* [Bug target/39633] [avr] loop bug
[not found] <bug-39633-4@http.gcc.gnu.org/bugzilla/>
@ 2011-04-14 19:55 ` avr at gjlay dot de
2011-07-09 15:51 ` gjl at gcc dot gnu.org
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To: gcc-bugs
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Georg-Johann Lay <avr at gjlay dot de> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |avr at gjlay dot de
--- Comment #5 from Georg-Johann Lay <avr at gjlay dot de> 2011-04-14 19:54:40 UTC ---
Did you try this with -fno-strict-overflow?
Code like
(INT8_MIN)-((int8_t)(si2))
might lead to signed overflow, and if gcc gets knowledge of si2 being strictly
positive, the results is undefined.
http://gcc.gnu.org/onlinedocs/gcc-4.3.5/gcc/Optimize-Options.html#Optimize-Options
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/39633] [avr] loop bug
[not found] <bug-39633-4@http.gcc.gnu.org/bugzilla/>
2011-04-14 19:55 ` [Bug target/39633] [avr] loop bug avr at gjlay dot de
@ 2011-07-09 15:51 ` gjl at gcc dot gnu.org
2011-07-09 16:40 ` gjl at gcc dot gnu.org
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From: gjl at gcc dot gnu.org @ 2011-07-09 15:51 UTC (permalink / raw)
To: gcc-bugs
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Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |wrong-code
Last reconfirmed|2009-08-17 12:12:00 |2010-07-09 12:12
CC|avr at gjlay dot de |gjl at gcc dot gnu.org
Known to fail| |4.5.2, 4.6.1
--- Comment #6 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-09 15:48:55 UTC ---
I confirm it on 4.6.1, 4.5.0 and 4.5.2 (-fno-strict-overflow does not help)
I see the bug only for -O1 (in which case g_52=1) and not for other
optimization levels (in which case g_52=5).
The bug disappears if l_116 in func_1 is declared as uint32_t instead of
uint64_t.
In 4.6.1, g_52 is as follows:
-Os -fsplit-wide-types: 5
-Os -fno-split-wide-types: 1
This remains after adding the no_inline attribute to safe_add_func_int8_t_s_s
that gets compiler to:
safe_add_func_int8_t_s_s.constprop.0:
cpi r24,lo8(125) ; _si1, ; 6 *cmpqi/3
brge .L2 ; , ; 7 branch
subi r24,lo8(-(3)) ; _si1, ; 9 addqi3/2
.L2:
ret ; 28 return
With -Os -fsplit-wide-types, the compile of func_1 is(g_52=5 ok):
func_1:
/* prologue: function */
ldi r24,lo8(0) ; l_116, ; 3 *movqi/1
.L4:
lds r25,g_52 ; tmp52, g_52 ; 15 *movqi/4
subi r25,lo8(-(1)) ; tmp52, ; 16 addqi3/2
sts g_52,r25 ; g_52, tmp52 ; 17 *movqi/3
rcall safe_add_func_int8_t_s_s.constprop.0 ; 20 call_value_insn/3
sbrc r24,7 ; l_116, ; 99 *sbrx_branchhi
rjmp .L3 ;
cpi r24,lo8(13) ; l_116, ; 60 *cmpqi/3
brlo .L4 ; , ; 61 branch
.L3:
ret ; 98 return
With -Os -fno-split-wide-types, the compile of func_1 is (g_52=1 wrong):
func_1:
push r8 ; ; 90 *pushqi/1
push r9 ; ; 91 *pushqi/1
push r10 ; ; 92 *pushqi/1
push r11 ; ; 93 *pushqi/1
push r12 ; ; 94 *pushqi/1
push r13 ; ; 95 *pushqi/1
push r14 ; ; 96 *pushqi/1
push r15 ; ; 97 *pushqi/1
/* prologue: function */
clr r8 ; l_116 ; 3 *movqi/1
.L4:
lds r24,g_52 ; tmp52, g_52 ; 15 *movqi/4
subi r24,lo8(-(1)) ; tmp52, ; 16 addqi3/2= 1]
sts g_52,r24 ; g_52, tmp52 ; 17 *movqi/3
mov r24,r8 ; , l_116 ; 19 *movqi/1
rcall safe_add_func_int8_t_s_s.constprop.0 ; 20 call_value_insn/3
mov r8,r24 ; l_116, D.2168 ; 22 *movqi/1
lsl r24 ; tmp54 ; 23 ashrqi3/5
sbc r24,r24 ; tmp54
brne .L3 ; , ; 33 branch
tst r24 ; l_116 ; 36 *cmpqi/1
brne .L3 ; , ; 37 branch
tst r24 ; l_116 ; 40 *cmpqi/1
brne .L3 ; , ; 41 branch
tst r24 ; l_116 ; 44 *cmpqi/1
brne .L3 ; , ; 45 branch
tst r24 ; l_116 ; 48 *cmpqi/1
brne .L3 ; , ; 49 branch
tst r24 ; l_116 ; 52 *cmpqi/1
brne .L3 ; , ; 53 branch
tst r24 ; l_116 ; 56 *cmpqi/1
brne .L3 ; , ; 57 branch
ldi r24,lo8(12) ; , ; 89 *movqi/2
cp r24,r8 ; , l_116 ; 60 *cmpqi/2
brsh .L4 ; , ; 61 branch
.L3:
/* epilogue start */
pop r15 ; ; 100 popqi
pop r14 ; ; 101 popqi
pop r13 ; ; 102 popqi
pop r12 ; ; 103 popqi
pop r11 ; ; 104 popqi
pop r10 ; ; 105 popqi
pop r9 ; ; 106 popqi
pop r8 ; ; 107 popqi
ret ; 108 return_from_epilogue
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/39633] [avr] loop bug
[not found] <bug-39633-4@http.gcc.gnu.org/bugzilla/>
2011-04-14 19:55 ` [Bug target/39633] [avr] loop bug avr at gjlay dot de
2011-07-09 15:51 ` gjl at gcc dot gnu.org
@ 2011-07-09 16:40 ` gjl at gcc dot gnu.org
2011-07-09 16:45 ` gjl at gcc dot gnu.org
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To: gcc-bugs
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--- Comment #7 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-09 16:39:24 UTC ---
The bug is here:
lsl r24 ashrqi3/5
sbc r24,r24
brne .L3 branch
The SBC doc says:
> Z: Previous value [of Z] remains unchanged when the
> result [of SBC] is zero; cleared otherwise.
I.e. the SBC leaves cc0 in a mess, and that's ashrqi3/5:
"r,0,n" and "cc=clobber".
I do not understand where the BRNE comes from because it's a conditional jump
and cc0 is in a mess.
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[not found] <bug-39633-4@http.gcc.gnu.org/bugzilla/>
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To: gcc-bugs
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--- Comment #8 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-09 16:45:20 UTC ---
Created attachment 24727
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24727
C file, reduced test case
Compiler with avr-gcc 4.6.1 -Os -S -fno-split-wide-types -dp
to get:
func_1:
push r8 ; 94 *pushqi/1 [length = 1]
push r9 ; 95 *pushqi/1 [length = 1]
push r10 ; 96 *pushqi/1 [length = 1]
push r11 ; 97 *pushqi/1 [length = 1]
push r12 ; 98 *pushqi/1 [length = 1]
push r13 ; 99 *pushqi/1 [length = 1]
push r14 ; 100 *pushqi/1 [length = 1]
push r15 ; 101 *pushqi/1 [length = 1]
clr r8 ; 3 *movqi/1 [length = 1]
.L2:
lds r24,g_52 ; 15 *movqi/4 [length = 2]
subi r24,lo8(-(1)) ; 16 addqi3/2 [length = 1]
sts g_52,r24 ; 17 *movqi/3 [length = 2]
mov r24,r8 ; 19 *movqi/1 [length = 1]
ldi r22,lo8(3) ; 20 *movqi/2 [length = 1]
rcall foo ; 21 call_value_insn/3 [length = 1]
mov r8,r24 ; 23 *movqi/1 [length = 1]
>>>> BUG START
lsl r24 ; 24 ashrqi3/5 [length = 2]
sbc r24,r24
brne .L1 ; 34 branch [length = 1]
>>>> BUG END
tst r24 ; 37 *cmpqi/1 [length = 1]
brne .L1 ; 38 branch [length = 1]
tst r24 ; 41 *cmpqi/1 [length = 1]
brne .L1 ; 42 branch [length = 1]
tst r24 ; 45 *cmpqi/1 [length = 1]
brne .L1 ; 46 branch [length = 1]
tst r24 ; 49 *cmpqi/1 [length = 1]
brne .L1 ; 50 branch [length = 1]
tst r24 ; 53 *cmpqi/1 [length = 1]
brne .L1 ; 54 branch [length = 1]
tst r24 ; 57 *cmpqi/1 [length = 1]
brne .L1 ; 58 branch [length = 1]
ldi r24,lo8(12) ; 93 *movqi/2 [length = 1]
cp r24,r8 ; 61 *cmpqi/2 [length = 1]
brsh .L2 ; 62 branch [length = 1]
.L1:
pop r15 ; 104 popqi [length = 1]
pop r14 ; 105 popqi [length = 1]
pop r13 ; 106 popqi [length = 1]
pop r12 ; 107 popqi [length = 1]
pop r11 ; 108 popqi [length = 1]
pop r10 ; 109 popqi [length = 1]
pop r9 ; 110 popqi [length = 1]
pop r8 ; 111 popqi [length = 1]
ret ; 112 return_from_epilogue [length = 1]
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/39633] [avr] loop bug
[not found] <bug-39633-4@http.gcc.gnu.org/bugzilla/>
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To: gcc-bugs
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--- Comment #9 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-09 17:24:47 UTC ---
The needed *cmpqi insn 33 can be tracked until .221r.nothrow dump; the last
dump that actually contains RTL dump.
But then the insn 33 is gone, even with -fno-peephole.
(insn 24 23 33 (set (reg:QI 24 r24 [52])
(ashiftrt:QI (reg:QI 24 r24 [orig:46 D.1929 ] [46])
(const_int 7 [0x7]))) testit.c:8 72 {ashrqi3}
(nil))
(insn 33 24 34 (set (cc0)
(compare (reg:QI 24 r24 [orig:15 l_116+7 ] [15])
(const_int 0 [0]))) testit.c:8 106 {*cmpqi}
(expr_list:REG_DEAD (reg:QI 15 r15 [ l_116+7 ])
(nil)))
(jump_insn 34 33 72 (set (pc)
(if_then_else (ne (cc0)
(const_int 0 [0]))
(label_ref:HI 69)
(pc))) testit.c:8 117 {branch}
(expr_list:REG_BR_PROB (const_int 989 [0x3dd])
(nil))
-> 69)
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/39633] [avr] loop bug: missing 8-bit comparison (*cmpqi)
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To: gcc-bugs
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--- Comment #10 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-10 08:29:04 UTC ---
Created attachment 24729
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24729
Minimal test case
Here is a minimal testcase:
char c;
void func_1 (char a)
{
a = a >> 7;
if (a)
c = a;
}
Code with 4.6.1 -Os -dp -S -mmcu=atmega88:
func_1:
lsl r24 ; 6 ashrqi3/5 [length = 2]
sbc r24,r24
breq .L1 ; 8 branch [length = 1]
sts c,r24 ; 10 *movqi/3 [length = 2]
.L1:
ret ; 20 return [length = 1]
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/39633] [avr] loop bug: missing 8-bit comparison (*cmpqi)
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To: gcc-bugs
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--- Comment #11 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-10 10:15:11 UTC ---
It's bug in avr.c:notice_update_cc() because for shift offset=7 cc0 is set as
if it contained meaningful state:
case CC_CLOBBER:
/* Insn doesn't leave CC in a usable state. */
CC_STATUS_INIT;
/* Correct CC for the ashrqi3 with the shift count as CONST_INT != 6 */
set = single_set (insn);
if (set)
{
rtx src = SET_SRC (set);
if (GET_CODE (src) == ASHIFTRT
&& GET_MODE (src) == QImode)
{
rtx x = XEXP (src, 1);
if (GET_CODE (x) == CONST_INT
&& INTVAL (x) > 0
&& INTVAL (x) != 6)
{
cc_status.value1 = SET_DEST (set);
cc_status.flags |= CC_OVERFLOW_UNUSABLE;
}
}
}
break;
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/39633] [avr] loop bug: missing 8-bit comparison (*cmpqi)
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To: gcc-bugs
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Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |4.6.2
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/39633] [avr] loop bug: missing 8-bit comparison (*cmpqi)
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To: gcc-bugs
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--- Comment #12 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-11 10:13:33 UTC ---
Author: gjl
Date: Mon Jul 11 10:13:30 2011
New Revision: 176141
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=176141
Log:
gcc/
PR target/39633
* config/avr/avr.c (notice_update_cc): For ashiftrt:QI, only
offsets 1..5 set cc0 in a usable way.
testsuite/
PR target/39633
* gcc.target/avr/torture/pr39633.c: New test case.
Added:
trunk/gcc/testsuite/gcc.target/avr/torture/pr39633.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/config/avr/avr.c
trunk/gcc/testsuite/ChangeLog
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--- Comment #13 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-11 10:24:48 UTC ---
Author: gjl
Date: Mon Jul 11 10:24:46 2011
New Revision: 176143
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=176143
Log:
PR target/39633
Backport from mainline r176141
2011-07-11 Georg-Johann Lay
* config/avr/avr.c (notice_update_cc): For ashiftrt:QI, only
offsets 1..5 set cc0 in a usable way.
Modified:
branches/gcc-4_6-branch/gcc/ChangeLog
branches/gcc-4_6-branch/gcc/config/avr/avr.c
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/39633] [avr] loop bug: missing 8-bit comparison (*cmpqi)
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From: gjl at gcc dot gnu.org @ 2011-07-11 10:29 UTC (permalink / raw)
To: gcc-bugs
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Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Known to work| |4.6.2
Resolution| |FIXED
--- Comment #14 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-11 10:28:17 UTC ---
Cloased as FIXED in 4.6.2 milestone.
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--- Comment #15 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2012-05-02 17:14:42 UTC ---
Author: gjl
Date: Wed May 2 17:14:32 2012
New Revision: 187056
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=187056
Log:
Backport from 2011-07-11 4.6-branch r176143
PR target/39633
* config/avr/avr.c (notice_update_cc): For ashiftrt:QI, only
offsets 1..5 set cc0 in a usable way.
Modified:
branches/gcc-4_5-branch/gcc/ChangeLog
branches/gcc-4_5-branch/gcc/config/avr/avr.c
^ permalink raw reply [flat|nested] 13+ messages in thread* [Bug target/39633] [avr] loop bug: missing 8-bit comparison (*cmpqi)
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From: gjl at gcc dot gnu.org @ 2012-05-02 17:16 UTC (permalink / raw)
To: gcc-bugs
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Georg-Johann Lay <gjl at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Known to work| |4.5.4
Known to fail| |4.5.3
--- Comment #16 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2012-05-02 17:16:01 UTC ---
Backported to 4.5.4
^ permalink raw reply [flat|nested] 13+ messages in thread