Implemented one-char cache lookup in generated code.

src/arm/codegen-arm.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
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@@ skipping 3396 matching lines @@
   __ jmp(&try_again_with_new_string);
 
   __ bind(&slow);
   __ LoadRoot(r0, Heap::kUndefinedValueRootIndex);
 
   __ bind(&end);
   frame_->EmitPush(r0);
 }
 
 
+void CodeGenerator::GenerateCharFromCode(ZoneList<Expression*>* args) {
+  Comment(masm_, "[ GenerateCharFromCode");
+  ASSERT(args->length() == 1);
+
+  LoadAndSpill(args->at(0));
+  frame_->EmitPop(r0);
+
+  JumpTarget slow_case;
+  JumpTarget exit;
+
+  // Fast case of Heap::LookupSingleCharacterStringFromCode.
+  ASSERT(kSmiTag == 0);
+  ASSERT(kSmiShiftSize == 0);
+  ASSERT(IsPowerOf2(String::kMaxAsciiCharCode + 1));
+  __ tst(r0, Operand(kSmiTagMask |
+                     ((~String::kMaxAsciiCharCode) << kSmiTagSize)));
+  slow_case.Branch(nz);
+
+  ASSERT(kSmiTag == 0);
+  ASSERT(kSmiTagSize == 1);
+  ASSERT(kSmiShiftSize == 0);
+  __ mov(r1, Operand(Factory::single_character_string_cache()));
+  __ add(r1, r1, Operand(r0));

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

I would prefer to use 

__ add(r1, r1, Operand(r0, LSL, kPointerSizeLog2 - kSmiTagSize)) 

instead of these two instructions. Also makes it more clear to me that you are
adding ((untagged r0) * kPointerSize) to r1.

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

Done.

+  __ add(r1, r1, Operand(r0));
+  __ ldr(r1, MemOperand(r1, FixedArray::kHeaderSize - kHeapObjectTag));
+  __ cmp(r1, Operand(Factory::undefined_value()));

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

You should use LoadRoot to ip followed by cmp here to use the RootArray instead
of embedding the object in the code.

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

Done.

+  slow_case.Branch(eq);
+
+  frame_->EmitPush(r1);
+  exit.Jump();
+
+  slow_case.Bind();
+  frame_->EmitPush(r0);
+  frame_->CallRuntime(Runtime::kCharFromCode, 1);
+  frame_->EmitPush(r0);
+
+  exit.Bind();
+}
+
+
 void CodeGenerator::GenerateIsArray(ZoneList<Expression*>* args) {
   VirtualFrame::SpilledScope spilled_scope;
   ASSERT(args->length() == 1);
   LoadAndSpill(args->at(0));
   JumpTarget answer;
   // We need the CC bits to come out as not_equal in the case where the
   // object is a smi.  This can't be done with the usual test opcode so
   // we use XOR to get the right CC bits.
   frame_->EmitPop(r0);
   __ and_(r1, r0, Operand(kSmiTagMask));
@@ skipping 4236 matching lines @@
 
   // Just jump to runtime to add the two strings.
   __ bind(&string_add_runtime);
   __ TailCallRuntime(Runtime::kStringAdd, 2, 1);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal