https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66191
Bug ID: 66191
Summary: GCC optimizes away if clause checking similar but not
same condition
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: DoDoEntertainment at gmail dot com
Target Milestone: ---
Created attachment 35561
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35561&action=edit
Program that causes issue, executable, preprocessed output, GCC info, etc.
Hello everyone,
this is my first GCC bug report so please tell me if something is missing. I've
added all required by 'https://gcc.gnu.org/bugs/' in provided tar.gz file.
The bug happens when using optimization level O2 or higher.
Consider this chunk of code:
static const double
double0_15[]={0.0,1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0,10.0,11.0,12.0,13.0,14.0,15.0};
static double _int2double(unsigned i){
if (i<16)
return double0_15[i];
else
return _int2double(i/16)*16.0+double0_15[i%16];
}
double int2double(int i){
if (i<0)
return -_int2double(-i);
else
return _int2double(i);
}
If 'int2double' is called with negative value (see attached tar.gz for complete
example that reproduces the bug) then if clause in '_int2double' is skipped
which causes a segfault if i<-16.
The code chunk is taken from free computer algebra system Giac
(http://www-fourier.ujf-grenoble.fr/~parisse/giac.html).
In attached tar.gz you can find the minimal program that reproduces the issue,
preprocessed outputs (.ii, .o and .s files) and invocation log (everything GCC
prints to stderr while working, including build configuration, correct version
etc.). The system is fully updated ArchLinux with GCC 4.9.2.
I've also attached full debug output of clang compiler for convenience because
the same program can be compiled with clang without causing error.
