Hi,
I've tripped myself over with these three options too many times,
actually, their behaviour is very simple.
This patch clarifies the language used to describe the options, and
puts them in a logical order. I'm happy to reword again if this
is still not clear.
OK?
Thanks,
James
---
gcc/
2014-01-27 James Greenhalgh <james.greenha...@arm.com>
PR target/59718
* doc/invoke.texi (-march=): Clarify documentation for ARM.
(-mtune=): Likewise.
(-mcpu=): Likewise.
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 8c620a5..38a55a0 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -12221,11 +12221,35 @@ 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{armv8-a}, @samp{armv8-a+crc},
+@samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}.
+
+@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 +12283,6 @@ 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
@@ -12291,24 +12295,21 @@ 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{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 override this option. 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.
