* Error in gcc version 2.96 20000731
@ 2001-09-13 14:15 Kjeld Borch Egevang
2001-09-13 15:10 ` H . J . Lu
2001-09-13 15:14 ` Maciej W. Rozycki
0 siblings, 2 replies; 13+ messages in thread
From: Kjeld Borch Egevang @ 2001-09-13 14:15 UTC (permalink / raw)
To: linux-mips
Hi all.
I discovered an optimization error in the current gcc for MIPS.
When I compile the code below with -O2 it clears the code-field just
after setting it. The instructions are mixed up. It works fine with -O1
and -O0.
If the "//" is removed in front of the first printf, it works too.
/Kjeld
--------------- cut here -----------------
#include <stdio.h>
typedef struct rtx_def
{
short code;
int dummy;
} rtx;
void put_code (rtx *rt, short code)
{
register int length;
length = 1;
for (; length >= 0; length--)
((int *) rt)[length] = 0;
// printf("put_code before\n");
rt->code = code;
printf("put_code after, code=%d %d\n", code, rt->code);
}
int main()
{
rtx rt;
put_code(&rt, 5);
printf("gen_rtx, code=%d\n", rt.code);
}
--------------- cut here -----------------
The assembler looks like:
.rdata
.align 2
$LC0:
.ascii "put_code after, code=%d %d\n\000"
.text
.align 2
.globl put_code
.ent put_code
.type put_code,@function
put_code:
.frame $sp,32,$31 # vars= 0, regs= 2/0, args= 16,
extra= 8
.mask 0x90000000,-4
.fmask 0x00000000,0
.set noreorder
.cpload $25
.set reorder
subu $sp,$sp,32
.cprestore 16
move $2,$5
sll $2,$2,16
sra $2,$2,16
move $5,$2
la $3,$LC0
sw $31,28($sp)
sw $28,24($sp)
move $6,$5
sh $2,0($4) <----- sets code field
sw $0,4($4) <----- clears structure
sw $0,0($4) <----- clears structure
move $4,$3
la $25,printf
jal $31,$25
lw $31,28($sp)
#nop
.set noreorder
.set nomacro
j $31
addu $sp,$sp,32
.set macro
.set reorder
.end put_code
^ permalink raw reply [flat|nested] 13+ messages in thread* Re: Error in gcc version 2.96 20000731
2001-09-13 14:15 Error in gcc version 2.96 20000731 Kjeld Borch Egevang
@ 2001-09-13 15:10 ` H . J . Lu
2001-09-13 21:09 ` Kjeld Borch Egevang
2001-09-13 15:14 ` Maciej W. Rozycki
1 sibling, 1 reply; 13+ messages in thread
From: H . J . Lu @ 2001-09-13 15:10 UTC (permalink / raw)
To: Kjeld Borch Egevang; +Cc: linux-mips
On Thu, Sep 13, 2001 at 04:15:10PM +0200, Kjeld Borch Egevang wrote:
> Hi all.
>
> I discovered an optimization error in the current gcc for MIPS.
>
> When I compile the code below with -O2 it clears the code-field just
> after setting it. The instructions are mixed up. It works fine with -O1
> and -O0.
>
> If the "//" is removed in front of the first printf, it works too.
>
The code isn't ISO C. You cannot declare something as short and then
access it as int. On x86:
# gcc alias.c -O
put_code after, code=5 5
gen_rtx, code=5
# gcc alias.c -O2
put_code after, code=5 0
gen_rtx, code=0
On mips,
# gcc alias.c -O
put_code after, code=5 5
gen_rtx, code=5
# gcc alias.c -O2
put_code after, code=5 5
gen_rtx, code=0
You can fix the code or add -fno-strict-aliasing
# gcc alias.c -O2 -fno-strict-aliasing
put_code after, code=5 5
gen_rtx, code=5
H.J.
^ permalink raw reply [flat|nested] 13+ messages in thread
* RE: Error in gcc version 2.96 20000731
@ 2001-09-13 21:09 ` Kjeld Borch Egevang
0 siblings, 0 replies; 13+ messages in thread
From: Kjeld Borch Egevang @ 2001-09-13 21:09 UTC (permalink / raw)
To: H . J . Lu; +Cc: linux-mips
Perhaps I don't get you point, but I get the same with:
int main()
{
rtx rt;
put_code(&rt, (short)5);
printf("gen_rtx, code=%d\n", (int)rt.code);
}
/Kjeld
-----Original Message-----
From: owner-linux-mips@oss.sgi.com
[mailto:owner-linux-mips@oss.sgi.com]On Behalf Of H . J . Lu
Sent: 13. september 2001 17:11
To: Kjeld Borch Egevang
Cc: linux-mips@oss.sgi.com
Subject: Re: Error in gcc version 2.96 20000731
On Thu, Sep 13, 2001 at 04:15:10PM +0200, Kjeld Borch Egevang wrote:
> Hi all.
>
> I discovered an optimization error in the current gcc for MIPS.
>
> When I compile the code below with -O2 it clears the code-field just
> after setting it. The instructions are mixed up. It works fine with -O1
> and -O0.
>
> If the "//" is removed in front of the first printf, it works too.
>
The code isn't ISO C. You cannot declare something as short and then
access it as int. On x86:
# gcc alias.c -O
put_code after, code=5 5
gen_rtx, code=5
# gcc alias.c -O2
put_code after, code=5 0
gen_rtx, code=0
On mips,
# gcc alias.c -O
put_code after, code=5 5
gen_rtx, code=5
# gcc alias.c -O2
put_code after, code=5 5
gen_rtx, code=0
You can fix the code or add -fno-strict-aliasing
# gcc alias.c -O2 -fno-strict-aliasing
put_code after, code=5 5
gen_rtx, code=5
H.J.
^ permalink raw reply [flat|nested] 13+ messages in thread* RE: Error in gcc version 2.96 20000731
@ 2001-09-13 21:09 ` Kjeld Borch Egevang
0 siblings, 0 replies; 13+ messages in thread
From: Kjeld Borch Egevang @ 2001-09-13 21:09 UTC (permalink / raw)
To: H . J . Lu; +Cc: linux-mips
Perhaps I don't get you point, but I get the same with:
int main()
{
rtx rt;
put_code(&rt, (short)5);
printf("gen_rtx, code=%d\n", (int)rt.code);
}
/Kjeld
-----Original Message-----
From: owner-linux-mips@oss.sgi.com
[mailto:owner-linux-mips@oss.sgi.com]On Behalf Of H . J . Lu
Sent: 13. september 2001 17:11
To: Kjeld Borch Egevang
Cc: linux-mips@oss.sgi.com
Subject: Re: Error in gcc version 2.96 20000731
On Thu, Sep 13, 2001 at 04:15:10PM +0200, Kjeld Borch Egevang wrote:
> Hi all.
>
> I discovered an optimization error in the current gcc for MIPS.
>
> When I compile the code below with -O2 it clears the code-field just
> after setting it. The instructions are mixed up. It works fine with -O1
> and -O0.
>
> If the "//" is removed in front of the first printf, it works too.
>
The code isn't ISO C. You cannot declare something as short and then
access it as int. On x86:
# gcc alias.c -O
put_code after, code=5 5
gen_rtx, code=5
# gcc alias.c -O2
put_code after, code=5 0
gen_rtx, code=0
On mips,
# gcc alias.c -O
put_code after, code=5 5
gen_rtx, code=5
# gcc alias.c -O2
put_code after, code=5 5
gen_rtx, code=0
You can fix the code or add -fno-strict-aliasing
# gcc alias.c -O2 -fno-strict-aliasing
put_code after, code=5 5
gen_rtx, code=5
H.J.
^ permalink raw reply [flat|nested] 13+ messages in thread* Re: Error in gcc version 2.96 20000731
2001-09-13 21:09 ` Kjeld Borch Egevang
(?)
@ 2001-09-13 21:14 ` H . J . Lu
2001-09-13 21:22 ` Kjeld Borch Egevang
-1 siblings, 1 reply; 13+ messages in thread
From: H . J . Lu @ 2001-09-13 21:14 UTC (permalink / raw)
To: Kjeld Borch Egevang; +Cc: linux-mips
On Thu, Sep 13, 2001 at 11:09:04PM +0200, Kjeld Borch Egevang wrote:
> Perhaps I don't get you point, but I get the same with:
>
> int main()
> {
> rtx rt;
>
> put_code(&rt, (short)5);
> printf("gen_rtx, code=%d\n", (int)rt.code);
> }
>
That is not what I meant. You have
typedef struct rtx_def
{
short code;
int dummy;
} rtx;
The first field of rtx_def is short.
for (; length >= 0; length--)
((int *) rt)[length] = 0;
But you access it as int. If you do
for (; length >= 0; length--)
((short *) rt)[length] = 0;
It will be ok.
H.J.
^ permalink raw reply [flat|nested] 13+ messages in thread* RE: Error in gcc version 2.96 20000731
@ 2001-09-13 21:22 ` Kjeld Borch Egevang
0 siblings, 0 replies; 13+ messages in thread
From: Kjeld Borch Egevang @ 2001-09-13 21:22 UTC (permalink / raw)
To: H . J . Lu; +Cc: linux-mips
I get your point. A bit suprising though. Do you consider it a bug?
/Kjeld
-----Original Message-----
From: owner-linux-mips@oss.sgi.com
[mailto:owner-linux-mips@oss.sgi.com]On Behalf Of H . J . Lu
Sent: 13. september 2001 23:15
To: Kjeld Borch Egevang
Cc: linux-mips@oss.sgi.com
Subject: Re: Error in gcc version 2.96 20000731
On Thu, Sep 13, 2001 at 11:09:04PM +0200, Kjeld Borch Egevang wrote:
> Perhaps I don't get you point, but I get the same with:
>
> int main()
> {
> rtx rt;
>
> put_code(&rt, (short)5);
> printf("gen_rtx, code=%d\n", (int)rt.code);
> }
>
That is not what I meant. You have
typedef struct rtx_def
{
short code;
int dummy;
} rtx;
The first field of rtx_def is short.
for (; length >= 0; length--)
((int *) rt)[length] = 0;
But you access it as int. If you do
for (; length >= 0; length--)
((short *) rt)[length] = 0;
It will be ok.
H.J.
^ permalink raw reply [flat|nested] 13+ messages in thread* RE: Error in gcc version 2.96 20000731
@ 2001-09-13 21:22 ` Kjeld Borch Egevang
0 siblings, 0 replies; 13+ messages in thread
From: Kjeld Borch Egevang @ 2001-09-13 21:22 UTC (permalink / raw)
To: H . J . Lu; +Cc: linux-mips
I get your point. A bit suprising though. Do you consider it a bug?
/Kjeld
-----Original Message-----
From: owner-linux-mips@oss.sgi.com
[mailto:owner-linux-mips@oss.sgi.com]On Behalf Of H . J . Lu
Sent: 13. september 2001 23:15
To: Kjeld Borch Egevang
Cc: linux-mips@oss.sgi.com
Subject: Re: Error in gcc version 2.96 20000731
On Thu, Sep 13, 2001 at 11:09:04PM +0200, Kjeld Borch Egevang wrote:
> Perhaps I don't get you point, but I get the same with:
>
> int main()
> {
> rtx rt;
>
> put_code(&rt, (short)5);
> printf("gen_rtx, code=%d\n", (int)rt.code);
> }
>
That is not what I meant. You have
typedef struct rtx_def
{
short code;
int dummy;
} rtx;
The first field of rtx_def is short.
for (; length >= 0; length--)
((int *) rt)[length] = 0;
But you access it as int. If you do
for (; length >= 0; length--)
((short *) rt)[length] = 0;
It will be ok.
H.J.
^ permalink raw reply [flat|nested] 13+ messages in thread* Re: Error in gcc version 2.96 20000731
2001-09-13 21:22 ` Kjeld Borch Egevang
(?)
@ 2001-09-13 21:26 ` H . J . Lu
-1 siblings, 0 replies; 13+ messages in thread
From: H . J . Lu @ 2001-09-13 21:26 UTC (permalink / raw)
To: Kjeld Borch Egevang; +Cc: linux-mips
On Thu, Sep 13, 2001 at 11:22:46PM +0200, Kjeld Borch Egevang wrote:
> I get your point. A bit suprising though. Do you consider it a bug?
It is an alias bug in your example.
H.J.
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: Error in gcc version 2.96 20000731
2001-09-13 14:15 Error in gcc version 2.96 20000731 Kjeld Borch Egevang
2001-09-13 15:10 ` H . J . Lu
@ 2001-09-13 15:14 ` Maciej W. Rozycki
2001-09-13 15:16 ` H . J . Lu
2001-09-13 20:47 ` Kjeld Borch Egevang
1 sibling, 2 replies; 13+ messages in thread
From: Maciej W. Rozycki @ 2001-09-13 15:14 UTC (permalink / raw)
To: Kjeld Borch Egevang; +Cc: linux-mips
On Thu, 13 Sep 2001, Kjeld Borch Egevang wrote:
> I discovered an optimization error in the current gcc for MIPS.
Is 2.96 20000731 current? I thought 3.0.1 is.
> When I compile the code below with -O2 it clears the code-field just
> after setting it. The instructions are mixed up. It works fine with -O1
> and -O0.
Use "-fno-strict-aliasing"?
> If the "//" is removed in front of the first printf, it works too.
Why don't you use memset() to clear the struct in the first place?
--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: macro@ds2.pg.gda.pl, PGP key available +
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: Error in gcc version 2.96 20000731
2001-09-13 15:14 ` Maciej W. Rozycki
@ 2001-09-13 15:16 ` H . J . Lu
2001-09-13 20:47 ` Kjeld Borch Egevang
1 sibling, 0 replies; 13+ messages in thread
From: H . J . Lu @ 2001-09-13 15:16 UTC (permalink / raw)
To: Maciej W. Rozycki; +Cc: Kjeld Borch Egevang, linux-mips
On Thu, Sep 13, 2001 at 05:14:45PM +0200, Maciej W. Rozycki wrote:
> On Thu, 13 Sep 2001, Kjeld Borch Egevang wrote:
>
> > I discovered an optimization error in the current gcc for MIPS.
>
> Is 2.96 20000731 current? I thought 3.0.1 is.
>
gcc 3.0.1 lacks many patches in my gcc 2.96 and gcc 3.x. I am trying to
get them backported to 3.0.x.
H.J.
^ permalink raw reply [flat|nested] 13+ messages in thread
* RE: Error in gcc version 2.96 20000731
@ 2001-09-13 20:47 ` Kjeld Borch Egevang
0 siblings, 0 replies; 13+ messages in thread
From: Kjeld Borch Egevang @ 2001-09-13 20:47 UTC (permalink / raw)
To: linux-mips
Thanks for your reply.
I was trying to port SPEC CPU 2000 (benchmarks), and one of the tests
failed. I boiled it down to the attached program. For performance reasons it
could be perfectly valid not to use memset(), but I agree that the code
looks a bit odd.
/Kjeld
-----Original Message-----
From: Maciej W. Rozycki [mailto:macro@ds2.pg.gda.pl]
Sent: 13. september 2001 17:15
To: Kjeld Borch Egevang
Cc: linux-mips@oss.sgi.com
Subject: Re: Error in gcc version 2.96 20000731
On Thu, 13 Sep 2001, Kjeld Borch Egevang wrote:
> I discovered an optimization error in the current gcc for MIPS.
Is 2.96 20000731 current? I thought 3.0.1 is.
> When I compile the code below with -O2 it clears the code-field just
> after setting it. The instructions are mixed up. It works fine with -O1
> and -O0.
Use "-fno-strict-aliasing"?
> If the "//" is removed in front of the first printf, it works too.
Why don't you use memset() to clear the struct in the first place?
--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: macro@ds2.pg.gda.pl, PGP key available +
^ permalink raw reply [flat|nested] 13+ messages in thread
* RE: Error in gcc version 2.96 20000731
@ 2001-09-13 20:47 ` Kjeld Borch Egevang
0 siblings, 0 replies; 13+ messages in thread
From: Kjeld Borch Egevang @ 2001-09-13 20:47 UTC (permalink / raw)
To: linux-mips
Thanks for your reply.
I was trying to port SPEC CPU 2000 (benchmarks), and one of the tests
failed. I boiled it down to the attached program. For performance reasons it
could be perfectly valid not to use memset(), but I agree that the code
looks a bit odd.
/Kjeld
-----Original Message-----
From: Maciej W. Rozycki [mailto:macro@ds2.pg.gda.pl]
Sent: 13. september 2001 17:15
To: Kjeld Borch Egevang
Cc: linux-mips@oss.sgi.com
Subject: Re: Error in gcc version 2.96 20000731
On Thu, 13 Sep 2001, Kjeld Borch Egevang wrote:
> I discovered an optimization error in the current gcc for MIPS.
Is 2.96 20000731 current? I thought 3.0.1 is.
> When I compile the code below with -O2 it clears the code-field just
> after setting it. The instructions are mixed up. It works fine with -O1
> and -O0.
Use "-fno-strict-aliasing"?
> If the "//" is removed in front of the first printf, it works too.
Why don't you use memset() to clear the struct in the first place?
--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: macro@ds2.pg.gda.pl, PGP key available +
^ permalink raw reply [flat|nested] 13+ messages in thread
* RE: Error in gcc version 2.96 20000731
2001-09-13 20:47 ` Kjeld Borch Egevang
(?)
@ 2001-09-14 14:42 ` Maciej W. Rozycki
-1 siblings, 0 replies; 13+ messages in thread
From: Maciej W. Rozycki @ 2001-09-14 14:42 UTC (permalink / raw)
To: Kjeld Borch Egevang; +Cc: linux-mips
On Thu, 13 Sep 2001, Kjeld Borch Egevang wrote:
> I was trying to port SPEC CPU 2000 (benchmarks), and one of the tests
> failed. I boiled it down to the attached program. For performance reasons it
> could be perfectly valid not to use memset(), but I agree that the code
> looks a bit odd.
With a high optimization level and a constant size of the area to set
(you'd likely use sizeof here, which is constant) gcc will happily inline
a memset() yielding no worse performance but no bugs and better
readability. You may have no loop at all as the result. Check yourself!
--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: macro@ds2.pg.gda.pl, PGP key available +
^ permalink raw reply [flat|nested] 13+ messages in thread
end of thread, other threads:[~2001-09-14 15:34 UTC | newest]
Thread overview: 13+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2001-09-13 14:15 Error in gcc version 2.96 20000731 Kjeld Borch Egevang
2001-09-13 15:10 ` H . J . Lu
2001-09-13 21:09 ` Kjeld Borch Egevang
2001-09-13 21:09 ` Kjeld Borch Egevang
2001-09-13 21:14 ` H . J . Lu
2001-09-13 21:22 ` Kjeld Borch Egevang
2001-09-13 21:22 ` Kjeld Borch Egevang
2001-09-13 21:26 ` H . J . Lu
2001-09-13 15:14 ` Maciej W. Rozycki
2001-09-13 15:16 ` H . J . Lu
2001-09-13 20:47 ` Kjeld Borch Egevang
2001-09-13 20:47 ` Kjeld Borch Egevang
2001-09-14 14:42 ` Maciej W. Rozycki
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.