| Summary: | Optimization level O2 nad O3 produces different output from level O1 and O0 | ||
|---|---|---|---|
| Product: | gcc | Reporter: | agamous |
| Component: | c++ | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED DUPLICATE | ||
| Severity: | normal | CC: | agamous |
| Priority: | P3 | ||
| Version: | 4.4.3 | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | ||
Source code to compile #include <stdio.h> int main() { int i32 =0x12345678; short *t = (short *)&i32; t[0] = 0xaa; t[1] = 0xbb; printf("i32 = %lx\n", i32); return 0; } We tried both gcc and g++ with the same compilation options and the same result. Compilation line (optimization O3 or O2) gcc -O3 -o foo foo.c run as ./foo output i32 = 12345678 If compiles with O1 or O0 gcc -O0 -o foo foo.c output i32 = bb00aa GCC version > * the exact version of GCC, as shown by "gcc -v"; Using built-in specs. Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.3-4ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i486 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5) CPU Intel(R) Core(TM)2 Duo CPU E8400 @ 3.00GHz system type uname -a displays the following Linux 2.6.32-24-generic #39-Ubuntu SMP Wed Jul 28 05:14:15 UTC 2010 x86_64 GNU/Linux