[X86] Mark pseudo instruction TEST8ri_NOEREX as hasSIdeEffects=0.

Also, add a case clause in X86InstrInfo::shouldScheduleAdjacent to enable
macro-fusion.

<rdar://problem/15680770>



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212747 91177308-0d34-0410-b5e6-96231b3b80d8
[DAG] Further improve the logic in DAGCombiner that folds a pair of shuffles into a single shuffle if the resulting mask is legal.

This patch teaches the DAGCombiner how to fold shuffles according to the
following new rules:
  1. shuffle(shuffle(x, y), undef) -> x
  2. shuffle(shuffle(x, y), undef) -> y
  3. shuffle(shuffle(x, y), undef) -> shuffle(x, undef)
  4. shuffle(shuffle(x, y), undef) -> shuffle(y, undef)

The backend avoids to combine shuffles according to rules 3. and 4. if
the resulting shuffle does not have a legal mask. This is to avoid introducing
illegal shuffles that are potentially expanded into a sub-optimal sequence of
target specific dag nodes during vector legalization.

Added test case combine-vec-shuffle-2.ll to verify that we correctly triggers
the new rules when combining shuffles.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212748 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "Revert r212640, "Add trunc (select c, a, b) -> select c (trunc a), (trunc b) combine.""

Don't try to convert the select condition type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212750 91177308-0d34-0410-b5e6-96231b3b80d8