Re: (define_address ...) suggestions needed

[Bernd Schmidt <bernds at balti dot cygnus dot co dot uk>]

On Tue, 11 Jan 2000, Denis Chertykov wrote:

> I have started work on implement (define_address ...) patterns in md
> file.

I'm really happy to see someone work on this.  I have a couple of ideas,
but never thought it through well enough to actually start working on it.

> RTL example:
> 
> (define_attr "address_cost" "" (const_int 0))
> (define_attr "address_mode_dependent" "no,yes" (const_string "no"))
> (define_attr "address_direction" "load,store,load_store"
>   (const_string "load_store"))
> 
> 
> (define_address "*immediate"
>   [(mem (match_operand:HI 0 "immediate_operand" "i"))]
>   ""
>   "* /* Only C code can be used here
>         because it's analog of PRINT_OPERAND_ADDRESS  */
>      output_addr_const (asm_out_file, operands[0]);
>      return \"\";"
>   [(set_attr "address_cost" "4")])
>   
> (define_address "post_inc"
>   [(mem (post_inc:HI (match_operand:HI 0 "register_operand" "e")))]
>   ""
>   "*{
>   switch (REGNO (operands[0]))
>     {
>     case REG_X: return \"X+\";
>     case REG_Y: return \"Y+\";
>     case REG_Z: return \"Z+\";
>     default:
>       fatal (\"Incorrect register as address\");
>     }
>   }"
>   [(set_attr "address_cost" "2")
>    (set_attr "address_mode_dependent" "yes")])
> ------------------------------------------------------
> I'm use `mem' only for checking mode and because `genrecog' generates
> ready code for a address recognizing.
> 
> Any predicate which uses `memory_operand' can't be used in
> (define_address ...) to avoid infinite loop.

Some machines support nested MEMs, so this has to be supported in some way.

What might be useful is to specify a constraint letter for every addressing
mode.  GCC currently has a few hardcoded ones ('<', '>', 'm', 'o', ...); it
would be nice if every pattern could specify exactly what kind of addresses
it can accept in an operand.  This might solve a problem we have on the Thumb
where different insns accept different base register classes when loading
from memory.

Bernd