[turbofan] Add the StackSlot operator to turbofan.

src/compiler/mips64/code-generator-mips64.cc

Index: src/compiler/mips64/code-generator-mips64.cc
diff --git a/src/compiler/mips64/code-generator-mips64.cc b/src/compiler/mips64/code-generator-mips64.cc
index f30a0a0a7fcab66a5ce3a43f9fa137059cf2c828..d5b60e9669a41d6f266b8db18f855ca1ac8fceb8 100644
--- a/src/compiler/mips64/code-generator-mips64.cc
+++ b/src/compiler/mips64/code-generator-mips64.cc
@@ -635,6 +635,13 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       __ bind(ool->exit());
       break;
     }
+    case kArchStackSlot: {
+      FrameOffset offset =
+          frame_access_state()->GetFrameOffset(i.InputInt32(0));
+      __ Daddu(i.OutputRegister(), offset.from_stack_pointer() ? sp : fp,
+               Operand(offset.offset()));
+      break;
+    }
     case kMips64Add:
       __ Addu(i.OutputRegister(), i.InputRegister(0), i.InputOperand(1));
       break;