[Patch][Aarch64] Implement Aarch64 SIMD ABI and aarch64_vector_pcs attribute

[Steve Ellcey]

Here is a new version of my patch to support the Aarch64 SIMD ABI [1]
in GCC. Â I think this is complete enought to be considered for check
in.  I wrote a few new tests and put them in a new gcc.target/torture
directory so they would be run with multiple optimization options.  I
also verified that there are no regressions in the GCC testsuite.

The significant difference between the standard ARM ABI and the SIMD
ABI is that in the normal ABI a callee saves only the lower 64 bits of 
registers V8-V15, in the SIMD ABI the callee must save all 128 bits of
registers V8-V23.

As I mentioned in my RFC, I intend to (eventually) follow this patch
with two more, one to define the TARGET_SIMD_CLONE* macros and one to
improve the GCC register allocation/usage when calling SIMD
functions.  Right now, a caller calling a SIMD function will save more
registers than it needs to because some of those registers will also be
saved by the callee.

Steve Ellcey
sellcey@cavium.com

[1] https://developer.arm.com/products/software-development-tools/hpc/a
rm-compiler-for-hpc/vector-function-abi

Compiler ChangeLog:

2018-07-31  Steve Ellcey  <sellcey@cavium.com>

	* config/aarch64/aarch64-protos.h (aarch64_use_simple_return_insn_p):
	New prototype.
	(aarch64_epilogue_uses): Ditto.
	* config/aarch64/aarch64.c (aarch64_attribute_table): New array.
	(aarch64_simd_decl_p): New function.
	(aarch64_reg_save_mode): New function.
	(aarch64_is_simd_call_p): New function.
	(aarch64_function_ok_for_sibcall): Check for simd calls.
	(aarch64_layout_frame): Check for simd function.
	(aarch64_gen_storewb_pair): Handle E_TFmode.
	(aarch64_push_regs): Use aarch64_reg_save_mode to get mode.
	(aarch64_gen_loadwb_pair): Handle E_TFmode.
	(aarch64_pop_regs): Use aarch64_reg_save_mode to get mode.
	(aarch64_gen_store_pair): Handle E_TFmode.
	(aarch64_gen_load_pair): Ditto.
	(aarch64_save_callee_saves): Handle different mode sizes.
	(aarch64_restore_callee_saves): Ditto.
	(aarch64_components_for_bb): Check for simd function.
	(aarch64_epilogue_uses): New function.
	(aarch64_process_components): Ditto.
	(aarch64_expand_prologue): Ditto.
	(aarch64_expand_epilogue): Ditto.
	(aarch64_expand_call): Ditto.
	(TARGET_ATTRIBUTE_TABLE): New define.
	* config/aarch64/aarch64.h (EPILOGUE_USES): Redefine.
	(FP_SIMD_SAVED_REGNUM_P): New macro.
	* config/aarch64/aarch64.md (V23_REGNUM) New constant.
	(simple_return): New define_expand.
	(load_pair_dw_tftf): New instruction.
	(store_pair_dw_tftf): Ditto.
	(loadwb_pair<TX:mode>_<P:mode>): Ditto.
	("storewb_pair<TX:mode>_<P:mode>): Ditto.

Testsuite ChangeLog:

2018-07-31  Steve Ellcey  <sellcey@cavium.com>

	* gcc.target/aarch64/torture/aarch64-torture.exp: New file.
	* gcc.target/aarch64/torture/simd-abi-1.c: New test.
	* gcc.target/aarch64/torture/simd-abi-2.c: Ditto.
	* gcc.target/aarch64/torture/simd-abi-3.c: Ditto.
	* gcc.target/aarch64/torture/simd-abi-4.c: Ditto.
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