Serendipitously arrange the tags so that String.length() becomes a branch-fre...

src/stub-cache-ia32.cc

Index: src/stub-cache-ia32.cc
===================================================================
--- src/stub-cache-ia32.cc	(revision 595)
+++ src/stub-cache-ia32.cc	(working copy)
@@ -159,69 +159,29 @@
 }
 
 
-void StubCompiler::GenerateLoadShortStringLength(MacroAssembler* masm,
-                                                 Register receiver,
-                                                 Register scratch,
-                                                 Label* miss_label) {
+void StubCompiler::GenerateLoadStringLength(MacroAssembler* masm,
+                                            Register receiver,
+                                            Register scratch,
+                                            Label* miss_label) {
   // Check that the receiver isn't a smi.
   __ test(receiver, Immediate(kSmiTagMask));
   __ j(zero, miss_label, not_taken);
 
-  // Check that the object is a short string.
+  // Check that the object is a string.
   __ mov(scratch, FieldOperand(receiver, HeapObject::kMapOffset));
   __ movzx_b(scratch, FieldOperand(scratch, Map::kInstanceTypeOffset));
-  __ and_(scratch, kIsNotStringMask | kStringSizeMask);
-  __ cmp(scratch, kStringTag | kShortStringTag);
-  __ j(not_equal, miss_label, not_taken);
+  ASSERT(kNotStringTag != 0);
+  __ test(scratch, Immediate(kNotStringTag));
+  __ j(not_zero, miss_label, not_taken);
 
-  // Load length directly from the string.
-  __ mov(eax, FieldOperand(receiver, String::kLengthOffset));
-  __ shr(eax, String::kShortLengthShift);
-  __ shl(eax, kSmiTagSize);
-  __ ret(0);
-}
+  __ and_(scratch, kStringSizeMask);
 
-void StubCompiler::GenerateLoadMediumStringLength(MacroAssembler* masm,
-                                                  Register receiver,
-                                                  Register scratch,
-                                                  Label* miss_label) {
-  // Check that the receiver isn't a smi.
-  __ test(receiver, Immediate(kSmiTagMask));
-  __ j(zero, miss_label, not_taken);
-
-  // Check that the object is a short string.
-  __ mov(scratch, FieldOperand(receiver, HeapObject::kMapOffset));
-  __ movzx_b(scratch, FieldOperand(scratch, Map::kInstanceTypeOffset));
-  __ and_(scratch, kIsNotStringMask | kStringSizeMask);
-  __ cmp(scratch, kStringTag | kMediumStringTag);
-  __ j(not_equal, miss_label, not_taken);
-
   // Load length directly from the string.
   __ mov(eax, FieldOperand(receiver, String::kLengthOffset));
-  __ shr(eax, String::kMediumLengthShift);
-  __ shl(eax, kSmiTagSize);
-  __ ret(0);
-}
 
-
-void StubCompiler::GenerateLoadLongStringLength(MacroAssembler* masm,
-                                                Register receiver,
-                                                Register scratch,
-                                                Label* miss_label) {
-  // Check that the receiver isn't a smi.
-  __ test(receiver, Immediate(kSmiTagMask));
-  __ j(zero, miss_label, not_taken);
-
-  // Check that the object is a short string.
-  __ mov(scratch, FieldOperand(receiver, HeapObject::kMapOffset));
-  __ movzx_b(scratch, FieldOperand(scratch, Map::kInstanceTypeOffset));
-  __ and_(scratch, kIsNotStringMask | kStringSizeMask);
-  __ cmp(scratch, kStringTag | kLongStringTag);
-  __ j(not_equal, miss_label, not_taken);
-
-  // Load length directly from the string.
-  __ mov(eax, FieldOperand(receiver, String::kLengthOffset));
-  __ shr(eax, String::kLongLengthShift);
+  // Ecx is also the receiver.

[Mads Ager (chromium), 2008/10/27 09:37:00]

Ecx -> ecx since it is a register name?

+  __ lea(ecx, Operand(scratch, String::kLongLengthShift));
+  __ shr(eax);  // Ecx is implicit shift register.

[Mads Ager (chromium), 2008/10/27 09:37:00]

Ditto?

   __ shl(eax, kSmiTagSize);
   __ ret(0);
 }
@@ -1153,7 +1113,7 @@
 }
 
 
-Object* KeyedLoadStubCompiler::CompileLoadShortStringLength(String* name) {
+Object* KeyedLoadStubCompiler::CompileLoadStringLength(String* name) {
   // ----------- S t a t e -------------
   //  -- esp[0] : return address
   //  -- esp[4] : name
@@ -1170,7 +1130,7 @@
   __ cmp(Operand(eax), Immediate(Handle<String>(name)));
   __ j(not_equal, &miss, not_taken);
 
-  GenerateLoadShortStringLength(masm(), ecx, edx, &miss);
+  GenerateLoadStringLength(masm(), ecx, edx, &miss);
   __ bind(&miss);
   __ DecrementCounter(&Counters::keyed_load_string_length, 1);
   GenerateLoadMiss(masm(), Code::KEYED_LOAD_IC);
@@ -1180,60 +1140,6 @@
 }
 
 
-Object* KeyedLoadStubCompiler::CompileLoadMediumStringLength(String* name) {
-  // ----------- S t a t e -------------
-  //  -- esp[0] : return address
-  //  -- esp[4] : name
-  //  -- esp[8] : receiver
-  // -----------------------------------
-  HandleScope scope;
-  Label miss;
-
-  __ mov(eax, (Operand(esp, kPointerSize)));
-  __ mov(ecx, (Operand(esp, 2 * kPointerSize)));
-  __ IncrementCounter(&Counters::keyed_load_string_length, 1);
-
-  // Check that the name has not changed.
-  __ cmp(Operand(eax), Immediate(Handle<String>(name)));
-  __ j(not_equal, &miss, not_taken);
-
-  GenerateLoadMediumStringLength(masm(), ecx, edx, &miss);
-  __ bind(&miss);
-  __ DecrementCounter(&Counters::keyed_load_string_length, 1);
-  GenerateLoadMiss(masm(), Code::KEYED_LOAD_IC);
-
-  // Return the generated code.
-  return GetCode(CALLBACKS);
-}
-
-
-Object* KeyedLoadStubCompiler::CompileLoadLongStringLength(String* name) {
-  // ----------- S t a t e -------------
-  //  -- esp[0] : return address
-  //  -- esp[4] : name
-  //  -- esp[8] : receiver
-  // -----------------------------------
-  HandleScope scope;
-  Label miss;
-
-  __ mov(eax, (Operand(esp, kPointerSize)));
-  __ mov(ecx, (Operand(esp, 2 * kPointerSize)));
-  __ IncrementCounter(&Counters::keyed_load_string_length, 1);
-
-  // Check that the name has not changed.
-  __ cmp(Operand(eax), Immediate(Handle<String>(name)));
-  __ j(not_equal, &miss, not_taken);
-
-  GenerateLoadLongStringLength(masm(), ecx, edx, &miss);
-  __ bind(&miss);
-  __ DecrementCounter(&Counters::keyed_load_string_length, 1);
-  GenerateLoadMiss(masm(), Code::KEYED_LOAD_IC);
-
-  // Return the generated code.
-  return GetCode(CALLBACKS);
-}
-
-
 Object* KeyedLoadStubCompiler::CompileLoadFunctionPrototype(String* name) {
   // ----------- S t a t e -------------
   //  -- esp[0] : return address