[webkit-dev] -fstrict-aliasing error

[Maciej Stachowiak]

Hi Andrea,

On May 14, 2006, at 7:56 AM, Andrea Mannori wrote:

> hi all,
> trying to compile webcore and webkit framework with -fstrict- 
> aliasing i get a lot of warning (considered error by default)
> ignoring them produce an unusefull code, as well as "correct" them  
> (bus error and segmentation fault on start)
> is just me?
> ther a way to have a solution? i' d like to use this flag to use - 
> ftree-vectorize also (on my g4)

-fstrict-aliasing makes stronger requirements on code correctness  
than many other optimizations. Specifically, it assumes that  
locations with different types never reside in the same memory  
location. That breaks code that does things like this:

void printFloatBits(float f)
{
	float* floatAddr = &f;
	int* intAddr = (int*)floatAddr; // bad! violates strict aliasing rules
	printf("%x", *intAddr);
}

Strict aliasing requires working around this using union types. It  
would be a good idea to make WebCore safe to use with -fstrict- 
aliasing and then turn it on in the default build, but it would take  
significant work.

More generally, it would be cool to try different optimizations that  
aren't on by defaut and see what effect they have on speed and code  
size.

Cheers,
Maciej