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* Re: optimization/10087: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array
@ 2003-03-21 19:46 Glen Nakamura
0 siblings, 0 replies; 5+ messages in thread
From: Glen Nakamura @ 2003-03-21 19:46 UTC (permalink / raw)
To: nobody; +Cc: gcc-prs
The following reply was made to PR optimization/10087; it has been noted by GNATS.
From: Glen Nakamura <glen@imodulo.com>
To: gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org, p.van-hoof@qub.ac.uk
Cc:
Subject: Re: optimization/10087: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array
Date: Fri, 21 Mar 2003 09:37:36 -1000
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10087
Additional analysis of the problem and patch located at:
http://gcc.gnu.org/ml/gcc-patches/2003-03/msg01932.html
The proposed fix is somewhat hackish, but it should fix the problem.
BTW, I didn't update the comments about the use of 'same' in struct induction
for bivs in loop.h
- glen
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: optimization/10087: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array
@ 2003-03-24 18:58 mmitchel
0 siblings, 0 replies; 5+ messages in thread
From: mmitchel @ 2003-03-24 18:58 UTC (permalink / raw)
To: gcc-bugs, gcc-prs, nobody, p.van-hoof
Synopsis: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array
State-Changed-From-To: analyzed->closed
State-Changed-By: mmitchel
State-Changed-When: Mon Mar 24 18:56:00 2003
State-Changed-Why:
Fixed in GCC 3.3, GCC 3.4.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10087
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: optimization/10087: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array
@ 2003-03-15 0:56 Steven Bosscher
0 siblings, 0 replies; 5+ messages in thread
From: Steven Bosscher @ 2003-03-15 0:56 UTC (permalink / raw)
To: nobody; +Cc: gcc-prs
The following reply was made to PR optimization/10087; it has been noted by GNATS.
From: Steven Bosscher <s.bosscher@student.tudelft.nl>
To: p.van-hoof@qub.ac.uk, gcc-gnats@gcc.gnu.org,
gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org, gcc-prs@gcc.gnu.org
Cc:
Subject: Re: optimization/10087: [3.3/3.4 regression] optimizer produces wrong
code when indexing 2D array
Date: Sat, 15 Mar 2003 01:48:02 +0100
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10087
A little more information...
A slightly smaller test case is:
----------------------------
static void
b (int *i, int *j)
{
}
int
main (void)
{
int i, j;
S x1[2][2];
S *x[2] = { x1[0], x1[1] };
S **E = x;
for (i = 0; i < 2; i++)
for (j = 0; j < 2; j++)
E[j][i].T1 = 1;
b (&j, &i);
printf ("result %.6e\n", E[1][1].T1);
return 0;
}
----------------------------
The line "E[j][i] =..." seems to be the problem:
With j first, then i, the output is wrong (and you get a segfault as a
bonus).
With i first, then j ("E[i][j]=..") you get the correct result.
# gcc-3.3 -O t.c
# a.out
result 1.000000e+00
# gcc-3.3 t.c -O -fstrength-reduce -fstrict-aliasing -fforce-mem -fgcse
# a.out
result 2.676500e+00
Segmentation fault
Again, disable any of these four options and you get the expected output.
(For the record, this is on i586-pc-linux-gnu.)
Greetz
Steven
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: optimization/10087: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array
@ 2003-03-15 0:06 Steven Bosscher
0 siblings, 0 replies; 5+ messages in thread
From: Steven Bosscher @ 2003-03-15 0:06 UTC (permalink / raw)
To: nobody; +Cc: gcc-prs
The following reply was made to PR optimization/10087; it has been noted by GNATS.
From: Steven Bosscher <s.bosscher@student.tudelft.nl>
To: p.van-hoof@qub.ac.uk, gcc-gnats@gcc.gnu.org,
gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org, gcc-prs@gcc.gnu.org
Cc:
Subject: Re: optimization/10087: [3.3/3.4 regression] optimizer produces wrong
code when indexing 2D array
Date: Sat, 15 Mar 2003 01:01:01 +0100
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10087
# gcc-3.3 10087.c -O
# a.out
result 1.000000e+00
# gcc-3.3 10087.c -O -fforce-mem -fstrength-reduce -fgcse
# a.out
result -1.997810e+00
Turning off any of these three options makes the output equal to
unoptimized or -O.
Greetz
Steven
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: optimization/10087: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array
@ 2003-03-14 23:45 bangerth
0 siblings, 0 replies; 5+ messages in thread
From: bangerth @ 2003-03-14 23:45 UTC (permalink / raw)
To: gcc-bugs, gcc-prs, nobody, p.van-hoof
Old Synopsis: optimizer produces wrong code when indexing malloc'ed 2D array
New Synopsis: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array
State-Changed-From-To: open->analyzed
State-Changed-By: bangerth
State-Changed-When: Fri Mar 14 23:45:17 2003
State-Changed-Why:
Confirmed also on x86 linux. Here's a slightly modified example:
--------------------------
void b(int*,int*);
typedef struct {
double T1;
char c;
} S;
int main(void)
{
int i,j;
double s;
S x1[2][2];
S *x[2] = { x1[0], x1[1] };
S **E = x;
for( i=0; i < 2; i++ )
for( j=0; j < 2; j++ )
E[j][i].T1 = 1;
for( i=0; i < 2; i++ )
for( j=0; j < 2; j++ )
s = E[j][i].T1;
b(&j,&i);
printf( "result %.6e\n", s);
return 0;
}
void b(int *i, int *j) {}
-------------------------------
This yields different results with and without -O2:
g/x> /home/bangerth/bin/gcc-3.4-pre/bin/gcc x.c
g/x> ./a.out
result 1.000000e+00
g/x> /home/bangerth/bin/gcc-3.4-pre/bin/gcc x.c -O2
g/x> ./a.out
result 2.171654e+00
The same holds for 3.3, but 3.2.2 is ok, so it's a regression.
W.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10087
^ permalink raw reply [flat|nested] 5+ messages in thread
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2003-03-21 19:46 optimization/10087: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array Glen Nakamura
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2003-03-24 18:58 mmitchel
2003-03-15 0:56 Steven Bosscher
2003-03-15 0:06 Steven Bosscher
2003-03-14 23:45 bangerth
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