[PR81647][AARCH64] Fix handling of Unordered Comparisons in aarch64-simd.md

[PR81647][AARCH64] Fix handling of Unordered Comparisons in aarch64-simd.md

This patch fixes the inconsistent behavior observed at -O3 for the unordered
comparisons. According to the online docs (https://gcc.gnu.org/onlinedocs
/gcc-7.2.0/gccint/Unary-and-Binary-Expressions.html), all of the following
should not raise an FP exception:
- UNGE_EXPR
- UNGT_EXPR
- UNLE_EXPR
- UNLT_EXPR
- UNEQ_EXPR
Also ORDERED_EXPR and UNORDERED_EXPR should only return zero or one.

The aarch64-simd.md handling of these were generating exception raising
instructions such as fcmgt. This patch changes the instructions that are
emitted in order to not give out the exceptions. We first check each
operand for NaNs and force any elements containing NaN to zero before using
them in the compare.

Example: UN<cc> (a, b) -> UNORDERED (a, b)
			  | (cm<cc> (isnan (a) ? 0.0 : a, isnan (b) ? 0.0 : b))

The ORDERED_EXPR is now handled as (cmeq (a, a) & cmeq (b, b)) and
UNORDERED_EXPR as ~ORDERED_EXPR and UNEQ as (~ORDERED_EXPR | cmeq (a,b)).

ChangeLog Entries:

*** gcc/ChangeLog ***

2018-03-19  Sudakshina Das  <sudi.das@arm.com>

	PR target/81647
	* config/aarch64/aarch64-simd.md (vec_cmp<mode><v_int_equiv>): Modify
	instructions for UNLT, UNLE, UNGT, UNGE, UNEQ, UNORDERED and ORDERED.

*** gcc/testsuite/ChangeLog ***

2018-03-19  Sudakshina Das  <sudi.das@arm.com>

	PR target/81647
	* gcc.target/aarch64/pr81647.c: New.

From-SVN: r258653