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* [Bug c/97276] New: A whole if-block is ignored by avr-gcc 9.3.0
@ 2020-10-03 0:33 tre at gmx dot de
2020-10-03 0:34 ` [Bug c/97276] " tre at gmx dot de
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: tre at gmx dot de @ 2020-10-03 0:33 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97276
Bug ID: 97276
Summary: A whole if-block is ignored by avr-gcc 9.3.0
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: tre at gmx dot de
Target Milestone: ---
Created attachment 49304
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49304&action=edit
Identical example compiled with avr-gcc 7.5.0 and avr-gcc 9.3.0
Hi,
I have a weird avr-gcc bug that costed me some months to find as I couldn't
believe it's the compiler actually. So, I use the avr-gcc 9.3.0 on Mac OS
10.15.7 to compile a little function used for PWM fading of LEDs. The function
update_pwm_timeslots()
contains an if-block (ll.119-125):
if (last_brightness < 181 && j >= 181)
{
/* middle interrupt: top 65k */
slot->top = 0xfe00;
slot->mask = ~mask;
++slot;
}
This block seems to be completely ignored by the compilers equal or newer than
avr-gcc 8.3.0, i.e. the block doesn't appear in the assembly. Here is the list
of compilers I tested:
avr-gcc 4.9.4 (working)
avr-gcc 5.5.0 (working)
avr-gcc 6.5.0 (working)
avr-gcc 7.5.0 (working)
avr-gcc 8.4.0 (broken)
avr-gcc 9.3.0 (broken)
The diff between the assemblies (pwm.s) perfectly reveals that the if-block is
skipped by avr-gcc 9.3.0:
277c274
< mov r15, r31
---
> mov r9, r31
278a276,305
> j = scalevalue(j, global_pwm.dim);
> mov r18, r22
> ldi r19, 0x00 ; 0
> rjmp .+0 ; 0x1b6 <update_pwm_timeslots+0x1b6> 1b4: R_AVR_13_PCREL .text+0x222
> if (j == 255) break;
> cpi r23, 0xFF ; 255
> brne .+0 ; 0x1ba <update_pwm_timeslots+0x1ba> 1b8: R_AVR_7_PCREL .text+0x1bc
> rjmp .+0 ; 0x1bc <update_pwm_timeslots+0x1bc> 1ba: R_AVR_13_PCREL .text+0x270
> if (last_brightness < 181 && j >= 181)
> ldi r30, 0xB4 ; 180
> cp r30, r11
> brcc .+0 ; 0x1c2 <update_pwm_timeslots+0x1c2> 1c0: R_AVR_7_PCREL .text+0x1c4
> rjmp .+0 ; 0x1c4 <update_pwm_timeslots+0x1c4> 1c2: R_AVR_13_PCREL .text+0x24c
> cpi r23, 0xB5 ; 181
> brcc .+0 ; 0x1c8 <update_pwm_timeslots+0x1c8> 1c6: R_AVR_7_PCREL .text+0x1ca
> rjmp .+0 ; 0x1ca <update_pwm_timeslots+0x1ca> 1c8: R_AVR_13_PCREL .text+0x24c
> slot->top = 0xfe00;
> st X+, r8
> st X, r9
> sbiw r26, 0x01 ; 1
> slot->mask = ~mask;
> movw r30, r24
> com r30
> com r31
> adiw r26, 0x02 ; 2
> st X+, r30
> st X, r31
> sbiw r26, 0x03 ; 3
> ++slot;
> adiw r26, 0x04 ; 4
I attached the example with a Makefile adapted to avr-gcc 7.5.0 and avr-gcc
9.3.0 and the corresponding assembly outputs (pwm.s) and all intermediate
files. The README.txt contains the individual log outputs.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug c/97276] A whole if-block is ignored by avr-gcc 9.3.0
2020-10-03 0:33 [Bug c/97276] New: A whole if-block is ignored by avr-gcc 9.3.0 tre at gmx dot de
@ 2020-10-03 0:34 ` tre at gmx dot de
2023-02-23 13:31 ` [Bug target/97276] " gjl at gcc dot gnu.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: tre at gmx dot de @ 2020-10-03 0:34 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97276
--- Comment #1 from David Weese <tre at gmx dot de> ---
The README.txt also contains the steps to reproduce the pwm.s assemblies.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/97276] A whole if-block is ignored by avr-gcc 9.3.0
2020-10-03 0:33 [Bug c/97276] New: A whole if-block is ignored by avr-gcc 9.3.0 tre at gmx dot de
2020-10-03 0:34 ` [Bug c/97276] " tre at gmx dot de
@ 2023-02-23 13:31 ` gjl at gcc dot gnu.org
2023-02-23 13:56 ` tre at gmx dot de
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: gjl at gcc dot gnu.org @ 2023-02-23 13:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97276
Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target|atxmega32a4 |avr
--- Comment #2 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
Can you provide the pre-compiled source pwm.i? Just add -save-temps to the
compile options.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/97276] A whole if-block is ignored by avr-gcc 9.3.0
2020-10-03 0:33 [Bug c/97276] New: A whole if-block is ignored by avr-gcc 9.3.0 tre at gmx dot de
2020-10-03 0:34 ` [Bug c/97276] " tre at gmx dot de
2023-02-23 13:31 ` [Bug target/97276] " gjl at gcc dot gnu.org
@ 2023-02-23 13:56 ` tre at gmx dot de
2023-02-23 15:44 ` gjl at gcc dot gnu.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: tre at gmx dot de @ 2023-02-23 13:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97276
--- Comment #3 from David Weese <tre at gmx dot de> ---
Have you seen the attachment? It's all in there.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/97276] A whole if-block is ignored by avr-gcc 9.3.0
2020-10-03 0:33 [Bug c/97276] New: A whole if-block is ignored by avr-gcc 9.3.0 tre at gmx dot de
` (2 preceding siblings ...)
2023-02-23 13:56 ` tre at gmx dot de
@ 2023-02-23 15:44 ` gjl at gcc dot gnu.org
2023-02-23 16:02 ` gjl at gcc dot gnu.org
2024-02-20 15:27 ` gjl at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: gjl at gcc dot gnu.org @ 2023-02-23 15:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97276
--- Comment #4 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
Created attachment 54518
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54518&action=edit
pwn-i.c pre-compiled test case
Ok, I found it and attached a cleaned-up version.
IIUC correctly, the relevant options you are using to compile are: -O1
-mmcu=atxmega32a4 -g -ggdb -std=gnu99
With these options (and with -fverbose-asm to easier navigate in asm) I could
not reproduce the problem with avr-gcc v8.5. The respective part of .s reads
(I dropped -g for legibility, but with -g it's same):
; pwm-i.c:287: if (last_brightness < 181 && j >= 181)
ldi r30,lo8(-76) ; , ; 320 [c=4 l=1] movqi_insn/1
cp r30,r11 ; , last_brightness ; 193 [c=4 l=1]
cmpqi3/1
brsh .+2 ; ; 194 [c=16 l=2] branch
rjmp .L16 ;
; pwm-i.c:287: if (last_brightness < 181 && j >= 181)
cpi r22,lo8(-75) ; iftmp.3_5, ; 196 [c=4 l=1] cmpqi3/2
brsh .+2 ; ; 197 [c=16 l=2] branch
rjmp .L16 ;
; pwm-i.c:289: slot->top = 0xfe00;
st X+,r8 ; tmp226 ; 200 [c=4 l=3] *movhi/3
st X,r9 ; tmp226
sbiw r26,1
; pwm-i.c:290: slot->mask = ~mask;
movw r30,r24 ; tmp200, mask ; 321 [c=4 l=1] *movhi/0
com r30 ; tmp200 ; 201 [c=8 l=2] one_cmplhi2
com r31 ; tmp200
; pwm-i.c:290: slot->mask = ~mask;
adiw r26,2 ; slot_172->mask ; 202 [c=4 l=4] *movhi/3
st X+,r30 ; tmp200
st X,r31 ; tmp200
sbiw r26,2+1 ; slot_172->mask
; pwm-i.c:291: ++slot;
adiw r26,4 ; slot, ; 203 [c=4 l=1] addhi3_clobber/0
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/97276] A whole if-block is ignored by avr-gcc 9.3.0
2020-10-03 0:33 [Bug c/97276] New: A whole if-block is ignored by avr-gcc 9.3.0 tre at gmx dot de
` (3 preceding siblings ...)
2023-02-23 15:44 ` gjl at gcc dot gnu.org
@ 2023-02-23 16:02 ` gjl at gcc dot gnu.org
2024-02-20 15:27 ` gjl at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: gjl at gcc dot gnu.org @ 2023-02-23 16:02 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97276
--- Comment #5 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
... also tried v9.2 via
https://godbolt.org/z/9r3vMj1e3
and just like with v8.5, the respective block is around asm line 350.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug target/97276] A whole if-block is ignored by avr-gcc 9.3.0
2020-10-03 0:33 [Bug c/97276] New: A whole if-block is ignored by avr-gcc 9.3.0 tre at gmx dot de
` (4 preceding siblings ...)
2023-02-23 16:02 ` gjl at gcc dot gnu.org
@ 2024-02-20 15:27 ` gjl at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: gjl at gcc dot gnu.org @ 2024-02-20 15:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97276
Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2024-02-20
Ever confirmed|0 |1
Status|UNCONFIRMED |WAITING
^ permalink raw reply [flat|nested] 7+ messages in thread
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2020-10-03 0:33 [Bug c/97276] New: A whole if-block is ignored by avr-gcc 9.3.0 tre at gmx dot de
2020-10-03 0:34 ` [Bug c/97276] " tre at gmx dot de
2023-02-23 13:31 ` [Bug target/97276] " gjl at gcc dot gnu.org
2023-02-23 13:56 ` tre at gmx dot de
2023-02-23 15:44 ` gjl at gcc dot gnu.org
2023-02-23 16:02 ` gjl at gcc dot gnu.org
2024-02-20 15:27 ` gjl at gcc dot gnu.org
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