On 09/28/2011 02:14 PM, Georg-Johann Lay wrote:
This leads to unpleasant code. The machine can access all RAM locations by
direct addressing. However, the resulting code is:
foo:
ldi r24,lo8(-86) ; 6 *movqi/2 [length = 1]
ldi r30,lo8(-64) ; 34 *movhi/5 [length = 2]
ldi r31,lo8(10)
std Z+3,r24 ; 7 *movqi/3 [length = 1]
.L2:
lds r24,2754 ; 10 *movqi/4 [length = 2]
sbrs r24,7 ; 43 *sbrx_branchhi [length = 2]
rjmp .L2
ldi r24,lo8(-69) ; 16 *movqi/2 [length = 1]
ldi r30,lo8(-64) ; 33 *movhi/5 [length = 2]
ldi r31,lo8(10)
std Z+3,r24 ; 17 *movqi/3 [length = 1]
.L3:
lds r24,2754 ; 20 *movqi/4 [length = 2]
sbrs r24,7 ; 42 *sbrx_branchhi [length = 2]
rjmp .L3
ret ; 39 return [length = 1]
Insn 34 loads 2752 (0xAC0) to r30/r31 (Z) and does an indirect access (*(Z+3),
i.e. *2755) in insn 7. The same happens in insn 33 (load 2752) and access
(insn 17).
Is there a way to avoid this? I tried -f[no-]rerun-cse-after-loop but without
effect, same for -Os/-O2 and trying to patch rtx_costs. cse_not_expected is
overridden in some places in the middle-end.
fwprop should take care of propagating the address. Have you tried
patching address_costs? Might be as simple as this (untested):
Index: avr.c
===================================================================
--- avr.c (revision 177688)
+++ avr.c (working copy)
@@ -5986,8 +5986,8 @@ avr_address_cost (rtx x, bool speed ATTR
return 18;
if (CONSTANT_ADDRESS_P (x))
{
- if (optimize > 0 && io_address_operand (x, QImode))
- return 2;
+ if (optimize > 0)
+ return io_address_operand (x, QImode) ? 2 : 3;
return 4;
}
return 4;
Paolo
