http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49073
Summary: g++ optimizer breaks do-while code
Product: gcc
Version: 4.5.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: p...@itee.uq.edu.au
Created attachment 24296
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24296
The .ii file produced with g++ -v -save-temps -Wall -Wextra -o dow dow.cc
I recently installed Ubuntu 11.04 on a new 64bit laptop :
Linux Kernel: 2.6.38-8-generic
processor: i7-2620M
On trying to build a project of mine on the new laptop I found a problem that
appears to be related to the optimizer. Below is a simple example that exhibits
the problem - execution of a do-while loop.
With the optimizer off it appears to work OK but with any optimization on it
does not break out of the do-while loop as required.
It works OK with optimization if I recode as a while loop.
---- dow.cc ------
#include <iostream>
using namespace std;
int main()
{
int a[] = {1,2,3,4,5,6,7};
bool flag = false;
int d = 1;
int i = 1;
do
{
d = a[i];
if (flag && (d == 4))
{
cerr << "break" << endl;
break;
}
i++;
flag = (d == 3);
} while (d < 7);
}
---------
Compiled as
g++ -Wall -Wextra -o dow dow.cc
and run as
./dow
outputs
break
(as it should)
Compiled with -O2
./dow
generates no output
