Re: [PATCH] C undefined behavior fix

From: Jakub Jelinek (
Date: Wed Jan 02 2002 - 10:50:13 EST

On Wed, Jan 02, 2002 at 08:39:20AM -0700, Tom Rini wrote:
> Well, Paulus wrote 'strcpy' not 'memcpy', so why does gcc get to assume
> it's safe to change it? In this case it's certainly not.

But unless you trigger undefined behaviour, strcpy(x, "foobar" + n) is
equal to memcpy(x, "foobar" + n, sizeof("foobar") - n); and the latter is
more efficient (you don't have to check for end-of-string during copying).

> > It is not a workaround, it is a fix to an invalid code, which gets
> > triggered by particular optimization.
> By a particular optimization that's not present before gcc-3.0, and
> happens to break things under some conditions, as you've seen.

It just happens to do a different thing than it used to when seeing code
with particular case of undefined behaviour.

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