On 16/11/2023 15:19, Tamar Christina wrote:
Hi All,
This documents the behavior of the generic CPU options on AArch64.
Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
Ok for master?
Thanks,
Tamar
gcc/ChangeLog:
* doc/invoke.texi (generic): Update defintion.
(generic-armv8-a, generic-armv9-a): Document.
--- inline copy of patch --
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index
d0b55fb106f908e8222394bbd07670aa583c5680..77684c5d7c9c0bdd587250acc190da81e0f7f032
100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -20759,7 +20759,8 @@ processors implementing the target architecture.
@item -mtune=@var{name}
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-a35}, @samp{cortex-a53}, @samp{cortex-a55},
+@samp{generic}, @samp{generic-armv8-a}, @samp{generic-armv9-a},
+@samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55},
@samp{cortex-a57}, @samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75},
@samp{cortex-a76}, @samp{cortex-a76ae}, @samp{cortex-a77},
@samp{cortex-a65}, @samp{cortex-a65ae}, @samp{cortex-a34},
@@ -20798,6 +20799,11 @@ arithmetic instructions per cycle (2 for 256-bit SVE,
4 for 128-bit SVE).
This is more general than tuning for a specific core like Neoverse V1
but is more specific than the default tuning described below.
+The value @samp{generic} should not be assumed to be a static configuration.
+Starting with GCC 14 this value can change over time in order to better reflect
+advancements in CPU microarchitecture. If a specific version is required you
are encouraged
+to use one of the architecture specific generic processors, e.g.
@samp{generic-armv8-a}.
+
Additionally on native AArch64 GNU/Linux systems the value
@samp{native} tunes performance to the host system. This option has no effect
if the compiler is unable to recognize the processor of the host system.
@opindex mcpu
@item -mcpu=@var{name}
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}.
^^^^^^^^^^^^^^^^^^^^
So what is the behaviour now if these are used for -mcpu? Do we really
want to permit their use here?
R.
