[turbofan] Add initial support for growing stores.

src/compiler/simplified-lowering.cc

Index: src/compiler/simplified-lowering.cc
diff --git a/src/compiler/simplified-lowering.cc b/src/compiler/simplified-lowering.cc
index 73b6078d841f7118940a8b5a26ee5c155e528c1c..18bbbf0d6bcb2c4cbc6fb09e6ad69b132fc2bed5 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -2389,6 +2389,15 @@ class RepresentationSelector {
       case IrOpcode::kEnsureWritableFastElements:
         return VisitBinop(node, UseInfo::AnyTagged(),
                           MachineRepresentation::kTagged);
+      case IrOpcode::kMaybeGrowFastElements: {
+        ProcessInput(node, 0, UseInfo::AnyTagged());
+        ProcessInput(node, 1, UseInfo::AnyTagged());
+        ProcessInput(node, 2, UseInfo::TruncatingWord32());
+        ProcessInput(node, 3, UseInfo::TruncatingWord32());

[Jarin, 2016/08/08 08:03:47]

Again, the magic indices are not helping readability here. Could we have at
least a one-word comment at the end of each line above? (Such as // length
etc.).

[Benedikt Meurer, 2016/08/08 08:12:56]

Done.

+        ProcessRemainingInputs(node, 4);
+        SetOutput(node, MachineRepresentation::kTagged);
+        return;
+      }
 
       //------------------------------------------------------------------
       // Machine-level operators.