gcc4.3.1 optimizations with restrict / -fargument-noalias / VLA

[Markus <markus dot stuermer at freenet dot de>]

I've been experimenting which optimizations gcc is willing to apply  
depending on the kind of function arguments and compiler flags.  
Perhaps someone can comment on what strange behavior I experienced:

If I understand the concept of C99's "restrict" qualifier for  
function arguments correctly, it gives basically the same  
"guarantees" to the compiler as -fargument-noalias-global.

However, gcc applies much more aggressive optimizations (for my test  
kernels the new predictive commoning seems to be most benefical) for - 
fargument-noalias, and seems to take no advantage of "restrict" in  
C99 (or the __restrict__ extension, in C99 as well as in C++).

Quite strange, optimization seems to be at least as good for C99's  
VLAs, even without restrict and without -fargument-noalias. I don't  
have the C99 standard to read that up, but could not find a hint on  
the web that VLA arguments are forbidden to alias.

Am I overlooking something here? Why is "restrict" not useful in that  
context (but -fargument-noalias is)? And why does it work for VLAs  
without any of both?

Regards,
Markus