e300c3-linux-gnu/gcc-9.0.0_alpha20181118/work/gcc-9-20181118/gcc/rtl-error.c:116
0x637d86 extract_insn(rtx_insn*)
       
/var/tmp/portage/cross-powerpc-e300c3-linux-gnu/gcc-9.0.0_alpha20181118/work/gcc-9-20181118/gcc/recog.c:2305
0xa2dbf2 instantiate_virtual_regs_in_insn
       
/var/tmp/portage/cross-powerpc-e300c3-linux-gnu/gcc-9.0.0_alpha20181118/work/gcc-9-20181118/gcc/function.c:1605
0xa2dbf2 instantiate_virtual_regs
       
/var/tmp/portage/cross-powerpc-e300c3-linux-gnu/gcc-9.0.0_alpha20181118/work/gcc-9-20181118/gcc/function.c:1975
0xa2dbf2 execute
       
/var/tmp/portage/cross-powerpc-e300c3-linux-gnu/gcc-9.0.0_alpha20181118/work/gcc-9-20181118/gcc/function.c:2024

gcc 4.9.4 correctly rejects it w/ "error: impossible constraint in 'asm'" and
w/o ICE, as does any version of the powerpcspe backend.

Also, shouldn't the rs6000 backend reject it when compiling for 85xx CPUs? I
see standard FPU instructions in the generated code which I believe shouldn't
be there. Maybe -mcpu=854[08] should be removed from the rs6000 backend
altogether, duplicating what was done in the powerpcspe backend previously w/
all non-SPE -mcpu's?