[patch,avr]: Increase branch costs after reload.

[Georg-Johann Lay]

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.
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