Cycles: add ConstantFolder class for constant folding boilerplate.

Reviewed By: brecht, sergey

Differential Revision: https://developer.blender.org/D2089

7 files changed, 347 insertions, 261 deletions

diff --git a/intern/cycles/render/CMakeLists.txt b/intern/cycles/render/CMakeLists.txt
index b14da3e63d0..a632ddc0598 100644
--- a/intern/cycles/render/CMakeLists.txt
+++ b/intern/cycles/render/CMakeLists.txt
@@ -22,6 +22,7 @@ set(SRC
 	bake.cpp
 	buffers.cpp
 	camera.cpp
+	constant_fold.cpp
 	film.cpp
 	graph.cpp
 	image.cpp
@@ -49,6 +50,7 @@ set(SRC_HEADERS
 	background.h
 	buffers.h
 	camera.h
+	constant_fold.h
 	film.h
 	graph.h
 	image.h
diff --git a/intern/cycles/render/constant_fold.cpp b/intern/cycles/render/constant_fold.cpp
new file mode 100644
index 00000000000..1fee6b2c081
--- /dev/null
+++ b/intern/cycles/render/constant_fold.cpp
@@ -0,0 +1,122 @@
+/*
+ * Copyright 2011-2013 Blender Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "constant_fold.h"
+#include "graph.h"
+
+#include "util_foreach.h"
+
+CCL_NAMESPACE_BEGIN
+
+ConstantFolder::ConstantFolder(ShaderGraph *graph, ShaderNode *node, ShaderOutput *output)
+: graph(graph), node(node), output(output)
+{
+}
+
+bool ConstantFolder::all_inputs_constant() const
+{
+	foreach(ShaderInput *input, node->inputs) {
+		if(input->link) {
+			return false;
+		}
+	}
+
+	return true;
+}
+
+void ConstantFolder::make_constant(float value) const
+{
+	foreach(ShaderInput *sock, output->links) {
+		sock->set(value);
+	}
+
+	graph->disconnect(output);
+}
+
+void ConstantFolder::make_constant(float3 value) const
+{
+	foreach(ShaderInput *sock, output->links) {
+		sock->set(value);
+	}
+
+	graph->disconnect(output);
+}
+
+void ConstantFolder::make_constant_clamp(float value, bool clamp) const
+{
+	make_constant(clamp ? saturate(value) : value);
+}
+
+void ConstantFolder::make_constant_clamp(float3 value, bool clamp) const
+{
+	if (clamp) {
+		value.x = saturate(value.x);
+		value.y = saturate(value.y);
+		value.z = saturate(value.z);
+	}
+
+	make_constant(value);
+}
+
+void ConstantFolder::bypass(ShaderOutput *new_output) const
+{
+	assert(new_output);
+
+	/* Remove all outgoing links from socket and connect them to new_output instead.
+	 * The graph->relink method affects node inputs, so it's not safe to use in constant
+	 * folding if the node has multiple outputs and will thus be folded multiple times. */
+	vector<ShaderInput*> outputs = output->links;
+
+	graph->disconnect(output);
+
+	foreach(ShaderInput *sock, outputs) {
+		graph->connect(new_output, sock);
+	}
+}
+
+void ConstantFolder::discard() const
+{
+	assert(output->type() == SocketType::CLOSURE);
+	graph->disconnect(output);
+}
+
+void ConstantFolder::bypass_or_discard(ShaderInput *input) const
+{
+	assert(input->type() == SocketType::CLOSURE);
+
+	if (input->link) {
+		bypass(input->link);
+	}
+	else {
+		discard();
+	}
+}
+
+bool ConstantFolder::try_bypass_or_make_constant(ShaderInput *input, float3 input_value, bool clamp) const
+{
+	if(!input->link) {
+		make_constant_clamp(input_value, clamp);
+		return true;
+	}
+	else if(!clamp) {
+		bypass(input->link);
+		return true;
+	}
+
+	return false;
+}
+
+CCL_NAMESPACE_END
diff --git a/intern/cycles/render/constant_fold.h b/intern/cycles/render/constant_fold.h
new file mode 100644
index 00000000000..978c8e5335a
--- /dev/null
+++ b/intern/cycles/render/constant_fold.h
@@ -0,0 +1,59 @@
+/*
+ * Copyright 2011-2013 Blender Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __CONSTANT_FOLD_H__
+#define __CONSTANT_FOLD_H__
+
+#include "util_types.h"
+
+CCL_NAMESPACE_BEGIN
+
+class ShaderGraph;
+class ShaderInput;
+class ShaderNode;
+class ShaderOutput;
+
+class ConstantFolder {
+public:
+	ShaderGraph *const graph;
+	ShaderNode *const node;
+	ShaderOutput *const output;
+
+	ConstantFolder(ShaderGraph *graph, ShaderNode *node, ShaderOutput *output);
+
+	bool all_inputs_constant() const;
+
+	/* Constant folding helpers, always return true for convenience. */
+	void make_constant(float value) const;
+	void make_constant(float3 value) const;
+	void make_constant_clamp(float value, bool clamp) const;
+	void make_constant_clamp(float3 value, bool clamp) const;
+
+	/* Bypass node, relinking to another output socket. */
+	void bypass(ShaderOutput *output) const;
+
+	/* For closure nodes, discard node entirely or bypass to one of its inputs. */
+	void discard() const;
+	void bypass_or_discard(ShaderInput *input) const;
+
+	/* Bypass or make constant, unless we can't due to clamp being true. */
+	bool try_bypass_or_make_constant(ShaderInput *input, float3 input_value, bool clamp) const;
+};
+
+CCL_NAMESPACE_END
+
+#endif /* __CONSTANT_FOLD_H__ */
+
diff --git a/intern/cycles/render/graph.cpp b/intern/cycles/render/graph.cpp
index fd48bf2631e..ac78238dfee 100644
--- a/intern/cycles/render/graph.cpp
+++ b/intern/cycles/render/graph.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright 2011-2013 Blender Foundation
+ * Copyright 2011-2016 Blender Foundation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@
 #include "graph.h"
 #include "nodes.h"
 #include "shader.h"
+#include "constant_fold.h"
 
 #include "util_algorithm.h"
 #include "util_debug.h"
@@ -126,17 +127,6 @@ ShaderOutput *ShaderNode::output(ustring name)
 	return NULL;
 }
 
-bool ShaderNode::all_inputs_constant() const
-{
-	foreach(ShaderInput *input, inputs) {
-		if(input->link) {
-			return false;
-		}
-	}
-
-	return true;
-}
-
 void ShaderNode::attributes(Shader *shader, AttributeRequestSet *attributes)
 {
 	foreach(ShaderInput *input, inputs) {
@@ -278,6 +268,17 @@ void ShaderGraph::connect(ShaderOutput *from, ShaderInput *to)
 	}
 }
 
+void ShaderGraph::disconnect(ShaderOutput *from)
+{
+	assert(!finalized);
+
+	foreach(ShaderInput *sock, from->links) {
+		sock->link = NULL;
+	}
+
+	from->links.clear();
+}
+
 void ShaderGraph::disconnect(ShaderInput *to)
 {
 	assert(!finalized);
@@ -525,15 +526,8 @@ void ShaderGraph::constant_fold()
 				}
 			}
 			/* Optimize current node. */
-			if(node->constant_fold(this, output, output->links[0])) {
-				/* Apply optimized value to other connected sockets and disconnect. */
-				vector<ShaderInput*> links(output->links);
-				for(size_t i = 0; i < links.size(); i++) {
-					if(i > 0)
-						links[i]->parent->copy_value(links[i]->socket_type, *links[0]->parent, links[0]->socket_type);
-					disconnect(links[i]);
-				}
-			}
+			ConstantFolder folder(this, node, output);
+			node->constant_fold(folder);
 		}
 	}
 }
diff --git a/intern/cycles/render/graph.h b/intern/cycles/render/graph.h
index 61100cda60b..b35be48d8ca 100644
--- a/intern/cycles/render/graph.h
+++ b/intern/cycles/render/graph.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2011-2013 Blender Foundation
+ * Copyright 2011-2016 Blender Foundation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -41,6 +41,7 @@ class ShaderGraph;
 class SVMCompiler;
 class OSLCompiler;
 class OutputNode;
+class ConstantFolder;
 
 /* Bump
  *
@@ -140,9 +141,7 @@ public:
 
 	/* ** Node optimization ** */
 	/* Check whether the node can be replaced with single constant. */
-	virtual bool constant_fold(ShaderGraph * /*graph*/, ShaderOutput * /*socket*/, ShaderInput * /*optimized*/) { return false; }
-
-	bool all_inputs_constant() const;
+	virtual void constant_fold(const ConstantFolder& /*folder*/) {}
 
 	/* Simplify settings used by artists to the ones which are simpler to
 	 * evaluate in the kernel but keep the final result unchanged.
@@ -251,6 +250,7 @@ public:
 	OutputNode *output();
 
 	void connect(ShaderOutput *from, ShaderInput *to);
+	void disconnect(ShaderOutput *from);
 	void disconnect(ShaderInput *to);
 	void relink(ShaderNode *node, ShaderOutput *from, ShaderOutput *to);
 
diff --git a/intern/cycles/render/nodes.cpp b/intern/cycles/render/nodes.cpp
index a8fd9da9ced..66c92bda54b 100644
--- a/intern/cycles/render/nodes.cpp
+++ b/intern/cycles/render/nodes.cpp
@@ -22,6 +22,7 @@
 #include "svm_color_util.h"
 #include "svm_math_util.h"
 #include "osl.h"
+#include "constant_fold.h"
 
 #include "util_sky_model.h"
 #include "util_foreach.h"
@@ -1576,16 +1577,11 @@ RGBToBWNode::RGBToBWNode()
 {
 }
 
-bool RGBToBWNode::constant_fold(ShaderGraph * /*graph*/,
-                                ShaderOutput * /*socket*/,
-                                ShaderInput *optimized)
+void RGBToBWNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
-		optimized->set(linear_rgb_to_gray(color));
-		return true;
+	if(folder.all_inputs_constant()) {
+		folder.make_constant(linear_rgb_to_gray(color));
 	}
-
-	return false;
 }
 
 void RGBToBWNode::compile(SVMCompiler& compiler)
@@ -1663,40 +1659,35 @@ ConvertNode::ConvertNode(SocketType::Type from_, SocketType::Type to_, bool auto
 		special_type = SHADER_SPECIAL_TYPE_AUTOCONVERT;
 }
 
-bool ConvertNode::constant_fold(ShaderGraph * /*graph*/,
-                                ShaderOutput * /*socket*/,
-                                ShaderInput *optimized)
+void ConvertNode::constant_fold(const ConstantFolder& folder)
 {
 	/* proxy nodes should have been removed at this point */
 	assert(special_type != SHADER_SPECIAL_TYPE_PROXY);
 
 	/* TODO(DingTo): conversion from/to int is not supported yet, don't fold in that case */
 
-	if(all_inputs_constant()) {
+	if(folder.all_inputs_constant()) {
 		if(from == SocketType::FLOAT) {
 			if(SocketType::is_float3(to)) {
-				optimized->set(make_float3(value_float, value_float, value_float));
-				return true;
+				folder.make_constant(make_float3(value_float, value_float, value_float));
 			}
 		}
 		else if(SocketType::is_float3(from)) {
 			if(to == SocketType::FLOAT) {
-				if(from == SocketType::COLOR)
+				if(from == SocketType::COLOR) {
 					/* color to float */
-					optimized->set(linear_rgb_to_gray(value_color));
-				else
+					folder.make_constant(linear_rgb_to_gray(value_color));
+				}
+				else {
 					/* vector/point/normal to float */
-					optimized->set(average(value_vector));
-				return true;
+					folder.make_constant(average(value_vector));
+				}
 			}
 			else if(SocketType::is_float3(to)) {
-				optimized->set(value_color);
-				return true;
+				folder.make_constant(value_color);
 			}
 		}
 	}
-
-	return false;
 }
 
 void ConvertNode::compile(SVMCompiler& compiler)
@@ -2366,15 +2357,15 @@ void EmissionNode::compile(OSLCompiler& compiler)
 	compiler.add(this, "node_emission");
 }
 
-bool EmissionNode::constant_fold(ShaderGraph * /*graph*/,
-                                ShaderOutput * /*socket*/,
-                                ShaderInput * /*optimized*/)
+void EmissionNode::constant_fold(const ConstantFolder& folder)
 {
 	ShaderInput *color_in = input("Color");
 	ShaderInput *strength_in = input("Strength");
 
-	return ((!color_in->link && color == make_float3(0.0f, 0.0f, 0.0f)) ||
-	        (!strength_in->link && strength == 0.0f));
+	if ((!color_in->link && color == make_float3(0.0f, 0.0f, 0.0f)) ||
+	    (!strength_in->link && strength == 0.0f)) {
+		folder.discard();
+	}
 }
 
 /* Background Closure */
@@ -2418,15 +2409,15 @@ void BackgroundNode::compile(OSLCompiler& compiler)
 	compiler.add(this, "node_background");
 }
 
-bool BackgroundNode::constant_fold(ShaderGraph * /*graph*/,
-                                   ShaderOutput * /*socket*/,
-                                   ShaderInput * /*optimized*/)
+void BackgroundNode::constant_fold(const ConstantFolder& folder)
 {
 	ShaderInput *color_in = input("Color");
 	ShaderInput *strength_in = input("Strength");
 
-	return ((!color_in->link && color == make_float3(0.0f, 0.0f, 0.0f)) ||
-	        (!strength_in->link && strength == 0.0f));
+	if ((!color_in->link && color == make_float3(0.0f, 0.0f, 0.0f)) ||
+	    (!strength_in->link && strength == 0.0f)) {
+		folder.discard();
+	}
 }
 
 /* Holdout Closure */
@@ -3388,12 +3379,9 @@ ValueNode::ValueNode()
 {
 }
 
-bool ValueNode::constant_fold(ShaderGraph * /*graph*/,
-                              ShaderOutput * /*socket*/,
-                              ShaderInput *optimized)
+void ValueNode::constant_fold(const ConstantFolder& folder)
 {
-	optimized->set(value);
-	return true;
+	folder.make_constant(value);
 }
 
 void ValueNode::compile(SVMCompiler& compiler)
@@ -3426,12 +3414,9 @@ ColorNode::ColorNode()
 {
 }
 
-bool ColorNode::constant_fold(ShaderGraph * /*graph*/,
-                              ShaderOutput * /*socket*/,
-                              ShaderInput *optimized)
+void ColorNode::constant_fold(const ConstantFolder& folder)
 {
-	optimized->set(value);
-	return true;
+	folder.make_constant(value);
 }
 
 void ColorNode::compile(SVMCompiler& compiler)
@@ -3480,6 +3465,20 @@ void AddClosureNode::compile(OSLCompiler& compiler)
 	compiler.add(this, "node_add_closure");
 }
 
+void AddClosureNode::constant_fold(const ConstantFolder& folder)
+{
+	ShaderInput *closure1_in = input("Closure1");
+	ShaderInput *closure2_in = input("Closure2");
+
+	/* remove useless add closures nodes */
+	if(!closure1_in->link) {
+		folder.bypass_or_discard(closure2_in);
+	}
+	else if(!closure2_in->link) {
+		folder.bypass_or_discard(closure1_in);
+	}
+}
+
 /* Mix Closure */
 
 NODE_DEFINE(MixClosureNode)
@@ -3511,37 +3510,28 @@ void MixClosureNode::compile(OSLCompiler& compiler)
 	compiler.add(this, "node_mix_closure");
 }
 
-bool MixClosureNode::constant_fold(ShaderGraph *graph,
-                                   ShaderOutput * /*socket*/,
-                                   ShaderInput * /*optimized*/)
+void MixClosureNode::constant_fold(const ConstantFolder& folder)
 {
 	ShaderInput *fac_in = input("Fac");
 	ShaderInput *closure1_in = input("Closure1");
 	ShaderInput *closure2_in = input("Closure2");
-	ShaderOutput *closure_out = output("Closure");
 
 	/* remove useless mix closures nodes */
 	if(closure1_in->link == closure2_in->link) {
-		graph->relink(this, closure_out, closure1_in->link);
-		return true;
+		folder.bypass_or_discard(closure1_in);
 	}
-
-	/* remove unused mix closure input when factor is 0.0 or 1.0 */
-	/* check for closure links and make sure factor link is disconnected */
-	if(closure1_in->link && closure2_in->link && !fac_in->link) {
+	/* remove unused mix closure input when factor is 0.0 or 1.0
+	 * check for closure links and make sure factor link is disconnected */
+	else if(!fac_in->link) {
 		/* factor 0.0 */
-		if(fac == 0.0f) {
-			graph->relink(this, closure_out, closure1_in->link);
-			return true;
+		if(fac <= 0.0f) {
+			folder.bypass_or_discard(closure1_in);
 		}
 		/* factor 1.0 */
-		else if(fac == 1.0f) {
-			graph->relink(this, closure_out, closure2_in->link);
-			return true;
+		else if(fac >= 1.0f) {
+			folder.bypass_or_discard(closure2_in);
 		}
 	}
-
-	return false;
 }
 
 /* Mix Closure */
@@ -3603,28 +3593,21 @@ InvertNode::InvertNode()
 {
 }
 
-bool InvertNode::constant_fold(ShaderGraph *graph,
-                               ShaderOutput * /*socket*/,
-                               ShaderInput *optimized)
+void InvertNode::constant_fold(const ConstantFolder& folder)
 {
 	ShaderInput *fac_in = input("Fac");
 	ShaderInput *color_in = input("Color");
-	ShaderOutput *color_out = output("Color");
 
 	if(!fac_in->link) {
 		/* evaluate fully constant node */
 		if(!color_in->link) {
-			optimized->set(interp(color, make_float3(1.0f, 1.0f, 1.0f) - color, fac));
-			return true;
+			folder.make_constant(interp(color, make_float3(1.0f, 1.0f, 1.0f) - color, fac));
 		}
 		/* remove no-op node */
 		else if(fac == 0.0f) {
-			graph->relink(this, color_out, color_in->link);
-			return true;
+			folder.bypass(color_in->link);
 		}
 	}
-
-	return false;
 }
 
 void InvertNode::compile(SVMCompiler& compiler)
@@ -3713,63 +3696,47 @@ void MixNode::compile(OSLCompiler& compiler)
 	compiler.add(this, "node_mix");
 }
 
-bool MixNode::constant_fold(ShaderGraph *graph,
-                            ShaderOutput * /*socket*/,
-                            ShaderInput *optimized)
+void MixNode::constant_fold(const ConstantFolder& folder)
 {
 	ShaderInput *fac_in = input("Fac");
 	ShaderInput *color1_in = input("Color1");
 	ShaderInput *color2_in = input("Color2");
-	ShaderOutput *color_out = output("Color");
 
 	/* evaluate fully constant node */
-	if(all_inputs_constant()) {
-		float3 result = svm_mix(type, fac, color1, color2);
-		optimized->set(use_clamp ? svm_mix_clamp(result) : result);
-		return true;
+	if(folder.all_inputs_constant()) {
+		folder.make_constant_clamp(svm_mix(type, fac, color1, color2), use_clamp);
+		return;
 	}
 
 	/* remove no-op node when factor is 0.0 */
 	if(!fac_in->link && fac <= 0.0f) {
 		/* note that some of the modes will clamp out of bounds values even without use_clamp */
-		if(!color1_in->link) {
-			float3 result = svm_mix(type, 0.0f, color1, color1);
-			optimized->set(use_clamp ? svm_mix_clamp(result) : result);
-			return true;
+		if(type == NODE_MIX_LIGHT || type == NODE_MIX_DODGE || type == NODE_MIX_BURN) {
+			if(!color1_in->link) {
+				folder.make_constant_clamp(svm_mix(type, 0.0f, color1, color1), use_clamp);
+				return;
+			}
 		}
-		else if(!use_clamp && type != NODE_MIX_LIGHT && type != NODE_MIX_DODGE && type != NODE_MIX_BURN) {
-			graph->relink(this, color_out, color1_in->link);
-			return true;
+		else if(folder.try_bypass_or_make_constant(color1_in, color1, use_clamp)) {
+			return;
 		}
 	}
 
-	if(type != NODE_MIX_BLEND) {
-		return false;
-	}
-
-	/* remove useless mix colors nodes */
-	if(color1_in->link && color1_in->link == color2_in->link && !use_clamp) {
-		graph->relink(this, color_out, color1_in->link);
-		return true;
-	}
-	if(!color1_in->link && !color2_in->link && color1 == color2) {
-		optimized->set(use_clamp ? svm_mix_clamp(color1) : color1);
-		return true;
-	}
-
-	/* remove no-op mix color node when factor is 1.0 */
-	if(!fac_in->link && fac >= 1.0f) {
-		if(!color2_in->link) {
-			optimized->set(use_clamp ? svm_mix_clamp(color2) : color2);
-			return true;
+	if(type == NODE_MIX_BLEND) {
+		/* remove useless mix colors nodes */
+		if(color1_in->link ? (color1_in->link == color2_in->link) : (!color2_in->link && color1 == color2)) {
+			if(folder.try_bypass_or_make_constant(color1_in, color1, use_clamp)) {
+				return;
+			}
 		}
-		else if(!use_clamp) {
-			graph->relink(this, color_out, color2_in->link);
-			return true;
+
+		/* remove no-op mix color node when factor is 1.0 */
+		if(!fac_in->link && fac >= 1.0f) {
+			if(folder.try_bypass_or_make_constant(color2_in, color2, use_clamp)) {
+				return;
+			}
 		}
 	}
-
-	return false;
 }
 
 /* Combine RGB */
@@ -3792,16 +3759,11 @@ CombineRGBNode::CombineRGBNode()
 {
 }
 
-bool CombineRGBNode::constant_fold(ShaderGraph * /*graph*/,
-                                   ShaderOutput * /*socket*/,
-                                   ShaderInput *optimized)
+void CombineRGBNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
-		optimized->set(make_float3(r, g, b));
-		return true;
+	if(folder.all_inputs_constant()) {
+		folder.make_constant(make_float3(r, g, b));
 	}
-
-	return false;
 }
 
 void CombineRGBNode::compile(SVMCompiler& compiler)
@@ -3849,16 +3811,11 @@ CombineXYZNode::CombineXYZNode()
 {
 }
 
-bool CombineXYZNode::constant_fold(ShaderGraph * /*graph*/,
-                                   ShaderOutput * /*socket*/,
-                                   ShaderInput *optimized)
+void CombineXYZNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
-		optimized->set(make_float3(x, y, z));
-		return true;
+	if(folder.all_inputs_constant()) {
+		folder.make_constant(make_float3(x, y, z));
 	}
-
-	return false;
 }
 
 void CombineXYZNode::compile(SVMCompiler& compiler)
@@ -3906,16 +3863,11 @@ CombineHSVNode::CombineHSVNode()
 {
 }
 
-bool CombineHSVNode::constant_fold(ShaderGraph * /*graph*/,
-                                   ShaderOutput * /*socket*/,
-                                   ShaderInput *optimized)
+void CombineHSVNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
-		optimized->set(hsv_to_rgb(make_float3(h, s, v)));
-		return true;
+	if(folder.all_inputs_constant()) {
+		folder.make_constant(hsv_to_rgb(make_float3(h, s, v)));
 	}
-
-	return false;
 }
 
 void CombineHSVNode::compile(SVMCompiler& compiler)
@@ -3956,16 +3908,11 @@ GammaNode::GammaNode()
 {
 }
 
-bool GammaNode::constant_fold(ShaderGraph * /*graph*/,
-                              ShaderOutput * /*socket*/,
-                              ShaderInput *optimized)
+void GammaNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
-		optimized->set(svm_math_gamma_color(color, gamma));
-		return true;
+	if(folder.all_inputs_constant()) {
+		folder.make_constant(svm_math_gamma_color(color, gamma));
 	}
-
-	return false;
 }
 
 void GammaNode::compile(SVMCompiler& compiler)
@@ -4005,16 +3952,11 @@ BrightContrastNode::BrightContrastNode()
 {
 }
 
-bool BrightContrastNode::constant_fold(ShaderGraph * /*graph*/,
-                                       ShaderOutput * /*socket*/,
-                                       ShaderInput *optimized)
+void BrightContrastNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
-		optimized->set(svm_brightness_contrast(color, bright, contrast));
-		return true;
+	if(folder.all_inputs_constant()) {
+		folder.make_constant(svm_brightness_contrast(color, bright, contrast));
 	}
-
-	return false;
 }
 
 void BrightContrastNode::compile(SVMCompiler& compiler)
@@ -4057,20 +3999,16 @@ SeparateRGBNode::SeparateRGBNode()
 {
 }
 
-bool SeparateRGBNode::constant_fold(ShaderGraph * /*graph*/,
-                                    ShaderOutput *socket,
-                                    ShaderInput *optimized)
+void SeparateRGBNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
+	if(folder.all_inputs_constant()) {
 		for(int channel = 0; channel < 3; channel++) {
-			if(outputs[channel] == socket) {
-				optimized->set(color[channel]);
-				return true;
+			if(outputs[channel] == folder.output) {
+				folder.make_constant(color[channel]);
+				return;
 			}
 		}
 	}
-
-	return false;
 }
 
 void SeparateRGBNode::compile(SVMCompiler& compiler)
@@ -4118,20 +4056,16 @@ SeparateXYZNode::SeparateXYZNode()
 {
 }
 
-bool SeparateXYZNode::constant_fold(ShaderGraph * /*graph*/,
-                                    ShaderOutput *socket,
-                                    ShaderInput *optimized)
+void SeparateXYZNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
+	if(folder.all_inputs_constant()) {
 		for(int channel = 0; channel < 3; channel++) {
-			if(outputs[channel] == socket) {
-				optimized->set(vector[channel]);
-				return true;
+			if(outputs[channel] == folder.output) {
+				folder.make_constant(vector[channel]);
+				return;
 			}
 		}
 	}
-
-	return false;
 }
 
 void SeparateXYZNode::compile(SVMCompiler& compiler)
@@ -4179,22 +4113,18 @@ SeparateHSVNode::SeparateHSVNode()
 {
 }
 
-bool SeparateHSVNode::constant_fold(ShaderGraph * /*graph*/,
-                                    ShaderOutput *socket,
-                                    ShaderInput *optimized)
+void SeparateHSVNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
+	if(folder.all_inputs_constant()) {
 		float3 hsv = rgb_to_hsv(color);
 
 		for(int channel = 0; channel < 3; channel++) {
-			if(outputs[channel] == socket) {
-				optimized->set(hsv[channel]);
-				return true;
+			if(outputs[channel] == folder.output) {
+				folder.make_constant(hsv[channel]);
+				return;
 			}
 		}
 	}
-
-	return false;
 }
 
 void SeparateHSVNode::compile(SVMCompiler& compiler)
@@ -4580,16 +4510,11 @@ BlackbodyNode::BlackbodyNode()
 {
 }
 
-bool BlackbodyNode::constant_fold(ShaderGraph * /*graph*/,
-                                  ShaderOutput * /*socket*/,
-                                  ShaderInput *optimized)
+void BlackbodyNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
-		optimized->set(svm_math_blackbody_color(temperature));
-		return true;
+	if(folder.all_inputs_constant()) {
+		folder.make_constant(svm_math_blackbody_color(temperature));
 	}
-
-	return false;
 }
 
 void BlackbodyNode::compile(SVMCompiler& compiler)
@@ -4691,17 +4616,11 @@ MathNode::MathNode()
 {
 }
 
-bool MathNode::constant_fold(ShaderGraph * /*graph*/,
-                             ShaderOutput * /*socket*/,
-                             ShaderInput *optimized)
+void MathNode::constant_fold(const ConstantFolder& folder)
 {
-	if(all_inputs_constant()) {
-		float value = svm_math(type, value1, value2);
-		optimized->set(use_clamp ? saturate(value) : value);
-		return true;
+	if(folder.all_inputs_constant()) {
+		folder.make_constant_clamp(svm_math(type, value1, value2), use_clamp);
 	}
-
-	return false;
 }
 
 void MathNode::compile(SVMCompiler& compiler)
@@ -4755,31 +4674,25 @@ VectorMathNode::VectorMathNode()
 {
 }
 
-bool VectorMathNode::constant_fold(ShaderGraph * /*graph*/,
-                                   ShaderOutput *socket,
-                                   ShaderInput *optimized)
+void VectorMathNode::constant_fold(const ConstantFolder& folder)
 {
 	float value;
 	float3 vector;
 
-	if(all_inputs_constant()) {
+	if(folder.all_inputs_constant()) {
 		svm_vector_math(&value,
 		                &vector,
 		                type,
 		                vector1,
 		                vector2);
 
-		if(socket == output("Value")) {
-			optimized->set(value);
-			return true;
+		if(folder.output == output("Value")) {
+			folder.make_constant(value);
 		}
-		else if(socket == output("Vector")) {
-			optimized->set(vector);
-			return true;
+		else if(folder.output == output("Vector")) {
+			folder.make_constant(vector);
 		}
 	}
-
-	return false;
 }
 
 void VectorMathNode::compile(SVMCompiler& compiler)
@@ -4913,9 +4826,7 @@ void BumpNode::compile(OSLCompiler& compiler)
 	compiler.add(this, "node_bump");
 }
 
-bool BumpNode::constant_fold(ShaderGraph *graph,
-                             ShaderOutput * /*socket*/,
-                             ShaderInput * /*optimized*/)
+void BumpNode::constant_fold(const ConstantFolder& folder)
 {
 	ShaderInput *height_in = input("Height");
 	ShaderInput *normal_in = input("Normal");
@@ -4923,18 +4834,15 @@ bool BumpNode::constant_fold(ShaderGraph *graph,
 	if(height_in->link == NULL) {
 		if(normal_in->link == NULL) {
 			GeometryNode *geom = new GeometryNode();
-			graph->add(geom);
-			graph->relink(this, outputs[0], geom->output("Normal"));
+			folder.graph->add(geom);
+			folder.bypass(geom->output("Normal"));
 		}
 		else {
-			graph->relink(this, outputs[0], normal_in->link);
+			folder.bypass(normal_in->link);
 		}
-		return true;
 	}
 
 	/* TODO(sergey): Ignore bump with zero strength. */
-
-	return false;
 }
 
 
diff --git a/intern/cycles/render/nodes.h b/intern/cycles/render/nodes.h
index 3245fdfb6d9..c98ff6f278d 100644
--- a/intern/cycles/render/nodes.h
+++ b/intern/cycles/render/nodes.h
@@ -289,7 +289,7 @@ public:
 class RGBToBWNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(RGBToBWNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 
 	float3 color;
 };
@@ -299,7 +299,7 @@ public:
 	ConvertNode(SocketType::Type from, SocketType::Type to, bool autoconvert = false);
 	SHADER_NODE_BASE_CLASS(ConvertNode)
 
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 
 	SocketType::Type from, to;
 
@@ -436,7 +436,7 @@ public:
 class EmissionNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(EmissionNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual ClosureType get_closure_type() { return CLOSURE_EMISSION_ID; }
 
 	bool has_surface_emission() { return true; }
@@ -449,7 +449,7 @@ public:
 class BackgroundNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(BackgroundNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual ClosureType get_closure_type() { return CLOSURE_BACKGROUND_ID; }
 
 	float3 color;
@@ -605,7 +605,7 @@ class ValueNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(ValueNode)
 
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 
 	float value;
 };
@@ -614,7 +614,7 @@ class ColorNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(ColorNode)
 
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 
 	float3 value;
 };
@@ -622,12 +622,13 @@ public:
 class AddClosureNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(AddClosureNode)
+	void constant_fold(const ConstantFolder& folder);
 };
 
 class MixClosureNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(MixClosureNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 
 	float fac;
 };
@@ -643,7 +644,7 @@ public:
 class InvertNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(InvertNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual int get_group() { return NODE_GROUP_LEVEL_3; }
 
 	float fac;
@@ -653,7 +654,7 @@ public:
 class MixNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(MixNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 
 	virtual int get_group() { return NODE_GROUP_LEVEL_3; }
 
@@ -667,7 +668,7 @@ public:
 class CombineRGBNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(CombineRGBNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual int get_group() { return NODE_GROUP_LEVEL_3; }
 
 	float r, g, b;
@@ -676,7 +677,7 @@ public:
 class CombineHSVNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(CombineHSVNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual int get_group() { return NODE_GROUP_LEVEL_3; }
 
 	float h, s, v;
@@ -685,7 +686,7 @@ public:
 class CombineXYZNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(CombineXYZNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual int get_group() { return NODE_GROUP_LEVEL_3; }
 
 	float x, y, z;
@@ -694,7 +695,7 @@ public:
 class GammaNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(GammaNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual int get_group() { return NODE_GROUP_LEVEL_1; }
 
 	float3 color;
@@ -704,7 +705,7 @@ public:
 class BrightContrastNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(BrightContrastNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual int get_group() { return NODE_GROUP_LEVEL_1; }
 
 	float3 color;
@@ -715,7 +716,7 @@ public:
 class SeparateRGBNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(SeparateRGBNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual int get_group() { return NODE_GROUP_LEVEL_3; }
 
 	float3 color;
@@ -724,7 +725,7 @@ public:
 class SeparateHSVNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(SeparateHSVNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual int get_group() { return NODE_GROUP_LEVEL_3; }
 
 	float3 color;
@@ -733,7 +734,7 @@ public:
 class SeparateXYZNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(SeparateXYZNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual int get_group() { return NODE_GROUP_LEVEL_3; }
 
 	float3 vector;
@@ -806,7 +807,7 @@ public:
 class BlackbodyNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(BlackbodyNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	virtual int get_group() { return NODE_GROUP_LEVEL_3; }
 
 	float temperature;
@@ -816,7 +817,7 @@ class MathNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(MathNode)
 	virtual int get_group() { return NODE_GROUP_LEVEL_1; }
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 
 	float value1;
 	float value2;
@@ -837,7 +838,7 @@ class VectorMathNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(VectorMathNode)
 	virtual int get_group() { return NODE_GROUP_LEVEL_1; }
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 
 	float3 vector1;
 	float3 vector2;
@@ -859,7 +860,7 @@ public:
 class BumpNode : public ShaderNode {
 public:
 	SHADER_NODE_CLASS(BumpNode)
-	bool constant_fold(ShaderGraph *graph, ShaderOutput *socket, ShaderInput *optimized);
+	void constant_fold(const ConstantFolder& folder);
 	bool has_spatial_varying() { return true; }
 	virtual int get_feature() {
 		return NODE_FEATURE_BUMP;