Track ascii-ness of data in externalized strings.

src/x64/codegen-x64.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
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 11174 matching lines @@
   __ SmiCompare(rbx, Smi::FromInt(String::kMinNonFlatLength));
   __ j(below, &string_add_flat_result);
   // Handle exceptionally long strings in the runtime system.
   ASSERT((String::kMaxLength & 0x80000000) == 0);
   __ SmiCompare(rbx, Smi::FromInt(String::kMaxLength));
   __ j(above, &string_add_runtime);
 
   // If result is not supposed to be flat, allocate a cons string object. If
   // both strings are ascii the result is an ascii cons string.
   // rax: first string
-  // ebx: length of resulting flat string
+  // rbx: length of resulting flat string
   // rdx: second string
   // r8: instance type of first string
   // r9: instance type of second string
-  Label non_ascii, allocated;
+  Label non_ascii, allocated, ascii_data;
   __ movl(rcx, r8);
   __ and_(rcx, r9);
   ASSERT(kStringEncodingMask == kAsciiStringTag);
   __ testl(rcx, Immediate(kAsciiStringTag));
   __ j(zero, &non_ascii);
+  __ bind(&ascii_data);
   // Allocate an acsii cons string.
   __ AllocateAsciiConsString(rcx, rdi, no_reg, &string_add_runtime);
   __ bind(&allocated);
   // Fill the fields of the cons string.
   __ movq(FieldOperand(rcx, ConsString::kLengthOffset), rbx);
   __ movq(FieldOperand(rcx, ConsString::kHashFieldOffset),
           Immediate(String::kEmptyHashField));
   __ movq(FieldOperand(rcx, ConsString::kFirstOffset), rax);
   __ movq(FieldOperand(rcx, ConsString::kSecondOffset), rdx);
   __ movq(rax, rcx);
   __ IncrementCounter(&Counters::string_add_native, 1);
   __ ret(2 * kPointerSize);
   __ bind(&non_ascii);
+  // At least one of the strings is two-byte. Check whether it happens
+  // to contain only ascii characters.
+  // rcx: first instance type AND second instance type.
+  // r8: first instance type.
+  // r9: second instance type.
+  __ testb(rcx, Immediate(kAsciiDataHintMask));
+  __ j(not_zero, &ascii_data);
+  __ xor_(r8, r9);
+  ASSERT(kAsciiStringTag != 0 && kAsciiDataHintTag != 0);
+  __ andb(r8, Immediate(kAsciiStringTag | kAsciiDataHintTag));
+  __ cmpb(r8, Immediate(kAsciiStringTag | kAsciiDataHintTag));
+  __ j(equal, &ascii_data);
   // Allocate a two byte cons string.
   __ AllocateConsString(rcx, rdi, no_reg, &string_add_runtime);
   __ jmp(&allocated);
 
   // Handle creating a flat result. First check that both strings are not
   // external strings.
   // rax: first string
-  // ebx: length of resulting flat string as smi
+  // rbx: length of resulting flat string as smi
   // rdx: second string
   // r8: instance type of first string
   // r9: instance type of first string
   __ bind(&string_add_flat_result);
   __ SmiToInteger32(rbx, rbx);
   __ movl(rcx, r8);
   __ and_(rcx, Immediate(kStringRepresentationMask));
   __ cmpl(rcx, Immediate(kExternalStringTag));
   __ j(equal, &string_add_runtime);
   __ movl(rcx, r9);
   __ and_(rcx, Immediate(kStringRepresentationMask));
   __ cmpl(rcx, Immediate(kExternalStringTag));
   __ j(equal, &string_add_runtime);
   // Now check if both strings are ascii strings.
   // rax: first string
-  // ebx: length of resulting flat string
+  // rbx: length of resulting flat string
   // rdx: second string
   // r8: instance type of first string
   // r9: instance type of second string
   Label non_ascii_string_add_flat_result;
   ASSERT(kStringEncodingMask == kAsciiStringTag);
   __ testl(r8, Immediate(kAsciiStringTag));
   __ j(zero, &non_ascii_string_add_flat_result);
   __ testl(r9, Immediate(kAsciiStringTag));
   __ j(zero, &string_add_runtime);
 
@@ skipping 678 matching lines @@
 }
 
 #endif
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64