Hi

This patch is part of a series that enables ARMv8.5-A in GCC and
adds Branch Target Identification Mechanism.
(https://developer.arm.com/products/architecture/cpu-architecture/a-profile/exploration-tools)

This patch adds a new pass called "bti" which is triggered by the
command line argument -mbranch-protection whenever "bti" is turned on.

The pass iterates through the instructions and adds appropriated BTI 
instructions based on the following:
    * Add a new "BTI C" at the beginning of a function, unless its already
      protected by a "PACIASP/PACIBSP". We exempt the functions that are
      only called directly.
    * Add a new "BTI J" for every target of an indirect jump, jump table
      targets, non-local goto targets or labels that might be referenced
      by variables, constant pools, etc (NOTE_INSN_DELETED_LABEL)

Since we have already changed the use of indirect tail calls to only x16 
and x17, we do not have to use "BTI JC".
(check patch 3/6).

Bootstrapped and regression tested with aarch64-none-linux-gnu. Added 
new tests.
Is this ok for trunk?

Thanks
Sudi

*** gcc/ChangeLog ***

2018-xx-xx  Sudakshina Das  <sudi.das@arm.com>
	    Ramana Radhakrishnan  <ramana.radhakrishnan@arm.com>

	* config.gcc (aarch64*-*-*): Add aarch64-bti-insert.o.
	* gcc/config/aarch64/aarch64.h: Update comment for
	TRAMPOLINE_SIZE.
	* config/aarch64/aarch64.c (aarch64_asm_trampoline_template):
	Update if bti is enabled.
	* config/aarch64/aarch64-bti-insert.c: New file.
	* config/aarch64/aarch64-passes.def (INSERT_PASS_BEFORE): Insert
	bti pass.
	* config/aarch64/aarch64-protos.h (make_pass_insert_bti):
	Declare the new bti pass.
	* config/aarch64/aarch64.md (bti_nop): Define.
	* config/aarch64/t-aarch64: Add rule for aarch64-bti-insert.o.

*** gcc/testsuite/ChangeLog ***

2018-xx-xx  Sudakshina Das  <sudi.das@arm.com>

	* gcc.target/aarch64/bti-1.c: New test.
	* gcc.target/aarch64/bti-2.c: New test.
	* lib/target-supports.exp
	(check_effective_target_aarch64_bti_hw): Add new check for
	BTI hw.