Re: [AArch64] Rework ARMv8.1 command line options.

[Matthew Wahab <matthew dot wahab at foss dot arm dot com>]

On 24/11/15 15:22, James Greenhalgh wrote:
> On Mon, Nov 16, 2015 at 04:31:32PM +0000, Matthew Wahab wrote:
>>
>> The command line options for target selection allow ARMv8.1 extensions
>> to be individually enabled/disabled. They also allow the extensions to
>> be enabled with -march=armv8-a. This doesn't reflect the ARMv8.1
>> architecture which requires all extensions to be enabled and doesn't make
>> them available for ARMv8.
>>
>> This patch removes the options for the individual ARMv8.1 extensions
>> except for +lse. This means that setting -march=armv8.1-a will enable
>> all extensions required by ARMv8.1 and that the ARMv8.1 extensions can't
>> be used with -march=armv8.

> I think I mentioned it in another review, but this patch seems a good place
> to solve the problem. Could you please update the documentation to explain
> what you've written above. As it stands I find myself confused by which
> features GCC will make available at -march=armv8-a and -march=armv8.1-a.

Attached is a patch with the documentation for the AArch64 -march option
reworked to try to make it clearer what the -march=armv8.1-a option will
do. Extensions with feature modifiers (+crc, +lse) are explicitly stated
as being enabled by -march=armv8.1-a. Extensions without feature
modifiers (RDMA, PAN, LOR) are treated as part of the generic 'ARMv8.1
architecture extension' term in the description of -march=armv8.1-a.

I've also rearranged the -march section, to put the description of the
values for -march together and reworded the description of the
-march=native option.

Matthew

2015-11-26  Matthew Wahab  <matthew.wahab@arm.com>

	* config/aarch64/aarch64-options-extensions.def: Remove
	AARCH64_FL_RDMA from "fp" and "simd".  Remove "pan", "lor",
	"rdma".
	* config/aarch64/aarch64.h (AARCH64_FL_PAN): Remove.
	(AARCH64_FL_LOR): Remove.
	(AARCH64_FL_RDMA): Remove.
	(AARCH64_FL_V8_1): New.
	(AARCH64_FL_FOR_AARCH8_1): Replace AARCH64_FL_PAN, AARCH64_FL_LOR
	and AARCH64_FL_RDMA with AARCH64_FL_V8_1.
	(AARCH64_ISA_RDMA): Replace AARCH64_FL_RDMA with AARCH64_FL_V8_1.
	* doc/invoke.texi (AArch64 -march): Rewrite initial paragraph and
	section on -march=native.  Group descriptions of permitted
	architecture names together.  Expand description of
	-march=armv8.1-a.
	(AArch64 -mtune): Slightly rework section on -march=native.
	(AArch64 -mcpu): Slightly rework section on -march=native.
	(AArch64 Feature Modifiers): Remove "pan", "lor" and "rdma".
	State that -march=armv8.1-a enables "crc" and "lse".

diff --git a/gcc/config/aarch64/aarch64-option-extensions.def b/gcc/config/aarch64/aarch64-option-extensions.def
index b261a0f7c3c6f5264fe4f95c85a59535aa951ce4..4f1d53515a9a4ff8920fadb13164c85e39990db5 100644
--- a/gcc/config/aarch64/aarch64-option-extensions.def
+++ b/gcc/config/aarch64/aarch64-option-extensions.def
@@ -34,11 +34,10 @@
    should contain a whitespace-separated list of the strings in 'Features'
    that are required.  Their order is not important.  */
 
-AARCH64_OPT_EXTENSION("fp",	AARCH64_FL_FP,                          AARCH64_FL_FPSIMD | AARCH64_FL_CRYPTO | AARCH64_FL_RDMA, "fp")
-AARCH64_OPT_EXTENSION("simd",	AARCH64_FL_FPSIMD,                      AARCH64_FL_SIMD | AARCH64_FL_CRYPTO | AARCH64_FL_RDMA,   "asimd")
+AARCH64_OPT_EXTENSION ("fp", AARCH64_FL_FP,
+		       AARCH64_FL_FPSIMD | AARCH64_FL_CRYPTO, "fp")
+AARCH64_OPT_EXTENSION ("simd", AARCH64_FL_FPSIMD,
+		       AARCH64_FL_SIMD | AARCH64_FL_CRYPTO, "asimd")
 AARCH64_OPT_EXTENSION("crypto",	AARCH64_FL_CRYPTO | AARCH64_FL_FPSIMD,  AARCH64_FL_CRYPTO,   "aes pmull sha1 sha2")
 AARCH64_OPT_EXTENSION("crc",	AARCH64_FL_CRC,                         AARCH64_FL_CRC,                        "crc32")
 AARCH64_OPT_EXTENSION("lse",	AARCH64_FL_LSE,                         AARCH64_FL_LSE,                        "lse")
-AARCH64_OPT_EXTENSION("pan",	AARCH64_FL_PAN,		AARCH64_FL_PAN,		"pan")
-AARCH64_OPT_EXTENSION("lor",	AARCH64_FL_LOR,		AARCH64_FL_LOR,		"lor")
-AARCH64_OPT_EXTENSION("rdma",	AARCH64_FL_RDMA | AARCH64_FL_FPSIMD,	AARCH64_FL_RDMA,	"rdma")
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 68c006fa91f6326140cf447c7f4578ac46c24f79..06345f0215ea190b7b089264a0039a201437ecec 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -134,9 +134,7 @@ extern unsigned aarch64_architecture_version;
 #define AARCH64_FL_CRC        (1 << 3)	/* Has CRC.  */
 /* ARMv8.1 architecture extensions.  */
 #define AARCH64_FL_LSE	      (1 << 4)  /* Has Large System Extensions.  */
-#define AARCH64_FL_PAN	      (1 << 5)  /* Has Privileged Access Never.  */
-#define AARCH64_FL_LOR	      (1 << 6)  /* Has Limited Ordering regions.  */
-#define AARCH64_FL_RDMA	      (1 << 7)  /* Has ARMv8.1 Adv.SIMD.  */
+#define AARCH64_FL_V8_1	      (1 << 5)  /* Has ARMv8.1 extensions.  */
 
 /* Has FP and SIMD.  */
 #define AARCH64_FL_FPSIMD     (AARCH64_FL_FP | AARCH64_FL_SIMD)
@@ -147,8 +145,7 @@ extern unsigned aarch64_architecture_version;
 /* Architecture flags that effect instruction selection.  */
 #define AARCH64_FL_FOR_ARCH8       (AARCH64_FL_FPSIMD)
 #define AARCH64_FL_FOR_ARCH8_1			       \
-  (AARCH64_FL_FOR_ARCH8 | AARCH64_FL_LSE | AARCH64_FL_PAN \
-   | AARCH64_FL_LOR | AARCH64_FL_RDMA)
+  (AARCH64_FL_FOR_ARCH8 | AARCH64_FL_LSE | AARCH64_FL_V8_1)
 
 /* Macros to test ISA flags.  */
 
@@ -157,7 +154,7 @@ extern unsigned aarch64_architecture_version;
 #define AARCH64_ISA_FP             (aarch64_isa_flags & AARCH64_FL_FP)
 #define AARCH64_ISA_SIMD           (aarch64_isa_flags & AARCH64_FL_SIMD)
 #define AARCH64_ISA_LSE		   (aarch64_isa_flags & AARCH64_FL_LSE)
-#define AARCH64_ISA_RDMA	   (aarch64_isa_flags & AARCH64_FL_RDMA)
+#define AARCH64_ISA_RDMA	   (aarch64_isa_flags & AARCH64_FL_V8_1)
 
 /* Crypto is an optional extension to AdvSIMD.  */
 #define TARGET_CRYPTO (TARGET_SIMD && AARCH64_ISA_CRYPTO)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index f8e8e5d477b08015445aa245acc00ae079e1eb9b..4332f42c4445e0d4c7455551aa4fa91e5cd2b73d 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -12566,23 +12566,27 @@ Which in turn depends on the target processor.
 
 @item -march=@var{name}
 @opindex march
-Specify the name of the target architecture, optionally suffixed by one or
+Specify the name of the target architecture and, optionally, one or
 more feature modifiers.  This option has the form
 @option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}.
 
-The permissible values for @var{arch} are @samp{armv8-a} or
-@samp{armv8.1-a}.
+The permissible values for @var{arch} are @samp{armv8-a},
+@samp{armv8.1-a} or @var{native}.
 
-For the permissible values for @var{feature}, see the sub-section on
-@ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu}
+The value @samp{armv8.1-a} implies @samp{armv8-a} and enables compiler
+support for the ARMv8.1 architecture extension.  In particular, it
+enables the @samp{+crc} and @samp{+lse} features.
+
+The value @samp{native} is available on native AArch64 GNU/Linux and
+causes the compiler to pick the architecture of the host system.  This
+option has no effect if the compiler is unable to recognize the
+architecture of the host system,
+
+The permissible values for @var{feature} are listed in the sub-section
+on @ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu}
 Feature Modifiers}.  Where conflicting feature modifiers are
 specified, the right-most feature is used.
 
-Additionally on native AArch64 GNU/Linux systems the value
-@samp{native} is available.  This option causes the compiler to pick the
-architecture of the host system.  If the compiler is unable to recognize the
-architecture of the host system this option has no effect.
-
 GCC uses @var{name} to determine what kind of instructions it can emit
 when generating assembly code.  If @option{-march} is specified
 without either of @option{-mtune} or @option{-mcpu} also being
@@ -12604,8 +12608,8 @@ option are: @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}.
 Additionally on native AArch64 GNU/Linux systems the value
 @samp{native} is available.  This option causes the compiler to pick
 the architecture of and tune the performance of the code for the
-processor of the host system.  If the compiler is unable to recognize
-the processor of the host system this option has no effect.
+processor of the host system.  This option has no effect if the
+compiler is unable to recognize the architecture of the host system.
 
 Where none of @option{-mtune=}, @option{-mcpu=} or @option{-march=}
 are specified, the code is tuned to perform well across a range
@@ -12627,9 +12631,9 @@ specified, the right-most feature is used.
 
 Additionally on native AArch64 GNU/Linux systems the value
 @samp{native} is available.  This option causes the compiler to tune
-the performance of the code for the processor of the host system.  If
-the compiler is unable to recognize the processor of the host system
-this option has no effect.
+the performance of the code for the processor of the host system.
+This option has no effect if the compiler is unable to recognize the
+architecture of the host system.
 
 GCC uses @var{name} to determine what kind of instructions it can emit when
 generating assembly code (as if by @option{-march}) and to determine
@@ -12665,7 +12669,8 @@ the following and their inverses @option{no@var{feature}}:
 
 @table @samp
 @item crc
-Enable CRC extension.
+Enable CRC extension.  This is on by default for
+@option{-march=armv8.1-a}.
 @item crypto
 Enable Crypto extension.  This also enables Advanced SIMD and floating-point
 instructions.
@@ -12677,14 +12682,8 @@ Enable Advanced SIMD instructions.  This also enables floating-point
 instructions.  This is on by default for all possible values for options
 @option{-march} and @option{-mcpu}.
 @item lse
-Enable Large System Extension instructions.
-@item pan
-Enable Privileged Access Never support.
-@item lor
-Enable Limited Ordering Regions support.
-@item rdma
-Enable ARMv8.1 Advanced SIMD instructions.  This implies Advanced SIMD
-is enabled.
+Enable Large System Extension instructions.  This is on by default for
+@option{-march=armv8.1-a}.
 
 @end table