Date: Tue, 28 Nov 1995 23:53:01 +1100 From: Bruce Evans <bde@zeta.org.au> To: hsu@freefall.freebsd.org, kaleb@x.org Cc: hackers@freefall.freebsd.org Subject: Re: gcc-2.7.1 compiled kernel Message-ID: <199511281253.XAA29508@godzilla.zeta.org.au>
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>Is the -O2 -fno-strength-reduce bug fixed?
No, according to this.
Bruce
Article 4048 of gnu.gcc.bug:
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From: anlauf@crunch.ikp.physik.th-darmstadt.de (Harald Anlauf)
Newsgroups: gnu.gcc.bug
Subject: Bug on i386/Linux with unsigned and -fstrength-reduce
Date: 22 Nov 1995 17:42:17 -0500
Organization: GNUs Not Usenet
Lines: 60
Sender: daemon@cis.ohio-state.edu
Approved: bug-gcc@prep.ai.mit.edu
Distribution: gnu
Message-ID: <9511222241.AA19094@crunch>
Hi,
I found an interesting bug in gcc versions 2.5.8, 2.7.0, and 2.7.1,
compiled as i486-*-linuxoldld and running under Linux.
Compiling the program given below with options:
-O2,
-O[123] -fstrength-reduce
-O[123] -fstrength-reduce -fno-unroll-loops
produces the (wrong) output:
A[0] = -3
A[1] = 0
A[2] = 0
whereas it gives the correct result with
-O[123] -fno-strength-reduce
-O[123] -fstrength-reduce -funroll-loops
produces the (correct) result:
A[0] = -3
A[1] = -2
A[2] = -1
The funny thing is that changing the unsigned integer B to a signed integer
fixes the problem. The problem persists with "unsigned long", but goes
away for "unsigned short", "unsigned char", or "unsigned long long".
Anybody knows what's going on?
Ciao,
Harald
[I am not the original author of this little demo program. Somebody posted it
to gnu.gcc.bug some time ago, but unfortunately I didn't keep the reference.
So please don't flame me.]
------------------------------> cut here <------------------------------
#include <stdio.h>
int A[3];
unsigned int B = 3;
void printit(void)
{
int i;
for(i = 0; i < B; i++)
fprintf(stdout, "A[%d] = %d\n", i, A[i]);
}
int main()
{
int i;
for(i = 0; i < B; i++)
A[i] = i - 3;
printit();
return 0;
}
------------------------------> cut here <------------------------------
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