Hi all,

This is one of the main patches in the series.
The backend compilation state can be described by the options in aarch64.opt marked as Save.
This causes the options-save.c machinery to save and restore them when asked them and the
TARGET_OPTION_SAVE and TARGET_OPTION_RESTORE should handle all the extra stuff that's required
to reinitialise the backend.

This patch marks the options that we want to support for SWITCHABLE_TARGET as Save and adds 3
extra variables: explicit_tune_core, explicit_arch and x_aarch64_isa_flags.
These 3 variables are used to store the explicit core to tune for (as specified by -mcpu or -mtune),
the explicitly specified architecture (as specified by -mcpu or -march) and the architecture
features (as specified by the extension string to -march,-mcpu or derived from them).

The aarch64_isa_flags definition is moved from aarch64.c into aarch64.opt and marked as a TargetVariable.
This means that the auto-generated machinery in options-save.c will automatically save and restore it for us.

The patch defines the TARGET_OPTION_RESTORE hook to extract the selected_tune and selected_arch from the
explicit_tune_core and explicit_arch variables and restore the backend compilation state using the
aarch64_override_options_internal machinery that we refactored earlier.

A TARGET_OPTION_PRINT implementation is added to print out the explicit_arch and explicit_tune_core options,
as well as aarch64_isa_flags.

As preparation for SWITCHABLE_TARGETS this patch also changes the output assembly format a bit.
Since we want to potentially handle multiple values of aarch64_isa_flags within a file in the future, we don't
want to just print out a global .arch or .cpu directive in the beginning of the assembly file.
Instead, we want to print out the .arch directive on a per-function basis. This is accomplished by
defining the ASM_DECLARE_FUNCTION_NAME hook and printing out selected_arch and aarch64_isa_flags there.
As an added bonus we can print out the tuning name in the comments and since we added a proper ident
field to the processor struct that we store in explicit_tune_core, we can print out the full tune name
in an assembly comment.

For example, compiling with -mcpu=cortex-a57.cortex-a53 we now get:

         .file   "sha1_1.c"
         .text
         .align  2
         .p2align 4,,15
         .global foo
         .arch armv8-a+fp+simd+crc
         //.tune cortex-a57.cortex-a53
         .type   foo, %function
foo:
         add     w0, w0, 5
         ret
         .size   foo, .-foo
         .ident  "GCC: (unknown) 6.0.0 20150522 (experimental)"

instead of:
         .cpu cortex-a57+fp+simd+crc
         .file   "sha1_1.c"
         .text
         .align  2
         .p2align 4,,15
         .global foo
         .type   foo, %function
foo:
         add     w0, w0, 5
         ret
         .size   foo, .-foo
         .ident  "GCC: (fsf-trunk.670) 6.0.0 20150416 (experimental)"

Consequently, TARGET_ASM_FILE_START is deleted.


Bootstrapped and tested on aarch64.
Ok for trunk?

Thanks,
Kyrill

2015-07-16  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     * config/aarch64/aarch64.opt (explicit_tune_core): New TargetVariable.
     (explicit_arch): Likewise.
     (x_aarch64_isa_flags): Likewise.
     (mgeneral-regs-only): Mark as Save.
     (mfix-cortex-a53-835769): Likewise.
     (mcmodel=): Likewise.
     (mstrict-align): Likewise.
     (momit-leaf-frame-pointer): Likewise.
     (mtls-dialect): Likewise.
     (master=): Likewise.
     * config/aarch64/aarch64.h (ASM_DECLARE_FUNCTION_NAME): Define.
     (aarch64_isa_flags): Remove extern declaration.
     * config/aarch64/aarch64.c (aarch64_validate_mcpu): Return a bool
     to indicate success or failure.
     (aarch64_validate_march): Likewise.
     (aarch64_validate_mtune): Likewise.
     (aarch64_isa_flags): Delete.
     (aarch64_override_options_internal): Access opts->x_aarch64_isa_flags
     instead of aarch64_isa_flags.
     (aarch64_get_tune_cpu): New function.
     (aarch64_get_arch): Likewise.
     (aarch64_override_options): Use above and set up explicit_tune_core
     and explicit_arch.
     (aarch64_print_extension): Move earlier in file.  Add isa_flags
     argument and use that instead of the global aarch64_isa_flags.
     (aarch64_option_restore): Likewise.
     (aarch64_option_print): Likewise.
     (aarch64_declare_function_name): Likewise.
     (aarch64_start_file): Delete.
     (TARGET_ASM_FILE_START): Do not define.
     (TARGET_OPTION_RESTORE, TARGET_OPTION_PRINT): Define.
     * config/aarch64/aarch64-protos.h (aarch64_declare_function_name):
     Declare prototype.