Re: [patch] Fix PR fortran/72743

[Richard Biener <rguenther@suse.de>]

On Wed, 31 Aug 2016, Chung-Lin Tang wrote:

> Hi Richard, Martin,
> this issue is actually sort of like PR 70856, basically the same ICE
> after IPA-ICF, due to DECL_PT_UIDs not consistent after reaching for the
> ultimate_alias_target().
> 
> The reason this wasn't covered by the PR70856 fix is that, in this case,
> the DECL_PT_UID was not set in original->decl, evading the condition, and
> hence the the merged alias doesn't have DECL_PT_UID set, and causes the
> ICE in the second round of IPA-PTA (under -fopenacc).
> 
> My fix is to simply remove the DECL_PT_UID_SET_P (original->decl) guard,
> and allow the DECL_PT_UID to be set using the DECL_UID in this case.
> 
> Does this fix make sense?
> Testing does show no regressions, and the PR testcase ICE is fixed.

If original is the ultimate alias target then this is indeed correct.

The IPA PTA code asserts that all decls that are an alias of the ultimate
alias target X have the same DECL_PT_UID as X DECL_UID (or if the new 
alias doesn't have DECL_PT_UID set it will set it that way).

So I'd say it should be

  SET_DECL_PT_UID (alias->decl, DECL_UID (original->decl));

instead.

If IPA-ICF would merge

static const int x = 1;
static const int xa __attribute__((alias("x")));
static const int y = 1;
static const int ya __attribute__((alias("y")));

we'd initially have DECL_PT_UID (xa) be DECL_UID (x) and
DECL_PT_UID (ya) be DECL_UID (y).  Depending on how exactly IPA-ICF
performs the merging of x and y (and thus adjusts the existing aliases)
IPA-ICF needs to adjust DECL_PT_UID of all aliases of the new
"ultimate alias target".  I don't think the current code with the
proposed patch makes sure this will happen.

Thanks,
Richard.

> Thanks,
> Chung-Lin
> 
> 	PR fortran/72743
> 	* ipa-icf.c (sem_variable::merge): Remove guard condition for
> 	setting DECL_PT_UID (alias->decl).
> 
> 	testsuite/
> 	* gfortran.dg/goacc/pr72743.f90: New test.
> 
> 
> 

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