I noticed that sizes of functions in generated code change when I do simple
unrelated changes. Example:
# diff -u vi_small.c vi_big.c
--- vi_small.c 2006-11-22 23:35:39.000000000 +0100
+++ vi_big.c 2006-11-22 23:35:42.000000000 +0100
@@ -3414,6 +3414,8 @@
} sockaddr_inet;
extern int dotted2sockaddr(const char *dotted, struct sockaddr* sp, int
socklen);
extern int create_and_bind_socket_ip4or6(const char *hostaddr, int port);
+extern int setsockopt_reuseaddr(int fd);
+extern int setsockopt_reuseaddr2(int fd);
extern char *xstrdup(const char *s);
extern char *xstrndup(const char *s, int n);
extern char *safe_strncpy(char *dst, const char *src, size_t size);
Both .c files have this simple function at the end:
Byte *find_pair(Byte * p, Byte c)
{
Byte match, *q;
int dir, level;
match = ')';
level = 1;
dir = 1;
switch (c) {
case '(':
match = ')';
break;
case '[':
match = ']';
break;
case '{':
match = '}';
break;
case ')':
match = '(';
dir = -1;
break;
case ']':
match = '[';
dir = -1;
break;
case '}':
match = '{';
dir = -1;
break;
}
for (q = p + dir; text <= q && q < end; q += dir) {
if (*q == c)
level++;
if (*q == match)
level--;
if (level == 0)
break;
}
if (level != 0)
q = ((void *)0);
return (q);
}
which is obviously does not depend on setsockopt_reuseaddr[2].
I made two extra copies of it, just for fun, but it happens without copies too.
Okay, when I compile those:
#!/bin/sh
function compile() {
gcc -fno-builtin-strlen -Os "$@"
}
compile -c -o vi_small.o vi_small.c
compile -c -o vi_big.o vi_big.c
nm --size-sort vi_small.o | grep find_pair
nm --size-sort vi_big.o | grep find_pair
I am getting:
000000a9 T find_pair (vi_small.c)
000000a9 T find_pairB
000000a9 T find_pairC
000000a9 T find_pairB (vi_big.c)
000000a9 T find_pairC
000000b9 T find_pair <--------- different??
How come gcc generates different code for identical source files?
You saw the diff, it cannot matter at all...
How come gcc generates different code for identical functions???
(vi_big.c:find_pairB is the same as vi_big.c:find_pair to the last byte)
# gcc -v
Using built-in specs.
Target: i386-pc-linux-gnu
Configured with: ../gcc-4.1.1.org/configure --prefix=/usr/app/gcc-4.1.1.org
--exec-prefix=/usr/app/gcc-4.1.1.org --bindir=/usr/bin --sbindir=/usr/sbin
--libexecdir=/usr/app/gcc-4.1.1.org/libexec
--datadir=/usr/app/gcc-4.1.1.org/share --sysconfdir=/etc
--sharedstatedir=/usr/app/gcc-4.1.1.org/var/com
--localstatedir=/usr/app/gcc-4.1.1.org/var --libdir=/usr/lib
--includedir=/usr/include --infodir=/usr/info --mandir=/usr/man
--with-slibdir=/usr/app/gcc-4.1.1.org/lib --with-local-prefix=/usr/local
--with-gxx-include-dir=/usr/app/gcc-4.1.1.org/include/g++-v3
--enable-languages=c,c++ --with-system-zlib --disable-nls
--enable-threads=posix i386-pc-linux-gnu
Thread model: posix
gcc version 4.1.1
--
Summary: Generated code changes after unrelated edits in source.
Product: gcc
Version: 4.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: vda dot linux at googlemail dot com
GCC build triplet: i386-pc-linux-gnu
GCC host triplet: i386-pc-linux-gnu
GCC target triplet: i386-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29950
