On Thu, 28 Jul 2016, Prathamesh Kulkarni wrote:
> On 28 July 2016 at 15:58, Andreas Schwab <sch...@suse.de> wrote:
> > On Mo, Jul 25 2016, Prathamesh Kulkarni <prathamesh.kulka...@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, sch...@suse.de
> > GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7
> > "And now for something completely different."
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
