Re: [PATCH] Staging/comedi: Fixes static analysis warning raised by sparse

[Sam Ravnborg <sam@ravnborg.org>]

Hi Josh.

On Wed, Jun 11, 2014 at 02:45:29PM -0700, josh@joshtriplett.org wrote:
> On Thu, Jun 12, 2014 at 12:24:25AM +0300, Dan Carpenter wrote:
> > Let's forward this to the Sparse mailing list.
> > 
> > We're seeing a Sparse false positive testing
> > drivers/staging/comedi/drivers/ni_pcimio.c.
> > 
> >   CHECK   drivers/staging/comedi/drivers/ni_pcimio.c
> > drivers/staging/comedi/drivers/ni_stc.h:720:26: warning: shift too big (4294967295) for type int
> > drivers/staging/comedi/drivers/ni_stc.h:720:26: warning: shift too big (4294967295) for type int
> > drivers/staging/comedi/drivers/ni_stc.h:720:26: warning: shift too big (4294967295) for type int
> > drivers/staging/comedi/drivers/ni_stc.h:720:26: warning: shift too big (4294967295) for type int
> > 
> > I have created some test code to demonstrate the problem (attached).
> > 
> > The check_shift_count() warning is only supposed to be printed for
> > number literals but because of the way inline functions are expanded it
> > still complains even though channel is a variable.
> 
> Thanks for the test case; this definitely makes no sense.  I don't think
> Sparse will suddenly develop enough range analysis or reachability
> analysis to handle this case; I think the right answer is to avoid
> giving such warnings for shifts with a non-constant RHS.

Something like the appended?

It seems to work for me - and it cured a lot of warnings in math-emu.c on sparc.
If it looks OK I will do a proper patch submission.

	Sam


diff --git a/expand.c b/expand.c
index 0f6720c..4a96de4 100644
--- a/expand.c
+++ b/expand.c
@@ -187,7 +187,7 @@ static int simplify_int_binop(struct expression *expr, struct symbol *ctype)
 		return 0;
 	r = right->value;
 	if (expr->op == SPECIAL_LEFTSHIFT || expr->op == SPECIAL_RIGHTSHIFT) {
-		if (r >= ctype->bit_size) {
+		if (expr->flags & Int_const_expr && r >= ctype->bit_size) {
 			if (conservative)
 				return 0;
 			r = check_shift_count(expr, ctype, r);