Fix va_arg for doubles. With this patch VAARG nodes always contain the

correct alignment information, which simplifies ExpandRes_VAARG a bit.

The patch introduces a new alignment information to TargetLoweringInfo. This is
needed since the two natural candidates cannot be used:

* The 's' in target data: If this is set to the minimal alignment of any
  argument, getCallFrameTypeAlignment would return 4 for doubles on ARM for
  example.
* The getTransientStackAlignment method. It is possible for an architecture to
  have argument less aligned than what we maintain the stack pointer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108072 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/LegalizeDAG.cpp

@@ -2658,7 +2658,9 @@ void SelectionDAGLegalize::ExpandNode(SDNode *Node,
                                      false, false, 0);
     SDValue VAList = VAListLoad;
 
-    if (Align != 0 ) {
+    if (Align > TLI.getMinStackArgumentAlignment()) {
+      assert(((Align & (Align-1)) == 0) && "Expected Align to be a power of 2");
+
       VAList = DAG.getNode(ISD::ADD, dl, TLI.getPointerTy(), VAList,
                            DAG.getConstant(Align - 1,
                                            TLI.getPointerTy()));