[ARM Documentation] Clarify -mcpu, -mtune, -march

gcc/

	PR target/59718
	* doc/invoke.texi (-march=): Clarify documentation for ARM.
	(-mtune=): Likewise.
	(-mcpu=): Likewise.

From-SVN: r207501

gcc/ChangeLog

+2014-02-05  James Greenhalgh  <james.greenhalgh@arm.com>
+
+	PR target/59718
+	* doc/invoke.texi (-march): Clarify documentation for ARM.
+	(-mtune): Likewise.
+	(-mcpu): Likewise.
+
 2014-02-05  Richard Biener  <rguenther@suse.de>
 
 	* tree-vect-loop.c (vect_analyze_loop_2): Be more informative

gcc/doc/invoke.texi

@@ -12221,11 +12221,38 @@ option should only be used if you require compatibility with code for
 big-endian ARM processors generated by versions of the compiler prior to
 2.8.  This option is now deprecated.
 
-@item -mcpu=@var{name}
-@opindex mcpu
-This specifies the name of the target ARM processor.  GCC uses this name
-to determine what kind of instructions it can emit when generating
-assembly code.  Permissible names are: @samp{arm2}, @samp{arm250},
+@item -march=@var{name}
+@opindex march
+This specifies the name of the target ARM architecture.  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.  Permissible names are: @samp{armv2},
+@samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
+@samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te},
+@samp{armv6}, @samp{armv6j},
+@samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
+@samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m}, @samp{armv7ve},
+@samp{armv8-a}, @samp{armv8-a+crc},
+@samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
+
+@option{-march=armv7ve} is the armv7-a architecture with virtualization
+extensions.
+
+@option{-march=armv8-a+crc} enables code generation for the ARMv8-A
+architecture together with the optional CRC32 extensions.
+
+@option{-march=native} causes the compiler to auto-detect the architecture
+of the build computer.  At present, this feature is only supported on
+Linux, and not all architectures are recognized.  If the auto-detect is
+unsuccessful the option has no effect.
+
+@item -mtune=@var{name}
+@opindex mtune
+This option specifies the name of the target ARM processor for
+which GCC should tune the performance of the code.
+For some ARM implementations better performance can be obtained by using
+this option.
+Permissible names are: @samp{arm2}, @samp{arm250},
 @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
 @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
 @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
@@ -12259,26 +12286,6 @@ Additionally, this option can specify that GCC should tune the performance
 of the code for a big.LITTLE system.  Permissible names are:
 @samp{cortex-a15.cortex-a7}, @samp{cortex-a57.cortex-a53}.
 
-@option{-mcpu=generic-@var{arch}} is also permissible, and is
-equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}.
-See @option{-mtune} for more information.
-
-@option{-mcpu=native} causes the compiler to auto-detect the CPU
-of the build computer.  At present, this feature is only supported on
-Linux, and not all architectures are recognized.  If the auto-detect is
-unsuccessful the option has no effect.
-
-@item -mtune=@var{name}
-@opindex mtune
-This option is very similar to the @option{-mcpu=} option, except that
-instead of specifying the actual target processor type, and hence
-restricting which instructions can be used, it specifies that GCC should
-tune the performance of the code as if the target were of the type
-specified in this option, but still choosing the instructions it
-generates based on the CPU specified by a @option{-mcpu=} option.
-For some ARM implementations better performance can be obtained by using
-this option.
-
 @option{-mtune=generic-@var{arch}} specifies that GCC should tune the
 performance for a blend of processors within architecture @var{arch}.
 The aim is to generate code that run well on the current most popular
@@ -12291,27 +12298,23 @@ of the build computer.  At present, this feature is only supported on
 Linux, and not all architectures are recognized.  If the auto-detect is
 unsuccessful the option has no effect.
 
-@item -march=@var{name}
-@opindex march
-This specifies the name of the target ARM architecture.  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.  Permissible names are: @samp{armv2},
-@samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
-@samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te},
-@samp{armv6}, @samp{armv6j},
-@samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m},
-@samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m}, @samp{armv7ve},
-@samp{armv8-a}, @samp{armv8-a+crc},
-@samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
+@item -mcpu=@var{name}
+@opindex mcpu
+This specifies the name of the target ARM processor.  GCC uses this name
+to derive the name of the target ARM architecture (as if specified
+by @option{-march}) and the ARM processor type for which to tune for
+performance (as if specified 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.
 
-@option{-march=armv7ve} is the armv7-a architecture with virtualization
-extensions.
+Permissible names for this option are the same as those for
+@option{-mtune}.
 
-@option{-march=armv8-a+crc} enables code generation for the ARMv8-A
-architecture together with the optional CRC32 extensions.
+@option{-mcpu=generic-@var{arch}} is also permissible, and is
+equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}.
+See @option{-mtune} for more information.
 
-@option{-march=native} causes the compiler to auto-detect the architecture
+@option{-mcpu=native} causes the compiler to auto-detect the CPU
 of the build computer.  At present, this feature is only supported on
 Linux, and not all architectures are recognized.  If the auto-detect is
 unsuccessful the option has no effect.