[turbofan] Add the StackSlot operator to turbofan.

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

Index: src/compiler/mips/code-generator-mips.cc
diff --git a/src/compiler/mips/code-generator-mips.cc b/src/compiler/mips/code-generator-mips.cc
index f13f7a3d38dcb6a73b6b5246ce856e7074805d80..58ab62c6189ef73ef5d9487da26ef96f2b5b4466 100644
--- a/src/compiler/mips/code-generator-mips.cc
+++ b/src/compiler/mips/code-generator-mips.cc
@@ -625,6 +625,13 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       __ bind(ool->exit());
       break;
     }
+    case kArchStackSlot: {
+      FrameOffset offset =
+          frame_access_state()->GetFrameOffset(i.InputInt32(0));
+      __ Addu(i.OutputRegister(), offset.from_stack_pointer() ? sp : fp,
+              Operand(offset.offset()));
+      break;
+    }
     case kMipsAdd:
       __ Addu(i.OutputRegister(), i.InputRegister(0), i.InputOperand(1));
       break;