Problem with modyfying "addsi3" in machine description

[Georg-Johann Lay]

Tomasz Jankowski schrieb:
> Ok, I fixed it using using pair of define_insn and define_expand below:
> 
>    (define_expand "addsi3"
>      [(set (match_operand:SI 0 "register_operand" "=r")
>            (plus:SI (match_operand:SI 1 "register_operand" "r")

Expanders don't get constraints.

>                     (match_operand:SI 2 "nonmemory_operand" "")))]
>      ""
>      {
>        if (CONST_INT_P (operands [2]))

If SI also acts as pointer mode, you may want to handle symbols, too.
For example in address computations.

>        {
>          if (can_create_pseudo_p ())
>          {
>            operands[2] = force_reg (SImode, operands[2]);
>            emit_insn (gen_rtx_SET (SImode, operands[0], gen_rtx_PLUS

SET should be VOIDmode, not SImode.

> (SImode, operands [1], operands [2])));
>          }
>        }
>        else
>        {
>          emit_insn (gen_rtx_SET (SImode, operands[0], gen_rtx_PLUS
> (SImode, operands [1], operands [2])));
>        }
>        DONE;
>      })
> 
>    (define_insn "*addsi3_internal"
>      [(set (match_operand:SI 0 "register_operand" "=r")
>            (plus:SI (match_operand:SI 1 "register_operand" "r")
>                     (match_operand:SI 2 "register_operand" "r")))]
>      ""
>      "l.radd   \t%0,%1,%2"
>      [(set_attr "type" "add")
>       (set_attr "length" "1")])
> 
> I have to admit, that I don't understand why it works... I figured out

I don't think it works.  You still have the problem with offsets during
reload.  addsi3 is special, I think you need const_int offsets.
Otherwise spill code generation cannot work.

> possible explanation. When define_expand doesn't emit any insns, but
> it finishes with DONE, GCC tries other strategy to fir RTL instruction
> to machine description, right?
> 
> I have also question about output assembly (compiled with -dP option).
> Sample C code:
> 
>     int b = 123;
>     int a = b + 998;
> 
> output:
> 
>     #(insn 8 7 19 simple_test.c:4 (set (reg:SI 3 r3 [44])
>     #        (const_int 998 [0x3e6])) 8 {*movsi_insn} (nil))
>     	l.addi  	r3,r0,998	 # move immediate I	# 8	*movsi_insn/1	[length = 1]
>     #(insn 19 8 9 (set (reg:SI 3 r3 [44])
>     #        (rto:SI (reg:SI 3 r3 [44]))) 72 {rto} (nil))
>     	l.rto    	r3,r3	# 19	rto	[length = 1]
>     #(insn 9 19 10 simple_test.c:4 (set:SI (reg:SI 3 r3 [43])
>     #        (plus:SI (reg:SI 4 r4 [42])
>     #            (reg:SI 3 r3 [44]))) 49 {*addsi3_internal}
> (expr_list:REG_EQUAL (plus:SI (reg:SI 4 r4 [42])
>     #            (const_int 998 [0x3e6]))
>     #        (nil)))
>     	l.radd   	r3,r4,r3	# 9	*addsi3_internal	[length = 1]
> 
> What "(expr_list:REG_EQUAL (..." stays for?

It says that content of r3 equals r4 + 998.