Optimize implementation of Math.floor a little by special casing

the comparison it uses in the code generator.  Use Math.floor for
date operations.
Review URL: http://codereview.chromium.org/509007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3508 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ia32/codegen-ia32.cc

@@ -5928,6 +5928,8 @@ void CodeGenerator::VisitThisFunction(ThisFunction* node) {
 void CodeGenerator::VisitCompareOperation(CompareOperation* node) {
   Comment cmnt(masm_, "[ CompareOperation");
 
+  bool left_already_loaded = false;
+
   // Get the expressions from the node.
   Expression* left = node->left();
   Expression* right = node->right();
@@ -6008,7 +6010,6 @@ void CodeGenerator::VisitCompareOperation(CompareOperation* node) {
       __ CmpInstanceType(answer.reg(), JS_REGEXP_TYPE);
       answer.Unuse();
       destination()->Split(equal);
-
     } else if (check->Equals(Heap::object_symbol())) {
       __ test(answer.reg(), Immediate(kSmiTagMask));
       destination()->false_target()->Branch(zero);
@@ -6040,6 +6041,38 @@ void CodeGenerator::VisitCompareOperation(CompareOperation* node) {
       destination()->Goto(false);
     }
     return;
+  } else if (op == Token::LT &&
+             right->AsLiteral() != NULL &&
+             right->AsLiteral()->handle()->IsHeapNumber()) {
+    Handle<HeapNumber> check(HeapNumber::cast(*right->AsLiteral()->handle()));
+    if (check->value() == 2147483648.0) {  // 0x80000000.
+      Load(left);
+      left_already_loaded = true;
+      Result lhs = frame_->Pop();
+      lhs.ToRegister();
+      __ test(lhs.reg(), Immediate(kSmiTagMask));
+      destination()->true_target()->Branch(zero);  // All Smis are less.
+      Result scratch = allocator()->Allocate();
+      ASSERT(scratch.is_valid());
+      __ mov(scratch.reg(), FieldOperand(lhs.reg(), HeapObject::kMapOffset));
+      __ cmp(scratch.reg(), Factory::heap_number_map());
+      JumpTarget not_a_number;
+      not_a_number.Branch(not_equal, &lhs);
+      __ mov(scratch.reg(),
+             FieldOperand(lhs.reg(), HeapNumber::kExponentOffset));
+      __ cmp(Operand(scratch.reg()), Immediate(0xfff00000));
+      not_a_number.Branch(above_equal, &lhs);  // It's a negative NaN or -Inf.
+      const uint32_t borderline_exponent =
+          (HeapNumber::kExponentBias + 31) << HeapNumber::kExponentShift;
+      __ cmp(Operand(scratch.reg()), Immediate(borderline_exponent));
+      scratch.Unuse();
+      lhs.Unuse();
+      destination()->true_target()->Branch(less);
+      destination()->false_target()->Jump();
+
+      not_a_number.Bind(&lhs);
+      frame_->Push(&lhs);
+    }
   }
 
   Condition cc = no_condition;
@@ -6064,14 +6097,14 @@ void CodeGenerator::VisitCompareOperation(CompareOperation* node) {
       cc = greater_equal;
       break;
     case Token::IN: {
-      Load(left);
+      if (!left_already_loaded) Load(left);
       Load(right);
       Result answer = frame_->InvokeBuiltin(Builtins::IN, CALL_FUNCTION, 2);
       frame_->Push(&answer);  // push the result
       return;
     }
     case Token::INSTANCEOF: {
-      Load(left);
+      if (!left_already_loaded) Load(left);
       Load(right);
       InstanceofStub stub;
       Result answer = frame_->CallStub(&stub, 2);
@@ -6084,7 +6117,7 @@ void CodeGenerator::VisitCompareOperation(CompareOperation* node) {
     default:
       UNREACHABLE();
   }
-  Load(left);
+  if (!left_already_loaded) Load(left);
   Load(right);
   Comparison(node, cc, strict, destination());
 }

src/jump-target.h

@@ -112,7 +112,8 @@ class JumpTarget : public ZoneObject {  // Shadows are dynamically allocated.
 
   // Emit a conditional branch to the target.  There must be a current
   // frame at the branch.  The current frame will fall through to the
-  // code after the branch.
+  // code after the branch.  The arg is a result that is live both at
+  // the target and the fall-through.
   virtual void Branch(Condition cc, Hint hint = no_hint);
   virtual void Branch(Condition cc, Result* arg, Hint hint = no_hint);
 

src/macros.py

@@ -92,7 +92,7 @@ macro IS_ERROR(arg)             = (%_ClassOf(arg) === 'Error');
 macro IS_SCRIPT(arg)            = (%_ClassOf(arg) === 'Script');
 macro IS_ARGUMENTS(arg)         = (%_ClassOf(arg) === 'Arguments');
 macro IS_GLOBAL(arg)            = (%_ClassOf(arg) === 'global');
-macro FLOOR(arg)                = %Math_floor(arg);
+macro FLOOR(arg)                = $floor(arg);
 
 # Inline macros. Use %IS_VAR to make sure arg is evaluated only once.
 macro NUMBER_IS_NAN(arg) = (!%_IsSmi(%IS_VAR(arg)) && !(arg == arg));

src/math.js

@@ -98,7 +98,7 @@ function MathFloor(x) {
   if (!IS_NUMBER(x)) x = ToNumber(x);
   // It's more common to call this with a positive number that's out
   // of range than negative numbers; check the upper bound first.
-  if (x <= 0x7FFFFFFF && x > 0) {
+  if (x < 0x80000000 && x > 0) {
     // Numbers in the range [0, 2^31) can be floored by converting
     // them to an unsigned 32-bit value using the shift operator.
     // We avoid doing so for -0, because the result of Math.floor(-0)