Add static analysis to AST expressions that records whether a negative zero w...

src/rewriter.cc

Index: src/rewriter.cc
===================================================================
--- src/rewriter.cc	(revision 4129)
+++ src/rewriter.cc	(working copy)
@@ -220,6 +220,7 @@
 
 
 void AstOptimizer::VisitConditional(Conditional* node) {
+  node->condition()->set_no_negative_zero(true);
   Visit(node->condition());
   Visit(node->then_expression());
   Visit(node->else_expression());
@@ -319,6 +320,7 @@
       node->type()->SetAsLikelySmiIfUnknown();
       node->target()->type()->SetAsLikelySmiIfUnknown();
       node->value()->type()->SetAsLikelySmiIfUnknown();
+      node->value()->set_no_negative_zero(true);
       break;
     case Token::ASSIGN_ADD:
     case Token::ASSIGN_SUB:
@@ -393,6 +395,7 @@
 
 
 void AstOptimizer::VisitProperty(Property* node) {
+  node->key()->set_no_negative_zero(true);
   Visit(node->obj());
   Visit(node->key());
 }
@@ -422,6 +425,11 @@
 
 
 void AstOptimizer::VisitUnaryOperation(UnaryOperation* node) {
+  if (node->op() == Token::ADD || node->op() == Token::SUB) {
+    node->expression()->set_no_negative_zero(node->no_negative_zero());
+  } else {
+    node->expression()->set_no_negative_zero(true);
+  }
   Visit(node->expression());
   if (FLAG_safe_int32_compiler) {
     switch (node->op()) {
@@ -449,6 +457,9 @@
 
 void AstOptimizer::VisitCountOperation(CountOperation* node) {
   // Count operations assume that they work on Smis.
+  node->expression()->set_no_negative_zero(node->is_prefix() ?
+                                           true :
+                                           node->no_negative_zero());
   node->type()->SetAsLikelySmiIfUnknown();
   node->expression()->type()->SetAsLikelySmiIfUnknown();
   Visit(node->expression());
@@ -461,7 +472,12 @@
   switch (node->op()) {
     case Token::COMMA:
     case Token::OR:
+      node->left()->set_no_negative_zero(true);
+      node->right()->set_no_negative_zero(node->no_negative_zero());
+      break;
     case Token::AND:
+      node->left()->set_no_negative_zero(node->no_negative_zero());
+      node->right()->set_no_negative_zero(node->no_negative_zero());
       break;
     case Token::BIT_OR:
     case Token::BIT_XOR:
@@ -474,6 +490,8 @@
       node->right()->type()->SetAsLikelySmiIfUnknown();
       node->left()->set_to_int32(true);
       node->right()->set_to_int32(true);
+      node->left()->set_no_negative_zero(true);
+      node->right()->set_no_negative_zero(true);
       break;
     case Token::ADD:
     case Token::SUB:
@@ -484,6 +502,13 @@
         node->left()->type()->SetAsLikelySmiIfUnknown();
         node->right()->type()->SetAsLikelySmiIfUnknown();
       }
+      node->left()->set_no_negative_zero(node->no_negative_zero());
+      node->right()->set_no_negative_zero(node->no_negative_zero());
+      if (node->op() == Token::DIV) {
+        node->right()->set_no_negative_zero(false);
+      } else if (node->op() == Token::MOD) {
+        node->right()->set_no_negative_zero(true);
+      }
       break;
     default:
       UNREACHABLE();
@@ -551,6 +576,10 @@
     node->right()->type()->SetAsLikelySmiIfUnknown();
   }
 
+  node->left()->set_no_negative_zero(true);
+  // Only [[HasInstance]] has the right argument passed unchanged to it.
+  node->right()->set_no_negative_zero(true);
+
   Visit(node->left());
   Visit(node->right());