[turbofan] Add the StackSlot operator to turbofan.

src/compiler/x64/code-generator-x64.cc

Index: src/compiler/x64/code-generator-x64.cc
diff --git a/src/compiler/x64/code-generator-x64.cc b/src/compiler/x64/code-generator-x64.cc
index 68aba0d371c523cdb0ee68b4a9999efecbceccde..295d3b3a37e79a64a99e52617dfac00da486491a 100644
--- a/src/compiler/x64/code-generator-x64.cc
+++ b/src/compiler/x64/code-generator-x64.cc
@@ -740,6 +740,18 @@ 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 = rsp;
+      } else {
+        base = rbp;
+      }
+      __ leaq(i.OutputRegister(), Operand(base, offset.offset()));
+      break;
+    }
     case kX64Add32:
       ASSEMBLE_BINOP(addl);
       break;