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extend.texi (scalar_storage_order type attribute): Document restriction on type punning and aliasing, and remove future tense. 

* doc/extend.texi (scalar_storage_order type attribute): Document
	restriction on type punning and aliasing, and remove future tense.

From-SVN: r232718
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Eric Botcazou 2016-01-22 09:25:58 +00:00 committed by Eric Botcazou
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commit e1cf192b12
2 changed files with 14 additions and 5 deletions
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@ -1,3 +1,8 @@
2016-01-22 Eric Botcazou <ebotcazou@adacore.com>
* doc/extend.texi (scalar_storage_order type attribute): Document
restriction on type punning and aliasing, and remove future tense.
2016-01-21 Roman Zhuykov <zhroma@ispras.ru>
PR target/69252

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gcc/doc/extend.texi
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@ -6496,22 +6496,26 @@ storage order with regard to the scalar storage order of the target:
@itemize
@item Taking the address of a scalar field of a @code{union} or a
@code{struct} with reverse scalar storage order is not permitted and will
yield an error.
@code{struct} with reverse scalar storage order is not permitted and yields
an error.
@item Taking the address of an array field, whose component is scalar, of
a @code{union} or a @code{struct} with reverse scalar storage order is
permitted but will yield a warning, unless @option{-Wno-scalar-storage-order}
permitted but yields a warning, unless @option{-Wno-scalar-storage-order}
is specified.
@item Taking the address of a @code{union} or a @code{struct} with reverse
scalar storage order is permitted.
@end itemize
These restrictions exist because the storage order attribute is lost when
the address of a scalar or the address of an array with scalar component
is taken, so storing indirectly through this address will generally not work.
the address of a scalar or the address of an array with scalar component is
taken, so storing indirectly through this address generally does not work.
The second case is nevertheless allowed to be able to perform a block copy
from or to the array.
Moreover, the use of type punning or aliasing to toggle the storage order
is not supported; that is to say, a given scalar object cannot be accessed
through distinct types that assign a different storage order to it.
@item transparent_union
@cindex @code{transparent_union} type attribute