Re: Could not identify that register is clobbered already

I answered to this on the GCC list:

http://gcc.gnu.org/ml/gcc/2013-02/msg00129.html

Please f'up there.


S, Pitchumani a écrit:
> Hi,
> 
> I was analyzing an issue for avr target (gcc-4.7.2).
> 
> Issue is that already clobbered register is used after the transformation
> in post reload pass.
> 
> insns after reload pass:
> 
> set (reg:HI r24
>     (const:HI (plus:HI (symbol_ref:HI ("array"))
>                        (const_int 4))
>     ))
> ...
> parallel set (reg:HI r14
>              (and:HI (reg:HI r14)
>                      (const_int 3)))
>          clobber:QI r25
> ...
> set (reg:HI r28
>     (const:HI (plus:HI (symbol_ref:HI ("array"))
>                        (const_int 4))
>     ))
> 
> After post reload pass, insn-3 transformed as follows:
> 
> set (reg:HI r28
>      reg:HI r24)
> 
> this transformation happened in reload_cse_move2add function.
> 
> Since r25 is clobbered in insn-2, above transformation (r28/29 <= r24/25) 
> become incorrect.
> 
> Function 'move2add_use_add3_insn' sets only r24 info for insn-1 instead
> of setting info for both r24/25. Function 'validate_change' checks only r24
> info for insn-3 transformation.
> is it possible to identify clobbered register and avoid transformation?
> 
> Regards,
> Pitchumani