[turbofan] Add the StackSlot operator to turbofan.

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

Index: src/compiler/ppc/code-generator-ppc.cc
diff --git a/src/compiler/ppc/code-generator-ppc.cc b/src/compiler/ppc/code-generator-ppc.cc
index dabd1bed7da03d41855e37f6431a291b1aa81462..b87585a7844eaf0bf7159779157762b56fb1dc05 100644
--- a/src/compiler/ppc/code-generator-ppc.cc
+++ b/src/compiler/ppc/code-generator-ppc.cc
@@ -823,6 +823,13 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       __ bind(ool->exit());
       break;
     }
+    case kArchStackSlot: {
+      FrameOffset offset =
+          frame_access_state()->GetFrameOffset(i.InputInt32(0));
+      __ addi(i.OutputRegister(), offset.from_stack_pointer() ? sp : fp,
+              Operand(offset.offset()));
+      break;
+    }
     case kPPC_And:
       if (HasRegisterInput(instr, 1)) {
         __ and_(i.OutputRegister(), i.InputRegister(0), i.InputRegister(1),