[PATCH, GCC/ARM, 9/10] Call nscall function with blxns

[PATCH, GCC/ARM, 9/10] Call nscall function with blxns

This change to use BLXNS to call a nonsecure function from secure
directly (not using a libcall) is made in 2 steps:
- change nonsecure_call patterns to use blxns instead of calling
  __gnu_cmse_nonsecure_call
- loosen requirement for function address to allow any register when
  doing BLXNS.

The former is a straightforward check over whether instructions added in
Armv8.1-M Mainline are available while the latter consist in making the
nonsecure call pattern accept any register by using match_operand and
changing the nonsecure_call_internal expander to no force r4 when
targeting Armv8.1-M Mainline.

The tricky bit is actually in the test update, specifically how to check
that register lists for CLRM have all registers except for the one
holding parameters (already done) and the one holding the address used
by BLXNS. This is achieved with 3 scan-assembler directives.

1) The first one lists all registers that can appear in CLRM but make
   each of them optional.
   Property guaranteed: no wrong register is cleared and none appears
   twice in the register list.
2) The second directive check that the CLRM is made of a fixed number
   of the right registers to be cleared. The number used is the number
   of registers that could contain a secret minus one (used to hold the
   address of the function to call.
   Property guaranteed: register list has the right number of registers
   Cumulated property guaranteed: only registers with a potential secret
   are cleared and they are all listed but ont
3) The last directive checks that we cannot find a CLRM with a register
   in it that also appears in BLXNS. This is check via the use of a
   back-reference on any of the allowed register in CLRM, the
   back-reference enforcing that whatever register match in CLRM must be
   the same in the BLXNS.
   Property guaranteed: register used for BLXNS is different from
   registers cleared in CLRM.

Some more care needs to happen for the gcc.target/arm/cmse/cmse-1.c
testcase due to there being two CLRM generated. To ensure the third
directive match the right CLRM to the BLXNS, a negative lookahead is
used between the CLRM register list and the BLXNS. The way negative
lookahead work is by matching the *position* where a given regular
expression does not match. In this case, since it comes after the CLRM
register list it is requesting that what comes after the register list
does not have a CLRM again followed by BLXNS. This guarantees that the
.*blxns after only matches a blxns without another CLRM before.

*** gcc/ChangeLog ***

2020-01-16  Mihail-Calin Ionescu  <mihail.ionescu@arm.com>
2020-01-16  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* config/arm/arm.md (nonsecure_call_internal): Do not force memory
	address in r4 when targeting Armv8.1-M Mainline.
	(nonsecure_call_value_internal): Likewise.
	* config/arm/thumb2.md (nonsecure_call_reg_thumb2): Make memory address
	a register match_operand again.  Emit BLXNS when targeting
	Armv8.1-M Mainline.
	(nonsecure_call_value_reg_thumb2): Likewise.

*** gcc/testsuite/ChangeLog ***

2020-01-16  Mihail-Calin Ionescu  <mihail.ionescu@arm.com>
2020-01-16  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* gcc.target/arm/cmse/cmse-1.c: Add check for BLXNS when instructions
	introduced in Armv8.1-M Mainline Security Extensions are available and
	restrict checks for libcall to __gnu_cmse_nonsecure_call to Armv8-M
	targets only.  Adapt CLRM check to verify register used for BLXNS is
	not in the CLRM register list.
	* gcc.target/arm/cmse/cmse-14.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/bitfield-4.c: Likewise and adapt
	check for LSB clearing bit to be using the same register as BLXNS when
	targeting Armv8.1-M Mainline.
	* gcc.target/arm/cmse/mainline/8_1m/bitfield-5.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/bitfield-6.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/bitfield-7.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/bitfield-8.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/bitfield-9.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/bitfield-and-union.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/hard-sp/cmse-13.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/hard-sp/cmse-7.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/hard-sp/cmse-8.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/hard/cmse-13.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/hard/cmse-7.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/hard/cmse-8.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/soft/cmse-13.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/soft/cmse-7.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/soft/cmse-8.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/softfp-sp/cmse-7.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/softfp-sp/cmse-8.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/softfp/cmse-13.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/softfp/cmse-7.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/softfp/cmse-8.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/union-1.c: Likewise.
	* gcc.target/arm/cmse/mainline/8_1m/union-2.c: Likewise.
	* gcc.target/arm/cmse/cmse-15.c: Count BLXNS when targeting Armv8.1-M
	Mainline and restrict libcall count to Armv8-M.