Fix: Unused variables now removed after joining consecutive assignments.

Previously joining assignments could sometimes result in a declared variable which is no longer needed.

Author: DeanEdisGG

ShaderShrinker/Shrinker.Parser/Optimizations/CombineAssignmentWithReturnExtension.cs

@@ -20,8 +20,9 @@ public static class CombineAssignmentWithReturnExtension
         /// <summary>
         /// Merge variable assignment with single use in an return statement on the next line.
         /// </summary>
-        public static void CombineAssignmentWithReturn(this SyntaxNode rootNode)
+        public static bool CombineAssignmentWithReturn(this SyntaxNode rootNode)
         {
+            var anyChanges = false;
             foreach (var functionNode in rootNode.FunctionDefinitions())
             {
                 foreach (var braces in functionNode.TheTree.OfType<BraceSyntaxNode>().ToList())
@@ -117,6 +118,7 @@ public static void CombineAssignmentWithReturn(this SyntaxNode rootNode)
                                 assignmentDecl.Remove(); // Declaration is now empty - Remove it.
 
                             didChange = true;
+                            anyChanges = true;
 
                             if (addBrackets)
                             {
@@ -137,6 +139,8 @@ public static void CombineAssignmentWithReturn(this SyntaxNode rootNode)
                     }
                 }
             }
+
+            return anyChanges;
         }
     }
 }

ShaderShrinker/Shrinker.Parser/Optimizations/CombineAssignmentWithSingleUseExtension.cs

@@ -20,8 +20,9 @@ public static class CombineAssignmentWithSingleUseExtension
         /// <summary>
         /// Merge variable assignment with single use in an assignment on the next line.
         /// </summary>
-        public static void CombineAssignmentWithSingleUse(this SyntaxNode rootNode)
+        public static bool CombineAssignmentWithSingleUse(this SyntaxNode rootNode)
         {
+            var anyChanges = false;
             var functionNodes = rootNode.FunctionDefinitions().ToList();
             foreach (var functionNode in functionNodes)
             {
@@ -116,12 +117,15 @@ public static void CombineAssignmentWithSingleUse(this SyntaxNode rootNode)
                             declParent.Remove();
 
                         didChange = true;
+                        anyChanges = true;
                     }
 
                     if (!didChange)
                         break;
                 }
             }
+
+            return anyChanges;
         }
     }
 }

ShaderShrinker/Shrinker.Parser/Shrinker.cs

@@ -82,8 +82,10 @@ public static SyntaxNode Simplify(this SyntaxNode rootNode, CustomOptions option
 
                 if (options.CombineAssignmentWithSingleUse)
                 {
-                    rootNode.CombineAssignmentWithReturn();
-                    rootNode.CombineAssignmentWithSingleUse();
+                    var anyChanges = rootNode.CombineAssignmentWithReturn();
+                    anyChanges |= rootNode.CombineAssignmentWithSingleUse();
+                    if (anyChanges && options.RemoveUnusedVariables)
+                        rootNode.RemoveUnusedVariables();
                 }
 
                 if (options.SimplifyBranching)

ShaderShrinker/UnitTests/ShrinkerTests.cs

@@ -1029,20 +1029,22 @@ public void CheckCombiningAssignmentWithUseWhenUsedOnlyOnce(
                     "int f(int i) { return i; } void main() { int a; for (int i = 0; i < 2; i++) { a = 2 + i; f(a); } return a; }",
                     "int main(out int i) { i = 2; return i; }",
                     "int main(inout int i) { i = 2; return i; }",
-                    "int main(int i) { i = 2; return i; }")] string code,
+                    "int main(int i) { i = 2; return i; }",
+                    "int main() { int a, b; a = 1; b = a + 1; return b; }")] string code,
             [Values("int main() { return 2 + 1; }",
                     "vec3 cam(vec3 ro, vec3 la, vec2 uv) { vec3 f = normalize(la - ro), r = normalize(cross(vec3(0, 1, 0), f)); return normalize(f + r * uv.x + cross(f, r) * uv.y); }",
                     "int f(int i) { return i; } void main() { int a; for (int i = 0; i < 2; i++) { a = 2 + i; f(a); } return a; }",
                     "int main(out int i) { i = 2; return i; }",
                     "int main(inout int i) { i = 2; return i; }",
-                    "int main(int i) { i = 2; return i; }")] string expected)
+                    "int main(int i) { i = 2; return i; }",
+                    "int main() { return 1 + 1; }")] string expected)
         {
             var lexer = new Lexer();
             lexer.Load(code);
 
             var options = CustomOptions.None();
             options.CombineAssignmentWithSingleUse = true;
-            options.GroupVariableDeclarations = true;
+            options.RemoveUnusedVariables = true;
             var rootNode = new Parser(lexer)
                 .Parse()
                 .Simplify(options);