From c38555ae41d3d80d94babd67439a7df03dc769ae Mon Sep 17 00:00:00 2001
From: Washi <washi1337@protonmail.com>
Date: Tue, 21 May 2024 21:04:19 +0200
Subject: [PATCH] Reduce redundant local variable reassignments.

---
 src/Core/Echo.Ast/AstFormatter.cs                        | 4 ++--
 src/Core/Echo.Ast/Construction/ControlFlowGraphLifter.cs | 6 +++++-
 src/Core/Echo.Ast/IAstNodeVisitor.cs                     | 2 +-
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/Core/Echo.Ast/AstFormatter.cs b/src/Core/Echo.Ast/AstFormatter.cs
index 67ba43bd..e739a3ef 100644
--- 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
index 006d67aa..fd0e585c 100644
--- 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
index b250dfbe..4c0619f4 100644
--- 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}"/>