Fix incorrect invariant check in DAG Combine

Earlier this summer I fixed an issue where we were incorrectly combining
multiple loads that had different constraints such alignment, invariance,
temporality, etc. Apparently in one case I made copt paste error and swapped
alignment and invariance.

Tests included.

rdar://18816719

llvm-svn: 220933
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index acea763..0d5caba 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -11542,7 +11542,7 @@
     // It is safe to replace the two loads if they have different alignments,
     // but the new load must be the minimum (most restrictive) alignment of the
     // inputs.
-    bool isInvariant = LLD->getAlignment() & RLD->getAlignment();
+    bool isInvariant = LLD->isInvariant() & RLD->isInvariant();
     unsigned Alignment = std::min(LLD->getAlignment(), RLD->getAlignment());
     if (LLD->getExtensionType() == ISD::NON_EXTLOAD) {
       Load = DAG.getLoad(TheSelect->getValueType(0),