Re: [git patches 1/2] warnings: attack valid cases spotted by warnings

[Jeff Garzik <jeff@garzik.org>]

Roland Dreier wrote:
> In this case the code is basically
> 
> 	u32 x;
> 
> 	for (n = 0; cond; ++n) {
> 		...
> 		if (!n)
> 			x = something;
> 		...
> 	}
> 
> 	if (n) {
> 		...
> 		use(x);
> 		...
> 	}
> 
> and gcc still warns...


Interestingly, the above accurately describes a common code pattern 
matching code which caused gcc to emit the uninit'd-var warnings.

For the record I think initializating 'f0' to zero is safer for the 
reasons Linus gave, and in addition, f0 is or'd with a value written to 
a hardware register, which means things should go awry (if they go) in a 
semi-predictable manner.

According to the assembly language produced, sure it is larger -- by one 
(per function) MOV that is adjacent to other initializations, making it 
highly likely the initializations are all streamed together.  I doubt 
one MOV per function will make a huge difference, considering the peace 
of mind it buys.

	Jeff