GCC 后端开发 - 编译简单程序时如何修复“insn 不满足其约束”？

Question

我正在为新架构编写 GCC 后端。当我尝试使用-O0 编译以下简单程序时（注意：启用优化时不会出现此错误）：

int main()
{
    int a = 10;
    a++;
}

我收到此错误：

test.c: In function ‘main’:
test.c:5:1: error: insn does not satisfy its constraints:
    5 | }
      | ^
(insn 8 7 9 (set (reg:SI 12)
        (plus:SI (reg:SI 13)
            (const_int 1 [0x1]))) "test.c":4:6 1 {addsi3}
     (nil))
during RTL pass: final
test.c:5:1: internal compiler error: in final_scan_insn_1, at final.c:3012
0x65f4b2 _fatal_insn(char const*, rtx_def const*, char const*, int, char const*)
    ../../gcc/gcc/rtl-error.c:108
0x65f4d8 _fatal_insn_not_found(rtx_def const*, char const*, int, char const*)
    ../../gcc/gcc/rtl-error.c:118
0x5e2fc8 final_scan_insn_1
    ../../gcc/gcc/final.c:3012
0xa23e0b final_scan_insn(rtx_insn*, _IO_FILE*, int, int, int*)
    ../../gcc/gcc/final.c:3152
0xa24099 final_1
    ../../gcc/gcc/final.c:2020
0xa249f2 rest_of_handle_final
    ../../gcc/gcc/final.c:4658
0xa249f2 execute
    ../../gcc/gcc/final.c:4736

根据错误消息的内容，问题似乎与addsi3 中的约束有关。这里是addsi3的定义：

(define_insn "addsi3"
  [(set (match_operand:SI 0 "register_operand" "=r,r")
        (plus:SI (match_operand:SI 1 "register_operand" "r,r")
                 (match_operand:SI 2 "reg_or_imm_operand" "r,I")))]
  "1"
  "@
   add %0 %1 %2
   addi %0 %1 %2")

如果addsi3 的定义中的约束被删除，则程序编译成功。这是I 约束的定义：

(define_constraint "I"
  "A 30-bit immediate."
  (and (match_code "const_int")
       (match_test "ival >= -536870912 && ival <= 536870911")))

这是reg_or_imm_operand谓词的定义。

(define_predicate "reg_or_imm_operand"
  (ior (and (match_code "const_int")
            (match_test "IN_RANGE (INTVAL (op), -536870912, 536870911)"))
       (match_operand 0 "register_operand")))

如果需要更具体的信息，请告诉我，我会编辑问题。

提前致谢。 :)

Answer 1

函数main被声明为返回一个整数，但缺少返回语句。

应该更好：

int main()
{
    int a = 10;
    a++;
    return 0;
}