From ea489c40680f9e8e90eeb163d17c8dddd53981d4 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 7 Apr 2021 15:28:24 +0300
Subject: [PATCH] Check that non-constant data is not accessed from constant
 expressions

---
 source/glsl/validate.cpp             | 42 ++++++++++++++++++++++++----
 source/glsl/validate.h               |  3 ++
 tests/glsl/constant_expressions.glsl | 15 ++++++++++
 3 files changed, 55 insertions(+), 5 deletions(-)
 create mode 100644 tests/glsl/constant_expressions.glsl

diff --git a/source/glsl/validate.cpp b/source/glsl/validate.cpp
index 4a5ffe84..62f997bb 100644
--- a/source/glsl/validate.cpp
+++ b/source/glsl/validate.cpp
@@ -508,9 +508,22 @@ void ReferenceValidator::visit(FunctionDeclaration &func)
 
 
 ExpressionValidator::ExpressionValidator():
-	current_function(0)
+	current_function(0),
+	constant_expression(false)
 { }
 
+void ExpressionValidator::visit(VariableReference &var)
+{
+	if(var.declaration && constant_expression && !var.declaration->constant)
+		error(var, format("Reference to non-constant variable '%s' in a constant expression", var.name));
+}
+
+void ExpressionValidator::visit(InterfaceBlockReference &iface)
+{
+	if(constant_expression)
+		error(iface, format("Reference to interface block '%s' in a constant expression", iface.name));
+}
+
 void ExpressionValidator::visit(Swizzle &swizzle)
 {
 	unsigned size = 0;
@@ -555,8 +568,13 @@ void ExpressionValidator::visit(UnaryExpression &unary)
 	{
 		if(!unary.type)
 			error(unary, format("No matching operator '%s' found for '%s'", unary.oper->token, unary.expression->type->name));
-		else if((unary.oper->token[1]=='+' || unary.oper->token[1]=='-') && !unary.expression->lvalue)
-			error(unary, format("Operand of '%s' is not an lvalue", unary.oper->token));
+		else if(unary.oper->token[1]=='+' || unary.oper->token[1]=='-')
+		{
+			if(constant_expression)
+				error(unary, format("Use of '%s' in a constant expression", unary.oper->token));
+			else if(!unary.expression->lvalue)
+				error(unary, format("Operand of '%s' is not an lvalue", unary.oper->token));
+		}
 	}
 	TraversingVisitor::visit(unary);
 }
@@ -579,7 +597,9 @@ void ExpressionValidator::visit(Assignment &assign)
 {
 	if(assign.left->type)
 	{
-		if(!assign.left->lvalue)
+		if(constant_expression)
+			error(assign, "Assignment in constant expression");
+		else if(!assign.left->lvalue)
 			error(assign, "Target of assignment is not an lvalue");
 		if(assign.right->type)
 		{
@@ -616,7 +636,19 @@ void ExpressionValidator::visit(VariableDeclaration &var)
 	if(var.init_expression && var.init_expression->type && var.type_declaration && var.init_expression->type!=var.type_declaration)
 		error(var, format("Initializing a variable of type '%s' with an expression of incompatible type '%s'",
 			var.type_declaration->name, var.init_expression->type->name));
-	TraversingVisitor::visit(var);
+
+	if(var.layout)
+		var.layout->visit(*this);
+	if(var.init_expression)
+	{
+		SetFlag set_const(constant_expression, var.constant);
+		TraversingVisitor::visit(var.init_expression);
+	}
+	if(var.array_size)
+	{
+		SetFlag set_const(constant_expression);
+		TraversingVisitor::visit(var.array_size);
+	}
 }
 
 void ExpressionValidator::visit(FunctionDeclaration &func)
diff --git a/source/glsl/validate.h b/source/glsl/validate.h
index 1a058170..fe52ff5a 100644
--- a/source/glsl/validate.h
+++ b/source/glsl/validate.h
@@ -118,6 +118,7 @@ class ExpressionValidator: private Validator
 {
 private:
 	FunctionDeclaration *current_function;
+	bool constant_expression;
 
 public:
 	ExpressionValidator();
@@ -125,6 +126,8 @@ public:
 	void apply(Stage &s) { stage = &s; s.content.visit(*this); }
 
 private:
+	virtual void visit(VariableReference &);
+	virtual void visit(InterfaceBlockReference &);
 	virtual void visit(Swizzle &);
 	virtual void visit(UnaryExpression &);
 	virtual void visit(BinaryExpression &);
diff --git a/tests/glsl/constant_expressions.glsl b/tests/glsl/constant_expressions.glsl
new file mode 100644
index 00000000..90eab787
--- /dev/null
+++ b/tests/glsl/constant_expressions.glsl
@@ -0,0 +1,15 @@
+uniform int n_lights;
+uniform vec3 light_dir[n_lights];
+
+#pragma MSP stage(vertex)
+layout(location=0) in vec4 position;
+const bool lower_half = position.y<0;
+void main()
+{
+	gl_Position = position;
+}
+
+/* Expected error:
+<test>:2: Reference to non-constant variable 'n_lights' in a constant expression
+<test>:6: Reference to non-constant variable 'position' in a constant expression
+*/
-- 
2.45.2