https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61578
--- Comment #23 from Fredrik Hederstierna
<fredrik.hederstie...@securitas-direct.com> ---
Thanks for your patch, I tried it out, and it solves the small example fine,
the code now is similar to GCC 4.8 for this particular example.
Though when I ran the full CSiBE benchmark, the code size unfortunately grew
approx +150 bytes overall for the full suite. So the patch did not solve the
generic root problem with code size increase unfortunately.
This is strange and I'm thinking of how to continue from here, this issue has
diverged a bit too much (mostly because of my own fault) with several examples
etc. Do you think we should create separate issues for different small examples
that compiles bad perhaps? but on the same time we need to keep track on the
'generic' overall code size issue as eg. CSiBE points out.
Here's is another small example I tested yesterday that also gives unnecessary
moves, both for arm7tdmi, arm966e-s and cortex-m0 tested.
extern void func(int data);
char cdata[4];
void test(void) {
int *idata = (int*)cdata;
func(*idata);
}
Compiles with GCC 4.8.5 (cortex-m0):
00000000 <test>:
0: b508 push {r3, lr}
2: 4b07 ldr r3, [pc, #28] ; (20 <test+0x20>)
4: 7858 ldrb r0, [r3, #1]
6: 781a ldrb r2, [r3, #0]
8: 0200 lsls r0, r0, #8
a: 4310 orrs r0, r2
c: 789a ldrb r2, [r3, #2]
e: 78db ldrb r3, [r3, #3]
10: 0412 lsls r2, r2, #16
12: 4310 orrs r0, r2
14: 061b lsls r3, r3, #24
16: 4318 orrs r0, r3
18: f7ff fffe bl 0 <func>
1c: bd08 pop {r3, pc}
1e: 46c0 nop ; (mov r8, r8)
20: 00000000 .word 0x00000000
With GCC 6 master with latest LRA patch (+4 bytes):
00000000 <test>:
0: b510 push {r4, lr}
2: 4c08 ldr r4, [pc, #32] ; (24 <test+0x24>)
4: 7863 ldrb r3, [r4, #1]
6: 7821 ldrb r1, [r4, #0]
8: 78a0 ldrb r0, [r4, #2]
a: 021b lsls r3, r3, #8
c: 430b orrs r3, r1
e: 0400 lsls r0, r0, #16
10: 001a movs r2, r3 ??? MOVE
12: 0003 movs r3, r0 ??? MOVE
14: 78e0 ldrb r0, [r4, #3]
16: 4313 orrs r3, r2
18: 0600 lsls r0, r0, #24
1a: 4318 orrs r0, r3
1c: f7ff fffe bl 0 <func>
20: bd10 pop {r4, pc}
22: 46c0 nop ; (mov r8, r8)
24: 00000000 .word 0x00000000
Kind Regards, Fredrik
