From f54133eaab45a20811d14e816ade220fe336a1cf Mon Sep 17 00:00:00 2001 From: Richard Earnshaw Date: Fri, 16 Jun 2017 21:07:03 +0000 Subject: [PATCH] [arm][doc] Document changes to -mcpu, -mtune and -mfpu. This patch adds the remainder of the main documentation changes. It adds the changes for -mcpu, -mtune and -mfpu. I've chosen to document the extension options under -mcpu rather than under -mtune because, while they are permitted with -mtune, they do not affect the behaviour of the tuning done by the compiler. I've also inverted the sense of the table (making the primary index the extension name and then listing the CPU names to which it applies. This is because the extensions are much more orthoganal in meaning here and having a primary entry via the CPU name would lead to enormous duplication. Finally, it adds the relevant changes to -mfpu. I haven't stated yet that any setting of -mfpu other than 'auto' is deprecated, but that is certainly the long-term goal of this patch series. * doc/invoke.texi (ARM Options, -mcpu): Document supported extension options. (ARM Options, -mtune): Document that this accepts the same extension options as -mcpu. (ARM Options, -mfpu): Document addition of -mfpu=auto. From-SVN: r249308 --- gcc/ChangeLog | 8 ++++++ gcc/doc/invoke.texi | 70 ++++++++++++++++++++++++++++++++++++++++----- 2 files changed, 71 insertions(+), 7 deletions(-) diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 38b28ab8d85..5b468a8b680 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,11 @@ +2017-06-16 Richard Earnshaw + + * doc/invoke.texi (ARM Options, -mcpu): Document supported + extension options. + (ARM Options, -mtune): Document that this accepts the same + extension options as -mcpu. + (ARM Options, -mfpu): Document addition of -mfpu=auto. + 2017-06-16 Richard Earnshaw * doc/invoke.texi (ARM Options, -march=): Document new syntax and diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 3567691cc32..86c8d62622d 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -15489,8 +15489,6 @@ Permissible names are: @samp{arm2}, @samp{arm250}, @samp{cortex-m0.small-multiply}, @samp{cortex-m0plus.small-multiply}, @samp{exynos-m1}, -@samp{falkor}, -@samp{qdf24xx}, @samp{marvell-pj4}, @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}, @samp{fa526}, @samp{fa626}, @@ -15510,12 +15508,15 @@ processors, balancing between optimizations that benefit some CPUs in the range, and avoiding performance pitfalls of other CPUs. The effects of this option may change in future GCC versions as CPU models come and go. +@option{-mtune} permits the same extension options as @option{-mcpu}, but +the extension options do not affect the tuning of the generated code. + @option{-mtune=native} causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect. -@item -mcpu=@var{name} +@item -mcpu=@var{name@r{[}+extension@dots{}@r{]}} @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 @@ -15524,9 +15525,62 @@ 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. +Many of the supported CPUs implement optional architectural +extensions. Where this is so the architectural extensions are +normally enabled by default. If implementations that lack the +extension exist, then the extension syntax can be used to disable +those extensions that have been omitted. For floating-point and +Advanced SIMD (Neon) instructions, the settings of the options +@option{-mfloat-abi} and @option{-mfpu} must also be considered: +floating-point and Advanced SIMD instructions will only be used if +@option{-mfloat-abi} is not set to @samp{soft}; and any setting of +@option{-mfpu} other than @samp{auto} will override the available +floating-point and SIMD extension instructions. + +For example, @samp{cortex-a9} can be found in three major +configurations: integer only, with just a floating-point unit or with +floating-point and Advanced SIMD. The default is to enable all the +instructions, but the extensions @samp{+nosimd} and @samp{+nofp} can +be used to disable just the SIMD or both the SIMD and floating-point +instructions respectively. + Permissible names for this option are the same as those for @option{-mtune}. +The following extension options are common to the listed CPUs: + +@table @samp +@item +nofp +Disables the floating-point instructions on @samp{arm9e}, +@samp{arm946e-s}, @samp{arm966e-s}, @samp{arm968e-s}, @samp{arm10e}, +@samp{arm1020e}, @samp{arm1022e}, @samp{arm926ej-s}, +@samp{arm1026ej-s}, @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-r8}, +@samp{cortex-m4}, @samp{cortex-m7} and @samp{cortex-m33}. +Disables the floating-point and SIMD instructions on +@samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7}, +@samp{cortex-a8}, @samp{cortex-a9}, @samp{cortex-a12}, +@samp{cortex-a15}, @samp{cortex-a17}, @samp{cortex-a15.cortex-a7}, +@samp{cortex-a17.cortex-a7}, @samp{cortex-a32}, @samp{cortex-a35} +and @samp{cortex-a53}. + +@item +nofp.dp +Disables the double-precision component of the floating-point instructions +on @samp{cortex-r5} and @samp{cortex-m7}. + +@item +nosimd +Disables the SIMD (but not floating-point) instructions on +@samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7} +and @samp{cortex-a9}. +@end table + +Additionally the @samp{generic-armv7-a} pseudo target defaults to +VFPv3 with 16 double-precision registers. It supports the following +extension options: @samp{vfpv3-d16}, @samp{vfpv3}, +@samp{vfpv3-d16-fp16}, @samp{vfpv3-fp16}, @samp{vfpv4-d16}, +@samp{vfpv4}, @samp{neon}, @samp{neon-vfpv3}, @samp{neon-fp16}, +@samp{neon-vfpv4}. The meanings are the same as for the extensions to +@option{-march=armv7-a}. + @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. @@ -15539,7 +15593,8 @@ is unsuccessful the option has no effect. @item -mfpu=@var{name} @opindex mfpu This specifies what floating-point hardware (or hardware emulation) is -available on the target. Permissible names are: @samp{vfpv2}, @samp{vfpv3}, +available on the target. Permissible names are: @samp{auto}, @samp{vfpv2}, +@samp{vfpv3}, @samp{vfpv3-fp16}, @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd}, @samp{vfpv3xd-fp16}, @samp{neon-vfpv3}, @samp{neon-fp16}, @samp{vfpv4}, @samp{vfpv4-d16}, @samp{fpv4-sp-d16}, @samp{neon-vfpv4}, @@ -15548,11 +15603,12 @@ available on the target. Permissible names are: @samp{vfpv2}, @samp{vfpv3}, Note that @samp{neon} is an alias for @samp{neon-vfpv3} and @samp{vfp} is an alias for @samp{vfpv2}. -If @option{-msoft-float} is specified this specifies the format of -floating-point values. +The setting @samp{auto} is the default and is special. It causes the +compiler to select the floating-point and Advanced SIMD instructions +based on the settings of @option{-mcpu} and @option{-march}. If the selected floating-point hardware includes the NEON extension -(e.g. @option{-mfpu}=@samp{neon}), note that floating-point +(e.g. @option{-mfpu=neon}), note that floating-point operations are not generated by GCC's auto-vectorization pass unless @option{-funsafe-math-optimizations} is also specified. This is because NEON hardware does not fully implement the IEEE 754 standard for -- 2.30.2