On 27/02/15 09:41, Richard Earnshaw wrote:
On 19/02/15 12:19, Matthew Wahab wrote:
The LEGITIMIZE_RELOAD_ADDRESS macro is only needed for reload. Since the
ARM backend no longer supports reload, this macro is not needed and this
patch removes it.
gcc/
2015-02-19 Matthew Wahab <matthew.wa...@arm.com>
* config/arm/arm.h (LEGITIMIZE_RELOAD_ADDRESS): Remove.
(ARM_LEGITIMIZE_RELOAD_ADDRESS): Remove.
(THUMB_LEGITIMIZE_RELOAD_ADDRESS): Remove.
* config/arm/arm.c (arm_legitimize_reload_address): Remove.
(thumb_legitimize_reload_address): Remove.
* config/arm/arm-protos.h (arm_legitimize_reload_address):
Remove.
(thumb_legitimize_reload_address): Remove.
This is OK for stage 1.
I have one open question: can LRA generate the optimizations that these
hooks used to provide through reload? If not, please could you file
some bugzilla reports so that we don't lose them.
Thanks,
R.
arm_legitimize_reload_address was added by
https://gcc.gnu.org/ml/gcc-patches/2011-04/msg00605.html. From
config/arm/arm.c, the optimization turns
add t1, r2, #4096
ldr r0, [t1, #4]
add t2, r2, #4096
ldr r1, [t2, #8]
into
add t1, r2, #4096
ldr r0, [t1, #4]
ldr r1, [t1, #8]
As far as I can tell, LRA does do this. Compiling the following with -O1:
----
int bar(int, int, int);
int test1(int* buf)
{
int a = buf[41000];
int b = buf[41004];
int c = buf[41008];
bar(a, b, c);
return a + b + c;
}
----
gcc version 4.5.1 (Sourcery G++ Lite 2010.09-51), which predates the
optimization, produces
ldr r3, .L2
ldr r4, [r0, r3]
add r3, r3, #16
ldr r5, [r0, r3]
add r3, r3, #16
ldr r6, [r0, r3]
gcc version 4.9.3 20141119 with and without -mno-lra produce
add r0, r0, #163840
ldr r4, [r0, #160]
ldr r6, [r0, #176]
ldr r5, [r0, #192]
so it looks the better sequence gets generated.
thumb_legitimize_reload_address was added by
https://gcc.gnu.org/ml/gcc-patches/2005-08/msg01140.html to fix PR
23436. It replaces sequences like
mov r3, r9
mov r2, r10
ldr r0, [r3, r2]
with
mov r3, r9
add r3, r3, r10
ldr r0, [r3]
This looks like it's missing from trunk so I'll open a bugzilla report
for it.
It's quite possible that I've got this all wrong so if I've missed
something or you'd like me to open a bugzilla report for the ARM
optimization as well, let me know.
Matthew
