Reduce redundant local variable reassignments.

Washi1337 · May 21, 2024 · c38555a · c38555a
1 parent 824eb9f
commit c38555a
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Showing 3 changed files with 8 additions and 4 deletions.
diff --git a/src/Core/Echo.Ast/AstFormatter.cs b/src/Core/Echo.Ast/AstFormatter.cs
@@ -86,9 +86,9 @@ public void Visit(AssignmentStatement<TInstruction> statement, IndentedTextWrite
     }
 
     /// <inheritdoc />
-    public void Visit(ExpressionStatement<TInstruction> expression, IndentedTextWriter state)
+    public void Visit(ExpressionStatement<TInstruction> statement, IndentedTextWriter state)
     {
-        expression.Expression.Accept(this, state);
+        statement.Expression.Accept(this, state);
         state.Write(';');
     }
 

diff --git a/src/Core/Echo.Ast/Construction/ControlFlowGraphLifter.cs b/src/Core/Echo.Ast/Construction/ControlFlowGraphLifter.cs
@@ -208,6 +208,10 @@ private static void FlushStackAndPush(LiftedNode<TInstruction> node, Stack<Expre
     {
         var variables = FlushStackInternal(node, stack, static (n, value) =>
         {
+            // Optimization: If we are simply reassigning variables, we can skip introducing a new variable (inlining).
+            if (value is VariableExpression<TInstruction> variableExpression)
+                return variableExpression.Variable;
+            
             var intermediate = n.DeclareStackIntermediate();
             n.Transformed.Contents.Instructions.Add(Statement.Assignment(intermediate, value));
             return intermediate;
@@ -245,7 +249,7 @@ private void FlushStackIfImpure(
     private static IList<IVariable> FlushStackInternal(
         LiftedNode<TInstruction> node, 
         Stack<Expression<TInstruction>> stack,
-        Func<LiftedNode<TInstruction>, Expression<TInstruction>, SyntheticVariable> flush)
+        Func<LiftedNode<TInstruction>, Expression<TInstruction>, IVariable> flush)
     {
         // Collect all values from the stack.
         var values = new Expression<TInstruction>[stack.Count];

diff --git a/src/Core/Echo.Ast/IAstNodeVisitor.cs b/src/Core/Echo.Ast/IAstNodeVisitor.cs
@@ -73,7 +73,7 @@ public interface IAstNodeVisitor<TInstruction, in TState>
         /// <summary>
         /// Visits a given <see cref="ExpressionStatement{TInstruction}"/>
         /// </summary>
-        void Visit(ExpressionStatement<TInstruction> expression, TState state);
+        void Visit(ExpressionStatement<TInstruction> statement, TState state);
 
         /// <summary>
         /// Visits a given <see cref="PhiStatement{TInstruction}"/>