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[Bug c/21332] New: -O2 makes a loop doesn't execute a body
- From: "akr at m17n dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 2 May 2005 10:24:30 -0000
- Subject: [Bug c/21332] New: -O2 makes a loop doesn't execute a body
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
4.1.0 20050502 (experimental) seems have a problem with optimization.
The for loop in the else clause in the main doesn't execute the loop body.
% cat t.c
extern int printf (__const char *__restrict __format, ...);
int f()
{
return -2;
}
int main(int argc, char **argv)
{
int c = f();
long i;
if (c > 0) {
for (i=0;i<c;i++) {
f();
}
}
else {
c = -c;
printf("beg %d\n", c);
for (i=0;i<c;i++) {
printf("%d\n", i);
}
printf("end %d\n", i);
}
return 0;
}
% gcc -v -O2 t.c
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../gcc/configure --prefix=/home/src/gcc/trunk --enable-languages=c
Thread model: posix
gcc version 4.1.0 20050502 (experimental)
/home/src/gcc/trunk/libexec/gcc/i686-pc-linux-gnu/4.1.0/cc1 -quiet -v t.c
-quiet -dumpbase t.c -mtune=pentiumpro -auxbase t -O2 -version -o /tmp/cc6LaTqE.s
ignoring nonexistent directory
"/home/src/gcc/trunk/lib/gcc/i686-pc-linux-gnu/4.1.0/../../../../i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/home/src/gcc/trunk/include
/home/src/gcc/trunk/lib/gcc/i686-pc-linux-gnu/4.1.0/include
/usr/include
End of search list.
GNU C version
4.1.0 20050502 (experimental) (i686-pc-linux-gnu)
compiled by GNU C version 4.1.0 20050502 (experimental).
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
as -V -Qy -o /tmp/cc6jWNoa.o /tmp/cc6LaTqE.s
GNU assembler version 2.15 (i386-linux) using BFD version 2.15
/home/src/gcc/trunk/libexec/gcc/i686-pc-linux-gnu/4.1.0/collect2 --eh-frame-hdr
-m elf_i386 -dynamic-linker /lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o
/home/src/gcc/trunk/lib/gcc/i686-pc-linux-gnu/4.1.0/crtbegin.o
-L/home/src/gcc/trunk/lib/gcc/i686-pc-linux-gnu/4.1.0
-L/home/src/gcc/trunk/lib/gcc/i686-pc-linux-gnu/4.1.0/../../.. /tmp/cc6jWNoa.o
-lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s
--no-as-needed /home/src/gcc/trunk/lib/gcc/i686-pc-linux-gnu/4.1.0/crtend.o
/usr/lib/crtn.o
% ./a.out
beg 2
end 0
It works well without optimization as follows.
% gcc t.c
% ./a.out
beg 2
0
1
end 2
--
Summary: -O2 makes a loop doesn't execute a body
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: akr at m17n dot org
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21332