Port string keyed load IC improvements (r4444) to ARM.

Review URL: http://codereview.chromium.org/1769014

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4573 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/codegen-arm.h

@@ -665,14 +665,46 @@ class GenericBinaryOpStub : public CodeStub {
 };
 
 
-class StringStubBase: public CodeStub {
+class StringHelper : public AllStatic {
  public:
+  // Generates fast code for getting a char code out of a string
+  // object at the given index. May bail out for four reasons (in the
+  // listed order):
+  //   * Receiver is not a string (receiver_not_string label).
+  //   * Index is not a smi (index_not_smi label).
+  //   * Index is out of range (index_out_of_range).
+  //   * Some other reason (slow_case label). In this case it's
+  //     guaranteed that the above conditions are not violated,
+  //     e.g. it's safe to assume the receiver is a string and the
+  //     index is a non-negative smi < length.
+  // When successful, object, index, and scratch are clobbered.
+  // Otherwise, scratch and result are clobbered.
+  static void GenerateFastCharCodeAt(MacroAssembler* masm,
+                                     Register object,
+                                     Register index,
+                                     Register scratch,
+                                     Register result,
+                                     Label* receiver_not_string,
+                                     Label* index_not_smi,
+                                     Label* index_out_of_range,
+                                     Label* slow_case);
+
+  // Generates code for creating a one-char string from the given char
+  // code. May do a runtime call, so any register can be clobbered
+  // and, if the given invoke flag specifies a call, an internal frame
+  // is required. In tail call mode the result must be r0 register.
+  static void GenerateCharFromCode(MacroAssembler* masm,
+                                   Register code,
+                                   Register scratch,
+                                   Register result,
+                                   InvokeFlag flag);
+
   // Generate code for copying characters using a simple loop. This should only
   // be used in places where the number of characters is small and the
   // additional setup and checking in GenerateCopyCharactersLong adds too much
   // overhead. Copying of overlapping regions is not supported.
   // Dest register ends at the position after the last character written.
-  void GenerateCopyCharacters(MacroAssembler* masm,
+  static void GenerateCopyCharacters(MacroAssembler* masm,
                                      Register dest,
                                      Register src,
                                      Register count,
@@ -683,7 +715,7 @@ class StringStubBase: public CodeStub {
   // is allowed to spend extra time setting up conditions to make copying
   // faster. Copying of overlapping regions is not supported.
   // Dest register ends at the position after the last character written.
-  void GenerateCopyCharactersLong(MacroAssembler* masm,
+  static void GenerateCopyCharactersLong(MacroAssembler* masm,
                                          Register dest,
                                          Register src,
                                          Register count,
@@ -702,7 +734,7 @@ class StringStubBase: public CodeStub {
   // Contents of both c1 and c2 registers are modified. At the exit c1 is
   // guaranteed to contain halfword with low and high bytes equal to
   // initial contents of c1 and c2 respectively.
-  void GenerateTwoCharacterSymbolTableProbe(MacroAssembler* masm,
+  static void GenerateTwoCharacterSymbolTableProbe(MacroAssembler* masm,
                                                    Register c1,
                                                    Register c2,
                                                    Register scratch1,
@@ -713,16 +745,19 @@ class StringStubBase: public CodeStub {
                                                    Label* not_found);
 
   // Generate string hash.
-  void GenerateHashInit(MacroAssembler* masm,
+  static void GenerateHashInit(MacroAssembler* masm,
                                Register hash,
                                Register character);
 
-  void GenerateHashAddCharacter(MacroAssembler* masm,
+  static void GenerateHashAddCharacter(MacroAssembler* masm,
                                        Register hash,
                                        Register character);
 
-  void GenerateHashGetHash(MacroAssembler* masm,
+  static void GenerateHashGetHash(MacroAssembler* masm,
                                   Register hash);
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(StringHelper);
 };
 
 
@@ -733,7 +768,7 @@ enum StringAddFlags {
 };
 
 
-class StringAddStub: public StringStubBase {
+class StringAddStub: public CodeStub {
  public:
   explicit StringAddStub(StringAddFlags flags) {
     string_check_ = ((flags & NO_STRING_CHECK_IN_STUB) == 0);
@@ -750,7 +785,7 @@ class StringAddStub: public StringStubBase {
 };
 
 
-class SubStringStub: public StringStubBase {
+class SubStringStub: public CodeStub {
  public:
   SubStringStub() {}
 

src/arm/ic-arm.cc

@@ -800,28 +800,67 @@ void KeyedLoadIC::GenerateString(MacroAssembler* masm) {
   //  -- sp[0]  : key
   //  -- sp[4]  : receiver
   // -----------------------------------
-
-  Label miss, index_ok;
+  Label miss;
+  Label index_not_smi;
+  Label index_out_of_range;
+  Label slow_char_code;
+  Label got_char_code;
 
   // Get the key and receiver object from the stack.
   __ ldm(ia, sp, r0.bit() | r1.bit());
 
-  // Check that the receiver isn't a smi.
-  __ BranchOnSmi(r1, &miss);
-
-  // Check that the receiver is a string.
-  Condition is_string = masm->IsObjectStringType(r1, r2);
-  __ b(NegateCondition(is_string), &miss);
+  Register object = r1;
+  Register index = r0;
+  Register code = r2;
+  Register scratch = r3;
 
-  // Check if key is a smi or a heap number.
-  __ BranchOnSmi(r0, &index_ok);
-  __ CheckMap(r0, r2, Factory::heap_number_map(), &miss, false);
+  StringHelper::GenerateFastCharCodeAt(masm,
+                                       object,
+                                       index,
+                                       scratch,
+                                       code,
+                                       &miss,  // When not a string.
+                                       &index_not_smi,
+                                       &index_out_of_range,
+                                       &slow_char_code);
+
+  // If we didn't bail out, code register contains smi tagged char
+  // code.
+  __ bind(&got_char_code);
+  StringHelper::GenerateCharFromCode(masm, code, scratch, r0, JUMP_FUNCTION);
+#ifdef DEBUG
+  __ Abort("Unexpected fall-through from char from code tail call");
+#endif
+
+  // Check if key is a heap number.
+  __ bind(&index_not_smi);
+  __ CheckMap(index, scratch, Factory::heap_number_map(), &miss, true);
+
+  // Push receiver and key on the stack (now that we know they are a
+  // string and a number), and call runtime.
+  __ bind(&slow_char_code);
+  __ EnterInternalFrame();
+  __ Push(object, index);
+  __ CallRuntime(Runtime::kStringCharCodeAt, 2);
+  ASSERT(!code.is(r0));
+  __ mov(code, r0);
+  __ LeaveInternalFrame();
 
-  __ bind(&index_ok);
-  // Duplicate receiver and key since they are expected on the stack after
-  // the KeyedLoadIC call.
-  __ Push(r1, r0);
-  __ InvokeBuiltin(Builtins::STRING_CHAR_AT, JUMP_JS);
+  // Check if the runtime call returned NaN char code. If yes, return
+  // undefined. Otherwise, we can continue.
+  if (FLAG_debug_code) {
+    __ BranchOnSmi(code, &got_char_code);
+    __ ldr(scratch, FieldMemOperand(code, HeapObject::kMapOffset));
+    __ LoadRoot(ip, Heap::kHeapNumberMapRootIndex);
+    __ cmp(scratch, ip);
+    __ Assert(eq, "StringCharCodeAt must return smi or heap number");
+  }
+  __ LoadRoot(scratch, Heap::kNanValueRootIndex);
+  __ cmp(code, scratch);
+  __ b(ne, &got_char_code);
+  __ bind(&index_out_of_range);
+  __ LoadRoot(r0, Heap::kUndefinedValueRootIndex);
+  __ Ret();
 
   __ bind(&miss);
   GenerateGeneric(masm);

src/builtins.h

@@ -164,8 +164,7 @@ enum BuiltinExtraArguments {
   V(STRING_ADD_LEFT, 1)                  \
   V(STRING_ADD_RIGHT, 1)                 \
   V(APPLY_PREPARE, 1)                    \
-  V(APPLY_OVERFLOW, 1)                   \
-  V(STRING_CHAR_AT, 1)
+  V(APPLY_OVERFLOW, 1)
 
 
 class ObjectVisitor;

src/runtime.js

@@ -471,17 +471,6 @@ function TO_STRING() {
 }
 
 
-// Specialized version of String.charAt. It assumes string as
-// the receiver type and that the index is a number.
-function STRING_CHAR_AT(pos) {
-  var char_code = %_FastCharCodeAt(this, pos);
-  if (!%_IsSmi(char_code)) {
-    return %StringCharAt(this, pos);
-  }
-  return %_CharFromCode(char_code);
-}
-
-
 /* -------------------------------------
    - - -   C o n v e r s i o n s   - - -
    -------------------------------------

src/x64/codegen-x64.h

@@ -913,6 +913,7 @@ class StringHelper : public AllStatic {
   static void GenerateHashGetHash(MacroAssembler* masm,
                                   Register hash,
                                   Register scratch);
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(StringHelper);
 };