[csa] Re-introduce automatic constant folding for IntPtrAdd and IntPtrSub

src/builtins/builtins-string.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/builtins/builtins-utils.h"
 #include "src/builtins/builtins.h"
 #include "src/code-factory.h"
 #include "src/code-stub-assembler.h"
 #include "src/regexp/regexp-utils.h"
 
@@ skipping 19 matching lines @@
   }
 
   Node* OneByteCharOffset(Node* index) {
     return CharOffset(String::ONE_BYTE_ENCODING, index);
   }
 
   Node* CharOffset(String::Encoding encoding, Node* index) {
     const int header = SeqOneByteString::kHeaderSize - kHeapObjectTag;
     Node* offset = index;
     if (encoding == String::TWO_BYTE_ENCODING) {
-      offset = IntPtrAddFoldConstants(offset, offset);
+      offset = IntPtrAdd(offset, offset);
     }
-    offset = IntPtrAddFoldConstants(offset, IntPtrConstant(header));
+    offset = IntPtrAdd(offset, IntPtrConstant(header));
     return offset;
   }
 
   void BranchIfSimpleOneByteStringInstanceType(Node* instance_type,
                                                Label* if_true,
                                                Label* if_false) {
     const int kMask = kStringRepresentationMask | kStringEncodingMask;
     const int kType = kOneByteStringTag | kSeqStringTag;
     Branch(Word32Equal(Word32And(instance_type, Int32Constant(kMask)),
                        Int32Constant(kType)),
@@ skipping 1596 matching lines @@
         Runtime::kThrowIncompatibleMethodReceiver, context,
         assembler.HeapConstant(assembler.factory()->NewStringFromAsciiChecked(
             "String Iterator.prototype.next", TENURED)),
         iterator);
     assembler.Return(result);  // Never reached.
   }
 }
 
 }  // namespace internal
 }  // namespace v8