Merge of the scalar-storage-order branch.

From-SVN: r229965

2 files changed, 79 insertions, 12 deletions

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 26afc00..08d4420 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -6395,6 +6395,42 @@ of the structure or union is placed to minimize the memory required.  When
 attached to an @code{enum} definition, it indicates that the smallest
 integral type should be used.
 
+@item scalar_storage_order ("@var{endianness}")
+@cindex @code{scalar_storage_order} type attribute
+When attached to a @code{union} or a @code{struct}, this attribute sets
+the storage order, aka endianness, of the scalar fields of the type, as
+well as the array fields whose component is scalar.  The supported
+endianness are @code{big-endian} and @code{little-endian}.  The attribute
+has no effects on fields which are themselves a @code{union}, a @code{struct}
+or an array whose component is a @code{union} or a @code{struct}, and it is
+possible to have fields with a different scalar storage order than the
+enclosing type.
+
+This attribute is supported only for targets that use a uniform default
+scalar storage order (fortunately, most of them), i.e. targets that store
+the scalars either all in big-endian or all in little-endian.
+
+Additional restrictions are enforced for types with the reverse scalar
+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.
+@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}
+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 second case is nevertheless allowed to be able to perform a block copy
+from or to the array.
+
 @item transparent_union
 @cindex @code{transparent_union} type attribute
 
@@ -18432,7 +18468,7 @@ for further explanation.
 * Darwin Pragmas::
 * Solaris Pragmas::
 * Symbol-Renaming Pragmas::
-* Structure-Packing Pragmas::
+* Structure-Layout Pragmas::
 * Weak Pragmas::
 * Diagnostic Pragmas::
 * Visibility Pragmas::
@@ -18708,8 +18744,8 @@ the name does not change.
 always the C-language name.
 @end enumerate
 
-@node Structure-Packing Pragmas
-@subsection Structure-Packing Pragmas
+@node Structure-Layout Pragmas
+@subsection Structure-Layout Pragmas
 
 For compatibility with Microsoft Windows compilers, GCC supports a
 set of @code{#pragma} directives that change the maximum alignment of
@@ -18732,17 +18768,30 @@ multiple @code{#pragma pack(@var{n})} instances and finalized by a single
 @code{#pragma pack(pop)}.
 @end enumerate
 
-Some targets, e.g.@: x86 and PowerPC, support the @code{ms_struct}
-@code{#pragma} which lays out a structure as the documented
-@code{__attribute__ ((ms_struct))}.
+Some targets, e.g.@: x86 and PowerPC, support the @code{#pragma ms_struct}
+directive which lays out structures and unions subsequently defined as the
+documented @code{__attribute__ ((ms_struct))}.
+
 @enumerate
-@item @code{#pragma ms_struct on} turns on the layout for structures
-declared.
-@item @code{#pragma ms_struct off} turns off the layout for structures
-declared.
+@item @code{#pragma ms_struct on} turns on the Microsoft layout.
+@item @code{#pragma ms_struct off} turns off the Microsoft layout.
 @item @code{#pragma ms_struct reset} goes back to the default layout.
 @end enumerate
 
+Most targets also support the @code{#pragma scalar_storage_order} directive
+which lays out structures and unions subsequently defined as the documented
+@code{__attribute__ ((scalar_storage_order))}.
+
+@enumerate
+@item @code{#pragma scalar_storage_order big-endian} sets the storage order
+of the scalar fields to big-endian.
+@item @code{#pragma scalar_storage_order little-endian} sets the storage order
+of the scalar fields to little-endian.
+@item @code{#pragma scalar_storage_order default} goes back to the endianness
+that was in effect when compilation started (see also command-line option
+@option{-fsso-struct=@var{endianness}} @pxref{C Dialect Options}).
+@end enumerate
+
 @node Weak Pragmas
 @subsection Weak Pragmas
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 2e5953b..dc9a4e7 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -169,10 +169,11 @@ in the following sections.
 -aux-info @var{filename} -fallow-parameterless-variadic-functions @gol
 -fno-asm  -fno-builtin  -fno-builtin-@var{function} @gol
 -fhosted  -ffreestanding -fopenacc -fopenmp -fopenmp-simd @gol
--fms-extensions -fplan9-extensions -trigraphs -traditional -traditional-cpp @gol
+-fms-extensions -fplan9-extensions -fsso-struct=@var{endianness}
 -fallow-single-precision  -fcond-mismatch -flax-vector-conversions @gol
 -fsigned-bitfields  -fsigned-char @gol
--funsigned-bitfields  -funsigned-char}
+-funsigned-bitfields  -funsigned-char @gol
+-trigraphs -traditional -traditional-cpp}
 
 @item C++ Language Options
 @xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
@@ -278,6 +279,7 @@ Objective-C and Objective-C++ Dialects}.
 -Wshift-overflow -Wshift-overflow=@var{n} @gol
 -Wshift-count-negative -Wshift-count-overflow -Wshift-negative-value @gol
 -Wsign-compare  -Wsign-conversion -Wfloat-conversion @gol
+-Wno-scalar-storage-order @gol
 -Wsizeof-pointer-memaccess  -Wsizeof-array-argument @gol
 -Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol
 -Wstrict-aliasing=n @gol -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
@@ -2076,6 +2078,17 @@ These options control whether a bit-field is signed or unsigned, when the
 declaration does not use either @code{signed} or @code{unsigned}.  By
 default, such a bit-field is signed, because this is consistent: the
 basic integer types such as @code{int} are signed types.
+
+@item -fsso-struct=@var{endianness}
+@opindex fsso-struct
+Set the default scalar storage order of structures and unions to the
+specified endianness.  The accepted values are @samp{big-endian} and
+@samp{little-endian}.  If the option is not passed, the compiler uses
+the native endianness of the target.  This option is not supported for C++.
+
+@strong{Warning:} the @option{-fsso-struct} switch causes GCC to generate
+code that is not binary compatible with code generated without it if the
+specified endianness is not the native endianness of the target.
 @end table
 
 @node C++ Dialect Options
@@ -5113,6 +5126,11 @@ This includes conversions from real to integer, and from higher precision
 real to lower precision real values.  This option is also enabled by
 @option{-Wconversion}.
 
+@item -Wno-scalar-storage-order
+@opindex -Wno-scalar-storage-order
+@opindex -Wscalar-storage-order
+Do not warn on suspicious constructs involving reverse scalar storage order.
+
 @item -Wsized-deallocation @r{(C++ and Objective-C++ only)}
 @opindex Wsized-deallocation
 @opindex Wno-sized-deallocation