Hi folks,
I'm retargetting GCC to a custom architecture
(https://github.com/jamieiles/gcc-oldland is the retarget) and have an
odd problem with function return values near the end of a function being
eliminated. For example:
extern int getreturn(void);
int foo(void)
{
if (getreturn() != 0)
return -1;
return 0;
}
I see that with optimization (-O1 or greater) that this gets compiled
into a call to getreturn() and then unconditionally sets the return
value to -1 (with a one_cmpl + eor + ior). Inserting a call to another
function inbetween the 'return -1' and 'return 0' is enough to cause
working code to be generated.
works fine at -O0 generating
00000000 <foo>:
0: f0 ce ff 93 str32 $lr, [$sp, 0x1ffc]
4: d0 8e ff 93 str32 $fp, [$sp, 0x1ff8]
8: 0d 8e 00 08 sub $fp, $sp, 0x8
c: 0e 8e 00 08 sub $sp, $sp, 0x8
10: fb ff ff 40 call 0 <foo>
10: R_OLDLAND_PC24 getreturn-0x4
14: 01 00 00 3e mov $r1, $r0
18: 00 00 00 3c mov $r0, 0x0
1c: 00 01 00 32 cmp $r1, $r0
20: 03 00 00 58 beq 30 <foo+0x30>
24: 00 fc ff ef movhi $r0, 0xffff
28: 00 fc ff f7 orlo $r0, $r0, 0xffff
2c: 01 00 00 50 b 34 <foo+0x34>
30: 00 00 00 3c mov $r0, 0x0
34: 0e 8e 00 00 add $sp, $sp, 0x8
38: 0d 8e 00 00 add $fp, $sp, 0x8
3c: 0d 8e ff 83 ldr32 $fp, [$sp, 0x1ff8]
40: 0f ce ff 83 ldr32 $lr, [$sp, 0x1ffc]
44: f0 00 00 46 ret
but at -O1 I get
00000000 <foo>:
0: f0 ce ff 93 str32 $lr, [$sp, 0x1ffc]
4: d0 8e ff 93 str32 $fp, [$sp, 0x1ff8]
8: 0d 8e 00 08 sub $fp, $sp, 0x8
c: 0e 8e 00 08 sub $sp, $sp, 0x8
10: fb ff ff 40 call 0 <foo>
10: R_OLDLAND_PC24 getreturn-0x4
14: 01 00 00 3c mov $r1, 0x0
18: 01 01 00 0a sub $r1, $r1, $r0
1c: 00 01 00 2a or $r0, $r1, $r0
20: 00 f0 01 38 asr $r0, $r0, 0x1f
24: 0e 8e 00 00 add $sp, $sp, 0x8
28: 0d 8e 00 00 add $fp, $sp, 0x8
2c: 0d 8e ff 83 ldr32 $fp, [$sp, 0x1ff8]
30: 0f ce ff 83 ldr32 $lr, [$sp, 0x1ffc]
34: f0 00 00 46 ret
I have $r0-$r5 as call used registers and my TARGET_FUNCTION_VALUE and
TARGET_FUNCTION_VALUE_REGNO_P using $r0.
Any pointers would be greatfully received.
Regards,
Jamie
