[turbofan] Add the StackSlot operator to turbofan.

src/compiler/arm64/code-generator-arm64.cc

Index: src/compiler/arm64/code-generator-arm64.cc
diff --git a/src/compiler/arm64/code-generator-arm64.cc b/src/compiler/arm64/code-generator-arm64.cc
index 749f581f696d50953de8ee75c3129082fa9838c9..a038c7155d44b5a15a4d92e2882d874696f13978 100644
--- a/src/compiler/arm64/code-generator-arm64.cc
+++ b/src/compiler/arm64/code-generator-arm64.cc
@@ -646,6 +646,18 @@ 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 = __ StackPointer();
+      } else {
+        base = fp;
+      }
+      __ Add(i.OutputRegister(0), base, Operand(offset.offset()));
+      break;
+    }
     case kArm64Float32RoundDown:
       __ Frintm(i.OutputFloat32Register(), i.InputFloat32Register(0));
       break;