Implemented one-char cache lookup in generated code.

src/ia32/codegen-ia32.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
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 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
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@@ skipping 5579 matching lines @@
   __ bind(&slow_case);
   // Move the undefined value into the result register, which will
   // trigger the slow case.
   __ Set(temp.reg(), Immediate(Factory::undefined_value()));
 
   __ bind(&end);
   frame_->Push(&temp);
 }
 
 
+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));
   Result value = frame_->Pop();
   value.ToRegister();
   ASSERT(value.is_valid());
   __ test(value.reg(), Immediate(kSmiTagMask));
   destination()->false_target()->Branch(equal);
   // It is a heap object - get map.
   Result temp = allocator()->Allocate();
@@ skipping 5622 matching lines @@
 
   // Call the runtime; it returns -1 (less), 0 (equal), or 1 (greater)
   // tagged as a small integer.
   __ bind(&runtime);
   __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
 }
 
 #undef __
 
 } }  // namespace v8::internal