X64: Fix bug in boolean conversion of empty string.

Review URL: http://codereview.chromium.org/165043


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2632 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -1669,7 +1669,7 @@ Object* Heap::AllocateSlicedString(String* buffer,
   int length = end - start;
 
   // If the resulting string is small make a sub string.
-  if (end - start <= String::kMinNonFlatLength) {
+  if (length <= String::kMinNonFlatLength) {
     return Heap::AllocateSubString(buffer, start, end);
   }
 

src/objects.h

@@ -4038,8 +4038,8 @@ class SlicedString: public String {
   // Layout description
 #if V8_HOST_ARCH_64_BIT
   // Optimizations expect buffer to be located at same offset as a ConsString's
-  // first substring. In 64 bit mode we have room for the size before the
-  // buffer.
+  // first substring. In 64 bit mode we have room for the start offset before
+  // the buffer.
   static const int kStartOffset = String::kSize;
   static const int kBufferOffset = kStartOffset + kIntSize;
   static const int kSize = kBufferOffset + kPointerSize;

src/x64/codegen-x64.cc

@@ -5695,7 +5695,7 @@ void ToBooleanStub::Generate(MacroAssembler* masm) {
   __ and_(rcx, Immediate(kStringSizeMask));
   __ cmpq(rcx, Immediate(kShortStringTag));
   __ j(not_equal, &true_result);  // Empty string is always short.
-  __ movq(rdx, FieldOperand(rax, String::kLengthOffset));
+  __ movl(rdx, FieldOperand(rax, String::kLengthOffset));
   __ shr(rdx, Immediate(String::kShortLengthShift));
   __ j(zero, &false_result);
   __ jmp(&true_result);