aarch64: unexpected result with -mgeneral-regs-only and sve [PR94678]

aarch64: unexpected result with -mgeneral-regs-only and sve [PR94678]

As the two testcases for PR94678 show, -mgeneral-regs-only is handled
properly with SVE.  We should issue an error message instead of expanding
SVE builtin funtions when -mgeneral-regs-only option is specified.

The middle end should never try to use vector patterns when the vector
modes have been disabled by !have_regs_of_mode.  But it's still wrong
for the target to provide patterns that would inevitably lead to spill
failure due to lack of registers.  So we should also add check for
!TARGET_GENERAL_REGS_ONLY in TARGET_SVE and other SVE related macros.

2020-04-22  Felix Yang  <felix.yang@huawei.com>

gcc/
	PR target/94678
	* config/aarch64/aarch64.h (TARGET_SVE):
	Add && !TARGET_GENERAL_REGS_ONLY.
	(TARGET_SVE2): Add && TARGET_SVE.
	(TARGET_SVE2_AES, TARGET_SVE2_BITPERM, TARGET_SVE2_SHA3,
	TARGET_SVE2_SM4): Add && TARGET_SVE2.
	* config/aarch64/aarch64-sve-builtins.h
	(sve_switcher::m_old_general_regs_only): New member.
	* config/aarch64/aarch64-sve-builtins.cc (check_required_registers):
	New function.
	(reported_missing_registers_p): New variable.
	(check_required_extensions): Call check_required_registers before
	return if all required extenstions are present.
	(sve_switcher::sve_switcher): Save TARGET_GENERAL_REGS_ONLY in
	m_old_general_regs_only and clear MASK_GENERAL_REGS_ONLY in
	global_options.x_target_flags.
	(sve_switcher::~sve_switcher): Set MASK_GENERAL_REGS_ONLY in
	global_options.x_target_flags if m_old_general_regs_only is true.

gcc/testsuite/
	PR target/94678
	* gcc.target/aarch64/sve/acle/general/nosve_6.c: New test.