[APX CCMP] Support APX CCMP

APX CCMP feature implements conditional compare which executes compare
when EFLAGS matches certain condition.

CCMP introduces default flags value (dfv), when conditional compare does
not execute, it will directly set the flags according to dfv.

The instruction goes like

ccmpeq {dfv=sf,of,cf,zf}  %rax, %r16

For this instruction, it will test EFLAGS regs if it matches conditional
code EQ, if yes, compare %rax and %r16 like legacy cmp. If no, the
EFLAGS will be updated according to dfv, which means SF,OF,CF,ZF are
set. PF will be set according to CF in dfv, and AF will always be
cleared.

The dfv part can be a combination of sf,of,cf,zf, like {dfv=cf,zf} which
sets CF and ZF only and clear others, or {dfv=} which clears all EFLAGS.

To enable CCMP, we implemented the target hook TARGET_GEN_CCMP_FIRST and
TARGET_GEN_CCMP_NEXT to reuse the current ccmp infrastructure. Also we
extended the cstorem4 optab to support storing different CCmode to fit
current ccmp infrasturcture.

gcc/ChangeLog:

	* config/i386/i386-expand.cc (ix86_gen_ccmp_first): New function
	that test if the first compare can be generated.
	(ix86_gen_ccmp_next): New function to emit a simgle compare and ccmp
	sequence.
	* config/i386/i386-opts.h (enum apx_features): Add apx_ccmp.
	* config/i386/i386-protos.h (ix86_gen_ccmp_first): New proto
	declare.
	(ix86_gen_ccmp_next): Likewise.
	(ix86_get_flags_cc): Likewise.
	* config/i386/i386.cc (ix86_flags_cc): New enum.
	(ix86_ccmp_dfv_mapping): New string array to map conditional
	code to dfv.
	(ix86_print_operand): Handle special dfv flag for CCMP.
	(ix86_get_flags_cc): New function to return x86 CC enum.
	(TARGET_GEN_CCMP_FIRST): Define.
	(TARGET_GEN_CCMP_NEXT): Likewise.
	* config/i386/i386.h (TARGET_APX_CCMP): Define.
	* config/i386/i386.md (@ccmp<mode>): New define_insn to support
	ccmp.
	(UNSPEC_APX_DFV): New unspec for ccmp dfv.
	(ALL_CC): New mode iterator.
	(cstorecc4): Change to ...
	(cstore<mode>4) ... this, use ALL_CC to loop through all
	available CCmodes.
	* config/i386/i386.opt (apx_ccmp): Add enum value for ccmp.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/apx-ccmp-1.c: New compile test.
	* gcc.target/i386/apx-ccmp-2.c: New runtime test.

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