correct target directive handling error handling

The target specific parser should return `false' if the target AsmParser handles
the directive, and `true' if the generic parser should handle the directive.
Many of the target specific directive handlers would `return Error' which does
not follow these semantics.  This change simply changes the target specific
routines to conform to the semantis of the ParseDirective correctly.

Conformance to the semantics improves diagnostics emitted for the invalid
directives.  X86 is taken as a sample to ensure that multiple diagnostics are
not presented for a single error.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199068 91177308-0d34-0410-b5e6-96231b3b80d8
[AArch64 NEON] Add more scenarios to use perm instructions when lowering shuffle_vector

This patch covered 2 more scenarios:

1.  Two operands of shuffle_vector are the same, like
%shuffle.i = shufflevector <8 x i8> %a, <8 x i8> %a, <8 x i32> <i32 0, i32 2, i32 4, i32 6, i32 8, i32 10, i32 12, i32 14>

2. One of operands is undef, like
%shuffle.i = shufflevector <8 x i8> %a, <8 x i8> undef, <8 x i32> <i32 0, i32 2, i32 4, i32 6, i32 8, i32 10, i32 12, i32 14>

After this patch, perm instructions will have chance to be emitted instead of lots of INS.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199069 91177308-0d34-0410-b5e6-96231b3b80d8
[AArch64 NEON] Add missing patterns for bitcast from or to v1f64

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199070 91177308-0d34-0410-b5e6-96231b3b80d8