From: Mikko Rasa <tdb@tdb.fi>
Date: Wed, 7 Dec 2016 00:31:45 +0000 (+0200)
Subject: Recognize backward references in GLSL loops
X-Git-Url: http://git.tdb.fi/?p=libs%2Fgl.git;a=commitdiff_plain;h=ced18c244f874638dc17ae486802bb3bb01ecf71

Recognize backward references in GLSL loops

A lone assignment at the end of a loop isn't unused if the next iteration
uses the value.
---

diff --git a/source/programcompiler.cpp b/source/programcompiler.cpp
index c7da6c55..4e4b4814 100644
--- a/source/programcompiler.cpp
+++ b/source/programcompiler.cpp
@@ -1212,7 +1212,8 @@ void ProgramCompiler::ConstantConditionEliminator::visit(Iteration &iter)
 ProgramCompiler::UnusedVariableLocator::UnusedVariableLocator():
 	aggregate(0),
 	assignment(0),
-	assignment_target(false)
+	assignment_target(false),
+	iteration(false)
 { }
 
 void ProgramCompiler::UnusedVariableLocator::apply(Stage &s)
@@ -1233,6 +1234,9 @@ void ProgramCompiler::UnusedVariableLocator::visit(VariableReference &var)
 	if(assignment_target)
 		return;
 
+	if(iteration)
+		used_in_iteration.insert(var.declaration);
+
 	for(vector<BlockAssignmentMap>::iterator j=assignments.end(); j!=assignments.begin(); )
 	{
 		--j;
@@ -1277,7 +1281,8 @@ void ProgramCompiler::UnusedVariableLocator::visit(Assignment &assign)
 
 void ProgramCompiler::UnusedVariableLocator::record_assignment(VariableDeclaration &var, Node &node, bool self_ref)
 {
-	unused_nodes.insert(&node);
+	if(!used_in_iteration.count(&var))
+		unused_nodes.insert(&node);
 	BlockAssignmentMap &block_assignments = assignments.back();
 	AssignmentList &var_assignments = block_assignments[&var];
 	if(!self_ref)
@@ -1404,8 +1409,13 @@ void ProgramCompiler::UnusedVariableLocator::visit(Conditional &cond)
 void ProgramCompiler::UnusedVariableLocator::visit(Iteration &iter)
 {
 	assignments.push_back(BlockAssignmentMap());
-	TraversingVisitor::visit(iter);
+	{
+		SetFlag set(iteration);
+		TraversingVisitor::visit(iter);
+	}
 	merge_down_assignments();
+	if(!iteration)
+		used_in_iteration.clear();
 }
 
 
diff --git a/source/programcompiler.h b/source/programcompiler.h
index e43b3a2d..db63eb36 100644
--- a/source/programcompiler.h
+++ b/source/programcompiler.h
@@ -262,6 +262,8 @@ private:
 		std::vector<BlockAssignmentMap> assignments;
 		ProgramSyntax::Assignment *assignment;
 		bool assignment_target;
+		bool iteration;
+		std::set<ProgramSyntax::Node *> used_in_iteration;
 
 		UnusedVariableLocator();