clang static analysis

[Jamey Sharp]

On Thu, May 20, 2010 at 11:59 PM, Jeremy Huddleston <jeremyhu at apple.com> wrote:
> In case anyone's interested, I've posted an updated log from building the XQuartz server with clang SA:
>
> http://people.freedesktop.org/~jeremyhu/clang/2010-05-20-1/

The first one I examined ("Assigned value is garbage or undefined",
mi/miwideline.c line 1918) assumes in steps 10 and 11 that
pGC->lineStyle == LineOnOffDash and pGC->capStyle == CapProjecting,
but took the false branch for that condition at step 8. Is it often
that wrong? (It makes the same mistake for line 1804, and the "Branch
condition evaluates to a garbage value" error is based on a similarly
contradictory assumption.) A tiny bit of abstract interpretation would
go a long way here...

"Assigned value is garbage or undefined" at dix/dixfonts.c line 1231
is correct, at least, except the real bug is that I didn't delete the
oldfid variable when I deleted the code that cared what value it had.
Patch for that shortly.

I suspect quite a few dead-store warnings would go away if we kill the
REGION_* macros. One particularly entertaining example, from
http://people.freedesktop.org/~jeremyhu/clang/2010-05-20-1/report-7FMXPb.html

    /* This prevents warnings about pScreen not being used. */
    pGC->pScreen = pScreen = pGC->pScreen;
	
clang says "Although the value stored to 'pScreen' is used in the
enclosing expression, the value is never actually read from
'pScreen'".

Jamey