Inserted string validation as separate task in compiler.

frog/leg/ssa/builder.dart

Index: frog/leg/ssa/builder.dart
diff --git a/frog/leg/ssa/builder.dart b/frog/leg/ssa/builder.dart
index b40cc2df2a58c5067b4d3efb6e2b1b401902ee6d..1ba1088b1bc82d5d93ad373238b4765a0e1d3fa6 100644
--- a/frog/leg/ssa/builder.dart
+++ b/frog/leg/ssa/builder.dart
@@ -1146,7 +1146,7 @@ class SsaBuilder implements Visitor {
   }
 
   void visitLiteralString(LiteralString node) {
-    push(new HLiteral(new QuotedString.explicit(node.value), HType.STRING));
+    push(new HLiteral(node.quotedString, HType.STRING));
   }
 
   void visitLiteralNull(LiteralNull node) {
@@ -1257,35 +1257,16 @@ class SsaBuilder implements Visitor {
     Operator op = new Operator.synthetic("+");
     HInstruction target = new HStatic(interceptors.getOperatorInterceptor(op));
     add(target);
-    // Ensure that string literals are marked with the correct quoting
-    // style and presence of quotes (left quote only on the first one,
-    // right quote only on the last one).
-    int quoteFlags = QuotedString.flagsFromLeftQuote(node.string.value);
-    // The loop is complicated because we have to do something extra for
-    // the *last* element. To do that, we handle the [string] of a part
-    // in the next iteration, or after the loop for the last element.
-    int firstPartFlags = quoteFlags | QuotedString.HAS_LEFT_QUOTE;
-    push(new HLiteral(new QuotedString(node.string.value, firstPartFlags),
-                      HType.STRING));
-
-    SourceString string = null;
+    visit(node.string);
+    // Handle the parts here, to avoid recreating [target].
     for (StringInterpolationPart part in node.parts) {
       HInstruction prefix = pop();
-      if (string != null) {
-        push(new HLiteral(new QuotedString(string, quoteFlags),
-                          HType.STRING));
-        push(new HAdd(target, prefix, pop()));
-        prefix = pop();
-      }
       visit(part.expression);
       push(new HAdd(target, prefix, pop()));
-      string = part.string.value;
+      prefix = pop();
+      visit(part.string);
+      push(new HAdd(target, prefix, pop()));
     }
-    HInstruction prefix = pop();
-    int lastPartFlags = quoteFlags | QuotedString.HAS_RIGHT_QUOTE;
-    push(new HLiteral(new QuotedString(string, lastPartFlags),
-                      HType.STRING));
-    push(new HAdd(target, prefix, pop()));
   }
 
   visitStringInterpolationPart(StringInterpolationPart node) {