http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51151
Bug #: 51151
Summary: Invalid -Woverflow warning in C++ frontend
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: i...@airs.com
Compile this C++ file with -Wall or -Woverflow:
template<typename T> class C {
public:
void f() {
m = c2 + 1;
}
static const long unsigned int c1 = 7;
static const int c2 = c1 - 1;
int m;
};
template class C<int>;
When I compile this with current mainline, I get:
foo.cc: In instantiation of ‘void C<T>::f() [with T = int]’:
foo.cc:10:16: required from here
foo.cc:4:5: warning: integer overflow in expression [-Woverflow]
This warning is invalid. There is no integer overflow here.
From a quick look, it appears that fold winds up being called with
((int) ((unsigned int) 7 + 4294967295U)) + 1
It decides to distribute the addition, groups the constants 4294967295 and 1
together, and gets an overflow when it adds them. At that point it is adding
together an unsigned and a signed constant, having decided to strip the type
conversion as a nop.
This does not happen when not using a template.
