Re: [PATCH] testsuite: Fix array size in gcc.dg/strlenopt-66.c

[Martin Sebor <msebor at gmail dot com>]

On 11/21/19 2:24 PM, Dimitar Dimitrov wrote:
> On Thu, 21 Nov 2019, 20:09:23 EET Martin Sebor wrote:
> > On 11/21/19 10:11 AM, Dimitar Dimitrov wrote:
> > > One of the passed arguments is actually a string with size 4 ("123").
> > > Adjust the destination buffer accordingly.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > > 2019-11-21  Dimitar Dimitrov  <dimitar@dinux.eu>
> > >
> > > 	* gcc.dg/strlenopt-66.c (test_strncmp_a4_cond_a5_a3_n): Fix array size.
> > >
> > > Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>
> > > ---
> > >
> > >    gcc/testsuite/gcc.dg/strlenopt-66.c | 2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/gcc/testsuite/gcc.dg/strlenopt-66.c
> > > b/gcc/testsuite/gcc.dg/strlenopt-66.c index 4ba31a845b0..3de22c18f4f
> > > 100644
> > > --- a/gcc/testsuite/gcc.dg/strlenopt-66.c
> > > +++ b/gcc/testsuite/gcc.dg/strlenopt-66.c
> > > @@ -88,7 +88,7 @@ __attribute__ ((noclone, noinline, noipa)) void
> > >
> > >    test_strncmp_a4_cond_a5_a3_n (const char *s1, const char *s2, const char
> > >    *s3,>
> > >    			      int i, unsigned n)
> > >    
> > >    {
> > >
> > > -  char a3[3], a4[4], a5[5];
> > > +  char a3[4], a4[4], a5[5];
> >
> > That does look like a mistake.  Thanks for bringing it up!
> >
> > The purpose of the test is to exercise strncmp calls whose first
> > two arguments involve arrays of all different sizes (and strings
> > of different lengths stored in them).  In this function,
> > the operands of the conditional expression should also be of
> > different sizes than the first argument: one should be smaller
> > and the other bigger.
> >
> > So to keep the test doing what it's meant to do I think we need
> > to change lengths of the strings passed to the function to fit
> > the arrays rather than the sizes of the locals.  (Adding even
> > more calls to cover all the permutations of lengths and sizes
> > would be a further improvement.)
> >
> > If this sounds too elaborate let me know and I'll fix the test.
> >
> > Martin
> Hi,
>
> I admit I'm a bit confused, so I'll let you fix the test as you see fit.
>
> With "noipa" function attribute the compiler should not be able to propagate
> the string constants, so a3/a4/a5 string lengths are unknown when strncmp is
> invoked. I don't understand how PR90626 would take effect in such case.

The optimization doesn't take effect but the lengths can be
assumed to be in the range of the arrays (e.g., the length
of a3 can be assumed to be less than 3).  The test tries to
verify that the comparison of the strncmp call with zero
doesn't get folded into false solely based on the ranges
of the lengths.  It's probably not a the best test.

> Also, I fail to see how the different sizes of local arrays influence the
> test.
They shouldn't influence the outcome of the test but they are
considered by the strncmp optimization (and others that deal
with strings) because they determine the ranges of lengths of
the strings that can be stored in them.

I committed r278608 with the fix and added a few more cases.

Martin