Re: GCC optimizes integer overflow: bug or feature?

[Robert Dewar]

Dave Korn wrote:
> On 22 December 2006 00:59, Denis Vlasenko wrote:
>
>
> > Or this, absolutely typical C code. i386 arch can compare
> > 16 bits at a time here (luckily, no alighment worries on this arch):
>
>   Whaddaya mean, no alignment worries?  Misaligned accesses *kill* your
> performance!

is it really worse to do one unaligned 16-bit read, than two separate
8-bit reads? I am surprised ... and of course you have the gain from
shorter code, reducing i-cache pressure.
>   I know this doesn't affect correctness, but the coder might well have known
> that the pointer is unaligned and written two separate byte-sized accesses on
> purpose; volatile isn't the answer because it's too extreme, there's nothing
> wrong with caching these values in registers and they don't spontaneously
> change on us.