==operator gives unexpected result using -O0

[Jakob Andreas Bærentzen]

Hello,

I do apologize if my ignorance is the problem here, but I am having a strange 
problem with the version of gcc included in suse 9.3: gcc version 3.3.5 
20050117 (prerelease) (SUSE Linux). The same problem was observed with gcc 
3.3.1. I have not tried later versions, but I can't find the problem in 
bugzilla so I assume it is either so trivial that I should be ashamed or 
unknown. It is an intel XEON processor.

It seems to me that if a,b, and c are float or double values and if a has been 
assigned b*c

then

a == (b*c)

should return true since a should contain the same bitpattern as the temporary 
being assigned the value of b*c. Is it not so? 

Never the less, the following piece of code does not work as expected when 
compiling with -O0. It works FINE when compiling with -O1 or higher.

-----------
#include <iostream>

using namespace std;
int main()
{
		double b = 9.5245435435564536; 
		double c = 7.98786542345446565;
		double a = b*c;

		//Does not work.
		cout << (a == (b*c)) << endl;
		
		// Works
		double d = b*c;
		cout << (a == d) << endl;
}
-----------

With O0 the output is 
0
1

With O1, O2 or O3 the output is
1
1

as one would expect.

I have made a similar program in C and I also changed double to float. It 
makes no difference. Nor does the actual float/double values. The 
optimization flag seems to decide what happens.

Any insight would be appreciated.

Andreas