This is a mini-patch to fix rtx_costs for SYMBOL_REF.
The cost of a SYMBOL_REF is the same as a CONST_INT because it can be
used the same way. I observed small performance regression in my code
and found that the reason is too high cost for SYMBOL_REF.
char x[10];
char getx2 (unsigned char i, unsigned char j)
{
return x[i] + x[j];
}
char getx1 (unsigned char i)
{
return x[i];
}
Without the patch, in getx2 symbol x in loaded in insn 8 and
then used in insn 9 and insn 12:
getx2:
ldi r18,lo8(x) ; 8 *movhi/4 [length = 2]
ldi r19,hi8(x)
movw r30,r18 ; 27 *movhi/1 [length = 1]
add r30,r22 ; 9 *addhi3_zero_extend [length = 2]
adc r31,__zero_reg__
movw r26,r18 ; 28 *movhi/1 [length = 1]
add r26,r24 ; 12 *addhi3_zero_extend [length = 2]
adc r27,__zero_reg__
ld r25,Z ; 13 *movqi/4 [length = 1]
ld r24,X ; 14 *movqi/4 [length = 1]
add r24,r25 ; 20 addqi3/1 [length = 1]
ret ; 31 return [length = 1]
getx1:
ldi r30,lo8(x) ; 7 *movhi/4 [length = 2]
ldi r31,hi8(x)
add r30,r24 ; 8 *addhi3_zero_extend [length = 2]
adc r31,__zero_reg__
ld r24,Z ; 14 *movqi/4 [length = 1]
ret ; 23 return [length = 1]
With the patch, the symbol is added directly resulting in smaller
and faster code for getx2. Moreover, register pressure is smaller.
getx1 performs the same as before.
getx2:
mov r30,r22 ; 27 *movqi/1 [length = 1]
ldi r31,lo8(0) ; 28 *movqi/1 [length = 1]
subi r30,lo8(-(x)) ; 9 *addhi3/4 [length = 2]
sbci r31,hi8(-(x))
mov r26,r24 ; 29 *movqi/1 [length = 1]
ldi r27,lo8(0) ; 30 *movqi/1 [length = 1]
subi r26,lo8(-(x)) ; 12 *addhi3/4 [length = 2]
sbci r27,hi8(-(x))
ld r25,Z ; 13 *movqi/4 [length = 1]
ld r24,X ; 14 *movqi/4 [length = 1]
add r24,r25 ; 20 addqi3/1 [length = 1]
ret ; 33 return [length = 1]
getx1:
mov r30,r24 ; 21 *movqi/1 [length = 1]
ldi r31,lo8(0) ; 22 *movqi/1 [length = 1]
subi r30,lo8(-(x)) ; 8 *addhi3/4 [length = 2]
sbci r31,hi8(-(x))
ld r24,Z ; 14 *movqi/4 [length = 1]
ret ; 25 return [length = 1]
OK to commit?
Johann
* config/avr/avr.c (avr_rtx_costs): Set cost of SYMBOL_REF to 0.
Index: config/avr/avr.c
===================================================================
--- config/avr/avr.c (revision 176276)
+++ config/avr/avr.c (working copy)
@@ -5341,6 +5341,7 @@ avr_rtx_costs (rtx x, int codearg, int o
{
case CONST_INT:
case CONST_DOUBLE:
+ case SYMBOL_REF:
/* Immediate constants are as cheap as registers. */
*total = 0;
return true;
@@ -5348,7 +5349,6 @@ avr_rtx_costs (rtx x, int codearg, int o
case MEM:
case CONST:
case LABEL_REF:
- case SYMBOL_REF:
*total = COSTS_N_INSNS (GET_MODE_SIZE (mode));
return true;
