https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69049
Bug ID: 69049
Summary: [avr] strange/unnecessary commands in compiled code
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: night_ghost at ykoctpa dot ru
Target Milestone: ---
small code
void deepSleep(uint16_t milliseconds) {
uint32_t microseconds = milliseconds * 1000L;
uint16_t sleep_periods = (microseconds - watchdogTime_us) /
watchdogTime_us;
while (sleep_periods >= 512) {
narcoleptic_sleep_down(WDTO_8S);
sleep_periods -= 512;
}
if (sleep_periods & 256) narcoleptic_sleep_down(WDTO_4S); /* xxx */
}
compiled as (see comments)
void deepSleep(uint16_t milliseconds) {
uint32_t microseconds = milliseconds * 1000L;
2fb2: 9c 01 movw r18, r24
2fb4: a8 ee ldi r26, 0xE8 ; 232
2fb6: b3 e0 ldi r27, 0x03 ; 3
2fb8: 0e 94 b8 33 call 0x6770 ; 0x6770 <__umulhisi3>
uint16_t sleep_periods = (microseconds - watchdogTime_us) /
watchdogTime_us;
2fbc: 6c 19 sub r22, r12
2fbe: 7d 09 sbc r23, r13
2fc0: 8e 09 sbc r24, r14
2fc2: 9f 09 sbc r25, r15
2fc4: a7 01 movw r20, r14
2fc6: 96 01 movw r18, r12
2fc8: 0e 94 71 33 call 0x66e2 ; 0x66e2 <__udivmodsi4>
2fcc: 69 01 movw r12, r18 // r12r13 === sleep_periods,
is'nt it?
while (sleep_periods >= 512) {
//{ why GCC adds 0 before comparison?
2fce: e1 2c mov r14, r1
2fd0: f1 2c mov r15, r1
2fd2: c7 01 movw r24, r14
2fd4: 8c 0d add r24, r12
2fd6: 9d 1d adc r25, r13
// carry NEVER can be set - r1===0
2fd8: 81 15 cp r24, r1
//}
2fda: 92 40 sbci r25, 0x02 ; 2
2fdc: 70 f0 brcs .+28 ; 0x2ffa
<_Z9deepSleepj+0x6c>
narcoleptic_sleep_down(WDTO_8S);
2fde: 89 e0 ldi r24, 0x09 ; 9
//{ why GCC saves unneeded LONG?
2fe0: 29 83 std Y+1, r18 ; 0x01
2fe2: 3a 83 std Y+2, r19 ; 0x02
2fe4: 4b 83 std Y+3, r20 ; 0x03
2fe6: 5c 83 std Y+4, r21 ; 0x04
//}
2fe8: 0e 94 c4 17 call 0x2f88 ; 0x2f88
<_Z22narcoleptic_sleep_downh>
2fec: 62 e0 ldi r22, 0x02 ; 2
2fee: f6 1a sub r15, r22
//{ why GCC restores unneeded LONG?
2ff0: 5c 81 ldd r21, Y+4 ; 0x04
2ff2: 4b 81 ldd r20, Y+3 ; 0x03
2ff4: 3a 81 ldd r19, Y+2 ; 0x02
2ff6: 29 81 ldd r18, Y+1 ; 0x01
//}
2ff8: ec cf rjmp .-40 ; 0x2fd2
<_Z9deepSleepj+0x44>
//{ what the hell here? where such calculations in C code?
2ffa: f9 01 movw r30, r18
2ffc: ef 2f mov r30, r31
2ffe: ff 27 eor r31, r31
3000: e6 95 lsr r30
3002: 60 e0 ldi r22, 0x00 ; 0
3004: 7e ef ldi r23, 0xFE ; 254
3006: e6 9f mul r30, r22
3008: c0 01 movw r24, r0
300a: e7 9f mul r30, r23
300c: 90 0d add r25, r0
300e: f6 9f mul r31, r22
3010: 90 0d add r25, r0
3012: 11 24 eor r1, r1
3014: 82 0f add r24, r18
3016: 93 1f adc r25, r19
//}
sleep_periods -= 512;
}
if (sleep_periods & 256) narcoleptic_sleep_down(WDTO_4S);
3018: 90 ff sbrs r25, 0
301a: 0d c0 rjmp .+26 ; 0x3036
<_Z9deepSleepj+0xa8>
301c: 88 e0 ldi r24, 0x08 ; 8
}
//{ optimization on size but GCC generates 2nd epilogue to escape tail
recursion while simple CALL takes less memory
301e: 0f 90 pop r0
3020: 0f 90 pop r0
3022: 0f 90 pop r0
3024: 0f 90 pop r0
3026: df 91 pop r29
3028: cf 91 pop r28
302a: ff 90 pop r15
302c: ef 90 pop r14
302e: df 90 pop r13
3030: cf 90 pop r12
while (sleep_periods >= 512) {
narcoleptic_sleep_down(WDTO_8S);
sleep_periods -= 512;
}
if (sleep_periods & 256) narcoleptic_sleep_down(WDTO_4S); /* xxx */
3032: 0c 94 c4 17 jmp 0x2f88 ; 0x2f88
<_Z22narcoleptic_sleep_downh>
//}
}
3036: 0f 90 pop r0
3038: 0f 90 pop r0
303a: 0f 90 pop r0
303c: 0f 90 pop r0
303e: df 91 pop r29
3040: cf 91 pop r28
3042: ff 90 pop r15
3044: ef 90 pop r14
3046: df 90 pop r13
3048: cf 90 pop r12
304a: 08 95 ret
But when line commented with "xxx" removed then hell code gone
void deepSleep(uint16_t milliseconds) {
uint32_t microseconds = milliseconds * 1000L;
2faa: 9c 01 movw r18, r24
2fac: a8 ee ldi r26, 0xE8 ; 232
2fae: b3 e0 ldi r27, 0x03 ; 3
2fb0: 0e 94 8a 33 call 0x6714 ; 0x6714 <__umulhisi3>
uint16_t sleep_periods = (microseconds - watchdogTime_us) /
watchdogTime_us;
2fb4: 6c 19 sub r22, r12
2fb6: 7d 09 sbc r23, r13
2fb8: 8e 09 sbc r24, r14
2fba: 9f 09 sbc r25, r15
2fbc: a7 01 movw r20, r14
2fbe: 96 01 movw r18, r12
2fc0: 0e 94 43 33 call 0x6686 ; 0x6686 <__udivmodsi4>
2fc4: e9 01 movw r28, r18
while (sleep_periods >= 512) {
//{ adding 0 still here
2fc6: e1 2c mov r14, r1
2fc8: f1 2c mov r15, r1
2fca: c7 01 movw r24, r14
2fcc: 8c 0f add r24, r28
2fce: 9d 1f adc r25, r29
2fd0: 81 15 cp r24, r1
//}
2fd2: 92 40 sbci r25, 0x02 ; 2
2fd4: 30 f0 brcs .+12 ; 0x2fe2
<_Z9deepSleepj+0x54>
narcoleptic_sleep_down(WDTO_8S);
2fd6: 89 e0 ldi r24, 0x09 ; 9
2fd8: 0e 94 c4 17 call 0x2f88 ; 0x2f88
<_Z22narcoleptic_sleep_downh>
2fdc: 22 e0 ldi r18, 0x02 ; 2
2fde: f2 1a sub r15, r18
2fe0: f4 cf rjmp .-24 ; 0x2fca
<_Z9deepSleepj+0x3c>
sleep_periods -= 512;
}
// if (sleep_periods & 256) narcoleptic_sleep_down(WDTO_4S); /* xxx */
}
2fe2: df 91 pop r29
2fe4: cf 91 pop r28
2fe6: ff 90 pop r15
2fe8: ef 90 pop r14
2fea: df 90 pop r13
2fec: cf 90 pop r12
2fee: 08 95 ret
if to move uint32_t variable to a different function, hell code gone too and
"add 0" code also
void doSleep(uint16_t sleep_periods){
while (sleep_periods >= 512) {
narcoleptic_sleep_down(WDTO_8S);
sleep_periods -= 512;
}
if (sleep_periods & 256) narcoleptic_sleep_down(WDTO_4S);
}
void deepSleep(uint16_t milliseconds) {
uint32_t microseconds = milliseconds * 1000L;
doSleep((microseconds - watchdogTime_us) / watchdogTime_us);
}
void doSleep(uint16_t sleep_periods){
2f8e: 0f 93 push r16
2f90: 1f 93 push r17
2f92: cf 93 push r28
2f94: df 93 push r29
2f96: 8c 01 movw r16, r24
while (sleep_periods >= 512) {
2f98: ec 01 movw r28, r24
2f9a: c1 15 cp r28, r1
2f9c: 82 e0 ldi r24, 0x02 ; 2
2f9e: d8 07 cpc r29, r24
2fa0: 28 f0 brcs .+10 ; 0x2fac
<_Z7doSleepj+0x1e>
narcoleptic_sleep_down(WDTO_8S);
2fa2: 89 e0 ldi r24, 0x09 ; 9
2fa4: 0e 94 c4 17 call 0x2f88 ; 0x2f88
<_Z22narcoleptic_sleep_downh>
sleep_periods -= 512;
2fa8: d2 50 subi r29, 0x02 ; 2
2faa: f7 cf rjmp .-18 ; 0x2f9a
<_Z7doSleepj+0xc>
}
if (sleep_periods & 256) narcoleptic_sleep_down(WDTO_4S);
2fac: 10 ff sbrs r17, 0
2fae: 07 c0 rjmp .+14 ; 0x2fbe
<_Z7doSleepj+0x30>
2fb0: 88 e0 ldi r24, 0x08 ; 8
}
2fb2: df 91 pop r29
2fb4: cf 91 pop r28
2fb6: 1f 91 pop r17
2fb8: 0f 91 pop r16
while (sleep_periods >= 512) {
narcoleptic_sleep_down(WDTO_8S);
sleep_periods -= 512;
}
if (sleep_periods & 256) narcoleptic_sleep_down(WDTO_4S);
2fba: 0c 94 c4 17 jmp 0x2f88 ; 0x2f88
<_Z22narcoleptic_sleep_downh>
}
2fbe: df 91 pop r29
2fc0: cf 91 pop r28
2fc2: 1f 91 pop r17
2fc4: 0f 91 pop r16
2fc6: 08 95 ret
for chip with liliputian memory this bug is very annoying
