The following test case will produce 0 when compile without compiler
optimizations, and 255 with optimizations:
=========================================================
#include <cmath>
#include <iostream>
int main()
{
double d = pow(2.0, 50.0);
std::cout << static_cast<int>(static_cast<unsigned char>(d)) << std::endl;
return 0;
}
=========================================================
$ g++ -v -save-temps main.cpp
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.3.3-5ubuntu4'
--with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.3
--program-suffix=-4.3 --enable-clocale=gnu --enable-libstdcxx-debug
--enable-objc-gc--enable-mpfr --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 4.3.3 (Ubuntu 4.3.3-5ubuntu4)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
/usr/lib/gcc/x86_64-linux-gnu/4.3.3/cc1plus -E -quiet -v -D_GNU_SOURCE
main.cpp -D_FORTIFY_SOURCE=2 -mtune=generic -fpch-preprocess -o main.ii
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/4.3.3/../../../../x86_64-linux-gnu/include"
ignoring nonexistent directory "/usr/include/x86_64-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
/usr/include/c++/4.3
/usr/include/c++/4.3/x86_64-linux-gnu
/usr/include/c++/4.3/backward
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/4.3.3/include
/usr/lib/gcc/x86_64-linux-gnu/4.3.3/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
/usr/lib/gcc/x86_64-linux-gnu/4.3.3/cc1plus -fpreprocessed main.ii -quiet
-dumpbase main.cpp -mtune=generic -auxbase main -version -fstack-protector -o
main.s
GNU C++ (Ubuntu 4.3.3-5ubuntu4) version 4.3.3 (x86_64-linux-gnu)
compiled by GNU C version 4.3.3, GMP version 4.2.4, MPFR version 2.4.0.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: d9dd67dcc191271ac69fd2c05266cf9c
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
as -V -Qy -o main.o main.s
GNU assembler version 2.19.1 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Ubuntu) 2.19.1
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.3.3/:/usr/lib/gcc/x86_64-linux-gnu/4.3.3/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.3.3/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.3.3/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.3.3/:/usr/lib/gcc/x86_64-linux-gnu/4.3.3/:/usr/lib/gcc/x86_64-linux-gnu/4.3.3/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.3.3/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
/usr/lib/gcc/x86_64-linux-gnu/4.3.3/collect2 --eh-frame-hdr -m elf_x86_64
--hash-style=both -dynamic-linker /lib64/ld-linux-x86-64.so.2 -z relro
/usr/lib/gcc/x86_64-linux-gnu/4.3.3/../../../../lib/crt1.o
/usr/lib/gcc/x86_64-linux-gnu/4.3.3/../../../../lib/crti.o
/usr/lib/gcc/x86_64-linux-gnu/4.3.3/crtbegin.o
-L/usr/lib/gcc/x86_64-linux-gnu/4.3.3 -L/usr/lib/gcc/x86_64-linux-gnu/4.3.3
-L/usr/lib/gcc/x86_64-linux-gnu/4.3.3/../../../../lib -L/lib/../lib
-L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/4.3.3/../../.. main.o
-lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/usr/lib/gcc/x86_64-linux-gnu/4.3.3/crtend.o
/usr/lib/gcc/x86_64-linux-gnu/4.3.3/../../../../lib/crtn.o
--
Summary: Optimization levels produce (the same) different result
for static_cast<unsigned char>(double)
Product: gcc
Version: 4.3.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: helder dot pereira dot correia at gmail dot com
GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45091
