From c4ae3a80623be4b0f17de4a9cc25f0bedf2dbef5 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Mon, 15 Mar 2021 11:05:26 +0200
Subject: [PATCH] Eliminate constant ternary expressions

---
 source/glsl/optimize.cpp                 | 18 +++++++++++++
 source/glsl/optimize.h                   |  3 +++
 tests/glsl/constant_ternary_removal.glsl | 33 ++++++++++++++++++++++++
 3 files changed, 54 insertions(+)
 create mode 100644 tests/glsl/constant_ternary_removal.glsl

diff --git a/source/glsl/optimize.cpp b/source/glsl/optimize.cpp
index 9cfad86a..7473fe2c 100644
--- a/source/glsl/optimize.cpp
+++ b/source/glsl/optimize.cpp
@@ -792,6 +792,24 @@ void ConstantConditionEliminator::visit(Block &block)
 	}
 }
 
+void ConstantConditionEliminator::visit(RefPtr<Expression> &expr)
+{
+	r_ternary_result = 0;
+	expr->visit(*this);
+	if(r_ternary_result)
+		expr = r_ternary_result;
+	r_ternary_result = 0;
+}
+
+void ConstantConditionEliminator::visit(TernaryExpression &ternary)
+{
+	ConstantStatus result = check_constant_condition(*ternary.condition);
+	if(result!=NOT_CONSTANT)
+		r_ternary_result = (result==CONSTANT_TRUE ? ternary.true_expr : ternary.false_expr);
+	else
+		r_ternary_result = 0;
+}
+
 void ConstantConditionEliminator::visit(Conditional &cond)
 {
 	ConstantStatus result = check_constant_condition(*cond.condition);
diff --git a/source/glsl/optimize.h b/source/glsl/optimize.h
index 1262823f..16038806 100644
--- a/source/glsl/optimize.h
+++ b/source/glsl/optimize.h
@@ -191,6 +191,7 @@ private:
 
 	NodeList<Statement>::iterator insert_point;
 	std::set<Node *> nodes_to_remove;
+	RefPtr<Expression> r_ternary_result;
 
 public:
 	void apply(Stage &);
@@ -199,6 +200,8 @@ private:
 	ConstantStatus check_constant_condition(const Expression &);
 
 	virtual void visit(Block &);
+	virtual void visit(RefPtr<Expression> &);
+	virtual void visit(TernaryExpression &);
 	virtual void visit(Conditional &);
 	virtual void visit(Iteration &);
 };
diff --git a/tests/glsl/constant_ternary_removal.glsl b/tests/glsl/constant_ternary_removal.glsl
new file mode 100644
index 00000000..02707103
--- /dev/null
+++ b/tests/glsl/constant_ternary_removal.glsl
@@ -0,0 +1,33 @@
+const bool use_color = false;
+
+#pragma MSP stage(vertex)
+layout(location=0) in vec4 position;
+layout(location=1) in vec4 color;
+void main()
+{
+	gl_Position = position;
+	passthrough;
+}
+
+#pragma MSP stage(fragment)
+layout(location=0) out vec4 frag_color;
+void main()
+{
+	frag_color = (use_color ? color : vec4(1.0));
+}
+
+/* Expected output: vertex
+layout(location=0) in vec4 position;
+void main()
+{
+	gl_Position = position;
+}
+*/
+
+/* Expected output: fragment
+layout(location=0) out vec4 frag_color;
+void main()
+{
+	frag_color = vec4(1.0);
+}
+*/
-- 
2.43.0