Make bit-operations return a positive result.

lib/compiler/implementation/ssa/codegen.dart

Index: lib/compiler/implementation/ssa/codegen.dart
diff --git a/lib/compiler/implementation/ssa/codegen.dart b/lib/compiler/implementation/ssa/codegen.dart
index 8e49b8ad54f732700bd4d3ea2d8c62f20486e525..0acd5e43d5b1659da394f5f7ec1989e46f18f60f 100644
--- a/lib/compiler/implementation/ssa/codegen.dart
+++ b/lib/compiler/implementation/ssa/codegen.dart
@@ -1100,6 +1100,21 @@ class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
     }
   }
 
+  // We want the outcome of bit-operations to be positive. We use the unsigned
+  // shift operator to achieve this.
+  visitBitInvokeBinary(HBinaryBitOp node, String op) {
+    if (node.builtin){
+      JSBinaryOperatorPrecedence unsignedShiftPrecedences =

[kasperl, 2012/05/03 07:05:50]

Could this be cached somewhere? It feels a bit over the top to look it up every
single time.

[floitsch, 2012/05/03 11:10:36]

cached as instance field now.

+          JSPrecedence.binary['>>>'];
+      beginExpression(unsignedShiftPrecedences.precedence);
+      visitInvokeBinary(node, op);
+      buffer.add(' >>> 0');
+      endExpression(unsignedShiftPrecedences.precedence);
+    } else {
+      visitInvokeBinary(node, op);
+    }
+  }
+
   visitInvokeUnary(HInvokeUnary node, String op) {
     if (node.builtin) {
       beginExpression(JSPrecedence.PREFIX_PRECEDENCE);
@@ -1111,6 +1126,21 @@ class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
     }
   }
 
+  // We want the outcome of bit-operations to be positive. We use the unsigned
+  // shift operator to achieve this.
+  visitBitInvokeUnary(HInvokeUnary node, String op) {
+    if (node.builtin){
+      JSBinaryOperatorPrecedence unsignedShiftPrecedences =
+          JSPrecedence.binary['>>>'];
+      beginExpression(unsignedShiftPrecedences.precedence);
+      visitInvokeUnary(node, op);
+      buffer.add(' >>> 0');
+      endExpression(unsignedShiftPrecedences.precedence);
+    } else {
+      visitInvokeUnary(node, op);
+    }
+  }
+
   visitEquals(HEquals node) {
     if (node.builtin) {
       beginExpression(JSPrecedence.EQUALITY_PRECEDENCE);
@@ -1140,10 +1170,10 @@ class SsaCodeGenerator implements HVisitor, HBlockInformationVisitor {
   // Modulo cannot be mapped to the native operator (different semantics).
   visitModulo(HModulo node)                     => visitInvokeStatic(node);
 
-  visitBitAnd(HBitAnd node)         => visitInvokeBinary(node, '&');
-  visitBitNot(HBitNot node)         => visitInvokeUnary(node, '~');
-  visitBitOr(HBitOr node)           => visitInvokeBinary(node, '|');
-  visitBitXor(HBitXor node)         => visitInvokeBinary(node, '^');
+  visitBitAnd(HBitAnd node)         => visitBitInvokeBinary(node, '&');
+  visitBitNot(HBitNot node)         => visitBitInvokeUnary(node, '~');
+  visitBitOr(HBitOr node)           => visitBitInvokeBinary(node, '|');
+  visitBitXor(HBitXor node)         => visitBitInvokeBinary(node, '^');
 
   // We need to check if the left operand is negative in order to use
   // the native operator.