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Re: [PATCH] Fix inconsistency with alias_sets_conflict_p and alias_set_subset_of

From: Paolo Bonzini <bonzini at gnu dot org>
To: Richard Guenther <rguenther at suse dot de>
Cc: Diego Novillo <dnovillo at google dot com>, gcc-patches at gcc dot gnu dot org
Date: Thu, 15 Apr 2010 15:49:31 +0200
Subject: Re: [PATCH] Fix inconsistency with alias_sets_conflict_p and alias_set_subset_of
References: <alpine.LNX.2.00.1004151318570.5522@zhemvz.fhfr.qr> <4BC705EE.7040403@google.com> <alpine.LNX.2.00.1004151430410.5522@zhemvz.fhfr.qr>

On 04/15/2010 02:38 PM, Richard Guenther wrote:

If alias set A has zero as subset, shouldn't it follow that A is
effectively alias set zero?  IOW, shouldn't alias set zero
propagate "upwards" as well?


Well, yes.  [...] The problem is that C character types use the magic
alias-set zero.  So we'd pessimize every structure containing a char
to effectively have disabled TBAA - the workaround was to have this
weird inversion.

Why should it apply to unions too, though? Unions with an alias-zero member should also get alias zero, period.

Paolo

Follow-Ups:
- Re: [PATCH] Fix inconsistency with alias_sets_conflict_p and alias_set_subset_of
  - From: Richard Guenther

References:
- [PATCH] Fix inconsistency with alias_sets_conflict_p and alias_set_subset_of
  - From: Richard Guenther
- Re: [PATCH] Fix inconsistency with alias_sets_conflict_p and alias_set_subset_of
  - From: Diego Novillo
- Re: [PATCH] Fix inconsistency with alias_sets_conflict_p and alias_set_subset_of
  - From: Richard Guenther

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