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RE: GCC optimizes integer overflow: bug or feature?
From: |
Dave Korn |
Subject: |
RE: GCC optimizes integer overflow: bug or feature? |
Date: |
Fri, 22 Dec 2006 17:08:01 -0000 |
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
--
Can't think of a witty .sigline today....
- Re: GCC optimizes integer overflow: bug or feature?, (continued)
- Re: GCC optimizes integer overflow: bug or feature?, Denis Vlasenko, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Paul Brook, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Denis Vlasenko, 2006/12/21
- Re: GCC optimizes integer overflow: bug or feature?, Paul Brook, 2006/12/21
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/21
- Re: GCC optimizes integer overflow: bug or feature?, Paul Brook, 2006/12/21
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/21
- Re: GCC optimizes integer overflow: bug or feature?, Denis Vlasenko, 2006/12/22
- RE: GCC optimizes integer overflow: bug or feature?,
Dave Korn <=
- RE: GCC optimizes integer overflow: bug or feature?, Andrew Pinski, 2006/12/22
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/22
- Re: GCC optimizes integer overflow: bug or feature?, Andrew Pinski, 2006/12/22
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/22
- Re: GCC optimizes integer overflow: bug or feature?, Rask Ingemann Lambertsen, 2006/12/23
- Re: GCC optimizes integer overflow: bug or feature?, Denis Vlasenko, 2006/12/23
- Re: GCC optimizes integer overflow: bug or feature?, Rask Ingemann Lambertsen, 2006/12/23
- Re: GCC optimizes integer overflow: bug or feature?, Gabriel Dos Reis, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/20
- Message not available
- Re: GCC optimizes integer overflow: bug or feature?, Paolo Bonzini, 2006/12/21