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Re: [PR70920] transform (intptr_t) x eq/ne CST to x eq/ne (typeof x) cst


On Thu, 28 Jul 2016, Prathamesh Kulkarni wrote:

> On 28 July 2016 at 15:58, Andreas Schwab <schwab@suse.de> wrote:
> > On Mo, Jul 25 2016, Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org> wrote:
> >
> >> diff --git a/gcc/testsuite/gcc.dg/pr70920-4.c b/gcc/testsuite/gcc.dg/pr70920-4.c
> >> new file mode 100644
> >> index 0000000..dedb895
> >> --- /dev/null
> >> +++ b/gcc/testsuite/gcc.dg/pr70920-4.c
> >> @@ -0,0 +1,21 @@
> >> +/* { dg-do compile } */
> >> +/* { dg-options "-O2 -fdump-tree-ccp-details -Wno-int-to-pointer-cast" } */
> >> +
> >> +#include <stdint.h>
> >> +
> >> +void f1();
> >> +void f2();
> >> +
> >> +void
> >> +foo (int a)
> >> +{
> >> +  void *cst = 0;
> >> +  if ((int *) a == cst)
> >> +    {
> >> +      f1 ();
> >> +      if (a)
> >> +     f2 ();
> >> +    }
> >> +}
> >> +
> >> +/* { dg-final { scan-tree-dump "gimple_simplified to if \\(_\[0-9\]* == 0\\)" "ccp1" } } */
> >
> > This fails on all ilp32 platforms.
> Oops, sorry for the breakage.
> With -m32, the pattern is applied during forwprop1 rather than ccp1.
> I wonder though why ccp1 fails to fold the pattern with -m32 ?
> Looking at the dumps:
> 
> without -m32:
> input to ccp1 pass:
>   <bb 2>:
>   cst_4 = 0B;
>   _1 = (long int) a_5(D);
>   _2 = (void *) _1;
>   if (cst_4 == _2)
>     goto <bb 3>;
>   else
>     goto <bb 5>;
> 
> cc1 pass dump shows:
> Substituting values and folding statements
> 
> Folding statement: _1 = (long int) a_5(D);
> Not folded
> Folding statement: _2 = (void *) _1;
> Not folded
> Folding statement: if (cst_4 == _2)
> which is likely CONSTANT
> Applying pattern match.pd:2537, gimple-match.c:6530
> gimple_simplified to if (_1 == 0)
> Folded into: if (_1 == 0)
> 
> with -m32:
> input to ccp1 pass:
>  <bb 2>:
>   cst_3 = 0B;
>   a.0_1 = (void *) a_4(D);
>   if (cst_3 == a.0_1)
>     goto <bb 3>;
>   else
>     goto <bb 5>;
> 
> ccp1 pass dump shows:
> Substituting values and folding statements
> 
> Folding statement: a.0_1 = (void *) a_4(D);
> Not folded
> Folding statement: if (cst_3 == a.0_1)
> which is likely CONSTANT
> Folded into: if (a.0_1 == 0B)
> 
> I am not able to understand why it doesn't fold it to
> if (a_4(D) == 0) ?
> forwprop1 folds a.0_1 == 0B to a_4(D) == 0.

It's because CCP folds with follow-single-use edges but the 
match-and-simplify code uses a single callback to valueize and
decide whether its valid to follow the SSA edge.  I did have some
old patches trying to fix that but never followed up on those.

> I suppose the test-case would need to scan ccp1 for non-ilp targets
> and forwprop1 for
> ilp targets. How do update the test-case to reflect this ?

It's simpler to verify that at some point (forwprop) we have the
expected IL rather than testing for the match debug prints.

Richard.

> Thanks,
> Prathamesh
> >
> > Andreas.
> >
> > --
> > Andreas Schwab, SUSE Labs, schwab@suse.de
> > GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
> > "And now for something completely different."
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)


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