http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51885
Bug #: 51885
Summary: g++ compiler options -O2 and -O3 modifies program
results
Classification: Unclassified
Product: gcc
Version: 4.6.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: [email protected]
ReportedBy: [email protected]
Created attachment 26356
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26356
example program with comments
platform : Fedora 16 x86_64
compiler : gcc-c++-4.6.2-1.fc16.x86_64
see attaches source file ; it is an example of the quicksort algorithm written
with pointers and templates
one template is specialised and uses a reinterpret_cast (it is part of a bigger
file)
it sorts this array : {12, -1, 2}
a) first test (compilation without any optimisation)
compilation : g++ main.cpp && ./a.out
result OK : {-1, 2, 12}
b) second test (-O2 optimisation)
compilation : g++ -O2 main.cpp && ./a.out
wrong result : {2, 12, -1}
3) third test (-O3 optimisation)
compilation : g++ -O3 main.cpp && ./a.out
wrong result : {2, 12, -1}
Strange behaviour : if i include between line #65 and line #67 (see attached
file)
std::cout<<*ptr_start<<std::endl;
then, the results are good in any case
i believe this is a bug ... the optimisation option should not change the
program result
best regards
Laurent
