Simplify generated code for string interpolation by delaying the constant folding.

lib/compiler/implementation/ssa/optimize.dart

Index: lib/compiler/implementation/ssa/optimize.dart
diff --git a/lib/compiler/implementation/ssa/optimize.dart b/lib/compiler/implementation/ssa/optimize.dart
index d29e599fd5bb3738e8498a0bd61ffd9c05405196..36c29cee48b56bd7ed7c7d46c6f2146755d5305c 100644
--- a/lib/compiler/implementation/ssa/optimize.dart
+++ b/lib/compiler/implementation/ssa/optimize.dart
@@ -590,6 +590,28 @@ class SsaConstantFolder extends HBaseVisitor implements OptimizationPhase {
     if (field === null) return node;
     return new HFieldSet(field, node.inputs[0], node.inputs[1]);
   }
+
+  bool isEmptyString(HInstruction node) {
+    if (!node.isConstantString()) return false;
+    HConstant constant = node;
+    StringConstant string = constant.constant;
+    return string.value.length == 0;
+  }
+
+  HInstruction visitStringConcat(HStringConcat node) {
+    if (isEmptyString(node.inputs[0])) return node.inputs[1];
+    if (isEmptyString(node.inputs[1])) return node.inputs[0];
+    DartString folded = const LiteralDartString("");
+    for (int i = 0; i < node.inputs.length; i++) {

[Lasse Reichstein Nielsen, 2012/06/06 12:11:40]

This seems to assume more than two inputs. Intentional?

+      HInstruction part = node.inputs[i];
+      if (!part.isConstant()) return node;
+      HConstant constant = part;
+      if (!constant.constant.isPrimitive()) return node;
+      PrimitiveConstant primitive = constant.constant;
+      folded = new DartString.concat(folded, primitive.toDartString());
+    }
+    return graph.addConstantString(folded, node);
+  }
 }
 
 class SsaCheckInserter extends HBaseVisitor implements OptimizationPhase {