gcc information:
Using built-in specs.
Target: i686-linux
Configured with: ../gcc-4.1.1/configure
--prefix=/build/toolchain/lin32/gcc-4.1.1 --disable-nls --enable-shared
--enable-threads=posix --enable-languages=c,c++ --with-gnu-as --with-gnu-ld
--target=i686-linux
--with-as=/build/toolchain/lin32/binutils-2.16.1-vt/bin/i686-linux-as
--with-ld=/build/toolchain/lin32/binutils-2.16.1-vt/bin/i686-linux-ld
--enable-__cxa_atexit --with-sysroot=/build/toolchain/lin32/glibc-2.2.5-44
--disable-tls
Thread model: posix
gcc version 4.1.1
When using the following script (which is probably only suitable for
my work environment):
#!/bin/bash
SRCDIR="/tmp/gcc4-error";
GCC4="/build/toolchain/lin32/gcc-4.1.1/bin/i686-linux-gcc
--sysroot=/build/toolchain/lin32/glibc-2.2.5-44";
${GCC4} -v
for OPT in $(seq 0 3) ; do
OUTPUT="${SRCDIR}/error-O${OPT}";
GCC_OPT="-Wall -Werror -O${OPT} -g3 --save-temps";
echo "Executing with optimization -O${OPT}"
rm -f ${OUTPUT};
${GCC4} ${GCC_OPT} -o ${OUTPUT} ${SRCDIR}/error.c
${OUTPUT}
done;
to compile the following source:
#include <stdio.h>
static const int loop_start = 118;
static const int loop_end = 127;
void fails_0_at_O1_O2(char *arr, int l)
{
int i;
for (i = loop_start; i < loop_end; ++i) {
printf("%s: arr[%3d] = %4d\t(char)(i + 5) = %3d\n",
__PRETTY_FUNCTION__, i, arr[i], (char)(i + 5));
}
printf("\n");
}
void fails_1_at_O1_O2(char *arr, int l)
{
int i;
for (i = loop_start; i < loop_end; ++i) {
char v = i + 5;
printf("%s: arr[%3d] = %4d\tv = %3d\n",
__PRETTY_FUNCTION__, i, arr[i], v);
}
printf("\n");
}
void works_at_all_O_levels(char *arr, int l)
{
int i;
for (i = loop_start; i < loop_end; ++i) {
volatile char v = i + 5;
printf("%s: arr[%3d] = %4d\tv = %3d\n",
__PRETTY_FUNCTION__, i, arr[i], v);
}
printf("\n");
}
int main(void)
{
const int l = 190;
char arr[256];
int i;
for (i = 0; i < l; ++i) {
arr[i] = (char)(i + 5);
}
fails_0_at_O1_O2(arr, l);
fails_1_at_O1_O2(arr, l);
works_at_all_O_levels(arr, l);
return 0;
}
At optimization levels {0..3}, the compiler does not honor the cast of
the 'i + 5' at levels O1 and O2.
The output for all optimization levels, around the boundary case, is
shown below. Notice how the value based on the induction variable
does not wrap to -128 in O1 and O2.
Executing with optimization -O0
fails_0_at_O1_O2: arr[118] = 123 (char)(i + 5) = 123
fails_0_at_O1_O2: arr[119] = 124 (char)(i + 5) = 124
fails_0_at_O1_O2: arr[120] = 125 (char)(i + 5) = 125
fails_0_at_O1_O2: arr[121] = 126 (char)(i + 5) = 126
fails_0_at_O1_O2: arr[122] = 127 (char)(i + 5) = 127
fails_0_at_O1_O2: arr[123] = -128 (char)(i + 5) = -128
fails_0_at_O1_O2: arr[124] = -127 (char)(i + 5) = -127
fails_0_at_O1_O2: arr[125] = -126 (char)(i + 5) = -126
fails_0_at_O1_O2: arr[126] = -125 (char)(i + 5) = -125
fails_1_at_O1_O2: arr[118] = 123 v = 123
fails_1_at_O1_O2: arr[119] = 124 v = 124
fails_1_at_O1_O2: arr[120] = 125 v = 125
fails_1_at_O1_O2: arr[121] = 126 v = 126
fails_1_at_O1_O2: arr[122] = 127 v = 127
fails_1_at_O1_O2: arr[123] = -128 v = -128
fails_1_at_O1_O2: arr[124] = -127 v = -127
fails_1_at_O1_O2: arr[125] = -126 v = -126
fails_1_at_O1_O2: arr[126] = -125 v = -125
works_at_all_O_levels: arr[118] = 123 v = 123
works_at_all_O_levels: arr[119] = 124 v = 124
works_at_all_O_levels: arr[120] = 125 v = 125
works_at_all_O_levels: arr[121] = 126 v = 126
works_at_all_O_levels: arr[122] = 127 v = 127
works_at_all_O_levels: arr[123] = -128 v = -128
works_at_all_O_levels: arr[124] = -127 v = -127
works_at_all_O_levels: arr[125] = -126 v = -126
works_at_all_O_levels: arr[126] = -125 v = -125
Executing with optimization -O1
fails_0_at_O1_O2: arr[118] = 123 (char)(i + 5) = 123
fails_0_at_O1_O2: arr[119] = 124 (char)(i + 5) = 124
fails_0_at_O1_O2: arr[120] = 125 (char)(i + 5) = 125
fails_0_at_O1_O2: arr[121] = 126 (char)(i + 5) = 126
fails_0_at_O1_O2: arr[122] = 127 (char)(i + 5) = 127
fails_0_at_O1_O2: arr[123] = -128 (char)(i + 5) = 128
fails_0_at_O1_O2: arr[124] = -127 (char)(i + 5) = 129
fails_0_at_O1_O2: arr[125] = -126 (char)(i + 5) = 130
fails_0_at_O1_O2: arr[126] = -125 (char)(i + 5) = 131
fails_1_at_O1_O2: arr[118] = 123 v = 123
fails_1_at_O1_O2: arr[119] = 124 v = 124
fails_1_at_O1_O2: arr[120] = 125 v = 125
fails_1_at_O1_O2: arr[121] = 126 v = 126
fails_1_at_O1_O2: arr[122] = 127 v = 127
fails_1_at_O1_O2: arr[123] = -128 v = 128
fails_1_at_O1_O2: arr[124] = -127 v = 129
fails_1_at_O1_O2: arr[125] = -126 v = 130
fails_1_at_O1_O2: arr[126] = -125 v = 131
works_at_all_O_levels: arr[118] = 123 v = 123
works_at_all_O_levels: arr[119] = 124 v = 124
works_at_all_O_levels: arr[120] = 125 v = 125
works_at_all_O_levels: arr[121] = 126 v = 126
works_at_all_O_levels: arr[122] = 127 v = 127
works_at_all_O_levels: arr[123] = -128 v = -128
works_at_all_O_levels: arr[124] = -127 v = -127
works_at_all_O_levels: arr[125] = -126 v = -126
works_at_all_O_levels: arr[126] = -125 v = -125
Executing with optimization -O2
fails_0_at_O1_O2: arr[118] = 123 (char)(i + 5) = 123
fails_0_at_O1_O2: arr[119] = 124 (char)(i + 5) = 124
fails_0_at_O1_O2: arr[120] = 125 (char)(i + 5) = 125
fails_0_at_O1_O2: arr[121] = 126 (char)(i + 5) = 126
fails_0_at_O1_O2: arr[122] = 127 (char)(i + 5) = 127
fails_0_at_O1_O2: arr[123] = -128 (char)(i + 5) = 128
fails_0_at_O1_O2: arr[124] = -127 (char)(i + 5) = 129
fails_0_at_O1_O2: arr[125] = -126 (char)(i + 5) = 130
fails_0_at_O1_O2: arr[126] = -125 (char)(i + 5) = 131
fails_1_at_O1_O2: arr[118] = 123 v = 123
fails_1_at_O1_O2: arr[119] = 124 v = 124
fails_1_at_O1_O2: arr[120] = 125 v = 125
fails_1_at_O1_O2: arr[121] = 126 v = 126
fails_1_at_O1_O2: arr[122] = 127 v = 127
fails_1_at_O1_O2: arr[123] = -128 v = 128
fails_1_at_O1_O2: arr[124] = -127 v = 129
fails_1_at_O1_O2: arr[125] = -126 v = 130
fails_1_at_O1_O2: arr[126] = -125 v = 131
works_at_all_O_levels: arr[118] = 123 v = 123
works_at_all_O_levels: arr[119] = 124 v = 124
works_at_all_O_levels: arr[120] = 125 v = 125
works_at_all_O_levels: arr[121] = 126 v = 126
works_at_all_O_levels: arr[122] = 127 v = 127
works_at_all_O_levels: arr[123] = -128 v = -128
works_at_all_O_levels: arr[124] = -127 v = -127
works_at_all_O_levels: arr[125] = -126 v = -126
works_at_all_O_levels: arr[126] = -125 v = -125
Executing with optimization -O3
fails_0_at_O1_O2: arr[118] = 123 (char)(i + 5) = 123
fails_0_at_O1_O2: arr[119] = 124 (char)(i + 5) = 124
fails_0_at_O1_O2: arr[120] = 125 (char)(i + 5) = 125
fails_0_at_O1_O2: arr[121] = 126 (char)(i + 5) = 126
fails_0_at_O1_O2: arr[122] = 127 (char)(i + 5) = 127
fails_0_at_O1_O2: arr[123] = -128 (char)(i + 5) = -128
fails_0_at_O1_O2: arr[124] = -127 (char)(i + 5) = -127
fails_0_at_O1_O2: arr[125] = -126 (char)(i + 5) = -126
fails_0_at_O1_O2: arr[126] = -125 (char)(i + 5) = -125
fails_1_at_O1_O2: arr[118] = 123 v = 123
fails_1_at_O1_O2: arr[119] = 124 v = 124
fails_1_at_O1_O2: arr[120] = 125 v = 125
fails_1_at_O1_O2: arr[121] = 126 v = 126
fails_1_at_O1_O2: arr[122] = 127 v = 127
fails_1_at_O1_O2: arr[123] = -128 v = -128
fails_1_at_O1_O2: arr[124] = -127 v = -127
fails_1_at_O1_O2: arr[125] = -126 v = -126
fails_1_at_O1_O2: arr[126] = -125 v = -125
works_at_all_O_levels: arr[118] = 123 v = 123
works_at_all_O_levels: arr[119] = 124 v = 124
works_at_all_O_levels: arr[120] = 125 v = 125
works_at_all_O_levels: arr[121] = 126 v = 126
works_at_all_O_levels: arr[122] = 127 v = 127
works_at_all_O_levels: arr[123] = -128 v = -128
works_at_all_O_levels: arr[124] = -127 v = -127
works_at_all_O_levels: arr[125] = -126 v = -126
works_at_all_O_levels: arr[126] = -125 v = -125
--
Summary: Cast on expression using induction variable not honored
at O1 and O2
Product: gcc
Version: 4.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: thutt at vmware dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31327
