[vala] Simplify while statements whose condition is false

[Jürg Billeter <juergbi src gnome org>]

commit 607dd99bc858155329bec6e225c891e3b0ffe9e0
Author: Jürg Billeter <j bitron ch>
Date:   Mon Mar 22 11:35:51 2010 +0100

    Simplify while statements whose condition is false
    
    Fixes bug 601339.

 vala/valawhilestatement.vala |   15 ++++++++++++---
 1 files changed, 12 insertions(+), 3 deletions(-)
---
diff --git a/vala/valawhilestatement.vala b/vala/valawhilestatement.vala
index 71f5405..8df427d 100644
--- a/vala/valawhilestatement.vala
+++ b/vala/valawhilestatement.vala
@@ -1,6 +1,6 @@
 /* valawhilestatement.vala
  *
- * Copyright (C) 2006-2009  Jürg Billeter
+ * Copyright (C) 2006-2010  Jürg Billeter
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -86,11 +86,20 @@ public class Vala.WhileStatement : CodeNode, Statement {
 		return (literal != null && literal.value);
 	}
 
+	bool always_false (Expression condition) {
+		var literal = condition as BooleanLiteral;
+		return (literal != null && !literal.value);
+	}
+
 	public override bool check (SemanticAnalyzer analyzer) {
 		// convert to simple loop
 
-		// do not generate if block if condition is always true
-		if (!always_true (condition)) {
+		if (always_true (condition)) {
+			// do not generate if block if condition is always true
+		} else if (always_false (condition)) {
+			// do not generate if block if condition is always false
+			body.insert_statement (0, new BreakStatement (condition.source_reference));
+		} else {
 			var if_condition = new UnaryExpression (UnaryOperator.LOGICAL_NEGATION, condition, condition.source_reference);
 			var true_block = new Block (condition.source_reference);
 			true_block.add_statement (new BreakStatement (condition.source_reference));