[builtins] Migrate String.prototype.charCodeAt and String.prototype.charAt to TurboFan.

src/compiler/code-stub-assembler.h

Index: src/compiler/code-stub-assembler.h
diff --git a/src/compiler/code-stub-assembler.h b/src/compiler/code-stub-assembler.h
index 7ad6fdfdbdf0218e9e0379e1ecafd509a30742d0..2523a8d1f107fe8c5d21aa0f4f8dbf4151a4969d 100644
--- a/src/compiler/code-stub-assembler.h
+++ b/src/compiler/code-stub-assembler.h
@@ -162,7 +162,10 @@ class CodeStubAssembler {
   Node* ExternalConstant(ExternalReference address);
   Node* Float64Constant(double value);
   Node* BooleanMapConstant();
+  Node* EmptyStringConstant();
   Node* HeapNumberMapConstant();
+  Node* NaNConstant();
+  Node* NoContextConstant();
   Node* NullConstant();
   Node* UndefinedConstant();
 
@@ -278,9 +281,11 @@ class CodeStubAssembler {
   Node* SmiTag(Node* value);
   // Untag a Smi value as a Word.
   Node* SmiUntag(Node* value);
+  Node* SmiToWord(Node* value) { return SmiUntag(value); }
 
   // Smi conversions.
   Node* SmiToFloat64(Node* value);
+  Node* SmiFromWord32(Node* value);
   Node* SmiToWord32(Node* value);
 
   // Smi operations.
@@ -289,6 +294,7 @@ class CodeStubAssembler {
   Node* SmiSub(Node* a, Node* b);
   Node* SmiSubWithOverflow(Node* a, Node* b);
   Node* SmiEqual(Node* a, Node* b);
+  Node* SmiAboveOrEqual(Node* a, Node* b);
   Node* SmiLessThan(Node* a, Node* b);
   Node* SmiLessThanOrEqual(Node* a, Node* b);
   Node* SmiMin(Node* a, Node* b);
@@ -343,13 +349,19 @@ class CodeStubAssembler {
 
   // Allocate an object of the given size.
   Node* Allocate(int size, AllocationFlags flags = kNone);
+  Node* InnerAllocate(Node* previous, int offset);
   // Allocate a HeapNumber without initializing its value.
   Node* AllocateHeapNumber();
   // Allocate a HeapNumber with a specific value.
   Node* AllocateHeapNumberWithValue(Node* value);
-  Node* InnerAllocate(Node* previous, int offset);
+  // Allocate a SeqOneByteString with the given length.
+  Node* AllocateSeqOneByteString(int length);
+  // Allocate a SeqTwoByteString with the given length.
+  Node* AllocateSeqTwoByteString(int length);
 
   // Store an array element to a FixedArray.
+  Node* StoreFixedArrayElementInt32Index(Node* object, Node* index,
+                                         Node* value);
   Node* StoreFixedArrayElementNoWriteBarrier(Node* object, Node* index,
                                              Node* value);
   // Load the Map of an HeapObject.
@@ -378,6 +390,17 @@ class CodeStubAssembler {
   Node* TruncateTaggedToFloat64(Node* context, Node* value);
   Node* TruncateTaggedToWord32(Node* context, Node* value);
 
+  // Type conversions.
+  // Throws a TypeError for {method_name} if {value} is not coercible to Object,
+  // or returns the {value} converted to a String otherwise.
+  Node* ToThisString(Node* context, Node* value, char const* method_name);
+
+  // String helpers.
+  // Load a character from a String (might flatten a ConsString).
+  Node* StringCharCodeAt(Node* string, Node* smi_index);
+  // Return the single character string with only {code}.
+  Node* StringFromCharCode(Node* code);
+
   // Branching helpers.
   // TODO(danno): Can we be more cleverish wrt. edge-split?
   void BranchIf(Node* condition, Label* if_true, Label* if_false);