2017-01-13 17:28 GMT+04:00 Georg-Johann Lay <a...@gjlay.de>:
> This adds a penalty of 4 to the post-reload branch costs.
>
> Purpose is reduce the number of out-of-line blocks like in
>
> unsigned long variant5 (unsigned in)
> {
> unsigned long out = 0;
> if (in & (1 << 0)) out |= 0xful << (4*0);
> if (in & (1 << 1)) out |= 0xful << (4*1);
> if (in & (1 << 2)) out |= 0xful << (4*2);
> if (in & (1 << 3)) out |= 0xful << (4*3);
> return out;
> }
>
> without the patch, code is
>
>
> variant5:
> mov r18,r24 ; 67 movqi_insn/1 [length = 1]
> sbrs r24,0 ; 10 *sbrx_branchhi [length = 2]
> rjmp .L6
> ldi r22,lo8(15) ; 5 *movsi/5 [length = 4]
> ldi r23,0
> ldi r24,0
> ldi r25,0
> .L2:
> <some_code_and_epilogue>
> .L6:
> ldi r22,0 ; 4 *movsi/2 [length = 3]
> ldi r23,0
> movw r24,r22
> rjmp .L2 ; 74 jump [length = 1]
>
>
> and with the patch it reads:
>
> variant5:
> mov r18,r24 ; 67 movqi_insn/1 [length = 1]
> ldi r22,lo8(15) ; 5 *movsi/5 [length = 4]
> ldi r23,0
> ldi r24,0
> ldi r25,0
> sbrc r18,0 ; 10 *sbrx_branchhi [length = 2]
> rjmp .L2
> ldi r22,0 ; 4 *movsi/2 [length = 3]
> ldi r23,0
> movw r24,r22
> .L2:
> <some_code_and_epilogue>
>
>
> Using fall-through safes insn 74.
>
> Main blocker for not increasing default branch costs in general
> is do_store_flag which is a heap of assertions not using
> rtx_costs and which gives the best results with the old
> default of 0, which is not changed.
>
> Tested without regressions.
>
> Ok for trunk?
>
> Johann
>
> * config/avr/avr.h (BRANCH_COST) [reload_completed]: Increase by 4.
Approved.
Please apply.
