Add ARM patterns to match EXTRACT_SUBVECTOR nodes.

Also fix an off-by-one in SelectionDAGBuilder that was preventing shuffle
vectors from being translated to EXTRACT_SUBVECTOR.
Patch by Tim Northover.

The test changes are needed to keep those spill-q tests from testing aligned
spills and restores.  If the only aligned stack objects are spill slots, we
no longer realign the stack frame.  Prior to this patch, an EXTRACT_SUBVECTOR
was legalized by loading from the stack, which created an aligned frame index.
Now, however, there is nothing except the spill slot in the stack frame, so
I added an aligned alloca.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122995 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -2745,7 +2745,7 @@ void SelectionDAGBuilder::visitShuffleVector(const User &I) {
         } else {
           StartIdx[Input] = (MinRange[Input]/MaskNumElts)*MaskNumElts;
           if (MaxRange[Input] - StartIdx[Input] < (int)MaskNumElts &&
-              StartIdx[Input] + MaskNumElts < SrcNumElts)
+              StartIdx[Input] + MaskNumElts <= SrcNumElts)
             RangeUse[Input] = 1; // Extract from a multiple of the mask length.
         }
       }