[wasm] Implement 128-bit endian swap for simd type

src/compiler/simd-scalar-lowering.cc

Index: src/compiler/simd-scalar-lowering.cc
diff --git a/src/compiler/simd-scalar-lowering.cc b/src/compiler/simd-scalar-lowering.cc
index 10c43f1aa38f1b077f7fe042478b51532b5577c0..af7dae91b9c4f3c92e87486b6e49ca6a8d7df48a 100644
--- a/src/compiler/simd-scalar-lowering.cc
+++ b/src/compiler/simd-scalar-lowering.cc
@@ -199,12 +199,17 @@ static int GetReturnCountAfterLowering(
   return result;
 }
 
+constexpr int SimdScalarLowering::kLaneOffsets[];
+
 void SimdScalarLowering::GetIndexNodes(Node* index, Node** new_indices) {
-  new_indices[0] = index;
+  int laneIndex = kLaneOffsets[0];
+  new_indices[laneIndex] = index;
   for (size_t i = 1; i < kMaxLanes; ++i) {
-    new_indices[i] = graph()->NewNode(machine()->Int32Add(), index,
-                                      graph()->NewNode(common()->Int32Constant(
-                                          static_cast<int>(i) * kLaneWidth)));
+    laneIndex = kLaneOffsets[i];
+    new_indices[laneIndex] = graph()->NewNode(
+        machine()->Int32Add(), index,
+        graph()->NewNode(
+            common()->Int32Constant(static_cast<int>(i) * kLaneWidth)));
   }
 }
 
@@ -229,6 +234,7 @@ void SimdScalarLowering::LowerLoadOp(MachineRepresentation rep, Node* node,
       rep_nodes[1] = graph()->NewNode(load_op, base, indices[1], rep_nodes[2],
                                       control_input);
       rep_nodes[0]->ReplaceInput(2, rep_nodes[1]);
+      rep_nodes[0]->ReplaceInput(1, indices[0]);

[aseemgarg, 2017/05/02 21:20:21]

This is not correct. The else case (without control and effect nodes) is not
covered. Also, this needs to be rebased. The code has changed somewhat over here
(Int16x8 was added). 

[john.yan, 2017/05/03 19:39:40]

Hello, do you mean the else case below? I don't understand how it will affect
anything from above. Could you please explain a bit more?

Thanks,
John

[aseemgarg, 2017/05/03 22:04:13]

yes the else case below. Since the indices have potentially moved around, the
index for rep_node[0] should be fixed even for the else case. 

     } else {
       for (size_t i = 1; i < kMaxLanes; ++i) {
         rep_nodes[i] = graph()->NewNode(load_op, base, indices[i]);
@@ -267,6 +273,7 @@ void SimdScalarLowering::LowerStoreOp(MachineRepresentation rep, Node* node,
       rep_nodes[1] = graph()->NewNode(store_op, base, indices[1], rep_inputs[1],
                                       rep_nodes[2], control_input);
       rep_nodes[0]->ReplaceInput(3, rep_nodes[1]);
+      rep_nodes[0]->ReplaceInput(1, indices[0]);
 
     } else {
       for (size_t i = 1; i < kMaxLanes; ++i) {