[AVX512] Generate masking instruction variants with tablegen

After adding the masking variants to several instructions, I have decided to
experiment with generating these from the non-masking/unconditional
variant. This will hopefully reduce the amount repetition that we currently
have in order to define an instruction with all its variants (for a reg/mem
instruction this would be 6 instruction defs and 2 Pat<> for the intrinsic).

The patch is the first cut that is currently only applied to valignd/q to make
the patch small.

A few notes on the approach:

  * In order to stitch together the dag for both the conditional and the
  unconditional patterns I pass the RHS of the set rather than the full
  pattern (set dest, RHS).
  * Rather than subclassing each instruction base class (e.g. AVX512AIi8),
  with a masking variant which wouldn't scale, I derived the masking
  instructions from a new base class AVX512 (this is just I<> with
  Requires<HasAVX512>).  The instructions derive from this now, plus a new set
  of classes that add the format bits and everything else that instruction
  base class provided (i.e. AVX512AIi8 vs. AVX512AIi8Base).

I hope we can go incrementally from here.  I expect that:

  * We will need different variants of the masking class.  One example is
  instructions requiring three vector sources.  In this case we tie one of the
  source operands to dest rather than a new implicit source operand ($src0)
  * Add the zero-masking variant
  * Add more AVX512*Base classes as new uses are added

I've looked at X86.td.expanded before and after to make sure that nothing got
lost for valignd/q.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215125 91177308-0d34-0410-b5e6-96231b3b80d8
Indent


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215126 91177308-0d34-0410-b5e6-96231b3b80d8
FileCheck: Add a flag to allow checking empty input

Currently FileCheck errors out on empty input. This is usually the
right thing to do, but makes testing things like "this command does
not emit some error message" hard to test. This usually leads to
people using "command 2>&1 | count 0" instead, and then the bots that
use guard malloc fail a few hours later.

By adding a flag to FileCheck that allows empty inputs, we can make
tests that consist entirely of "CHECK-NOT" lines feasible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215127 91177308-0d34-0410-b5e6-96231b3b80d8