[Bug tree-optimization/54004] New: __atomic_always_lock_free has a fault implementation in which the target has no saying
hp at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Tue Jul 17 20:57:00 GMT 2012
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54004
Bug #: 54004
Summary: __atomic_always_lock_free has a fault implementation
in which the target has no saying
Classification: Unclassified
Product: gcc
Version: 4.8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: hp@gcc.gnu.org
Depends on: 54003
Created attachment 27819
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27819
Conceptual patch - note comments
Basically, fold_builtin_atomic_always_lock_free compares alignment of the type
of the atomic data to that of the normal alignment for a mode. A better
default is to compare to the *natural* alignment. For most targets, the two
are the same. If that's approach is not ok, then a target hook is needed.
Conceptual patch (i.e. untested, uncompiled) for the first approach attached.
Note that this suggestion is counter to the documented dogma of "presence of
library or atomic pattern implies lock-free-ness", but that already has
inconsistencies, see linked PR.
Note that this likely means we need a libgcc implementation for
__atomic_is_lock_free or at least document that the target needs to supply one.
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