[Bug inline-asm/47419] missed 'mov (base,index,scale),reg' optimization?

[pluto at agmk dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47419

--- Comment #3 from Pawel Sikora <pluto at agmk dot net> 2011-01-23 13:02:02 UTC ---
(In reply to comment #2)
> Well there is no constraint for reg+reg*N really. You should do:
>   asm /* reading has side-effects in hardware */ volatile (
>                 "movl %1, %0"
>                 : /* output operands */ "=r" ( value )
>                 : /* input operands */ "m" ( *(address + index) )
>                 : /* clobbers */
>         );
> 
> 
> This will be the correct way of expressing it and not to mention will produce
> the code you want.

thanks, this assembly with "m" constraint produces one nice move i need.

> Though you might as well just do:
> unsigned __attribute__((regparm(2)))
> asm_read_mapped_register( unsigned* address, unsigned long index )
> {
>   volatile *unsigned a = address + index;
>   return *a;
> }

this access via volatile pointer produces unoptimal lea+mov combo.
i'll stay with improved asm inline.