From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 7 Apr 2021 20:35:12 +0000 (+0300)
Subject: Remove unreachable code after a jump statement
X-Git-Url: http://git.tdb.fi/?p=libs%2Fgl.git;a=commitdiff_plain;h=55a18f710f07c51f05d0dc55741a7f3cc8e70cdd

Remove unreachable code after a jump statement
---

diff --git a/source/glsl/compiler.cpp b/source/glsl/compiler.cpp
index 0ad41dfa..e2745e1b 100644
--- a/source/glsl/compiler.cpp
+++ b/source/glsl/compiler.cpp
@@ -372,7 +372,8 @@ Compiler::OptimizeResult Compiler::optimize(Stage &stage)
 
 	/* Removing variables or functions may cause things from the previous stage
 	to become unused. */
-	bool any_removed = UnusedVariableRemover().apply(stage);
+	bool any_removed = UnreachableCodeRemover().apply(stage);
+	any_removed |= UnusedVariableRemover().apply(stage);
 	any_removed |= UnusedFunctionRemover().apply(stage);
 	any_removed |= UnusedTypeRemover().apply(stage);
 
diff --git a/source/glsl/optimize.cpp b/source/glsl/optimize.cpp
index 0f765c2a..f333ef44 100644
--- a/source/glsl/optimize.cpp
+++ b/source/glsl/optimize.cpp
@@ -907,6 +907,52 @@ void ConstantConditionEliminator::visit(Iteration &iter)
 }
 
 
+UnreachableCodeRemover::UnreachableCodeRemover():
+	reachable(true)
+{ }
+
+bool UnreachableCodeRemover::apply(Stage &stage)
+{
+	stage.content.visit(*this);
+	NodeRemover().apply(stage, unreachable_nodes);
+	return !unreachable_nodes.empty();
+}
+
+void UnreachableCodeRemover::visit(Block &block)
+{
+	NodeList<Statement>::iterator i = block.body.begin();
+	for(; (reachable && i!=block.body.end()); ++i)
+		(*i)->visit(*this);
+	for(; i!=block.body.end(); ++i)
+		unreachable_nodes.insert(i->get());
+}
+
+void UnreachableCodeRemover::visit(FunctionDeclaration &func)
+{
+	TraversingVisitor::visit(func);
+	reachable = true;
+}
+
+void UnreachableCodeRemover::visit(Conditional &cond)
+{
+	cond.body.visit(*this);
+	bool reachable_if_true = reachable;
+	reachable = true;
+	cond.else_body.visit(*this);
+
+	reachable |= reachable_if_true;
+}
+
+void UnreachableCodeRemover::visit(Iteration &iter)
+{
+	TraversingVisitor::visit(iter);
+
+	/* Always consider code after a loop reachable, since there's no checking
+	for whether the loop executes. */
+	reachable = true;
+}
+
+
 bool UnusedTypeRemover::apply(Stage &stage)
 {
 	stage.content.visit(*this);
diff --git a/source/glsl/optimize.h b/source/glsl/optimize.h
index b7b39176..e21dd98f 100644
--- a/source/glsl/optimize.h
+++ b/source/glsl/optimize.h
@@ -227,6 +227,26 @@ private:
 	virtual void visit(Iteration &);
 };
 
+class UnreachableCodeRemover: private TraversingVisitor
+{
+private:
+	bool reachable;
+	std::set<Node *> unreachable_nodes;
+
+public:
+	UnreachableCodeRemover();
+
+	virtual bool apply(Stage &);
+
+private:
+	virtual void visit(Block &);
+	virtual void visit(FunctionDeclaration &);
+	virtual void visit(Conditional &);
+	virtual void visit(Iteration &);
+	virtual void visit(Return &) { reachable = false; }
+	virtual void visit(Jump &) { reachable = false; }
+};
+
 /** Removes types which are not used anywhere. */
 class UnusedTypeRemover: private TraversingVisitor
 {
diff --git a/tests/glsl/dead_code.glsl b/tests/glsl/dead_code.glsl
new file mode 100644
index 00000000..bdfd4503
--- /dev/null
+++ b/tests/glsl/dead_code.glsl
@@ -0,0 +1,20 @@
+uniform mat4 mvp;
+
+#pragma MSP stage(vertex)
+layout(location=0) in vec4 position;
+void main()
+{
+	gl_Position = mvp*position;
+	return;
+	gl_Position = position;
+}
+
+/* Expected output: vertex
+layout(location=0) uniform mat4 mvp;
+layout(location=0) in vec4 position;
+void main()
+{
+	gl_Position = mvp*position;
+	return;
+}
+*/