http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48973
Summary: Inliner bug with one-bit (1-bit) bitfield
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: arthur.j.odw...@gmail.com
Created attachment 24231
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24231
Output of "ajo-gcc -w -O1 -finline-small-functions test.c -v"
This reproduces for me with svn revision 173589 (2011-05-09). Since this
reproduces all the way back to 4.4, it *must* be a duplicate of *something*,
but I didn't find anything likely-looking in a Bugzilla search. I'm on Ubuntu
10.10, x86-64.
cat >test.c <<EOF
struct S0 {
signed f0 : 1;
} g_72 = {0};
int f5 = -1;
void func_46(int f4) {
g_72.f0 = (f5 & 1) > 0;
}
int main() {
func_46(-1);
printf("%x\n", (unsigned int)(g_72.f0));
return 0;
}
EOF
gcc -w -O1 test.c -o a.out ; ./a.out
gcc -w -O2 test.c -o a.out ; ./a.out
REDUCED: gcc -w -O1 -finline-small-functions test.c -o a.out ; ./a.out
With -O1 the output is "ffffffff". With -O2 the output is "1". g_72.f0 should
evaluate to -1, and then casting that to (unsigned int) should always yield
0xffffffff regardless of optimization level. This looks to me like an inliner
bug.
In gcc 4.4.5 and 4.5.1, the bug also reproduces when you use "f4" instead of
"f5" inside func_46(). In trunk, you need to use a global variable to see the
bug.
This test case is reduced from the output of Csmith 2.1.0 (git hash 541a6480,
https://github.com/csmith-project/csmith/), using the following command line:
csmith --no-paranoid --no-longlong --no-pointers --arrays --no-jumps --consts
--no-volatiles --checksum --no-divs --no-muls --bitfields --packed-struct -s
1281232940
