https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78438
Bug ID: 78438
Summary: incorrect comparison optimization
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: babokin at gmail dot com
Target Milestone: ---
Created attachment 40093
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40093&action=edit
reproducer
> g++ -O0 main.cpp func.cpp -o no_opt; ./no_opt
0
> g++ -O1 main.cpp func.cpp -o opt; ./opt
2
> cat main.cpp
#include <stdio.h>
char C = 0;
int I = 197412621;
void foo();
int main() {
foo();
printf("%d\n", C);
}
> cat func.cpp
extern char C;
extern int I;
void foo() {
C = 0 > (short) (I >> 11);
}
> g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/home/dybaboki/gcc/bin/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc/configure --with-arch=corei7 --with-cpu=corei7
--enable-clocale=gnu --with-system-zlib --enable-shared --with-demangler-in-ld
--enable-cloog-backend=isl --with-fpmath=sse --prefix=/home/dybaboki/gcc/bin
--enable-languages=c,c++,fortran,lto : (reconfigured) ../gcc/configure
--with-arch=corei7 --with-cpu=corei7 --enable-clocale=gnu --with-system-zlib
--enable-shared --with-demangler-in-ld --enable-cloog-backend=isl
--with-fpmath=sse --prefix=/home/dybaboki/gcc/bin
--enable-languages=c,c++,fortran,lto : (reconfigured) ../gcc/configure
--with-arch=corei7 --with-cpu=corei7 --enable-clocale=gnu --with-system-zlib
--enable-shared --with-demangler-in-ld --enable-cloog-backend=isl
--with-fpmath=sse --prefix=/home/dybaboki/gcc/bin
--enable-languages=c,c++,fortran,lto : (reconfigured) ../gcc_github/configure
--with-arch=corei7 --with-cpu=corei7 --enable-clocale=gnu --with-system-zlib
--enable-shared --with-demangler-in-ld --enable-cloog-backend=isl
--with-fpmath=sse --prefix=/home/dybaboki/gcc/bin
--enable-languages=c,c++,fortran,lto --no-create --no-recursion :
(reconfigured) ../gcc/configure --with-arch=corei7 --with-cpu=corei7
--enable-clocale=gnu --with-system-zlib --enable-shared --with-demangler-in-ld
--enable-cloog-backend=isl --with-fpmath=sse --prefix=/home/dybaboki/gcc/bin
--enable-languages=c,c++,fortran,lto --no-create --no-recursion
Thread model: posix
gcc version 7.0.0 20161119 (experimental) (GCC)
