[arm] Early split addvdi4

[arm] Early split addvdi4

This patch adds early splitting for addvdi4; it's very similar to the
uaddvdi4 splitter, but the details are just different enough in
places, especially for the patterns that match the splitting, where we
have to compare against the non-widened version to detect if overflow
occurred.

I've also added a testcase to the testsuite for a couple of constants
that caught me out during the development of this patch.  They're
probably arm-specific values, but the test is generic enough that I've
included it for all targets.

[gcc]
	* config/arm/arm.c (arm_select_cc_mode): Allow either the first
	or second operand of the PLUS inside a DImode equality test to be
	sign-extend when selecting CC_Vmode.
	* config/arm/arm.md (addvdi4): Early-split the operation into SImode
	instructions.
	(addsi3_cin_vout_reg, addsi3_cin_vout_imm, addsi3_cin_vout_0): New
	expand patterns.
	(addsi3_cin_vout_reg_insn, addsi3_cin_vout_imm_insn): New patterns.
	(addsi3_cin_vout_0): Likewise.
	(adddi3_compareV): Delete.

[gcc/testsuite]
	* gcc.dg/builtin-arith-overflow-3.c: New test.

From-SVN: r277186