Dear all,
I've been trying to play with the RTX costs by using a target function
using the macro TARGET_RTX_COSTS. However, I haven't been able to
really make any good progress. This is the program I have:
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
long a = 0xcafe;
printf("Final: %lx %lx\n", a, a+5);
return EXIT_SUCCESS;
}
What I would like to see is not have the two elements set as constants
in registers but only one and the other set with an add instruction.
I first looked at what rtx were sent to this function and I am
perplexed about how this would work. After many calls to the function,
I finally get this :
(const_int 51966 [0xcafe])
(const_int 51966 [0xcafe])
(const_int 51971 [0xcb03])
(const_int 51971 [0xcb03])
All of these have an outer code of SET. Therefore, I'm not quite
positive of how I'm supposed to implement my rtx_cost function. Since
I don't seem to get a choice between a set 0xcb03 and a (plus 0xcafe
5), how can I tell the compiler the different costs?
Jc
On Thu, Feb 5, 2009 at 4:10 PM, Ian Lance Taylor <i...@google.com> wrote:
> Jean Christophe Beyler <jean.christophe.bey...@gmail.com> writes:
>
>> I'm currently working on removing the constant folding and constant
>> propagation because, on the architecture I'm working on, it is highly
>> costly to move a constant into a register if the number is big (we can
>> say over 16 bits).
>>
>> Currently, I've been looking into this and it seems that I have to
>> hack into the fold-const.c file, CCP, SCCVN and probably the propagate
>> passes to tell the compiler to be careful if the number is too big.
>> But I'm sure there are many other places I'll have to hack and slash
>> to tell him to stop the folding and propagation. Is there an easier
>> way to do this ?
>
> This type of thing is normally controlled by the TARGET_RTX_COSTS
> hook. E.g., see the handling of CONST_INT mips_rtx_costs in
> config/mips/mips.c.
>
> Ian
>
