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[AArch64 Documentation] Clarify meaning of -mcpu, -mtune, -march

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gcc/

	* doc/invoke.texi (-march): Clarify documentation for AArch64.
	(-mtune): Likewise.
	(-mcpu): Likewise.

From-SVN: r206840
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James Greenhalgh 2014-01-20 15:57:50 +00:00 • committed by James Greenhalgh
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gcc/ChangeLog
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@ -1,3 +1,9 @@
2014-01-20 James Greenhalgh <james.greenhalgh@arm.com>
* doc/invoke.texi (-march): Clarify documentation for AArch64.
(-mtune): Likewise.
(-mcpu): Likewise.
2014-01-20 Tejas Belagod <tejas.belagod@arm.com>
* config/aarch64/aarch64-protos.h

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gcc/doc/invoke.texi
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@ -11379,27 +11379,8 @@ of TLS variables.
Specify the name of the target architecture, optionally suffixed by one or
more feature modifiers. This option has the form
@option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the
only value for @var{arch} is @samp{armv8-a}. The possible values for
@var{feature} are documented in the sub-section below.
Where conflicting feature modifiers are specified, the right-most feature is
used.
GCC uses this name to determine what kind of instructions it can emit when
generating assembly code. This option can be used in conjunction with or
instead of the @option{-mcpu=} option.
@item -mcpu=@var{name}
@opindex mcpu
Specify the name of the target processor, optionally suffixed by one or more
feature modifiers. This option has the form
@option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the
possible values for @var{cpu} are @samp{generic}, @samp{cortex-a53},
@samp{cortex-a57}. The possible values for @var{feature} are documented
in the sub-section below.
Additionally, this option can specify that the target is a big.LITTLE system.
The only possible value is @samp{cortex-a57.cortex-a53}.
only permissible value for @var{arch} is @samp{armv8-a}. The permissible
values for @var{feature} are documented in the sub-section below.
Where conflicting feature modifiers are specified, the right-most feature is
used.
@ -11407,18 +11388,47 @@ used.
GCC uses this name to determine what kind of instructions it can emit when
generating assembly code.
Where @option{-march} is specified without either of @option{-mtune}
or @option{-mcpu} also being specified, the code will be tuned to perform
well across a range of target processors implementing the target
architecture.
@item -mtune=@var{name}
@opindex mtune
Specify the name of the processor to tune the performance for. The code will
be tuned as if the target processor were of the type specified in this option,
but still using instructions compatible with the target processor specified
by a @option{-mcpu=} option. Where no @option{-mtune=} option is
specified, the code will be tuned to perform well on the target processor
given by @option{-mcpu=} or @option{-march=}. Where none of
@option{-mtune=}, @option{-mcpu=} or @option{-march=} are specified,
the code will be tuned to perform well across a range of target
processors. This option cannot be suffixed by feature modifiers.
Specify the name of the target processor for which GCC should tune the
performance of the code. Permissible values for this option are:
@samp{generic}, @samp{cortex-a53}, @samp{cortex-a57}.
Additionally, this option can specify that GCC should tune the performance
of the code for a big.LITTLE system. The only permissible value is
@samp{cortex-a57.cortex-a53}.
Where none of @option{-mtune=}, @option{-mcpu=} or @option{-march=}
are specified, the code will be tuned to perform well across a range
of target processors.
This option cannot be suffixed by feature modifiers.
@item -mcpu=@var{name}
@opindex mcpu
Specify the name of the target processor, optionally suffixed by one or more
feature modifiers. This option has the form
@option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the
permissible values for @var{cpu} are the same as those available for
@option{-mtune}.
The permissible values for @var{feature} are documented in the sub-section
below.
Where conflicting feature modifiers are specified, the right-most feature is
used.
GCC uses this name to determine what kind of instructions it can emit when
generating assembly code (as if by @option{-march}) and to determine
the target processor for which to tune for performance (as if
by @option{-mtune}). Where this option is used in conjunction
with @option{-march} or @option{-mtune}, those options take precedence
over the appropriate part of this option.
@end table
@subsubsection @option{-march} and @option{-mcpu} feature modifiers