AVR: target/107957 - Propagate zero_reg to store sources.

When -msplit-ldst is on, it may be possible to propagate __zero_reg__
to the sources of the new stores.  For example, without this patch,

unsigned long lx;

void store_lsr17 (void)
{
   lx >>= 17;
}

compiles to:

store_lsr17:
   lds r26,lx+2           ;  movqi_insn
   lds r27,lx+3           ;  movqi_insn
   movw r24,r26           ;  *movhi
   lsr r25                ;  *lshrhi3_const
   ror r24
   ldi r26,0              ;  movqi_insn
   ldi r27,0              ;  movqi_insn
   sts lx,r24             ;  movqi_insn
   sts lx+1,r25           ;  movqi_insn
   sts lx+2,r26           ;  movqi_insn
   sts lx+3,r27           ;  movqi_insn
   ret

but with this patch it becomes:

store_lsr17:
   lds r26,lx+2           ;  movqi_insn
   lds r27,lx+3           ;  movqi_insn
   movw r24,r26           ;  *movhi
   lsr r25                ;  *lshrhi3_const
   ror r24
   sts lx,r24             ;  movqi_insn
   sts lx+1,r25           ;  movqi_insn
   sts lx+2,__zero_reg__  ;  movqi_insn
   sts lx+3,__zero_reg__  ;  movqi_insn
   ret

gcc/
	PR target/107957
	* config/avr/avr-passes-fuse-move.h (bbinfo_t) <try_mem0_p>:
	Add static property.
	* config/avr/avr-passes.cc (bbinfo_t::try_mem0_p): Define it.
	(optimize_data_t::try_mem0): New method.
	(bbinfo_t::optimize_one_block) [bbinfo_t::try_mem0_p]: Run try_mem0.
	(bbinfo_t::optimize_one_function): Set bbinfo_t::try_mem0_p.
	* config/avr/avr.md (pushhi1_insn): Also allow zero as source.
	(define_split) [avropt_split_ldst]: Only run avr_split_ldst()
	when avr-fuse-move has been run at least once.
	* doc/invoke.texi (AVR Options) <-msplit-ldst>: Document it.

0 files changed, 0 insertions, 0 deletions