Re: [patch] Fix PR fortran/72743

[Chung-Lin Tang <chunglin_tang at mentor dot com>]

On 2016/9/1 03:13 PM, Richard Biener wrote:
> 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.

How about this fix? The code now sets all DECLs reachable through referring
IPA_REF_ALIAS references. I am not sure of the possibility of cycles,
though it appears there's other code catching alias cycles, issuing an error
to the user.

Again tested without regressions.

Thanks,
Chung-Lin

	* ipa-icf.c (set_alias_uids): New function.
	(sem_variable::merge): Use set_alias_uids to set DECL_PT_UID of
	all the merged variable's referring aliases.

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