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[Bug c/40762] New: possible integer miscompilation
- From: "regehr at cs dot utah dot edu" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 15 Jul 2009 06:32:59 -0000
- Subject: [Bug c/40762] New: possible integer miscompilation
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
Seen on Ubuntu Hardy. The -O2 result seems to be wrong. Also valgrind says
this about the -O2 compilation:
==6729== Conditional jump or move depends on uninitialised value(s)
==6729== at 0x84F22CB: solve_graph (tree-ssa-structalias.c:1570)
regehr@john-home:~/volatile/tmp174$ current-gcc -O1 small.c -o small
regehr@john-home:~/volatile/tmp174$ ./small
checksum = 0
regehr@john-home:~/volatile/tmp174$ current-gcc -O2 small.c -o small
regehr@john-home:~/volatile/tmp174$ ./small
checksum = 1
regehr@john-home:~/volatile/tmp174$ current-gcc -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../configure --prefix=/home/regehr/z/tmp/gcc-r149650-install
--program-prefix=r149650- --enable-languages=c,c++
Thread model: posix
gcc version 4.5.0 20090714 (experimental) (GCC)
regehr@john-home:~/volatile/tmp174$ cat small.c
#include <stdint.h>
#include <limits.h>
#include <stdio.h>
uint8_t g_4;
int64_t g_10;
uint8_t g_56;
uint8_t g_64;
static uint8_t safe_rshift_func_uint8_t_u_u(uint8_t left, unsigned int right)
{
return ((((unsigned int)(right)) >= sizeof(uint8_t)*CHAR_BIT)
? ((uint8_t)(left))
: (((uint8_t)(left)) >> ((unsigned int)(right))));
}
int32_t func_53 (void);
int32_t func_53 (void)
{
if (safe_rshift_func_uint8_t_u_u (g_56, g_10))
{
}
else
for (g_10 = 0; g_10; g_10 = 1)
{
}
return 1;
}
int32_t func_36 (void);
int32_t func_36 (void)
{
uint8_t p_40;
g_10 = 1;
g_10 && func_53 ();
p_40 = g_10 || g_4;
g_64 = g_10;
return 1;
}
int
main (void)
{
func_36 ();
printf ("checksum = %d\n", g_64);
return 0;
}
--
Summary: possible integer miscompilation
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: regehr at cs dot utah dot edu
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40762