From c1e151ac196a4be006fdbb2616d0361cd49fcfa7 Mon Sep 17 00:00:00 2001
From: TomyLobo <tomylobo@nurfuerspam.de>
Date: Thu, 24 Nov 2011 20:51:11 +0100
Subject: [PATCH] Improved the expression parser's optimizer.

Added optimizers for Conditional, For, SimpleFor and While.
Improved the Sequence optimizer.
Removed the optimizer TODOs from Break and Return.
---
 .../worldedit/expression/runtime/Break.java    |  2 --
 .../expression/runtime/Conditional.java        | 17 +++++++++++++++--
 .../worldedit/expression/runtime/For.java      | 14 +++++++++++++-
 .../worldedit/expression/runtime/Return.java   |  2 --
 .../worldedit/expression/runtime/Sequence.java |  4 ++++
 .../expression/runtime/SimpleFor.java          |  7 ++++++-
 .../worldedit/expression/runtime/While.java    | 18 +++++++++++++++++-
 7 files changed, 55 insertions(+), 9 deletions(-)

diff --git a/src/main/java/com/sk89q/worldedit/expression/runtime/Break.java b/src/main/java/com/sk89q/worldedit/expression/runtime/Break.java
index 3a01fa4b3..b35303850 100644
--- a/src/main/java/com/sk89q/worldedit/expression/runtime/Break.java
+++ b/src/main/java/com/sk89q/worldedit/expression/runtime/Break.java
@@ -47,6 +47,4 @@ public class Break extends Node {
     public String toString() {
         return doContinue ? "continue" : "break";
     }
-
-    //TODO: optimizer
 }
diff --git a/src/main/java/com/sk89q/worldedit/expression/runtime/Conditional.java b/src/main/java/com/sk89q/worldedit/expression/runtime/Conditional.java
index c6c7d1c7c..06495a67f 100644
--- a/src/main/java/com/sk89q/worldedit/expression/runtime/Conditional.java
+++ b/src/main/java/com/sk89q/worldedit/expression/runtime/Conditional.java
@@ -42,7 +42,7 @@ public class Conditional extends Node {
         if (condition.getValue() > 0.0) {
             return truePart.getValue();
         } else {
-            return falsePart == null ? 0 : falsePart.getValue();
+            return falsePart == null ? 0.0 : falsePart.getValue();
         }
     }
 
@@ -62,5 +62,18 @@ public class Conditional extends Node {
         }
     }
 
-    //TODO: optimizer
+    @Override
+    public RValue optimize() throws EvaluationException {
+        final RValue newCondition = condition.optimize();
+
+        if (newCondition instanceof Constant) {
+            if (newCondition.getValue() > 0) {
+                return truePart.optimize();
+            } else {
+                return falsePart == null ? new Constant(getPosition(), 0.0) : falsePart.optimize();
+            }
+        }
+
+        return new Conditional(getPosition(), newCondition, truePart.optimize(), falsePart.optimize());
+    }
 }
diff --git a/src/main/java/com/sk89q/worldedit/expression/runtime/For.java b/src/main/java/com/sk89q/worldedit/expression/runtime/For.java
index 515fb2812..b3c397c34 100644
--- a/src/main/java/com/sk89q/worldedit/expression/runtime/For.java
+++ b/src/main/java/com/sk89q/worldedit/expression/runtime/For.java
@@ -74,5 +74,17 @@ public class For extends Node {
         return "for (" + init + "; " + condition + "; " + increment + ") { " + body + " }";
     }
 
-    //TODO: optimizer
+    @Override
+    public RValue optimize() throws EvaluationException {
+        final RValue newCondition = condition.optimize();
+
+        if (newCondition instanceof Constant && newCondition.getValue() <= 0) {
+            // If the condition is always false, the loop can be flattened.
+            // So we run the init part and then return 0.0.
+            return new Sequence(getPosition(), init, new Constant(getPosition(), 0.0)).optimize();
+        }
+
+        //return new Sequence(getPosition(), init.optimize(), new While(getPosition(), condition, new Sequence(getPosition(), body, increment), false)).optimize();
+        return new For(getPosition(), init.optimize(), newCondition, increment.optimize(), body.optimize());
+    }
 }
diff --git a/src/main/java/com/sk89q/worldedit/expression/runtime/Return.java b/src/main/java/com/sk89q/worldedit/expression/runtime/Return.java
index 30e97845d..c9905eb63 100644
--- a/src/main/java/com/sk89q/worldedit/expression/runtime/Return.java
+++ b/src/main/java/com/sk89q/worldedit/expression/runtime/Return.java
@@ -47,6 +47,4 @@ public class Return extends Node {
     public String toString() {
         return "return " + value;
     }
-
-    //TODO: optimizer
 }
diff --git a/src/main/java/com/sk89q/worldedit/expression/runtime/Sequence.java b/src/main/java/com/sk89q/worldedit/expression/runtime/Sequence.java
index 8da1db87d..bdf9615b8 100644
--- a/src/main/java/com/sk89q/worldedit/expression/runtime/Sequence.java
+++ b/src/main/java/com/sk89q/worldedit/expression/runtime/Sequence.java
@@ -88,6 +88,10 @@ public class Sequence extends Node {
             newSequence.add(droppedLast);
         }
 
+        if (newSequence.size() == 1) {
+            return newSequence.get(0);
+        }
+
         return new Sequence(getPosition(), newSequence.toArray(new RValue[newSequence.size()]));
     }
 }
diff --git a/src/main/java/com/sk89q/worldedit/expression/runtime/SimpleFor.java b/src/main/java/com/sk89q/worldedit/expression/runtime/SimpleFor.java
index 44c43e775..2016873b6 100644
--- a/src/main/java/com/sk89q/worldedit/expression/runtime/SimpleFor.java
+++ b/src/main/java/com/sk89q/worldedit/expression/runtime/SimpleFor.java
@@ -78,5 +78,10 @@ public class SimpleFor extends Node {
         return "for (" + counter + " = " + first + ", " + last + ") { " + body + " }";
     }
 
-    //TODO: optimizer
+    @Override
+    public RValue optimize() throws EvaluationException {
+        // TODO: unroll small loops into Sequences
+
+        return new SimpleFor(getPosition(), (LValue) counter.optimize(), first.optimize(), last.optimize(), body.optimize());
+    }
 }
diff --git a/src/main/java/com/sk89q/worldedit/expression/runtime/While.java b/src/main/java/com/sk89q/worldedit/expression/runtime/While.java
index 3f6e86200..6659502c4 100644
--- a/src/main/java/com/sk89q/worldedit/expression/runtime/While.java
+++ b/src/main/java/com/sk89q/worldedit/expression/runtime/While.java
@@ -95,5 +95,21 @@ public class While extends Node {
         }
     }
 
-    //TODO: optimizer
+    @Override
+    public RValue optimize() throws EvaluationException {
+        final RValue newCondition = condition.optimize();
+
+        if (newCondition instanceof Constant && newCondition.getValue() <= 0) {
+            // If the condition is always false, the loop can be flattened.
+            if (footChecked) {
+                // Foot-checked loops run at least once.
+                return body.optimize();
+            } else {
+                // Loops that never run always return 0.0.
+                return new Constant(getPosition(), 0.0);
+            }
+        }
+
+        return new While(getPosition(), newCondition, body.optimize(), footChecked);
+    }
 }