From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 7 Apr 2021 20:49:31 +0000 (+0300)
Subject: Validate GLSL flow control
X-Git-Url: http://git.tdb.fi/?p=libs%2Fgl.git;a=commitdiff_plain;h=9d9e008291a447b5d192e724e9022180503c8c3e

Validate GLSL flow control

In particular, it's an error to reach the end of a non-void function
without a return statement.
---

diff --git a/source/glsl/compiler.cpp b/source/glsl/compiler.cpp
index e2745e1b..7021c62d 100644
--- a/source/glsl/compiler.cpp
+++ b/source/glsl/compiler.cpp
@@ -323,6 +323,7 @@ void Compiler::validate(Stage &stage)
 	IdentifierValidator().apply(stage);
 	ReferenceValidator().apply(stage);
 	ExpressionValidator().apply(stage);
+	FlowControlValidator().apply(stage);
 	StageInterfaceValidator().apply(stage);
 }
 
diff --git a/source/glsl/validate.cpp b/source/glsl/validate.cpp
index 62f997bb..86afebed 100644
--- a/source/glsl/validate.cpp
+++ b/source/glsl/validate.cpp
@@ -699,6 +699,52 @@ void ExpressionValidator::visit(Return &ret)
 }
 
 
+FlowControlValidator::FlowControlValidator():
+	reachable(true)
+{ }
+
+void FlowControlValidator::visit(Block &block)
+{
+	for(NodeList<Statement>::const_iterator i=block.body.begin(); i!=block.body.end(); ++i)
+	{
+		if(!reachable)
+		{
+			diagnose(**i, Diagnostic::WARN, "Unreachable code detected");
+			break;
+		}
+		(*i)->visit(*this);
+	}
+}
+
+void FlowControlValidator::visit(FunctionDeclaration &func)
+{
+	func.body.visit(*this);
+
+	if(func.definition==&func && func.return_type_declaration)
+	{
+		const BasicTypeDeclaration *basic_ret = dynamic_cast<const BasicTypeDeclaration *>(func.return_type_declaration);
+		if(reachable && (!basic_ret || basic_ret->kind!=BasicTypeDeclaration::VOID))
+			error(func, "Missing return statement at the end of a function not returning 'void'");
+	}
+	reachable = true;
+}
+
+void FlowControlValidator::visit(Conditional &cond)
+{
+	cond.body.visit(*this);
+	bool reachable_if_true = reachable;
+	reachable = true;
+	cond.else_body.visit(*this);
+	reachable |= reachable_if_true;
+}
+
+void FlowControlValidator::visit(Iteration &iter)
+{
+	iter.body.visit(*this);
+	reachable = true;
+}
+
+
 int StageInterfaceValidator::get_location(const Layout &layout)
 {
 	for(vector<Layout::Qualifier>::const_iterator i=layout.qualifiers.begin(); i!=layout.qualifiers.end(); ++i)
diff --git a/source/glsl/validate.h b/source/glsl/validate.h
index fe52ff5a..d3884901 100644
--- a/source/glsl/validate.h
+++ b/source/glsl/validate.h
@@ -140,6 +140,27 @@ private:
 	virtual void visit(Return &);
 };
 
+/** Verifies flow control constructs.  Functions returning non-void must have
+return statements.  Warnings are given about dead code. */
+class FlowControlValidator: private Validator
+{
+private:
+	bool reachable;
+
+public:
+	FlowControlValidator();
+
+	void apply(Stage &s) { stage = &s; s.content.visit(*this); }
+
+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; }
+};
+
 /** Verifies that stage input and output interfaces are valid.  Linked
 variables must have matching types and locations and there must not be any
 overlap in locations. */
diff --git a/tests/glsl/dead_code.glsl b/tests/glsl/dead_code.glsl
index bdfd4503..4c15cc18 100644
--- a/tests/glsl/dead_code.glsl
+++ b/tests/glsl/dead_code.glsl
@@ -9,6 +9,10 @@ void main()
 	gl_Position = position;
 }
 
+/* Expected diagnostic:
+<test>:9: Unreachable code detected
+*/
+
 /* Expected output: vertex
 layout(location=0) uniform mat4 mvp;
 layout(location=0) in vec4 position;
diff --git a/tests/glsl/function_override.glsl b/tests/glsl/function_override.glsl
index c7e64d52..746ea8d3 100644
--- a/tests/glsl/function_override.glsl
+++ b/tests/glsl/function_override.glsl
@@ -4,7 +4,7 @@ virtual float get_scale()
 {
 	return 1.0;
 }
-int main()
+void main()
 {
 	gl_Position = position*get_scale();
 }
@@ -15,7 +15,7 @@ float get_scale() override
 
 /* Expected output: vertex
 layout(location=0) in vec4 position;
-int main()
+void main()
 {
 	gl_Position = position*2.0;
 }
diff --git a/tests/glsl/invalid_subscript.glsl b/tests/glsl/invalid_subscript.glsl
index 6826feff..5f959ffb 100644
--- a/tests/glsl/invalid_subscript.glsl
+++ b/tests/glsl/invalid_subscript.glsl
@@ -1,7 +1,7 @@
 #pragma MSP stage(vertex)
 layout(location=0) in vec4 position;
 layout(location=1) in float scale;
-int main()
+void main()
 {
 	gl_Position = position[scale];
 	gl_Position = scale[position];
diff --git a/tests/glsl/no_op_conversion.glsl b/tests/glsl/no_op_conversion.glsl
index 2e3ff57b..f0f887e9 100644
--- a/tests/glsl/no_op_conversion.glsl
+++ b/tests/glsl/no_op_conversion.glsl
@@ -2,7 +2,7 @@ uniform mat4 mvp;
 
 #pragma MSP stage(vertex)
 layout(location=0) in vec4 position;
-int main()
+void main()
 {
 	gl_Position = mat4(mvp)*vec4(position);
 }
@@ -10,7 +10,7 @@ int main()
 /* Expected output: vertex
 layout(location=0) uniform mat4 mvp;
 layout(location=0) in vec4 position;
-int main()
+void main()
 {
   gl_Position = mat4(mvp)*vec4(position);
 }
diff --git a/tests/glsl/unused_component_assignment.glsl b/tests/glsl/unused_component_assignment.glsl
index 0febd561..af880f5d 100644
--- a/tests/glsl/unused_component_assignment.glsl
+++ b/tests/glsl/unused_component_assignment.glsl
@@ -2,7 +2,7 @@ uniform mat4 mvp;
 
 #pragma MSP stage(vertex)
 layout(location=0) in vec4 position;
-int main()
+void main()
 {
 	vec4 c0 = mvp[0]*position;
 	vec4 c1 = mvp[1]*position;
@@ -19,7 +19,7 @@ int main()
 /* Expected output: vertex
 layout(location=0) uniform mat4 mvp;
 layout(location=0) in vec4 position;
-int main()
+void main()
 {
   vec4 c0 = mvp[0]*position;
   vec4 c1 = mvp[1]*position;