Why doesn't this pattern match?

[Andras Tantos <andras@tantosonline.com>]

Hello!

My name is Andras Tantos and I just joined this list, so if I'm asking
something off-topic or not following the rules of the community, please
let me know.

What I'm working on is to port GCC (and Binutils) to a new CPU ISA, I
call 'brew'. During developing for this target, I got the following
error:

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
first.c: In function ‘test_call’:
first.c:61:52: error: insn does not satisfy its constraints:
   61 | int test_call(int a, int b) { return test_qm(a,b); }
      |                                                    ^
(insn 25 8 9 (set (reg:SI 6 $r6)
        (reg:SI 0 $pc)) "first.c":61:38 17 {*movsi}
     (nil))
during RTL pass: final
first.c:61:52: internal compiler error: in final_scan_insn_1, at
final.c:2811
0x6c4c23 _fatal_insn(char const*, rtx_def const*, char const*, int,
char const*)
	../../brew-gcc/gcc/rtl-error.c:108
0x6c4c4f _fatal_insn_not_found(rtx_def const*, char const*, int, char
const*)
	../../brew-gcc/gcc/rtl-error.c:118
0x643585 final_scan_insn_1
	../../brew-gcc/gcc/final.c:2811
0xb1ef3f final_scan_insn(rtx_insn*, _IO_FILE*, int, int, int*)
	../../brew-gcc/gcc/final.c:2940
0xb1f207 final_1
	../../brew-gcc/gcc/final.c:1997
0xb1fbe6 rest_of_handle_final
	../../brew-gcc/gcc/final.c:4285
0xb1fbe6 execute
	../../brew-gcc/gcc/final.c:4363
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Clearly, the compiler couldn't find a rule that works for this register
move. The relevant section of the .md file is:

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
(define_expand "movsi"
   [(set (match_operand:SI 0 "general_operand" "")
         (match_operand:SI 1 "general_operand" ""))]
   ""
  "
{
  /* If this is a store, force the value into a register.  */
  if (! (reload_in_progress || reload_completed))
  {
    if (MEM_P (operands[0]))
    {
      operands[1] = force_reg (SImode, operands[1]);
      if (MEM_P (XEXP (operands[0], 0)))
        operands[0] = gen_rtx_MEM (SImode, force_reg (SImode, XEXP
(operands[0], 0)));
    }
    else 
      if (MEM_P (operands[1])
          && MEM_P (XEXP (operands[1], 0)))
        operands[1] = gen_rtx_MEM (SImode, force_reg (SImode, XEXP
(operands[1], 0)));
  }
}")

(define_insn "*movsi"
  [(set (match_operand:SI 0
"nonimmediate_operand"        "=r,r,r,W,A,B,r,r,r")
        (match_operand:SI 1 "brew_general_mov_src_operand"
"O,r,i,r,r,r,W,A,B"))]
  "register_operand (operands[0], SImode)
   || register_operand (operands[1], SImode)"
  "@
   %0 <- %0 - %0
   %0 <- %1
   %0 <- %1
   mem[%0] <- %1
   mem[%0] <- %1
   mem[%0] <- %1
   %0 <- mem[%1]
   %0 <- mem[%1]
   %0 <- mem[%1]"
)
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

As you can imagine, I'm fairly new to GCC development, so I must be
making some rookie mistake here, but I would have thought that the
second alternative in the "*movsi" rule above would match the pattern.

brew_general_mov_src_operand is defined as follows:

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
(define_predicate "brew_general_mov_src_operand"
  (match_code "mem,const_int,reg,subreg,symbol_ref,label_ref,const")
{
  /* Any (MEM LABEL_REF) is OK.  That is a pc-relative load.  */
  if (MEM_P (op) && GET_CODE (XEXP (op, 0)) == LABEL_REF)
    return 1;

  if (MEM_P (op)
      && GET_CODE (XEXP (op, 0)) == PLUS
      && GET_CODE (XEXP (XEXP (op, 0), 0)) == REG
      && GET_CODE (XEXP (XEXP (op, 0), 1)) == CONST_INT
  )
    return 1;
  /* Any register is good too */
  if (REG_P(op))
    return 1;
  /* PC as source is also acceptable */
  if (op == pc_rtx)
    return 1;
  return general_operand (op, mode);
})
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Thanks for all the help,
Andras