Speed up conversion of untagged int32 result if we know it must be a smi.

src/ast.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 154 matching lines @@
 void TargetCollector::AddTarget(BreakTarget* target) {
   // Add the label to the collector, but discard duplicates.
   int length = targets_->length();
   for (int i = 0; i < length; i++) {
     if (targets_->at(i) == target) return;
   }
   targets_->Add(target);
 }
 
 
+bool Expression::GuaranteedSmiResult() {
+  BinaryOperation* node = AsBinaryOperation();
+  if (node == NULL) return false;
+  Token::Value op = node->op();
+  switch (op) {
+    case Token::COMMA:
+    case Token::OR:
+    case Token::AND:
+    case Token::ADD:
+    case Token::SUB:
+    case Token::MUL:
+    case Token::DIV:
+    case Token::MOD:
+    case Token::BIT_XOR:
+    case Token::SHL:
+      return false;
+      break;
+    case Token::BIT_OR:
+    case Token::BIT_AND: {
+      Literal* left = node->left()->AsLiteral();
+      Literal* right = node->right()->AsLiteral();
+      if (left != NULL && left->handle()->IsSmi()) {
+        int value = Smi::cast(*left->handle())->value();
+        if (op == Token::BIT_OR && ((value & 0xc0000000) == 0xc0000000)) {
+          // Result of bitwise or is always a negative Smi.
+          return true;
+        }
+        if (op == Token::BIT_AND && ((value & 0xc0000000) == 0)) {
+          // Result of bitwise and is always a positive Smi.
+          return true;
+        }
+      }
+      if (right != NULL && right->handle()->IsSmi()) {
+        int value = Smi::cast(*right->handle())->value();
+        if (op == Token::BIT_OR && ((value & 0xc0000000) == 0xc0000000)) {
+          // Result of bitwise or is always a negative Smi.
+          return true;
+        }
+        if (op == Token::BIT_AND && ((value & 0xc0000000) == 0)) {
+          // Result of bitwise and is always a positive Smi.
+          return true;
+        }
+      }
+      return false;
+      break;
+    }
+    case Token::SAR:
+    case Token::SHR: {
+      Literal* right = node->right()->AsLiteral();
+       if (right != NULL && right->handle()->IsSmi()) {
+        int value = Smi::cast(*right->handle())->value();
+        if ((value & 0x1F) > 1 ||
+            (op == Token::SAR && (value & 0x1F) == 1)) {
+          return true;
+        }
+       }
+       return false;
+       break;
+    }
+    default:
+      UNREACHABLE();
+      break;
+  }
+  return false;
+}
+
 // ----------------------------------------------------------------------------
 // Implementation of AstVisitor
 
 
 void AstVisitor::VisitDeclarations(ZoneList<Declaration*>* declarations) {
   for (int i = 0; i < declarations->length(); i++) {
     Visit(declarations->at(i));
   }
 }
 
@@ skipping 986 matching lines @@
   SetStackOverflow();
 }
 
 
 void CopyAstVisitor::VisitDeclaration(Declaration* decl) {
   UNREACHABLE();
 }
 
 
 } }  // namespace v8::internal