From: Mikko Rasa <tdb@tdb.fi>
Date: Tue, 9 Mar 2021 20:27:04 +0000 (+0200)
Subject: Avoid removing outputs which are referenced but not assigned
X-Git-Url: http://git.tdb.fi/?p=libs%2Fgl.git;a=commitdiff_plain;h=5b33d00373c6f4953d684f8cc75c9353df469735

Avoid removing outputs which are referenced but not assigned

The values from such reads are undefined but the variables should be
kept nevertheless.
---

diff --git a/source/glsl/optimize.cpp b/source/glsl/optimize.cpp
index 7f60e67c..500c8417 100644
--- a/source/glsl/optimize.cpp
+++ b/source/glsl/optimize.cpp
@@ -661,7 +661,7 @@ bool UnusedVariableRemover::apply(Stage &s)
 		}
 		if(output)
 		{
-			if(!i->second.assignments.empty() && i->second.interface_block)
+			if((i->second.referenced || !i->second.assignments.empty()) && i->second.interface_block)
 				used_interface_blocks.insert(i->second.interface_block);
 			continue;
 		}
diff --git a/tests/glsl/referenced_but_unassigned_output.glsl b/tests/glsl/referenced_but_unassigned_output.glsl
new file mode 100644
index 00000000..aabff089
--- /dev/null
+++ b/tests/glsl/referenced_but_unassigned_output.glsl
@@ -0,0 +1,50 @@
+uniform mat4 projection;
+
+#pragma MSP stage(vertex)
+layout(location=0) in vec4 position;
+layout(location=1) in vec3 normal;
+out vec4 eye_vertex;
+out VertexOut
+{
+	vec4 color;
+};
+void main()
+{
+	gl_Position = projection*eye_vertex;
+	out float alpha = color.a;
+}
+
+#pragma MSP stage(fragment)
+layout(location=0) out vec4 frag_color;
+void main()
+{
+	frag_color = vec4(color.rgb, alpha);
+}
+
+/* Expected output: vertex
+uniform mat4 projection;
+out vec4 eye_vertex;
+out VertexOut
+{
+  vec4 color;
+};
+out float alpha;
+void main()
+{
+  gl_Position = projection*eye_vertex;
+  alpha = color.a;
+}
+*/
+
+/* Expected output: fragment
+layout(location=0) out vec4 frag_color;
+in VertexOut
+{
+  vec4 color;
+};
+in float alpha;
+void main()
+{
+  frag_color = vec4(color.rgb, alpha);
+}
+*/