[turbofan] Add the StackSlot operator to turbofan.

src/compiler/arm/code-generator-arm.cc

Index: src/compiler/arm/code-generator-arm.cc
diff --git a/src/compiler/arm/code-generator-arm.cc b/src/compiler/arm/code-generator-arm.cc
index 13ce301560d0be7883981a0037661a05211f4171..35876621913ad674a4671448f7d9aba98c51bc3e 100644
--- a/src/compiler/arm/code-generator-arm.cc
+++ b/src/compiler/arm/code-generator-arm.cc
@@ -535,6 +535,18 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       __ bind(ool->exit());
       break;
     }
+    case kArchStackSlot: {
+      FrameOffset offset =
+          frame_access_state()->GetFrameOffset(i.InputInt32(0));
+      Register base;
+      if (offset.from_stack_pointer()) {
+        base = sp;
+      } else {
+        base = fp;
+      }
+      __ add(i.OutputRegister(0), base, Operand(offset.offset()));
+      break;
+    }
     case kArmAdd:
       __ add(i.OutputRegister(), i.InputRegister(0), i.InputOperand2(1),
              i.OutputSBit());