https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61531
Bug ID: 61531
Summary: Optimizer completely removes some bitset code
Product: gcc
Version: 4.3.4
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: Ulrich.Windl at rz dot uni-regensburg.de
I wrote a simple test code for <bitset> that the default optimization complete
removes. Only -O0 keept the code. However the default code should output. Thus
I consider the optimization bad. Preprocessed input will follow, but here is
the basic test:
---
~/src/C++/bitsettest> cat bstest.cc
#include <iostream>
#include <bitset>
int main(int argc, char *argv[])
{
std::bitset<32> b;
#if 0
std::cout << "size " << b.size() << std::endl;
#endif
b.set(2);
if (b.test(2))
std::cout << "set 2" << std::endl;
if (b[3])
std::cout << "set 3" << std::endl;
return 0;
}
~/src/C++/bitsettest> make
g++ -Wall -Wextra -Wshadow -pipe -O2 -g --save-temps -c -o bstest.o
bstest.cc
g++: warning: -pipe ignored because -save-temps specified
bstest.cc:4: warning: unused parameter ‘argc’
bstest.cc:4: warning: unused parameter ‘argv’
g++ -o bstest bstest.o
~/src/C++/bitsettest>
(gdb) disassemble /m main
Dump of assembler code for function main(int, char**):
4 int main(int argc, char *argv[])
0x00000000004008b0 <+0>: sub $0x8,%rsp
5 {
6 std::bitset<32> b;
7
8 #if 0
9 std::cout << "size " << b.size() << std::endl;
10 #endif
11 b.set(2);
12 if (b.test(2))
13 std::cout << "set 2" << std::endl;
14 if (b[3])
15 std::cout << "set 3" << std::endl;
16 return 0;
17 }
0x00000000004008d2 <+34>: xor %eax,%eax
0x00000000004008d4 <+36>: add $0x8,%rsp
0x00000000004008d8 <+40>: retq
End of assembler dump.
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