[Bug target/81426] [SH]: unable to find a register to spill in class 'R0_REGS' when building webkit2gtk

[slyfox at inbox dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81426

Sergei Trofimovich <slyfox at inbox dot ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |slyfox at inbox dot ru

--- Comment #7 from Sergei Trofimovich <slyfox at inbox dot ru> ---
Not sure if it's the same bug or not, but I get the same error building GHC for
SH4. Reproducible on gcc-master and on gcc-9.2.0.

Here is the minimal reproducer extracted by creduce:

$ cat bug.c
  /*
    works:
       $ sh4-unknown-linux-gnu-gcc    -o bug.o -c bug.c
    fails:
      $ sh4-unknown-linux-gnu-gcc -O -o bug.o -c bug.c
    error:
      error: unable to find a register to spill in class 'R0_REGS'
   */
  inline int a(char *b, char c) { __sync_val_compare_and_swap(b, c, 0); }
  int d(void) {
    while (1) {
      char e;
      a(&e, e);
    }
  }

$ LANG=C sh4-unknown-linux-gnu-gcc    -o bug.o -c bug.c
<ok>
$ LANG=C sh4-unknown-linux-gnu-gcc -O -o bug.o -c bug.c
bug.c: In function 'd':
bug.c:15:1: error: unable to find a register to spill in class 'R0_REGS'
   15 | }
      | ^
bug.c:15:1: error: this is the insn:
(insn 18 13 41 4 (parallel [
            (set (subreg:SI (reg:QI 6 r6 [174]) 0)
                (unspec_volatile:SI [
                        (mem/v:QI (reg/f:SI 2 r2 [176]) [-1  S1 A8])
                        (reg:QI 173 [ e ])
                        (reg:QI 3 r3 [177])
                    ] UNSPECV_CMPXCHG_1))
            (set (mem/v:QI (reg/f:SI 2 r2 [176]) [-1  S1 A8])
                (unspec_volatile:QI [
                        (const_int 0 [0])
                    ] UNSPECV_CMPXCHG_2))
            (set (reg:SI 147 t)
                (unspec_volatile:SI [
                        (const_int 0 [0])
                    ] UNSPECV_CMPXCHG_3))
            (clobber (scratch:SI))
            (clobber (reg:SI 0 r0))
            (clobber (reg:SI 1 r1))
        ]) "bug.c":9:33 401 {atomic_compare_and_swapqi_soft_gusa}
     (expr_list:REG_DEAD (reg:QI 173 [ e ])
        (expr_list:REG_UNUSED (reg:QI 6 r6 [174])
            (expr_list:REG_UNUSED (reg:SI 147 t)
                (expr_list:REG_UNUSED (reg:SI 1 r1)
                    (expr_list:REG_UNUSED (reg:SI 0 r0)
                        (nil)))))))
bug.c:15: confused by earlier errors, bailing out

$ ./xgcc -B. -v
Reading specs from ./specs
COLLECT_GCC=./xgcc
COLLECT_LTO_WRAPPER=./lto-wrapper
Target: sh4-unknown-linux-gnu
Configured with: ../gcc/configure --target=sh4-unknown-linux-gnu
--prefix=/home/slyfox/dev/git/gcc-sh4/../gcc-sh4-installed
--with-sysroot=/usr/sh4-unknown-linux-gnu --disable-bootstrap
--enable-languages=c --disable-nls CFLAGS=-O0 CXXFLAGS=-O0
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.0.0 20191103 (experimental) (GCC)