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RE: GCC optimizes integer overflow: bug or feature?
- From: "Dave Korn" <dave dot korn at artimi dot com>
- To: "'Denis Vlasenko'" <vda dot linux at googlemail dot com>, "'Paul Brook'" <paul at codesourcery dot com>
- Cc: <gcc at gcc dot gnu dot org>, "'Andrew Haley'" <aph at redhat dot com>, "'Paolo Bonzini'" <bonzini at gnu dot org>, <bug-gnulib at gnu dot org>
- Date: Fri, 22 Dec 2006 17:08:01 -0000
- Subject: RE: GCC optimizes integer overflow: bug or feature?
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!
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.
cheers,
DaveK
--
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