Implemented one-char cache lookup in generated code.

src/ia32/codegen-ia32.cc

Index: src/ia32/codegen-ia32.cc
diff --git a/src/ia32/codegen-ia32.cc b/src/ia32/codegen-ia32.cc
index 42ab6a88df6914938abd820805cc5a7e446da570..b3c418f251a2f6bd0eae5f174fe39c21b77e60c2 100644
--- a/src/ia32/codegen-ia32.cc
+++ b/src/ia32/codegen-ia32.cc
@@ -5597,6 +5597,53 @@ void CodeGenerator::GenerateFastCharCodeAt(ZoneList<Expression*>* args) {
 }
 
 
+void CodeGenerator::GenerateCharFromCode(ZoneList<Expression*>* args) {
+  Comment(masm_, "[ GenerateCharFromCode");
+  ASSERT(args->length() == 1);
+
+  Load(args->at(0));
+  frame_->Dup();

[Mads Ager (chromium), 2010/02/26 17:59:06]

Do you need the Dup here?  You never modify code as far as I can tell, so I
guess you could just Pop it from the frame and push it back if you need it on
the frame.  Then you can just push the result instead of overwriting element
zero on the frame with the result.

[Vitaly Repeshko, 2010/02/26 20:14:48]

Well, I tried this approach and couldn't make it work. After you comment I tried
a bit more and found out it requires passing live values along branches. Now it
works (and on x64 as well).

+  Result code = frame_->Pop();
+  code.ToRegister();
+  ASSERT(code.is_valid());
+
+  Result temp = allocator()->Allocate();
+  ASSERT(temp.is_valid());
+
+  JumpTarget slow_case;
+  JumpTarget exit;
+
+  // Fast case of Heap::LookupSingleCharacterStringFromCode.
+  ASSERT(kSmiTag == 0);
+  ASSERT(kSmiShiftSize == 0);
+  ASSERT(IsPowerOf2(String::kMaxAsciiCharCode + 1));
+  __ test(code.reg(),
+          Immediate(kSmiTagMask |
+                    ((~String::kMaxAsciiCharCode) << kSmiTagSize)));
+  slow_case.Branch(not_zero, not_taken);
+
+  __ Set(temp.reg(), Immediate(Factory::single_character_string_cache()));

[Mads Ager (chromium), 2010/02/26 17:59:06]

Adding a comment here stating that code contains a smi tagged ascii char code
might be good to explain the times_hafl_pointer_size in the Operand below.

[Vitaly Repeshko, 2010/02/26 20:14:48]

Done.

+  ASSERT(kSmiTag == 0);
+  ASSERT(kSmiTagSize == 1);
+  ASSERT(kSmiShiftSize == 0);
+  __ mov(temp.reg(), Operand(temp.reg(),

[Mads Ager (chromium), 2010/02/26 17:59:06]

Use FieldOperand and drop the "- kHeapObjectTag" on the offset?

[Vitaly Repeshko, 2010/02/26 20:14:48]

Done.

+                             code.reg(), times_half_pointer_size,
+                             FixedArray::kHeaderSize - kHeapObjectTag));
+  __ cmp(temp.reg(), Factory::undefined_value());
+  slow_case.Branch(equal, not_taken);
+  code.Unuse();
+
+  frame_->SetElementAt(0, &temp);
+  exit.Jump();
+
+  slow_case.Bind();
+  Result result = frame_->CallRuntime(Runtime::kCharFromCode, 1);
+  frame_->Push(&result);
+
+  exit.Bind();
+}
+
+
 void CodeGenerator::GenerateIsArray(ZoneList<Expression*>* args) {
   ASSERT(args->length() == 1);
   Load(args->at(0));