Cycles: Wrap SVM compiler state variables into a single struct

This way it's easier to pass stuff around and also much easier to add more
state variables.

So far should be no functional changes for artists.

intern/cycles/render/svm.h

@@ -152,6 +152,15 @@ protected:
 		ShaderNodeSet done;
 	};
 
+	/* Global state of the compiler accessible from the compilation routines. */
+	struct CompilerState {
+		/* Set of nodes which were already compiled. */
+		ShaderNodeSet nodes_done;
+
+		/* Set of closures which were already compiled. */
+		ShaderNodeSet closure_done;
+	};
+
 	void stack_backup(StackBackup& backup, ShaderNodeSet& done);
 	void stack_restore(StackBackup& backup, ShaderNodeSet& done);
 
@@ -167,18 +176,18 @@ protected:
 	                       ShaderInput *input,
 	                       ShaderNode *skip_node = NULL);
 	void generate_node(ShaderNode *node, ShaderNodeSet& done);
-	void generate_closure_node(ShaderNode *node, ShaderNodeSet& done);
-	void generated_shared_closure_nodes(ShaderNode *root_node, ShaderNode *node,
-	                                    ShaderNodeSet& done,
-	                                    ShaderNodeSet& closure_done,
+	void generate_closure_node(ShaderNode *node, CompilerState *state);
+	void generated_shared_closure_nodes(ShaderNode *root_node,
+	                                    ShaderNode *node,
+	                                    CompilerState *state,
 	                                    const ShaderNodeSet& shared);
-	void generate_svm_nodes(const ShaderNodeSet& nodes, ShaderNodeSet& done);
+	void generate_svm_nodes(const ShaderNodeSet& nodes,
+	                        CompilerState *state);
 
 	/* multi closure */
 	void generate_multi_closure(ShaderNode *root_node,
 	                            ShaderNode *node,
-	                            ShaderNodeSet& done,
-	                            ShaderNodeSet& closure_done);
+	                            CompilerState *state);
 
 	/* compile */
 	void compile_type(Shader *shader, ShaderGraph *graph, ShaderType type);