ARM native regexps.

src/arm/regexp-macro-assembler-arm.cc

Index: src/arm/regexp-macro-assembler-arm.cc
diff --git a/src/arm/regexp-macro-assembler-arm.cc b/src/arm/regexp-macro-assembler-arm.cc
index 78ebc7e8011f1bce77ddb193a3ba78e06373f88d..08f2e99830d5af86002bb9396b9556de0e64bf49 100644
--- a/src/arm/regexp-macro-assembler-arm.cc
+++ b/src/arm/regexp-macro-assembler-arm.cc
@@ -1,4 +1,4 @@
-// Copyright 2006-2008 the V8 project authors. All rights reserved.
+// Copyright 2009 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:
@@ -26,19 +26,1198 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "v8.h"
+#include "unicode.h"
+#include "log.h"
 #include "ast.h"
+#include "regexp-stack.h"
+#include "macro-assembler.h"
 #include "regexp-macro-assembler.h"
+#include "arm/macro-assembler-arm.h"
 #include "arm/regexp-macro-assembler-arm.h"
 
 namespace v8 {
 namespace internal {
 
-RegExpMacroAssemblerARM::RegExpMacroAssemblerARM() {
-  UNIMPLEMENTED();
+#ifdef V8_NATIVE_REGEXP
+/*
+ * This assembler uses the following register assignment convention
+ * - r6 : Current position in input, as negative offset from end of string.
+ *        Please notice that this is the byte offset, not the character offset!
+ * - r7 : Currently loaded character. Must be loaded using
+ *        LoadCurrentCharacter before using any of the dispatch methods.
+ * - r8 : points to tip of backtrack stack
+ * - r9 : Unused, might be used by C code and expected unchanged.
+ * - r10 : End of input (points to byte after last character in input).
+ * - r11 : Frame pointer. Used to access arguments, local variables and
+ *         RegExp registers.
+ * - r12 : IP register, used by assembler. Very volatile.
+ * - r13/sp : points to tip of C stack.
+ *
+ * The remaining registers are free for computations.
+ *
+ * Each call to a public method should retain this convention.
+ * The stack will have the following structure:
+ *       - stack_area_base    (High end of the memory area to use as
+ *                             backtracking stack)
+ *       - at_start           (if 1, start at start of string, if 0, don't)
+ *       --- sp when called ---
+ *       - link address
+ *       - backup of registers r5..r11
+ *       - int* capture_array (int[num_saved_registers_], for output).
+ *       - end of input       (Address of end of string)
+ *       - start of input     (Address of first character in string)
+ *       --- frame pointer ----
+ *       - void* input_string (location of a handle containing the string)
+ *       - Offset of location before start of input (effectively character
+ *         position -1). Used to initialize capture registers to a non-position.
+ *       - register 0         (Only positions must be stored in the first
+ *       - register 1          num_saved_registers_ registers)
+ *       - ...
+ *       - register num_registers-1
+ *       --- sp ---
+ *
+ * The first num_saved_registers_ registers are initialized to point to
+ * "character -1" in the string (i.e., char_size() bytes before the first
+ * character of the string). The remaining registers starts out as garbage.

[Erik Corry, 2009/08/27 14:43:05]

starts -> start

+ *
+ * The data up to the return address must be placed there by the calling
+ * code, by calling the code entry as cast to a function with the signature:
+ * int (*match)(String* input_string,

[Erik Corry, 2009/08/27 14:43:05]

There should be a typedef for this in the .h file.

[Lasse Reichstein, 2009/08/28 09:15:18]

It's in NativeRegExpMacroAssembler::Execute in regexp-macro-assembler.cc. I'll
add a reference.

+ *              Address start,
+ *              Address end,
+ *              int* capture_output_array,
+ *              bool at_start,
+ *              byte* stack_area_base)
+ */
+
+#define __ ACCESS_MASM(masm_)
+
+RegExpMacroAssemblerARM::RegExpMacroAssemblerARM(
+    Mode mode,
+    int registers_to_save)
+    : masm_(new MacroAssembler(NULL, kRegExpCodeSize)),
+      mode_(mode),
+      num_registers_(registers_to_save),
+      num_saved_registers_(registers_to_save),
+      entry_label_(),
+      start_label_(),
+      success_label_(),
+      backtrack_label_(),
+      exit_label_() {
+  __ jmp(&entry_label_);   // We'll write the entry code later.
+  EmitBacktrackConstantPool();
+  __ bind(&start_label_);  // And then continue from here.
 }
 
 
-RegExpMacroAssemblerARM::~RegExpMacroAssemblerARM() {}
+RegExpMacroAssemblerARM::~RegExpMacroAssemblerARM() {
+  delete masm_;
+  // Unuse labels in case we throw away the assembler without calling GetCode.
+  entry_label_.Unuse();
+  start_label_.Unuse();
+  success_label_.Unuse();
+  backtrack_label_.Unuse();
+  exit_label_.Unuse();
+  check_preempt_label_.Unuse();
+  stack_overflow_label_.Unuse();
+}
 
-}}  // namespace v8::internal
 
+int RegExpMacroAssemblerARM::stack_limit_slack()  {
+  return RegExpStack::kStackLimitSlack;
+}
+
+
+void RegExpMacroAssemblerARM::AdvanceCurrentPosition(int by) {
+  if (by != 0) {
+    Label inside_string;
+    __ add(current_input_offset(),
+           current_input_offset(), Operand(by * char_size()));
+  }
+}
+
+
+void RegExpMacroAssemblerARM::AdvanceRegister(int reg, int by) {

[Erik Corry, 2009/08/27 14:43:05]

We should consider putting 'register 0' in a real register.

[Lasse Reichstein, 2009/08/28 09:15:18]

No real need. It's at a fixed offset from the frame pointer, so we can load it
in one ldr in any case.

+  ASSERT(reg >= 0);
+  ASSERT(reg < num_registers_);
+  if (by != 0) {
+    __ ldr(r0, register_location(reg));
+    __ add(r0, r0, Operand(by));
+    __ str(r0, register_location(reg));
+  }
+}
+
+
+void RegExpMacroAssemblerARM::Backtrack() {
+  CheckPreemption();
+  // Pop Code* offset from backtrack stack, add Code* and jump to location.
+  Pop(r0);
+  __ add(pc, r0, Operand(masm_->CodeObject()));

[Erik Corry, 2009/08/27 14:43:05]

I like the alternative better, because the add above turns into a pc-relative
load into the scratch register, followed by the add.

[Lasse Reichstein, 2009/08/28 09:15:18]

Good point. It might have the same number of opcodes, but due to the memory
read, it will be slower.

+  // Alternative: Compute address of Code* from pc.
+  // __ sub(r1, pc, Operand(8 + masm_->pc_offset() + Code::kHeaderSize));
+  // __ add(pc, r0, Operand(r1));
+}
+
+
+void RegExpMacroAssemblerARM::Bind(Label* label) {
+  __ bind(label);
+}
+
+
+void RegExpMacroAssemblerARM::CheckCharacter(uint32_t c, Label* on_equal) {
+  __ cmp(current_character(), Operand(c));
+  BranchOrBacktrack(eq, on_equal);
+}
+
+
+void RegExpMacroAssemblerARM::CheckCharacterGT(uc16 limit, Label* on_greater) {
+  __ cmp(current_character(), Operand(limit));
+  BranchOrBacktrack(gt, on_greater);
+}
+
+
+void RegExpMacroAssemblerARM::CheckAtStart(Label* on_at_start) {
+  Label not_at_start;
+  // Did we start the match at the start of the string at all?
+  __ ldrb(r0, MemOperand(frame_pointer(), kAtStart));

[Erik Corry, 2009/08/27 14:43:05]

Don't use ldrb if you don't have to - costs a cycle.

[Lasse Reichstein, 2009/08/28 09:15:18]

Done.

+  __ cmp(r0, Operand(0));
+  BranchOrBacktrack(eq, &not_at_start);
+
+  // If we did, are we still at the start of the input?
+  __ add(r0, end_of_input_address(), Operand(current_input_offset()));

[Erik Corry, 2009/08/27 14:43:05]

Reorder here to put the add in the delay slot of the load.

[Lasse Reichstein, 2009/08/28 09:15:18]

Done

+  __ ldr(r1, MemOperand(frame_pointer(), kInputStart));
+  __ cmp(r0, r1);
+  BranchOrBacktrack(eq, on_at_start);
+  __ bind(&not_at_start);
+}
+
+
+void RegExpMacroAssemblerARM::CheckNotAtStart(Label* on_not_at_start) {
+  // Did we start the match at the start of the string at all?
+  __ ldr(r0, MemOperand(frame_pointer(), kAtStart));
+  __ cmp(r0, Operand(0));
+  BranchOrBacktrack(eq, on_not_at_start);
+  // If we did, are we still at the start of the input?
+  __ add(r0, end_of_input_address(), Operand(current_input_offset()));

[Erik Corry, 2009/08/27 14:43:05]

And here.

[Lasse Reichstein, 2009/08/28 09:15:18]

Done

+  __ ldr(r1, MemOperand(frame_pointer(), kInputStart));
+  __ cmp(r0, r1);
+  BranchOrBacktrack(ne, on_not_at_start);
+}
+
+
+void RegExpMacroAssemblerARM::CheckCharacterLT(uc16 limit, Label* on_less) {
+  __ cmp(current_character(), Operand(limit));
+  BranchOrBacktrack(lt, on_less);
+}
+
+
+void RegExpMacroAssemblerARM::CheckCharacters(Vector<const uc16> str,
+                                              int cp_offset,
+                                              Label* on_failure,
+                                              bool check_end_of_string) {
+  int byte_length = str.length() * char_size();
+  int byte_offset = cp_offset * char_size();
+  if (check_end_of_string) {
+    // Check that there are at least str.length() characters left in the input.
+    __ cmp(end_of_input_address(), Operand(-(byte_offset + byte_length)));
+    BranchOrBacktrack(gt, on_failure);
+  }
+
+  if (on_failure == NULL) {
+    // Instead of inlining a backtrack, (re)use the global backtrack target.
+    on_failure = &backtrack_label_;
+  }
+
+  __ add(r0, end_of_input_address(), Operand(current_input_offset()));
+  for (int i = 0; i < str.length(); i++) {
+    if (mode_ == ASCII) {
+      __ ldrb(r1, MemOperand(r0, char_size(), PostIndex));
+    } else {
+      __ ldrh(r1, MemOperand(r0, char_size(), PostIndex));
+    }
+    __ cmp(r1, Operand(str[i]));

[Erik Corry, 2009/08/27 14:43:05]

For 16 bit strings this will generate constant pool entries like animal!  How
about loading the high byte into a different register then for each iteration
you update the high byte if necessary (rarely) and or-in the low byte.  Or we
just have the string as a literal in the constant pool somehow.

[Lasse Reichstein, 2009/08/28 09:15:18]

String-in-constant-pool sounds like something the security people would barf
over (it's executable after all :).
I'll load low and high bytes separately (if necessary), and only load the high
bits if necessary. It will take an extra opcode, but it goes between the load
and the compare, so timing should be fine.

+    BranchOrBacktrack(ne, on_failure);
+  }
+}
+
+
+void RegExpMacroAssemblerARM::CheckGreedyLoop(Label* on_equal) {
+  __ ldr(r0, MemOperand(backtrack_stackpointer(), 0));
+  __ cmp(current_input_offset(), r0);
+  __ add(backtrack_stackpointer(),
+         backtrack_stackpointer(), Operand(kPointerSize), LeaveCC, eq);
+  BranchOrBacktrack(eq, on_equal);
+}
+
+
+void RegExpMacroAssemblerARM::CheckNotBackReferenceIgnoreCase(
+    int start_reg,
+    Label* on_no_match) {
+  Label fallthrough;
+  __ ldr(r0, register_location(start_reg));  // Index of start of capture
+  __ ldr(r1, register_location(start_reg + 1));  // Index of end of capture
+  __ sub(r1, r1, r0, SetCC);  // Length of capture.
+
+  // If length is zero, either the capture is empty or it is not participating.
+  // In either case succeed immediately.
+  __ b(eq, &fallthrough);
+
+  // Check that there are enough characters left in the input.
+  __ cmn(r1, Operand(current_input_offset()));
+  BranchOrBacktrack(gt, on_no_match);
+
+  if (mode_ == ASCII) {
+    Label success;
+    Label fail;
+    Label loop_check;
+
+    // r0 - offset of start of capture
+    // r1 - length of capture
+
+    __ add(r0, r0, Operand(end_of_input_address()));
+    __ add(r2, end_of_input_address(), Operand(current_input_offset()));
+    __ add(r1, r0, Operand(r1));
+
+    // r0 - Address of start of capture.
+    // r1 - Address of end of capture
+    // r2 - Address of current input position.
+
+    Label loop;
+    __ bind(&loop);
+    __ ldrb(r5, MemOperand(r0, char_size(), PostIndex));
+    __ ldrb(r4, MemOperand(r2, char_size(), PostIndex));
+    __ cmp(r4, r5);
+    __ b(eq, &loop_check);
+
+    // Mismatch, try case-insensitive match (converting letters to lower-case).
+    __ orr(r5, r5, Operand(0x20));  // Convert capture character to lower-case.
+    __ sub(r3, r5, Operand('a'));
+    __ cmp(r3, Operand('z' - 'a'));  // Is r5 a lowercase letter?
+    __ b(hi, &fail);
+    // Also convert capture character.
+    __ orr(r4, r4, Operand(0x20));
+    __ cmp(r4, r5);
+    __ b(ne, &fail);
+
+    __ bind(&loop_check);
+    __ cmp(r0, r1);
+    __ b(lt, &loop);
+    __ jmp(&success);
+
+    __ bind(&fail);
+    // Restore original values before failing.

[Erik Corry, 2009/08/27 14:43:05]

Misplaced comment?

[Lasse Reichstein, 2009/08/28 09:15:18]

Mis-retained from the ia32 version. We didn't need to save any registers in the
ARM code.

+    BranchOrBacktrack(al, on_no_match);
+
+    __ bind(&success);
+    // Compute new value of character position after the matched part.
+    __ sub(current_input_offset(), r2, end_of_input_address());
+  } else {
+    ASSERT(mode_ == UC16);
+    int argument_count = 3;
+    FrameAlign(argument_count, r2);
+
+    // r0 - offset of start of capture
+    // r1 - length of capture
+
+    // Put arguments into arguments registers.
+    // Parameters are
+    //   r0: Address byte_offset1 - Address captured substring's start.
+    //   r1: Address byte_offset2 - Address of current character position.
+    //   r2: size_t byte_length - length of capture in bytes(!)
+
+    // Address of start of capture.
+    __ add(r0, r0, Operand(end_of_input_address()));
+    // Length of capture.
+    __ mov(r2, Operand(r1));
+    // Save length in callee-save register for use on return.
+    __ mov(r4, Operand(r1));
+    // Address of current input position.
+    __ add(r1, current_input_offset(), Operand(end_of_input_address()));
+
+    ExternalReference function =
+        ExternalReference::re_case_insensitive_compare_uc16();
+    CallCFunction(function, argument_count);
+
+    // Check if function returned non-zero for success or zero for failure.
+    __ cmp(r0, Operand(0));
+    BranchOrBacktrack(eq, on_no_match);
+    // On success, increment position by length of capture.
+    __ add(current_input_offset(), current_input_offset(), Operand(r4));
+  }
+
+  __ bind(&fallthrough);
+}
+
+
+void RegExpMacroAssemblerARM::CheckNotBackReference(
+    int start_reg,
+    Label* on_no_match) {
+  Label fallthrough;
+  Label success;
+
+  // Find length of back-referenced capture.
+  __ ldr(r0, register_location(start_reg));
+  __ ldr(r1, register_location(start_reg + 1));
+  __ sub(r1, r1, r0, SetCC);  // Length to check.
+  // Succeed on empty capture (including no capture)

[Erik Corry, 2009/08/27 14:43:05]

Missing full stop.

+  __ b(eq, &fallthrough);
+
+  // Check that there are enough characters left in the input.
+  __ cmn(r1, Operand(current_input_offset()));
+  BranchOrBacktrack(gt, on_no_match);
+
+  // Compute pointers to match string and capture string
+  __ add(r0, r0, Operand(end_of_input_address()));
+  __ add(r2, end_of_input_address(), Operand(current_input_offset()));
+  __ add(r1, r1, Operand(r0));
+
+  Label loop;
+  __ bind(&loop);
+  if (mode_ == ASCII) {
+    __ ldrb(r4, MemOperand(r0, char_size(), PostIndex));
+    __ ldrb(r5, MemOperand(r2, char_size(), PostIndex));
+  } else {
+    ASSERT(mode_ == UC16);
+    __ ldrh(r4, MemOperand(r0, char_size(), PostIndex));
+    __ ldrh(r5, MemOperand(r2, char_size(), PostIndex));
+  }
+  __ cmp(r4, r5);
+  BranchOrBacktrack(ne, on_no_match);
+  __ cmp(r0, r1);
+  __ b(lt, &loop);
+
+  // Move current character position to position after match.
+  __ sub(current_input_offset(), r2, end_of_input_address());
+  __ bind(&fallthrough);
+}
+
+
+void RegExpMacroAssemblerARM::CheckNotRegistersEqual(int reg1,
+                                                      int reg2,
+                                                      Label* on_not_equal) {
+  __ ldr(r0, register_location(reg1));
+  __ ldr(r1, register_location(reg2));
+  __ cmp(r0, r1);
+  BranchOrBacktrack(ne, on_not_equal);
+}
+
+
+void RegExpMacroAssemblerARM::CheckNotCharacter(uint32_t c,
+                                                Label* on_not_equal) {
+  __ cmp(current_character(), Operand(c));
+  BranchOrBacktrack(ne, on_not_equal);
+}
+
+
+void RegExpMacroAssemblerARM::CheckCharacterAfterAnd(uint32_t c,
+                                                     uint32_t mask,
+                                                     Label* on_equal) {
+  __ and_(r0, current_character(), Operand(mask));
+  __ cmp(r0, Operand(c));
+  BranchOrBacktrack(eq, on_equal);
+}
+
+
+void RegExpMacroAssemblerARM::CheckNotCharacterAfterAnd(uint32_t c,
+                                                        uint32_t mask,
+                                                        Label* on_not_equal) {
+  __ and_(r0, current_character(), Operand(mask));
+  __ cmp(r0, Operand(c));
+  BranchOrBacktrack(ne, on_not_equal);
+}
+
+
+void RegExpMacroAssemblerARM::CheckNotCharacterAfterMinusAnd(
+    uc16 c,
+    uc16 minus,
+    uc16 mask,
+    Label* on_not_equal) {
+  ASSERT(minus < String::kMaxUC16CharCode);
+  __ sub(r0, current_character(), Operand(minus));
+  __ and_(r0, r0, Operand(mask));
+  __ cmp(r0, Operand(c));
+  BranchOrBacktrack(ne, on_not_equal);
+}
+
+
+bool RegExpMacroAssemblerARM::CheckSpecialCharacterClass(uc16 type,
+                                                         int cp_offset,
+                                                         bool check_offset,
+                                                         Label* on_no_match) {
+  // Range checks (c in min..max) are generally implemented by an unsigned
+  // (c - min) <= (max - min) check
+  switch (type) {
+  case 's':
+    // Match space-characters
+    if (mode_ == ASCII) {
+      // ASCII space characters are '\t'..'\r' and ' '.
+      if (check_offset) {
+        LoadCurrentCharacter(cp_offset, on_no_match);
+      } else {
+        LoadCurrentCharacterUnchecked(cp_offset, 1);
+      }
+      Label success;
+      __ cmp(current_character(), Operand(' '));
+      __ b(eq, &success);
+      // Check range 0x09..0x0d
+      __ sub(r0, current_character(), Operand('\t'));
+      __ cmp(r0, Operand('\r' - '\t'));
+      BranchOrBacktrack(hi, on_no_match);
+      __ bind(&success);
+      return true;
+    }
+    return false;
+  case 'S':
+    // Match non-space characters.
+    if (check_offset) {
+      LoadCurrentCharacter(cp_offset, on_no_match, 1);
+    } else {
+      LoadCurrentCharacterUnchecked(cp_offset, 1);
+    }
+    if (mode_ == ASCII) {
+      // ASCII space characters are '\t'..'\r' and ' '.
+      __ cmp(current_character(), Operand(' '));
+      BranchOrBacktrack(eq, on_no_match);
+      __ sub(r0, current_character(), Operand('\t'));
+      __ cmp(r0, Operand('\r' - '\t'));
+      BranchOrBacktrack(ls, on_no_match);
+      return true;
+    }
+    return false;
+  case 'd':
+    // Match ASCII digits ('0'..'9')
+    if (check_offset) {
+      LoadCurrentCharacter(cp_offset, on_no_match, 1);
+    } else {
+      LoadCurrentCharacterUnchecked(cp_offset, 1);
+    }
+    __ sub(r0, current_character(), Operand('0'));
+    __ cmp(current_character(), Operand('9' - '0'));
+    BranchOrBacktrack(hi, on_no_match);
+    return true;
+  case 'D':
+    // Match non ASCII-digits
+    if (check_offset) {
+      LoadCurrentCharacter(cp_offset, on_no_match, 1);
+    } else {
+      LoadCurrentCharacterUnchecked(cp_offset, 1);
+    }
+    __ sub(r0, current_character(), Operand('0'));
+    __ cmp(r0, Operand('9' - '0'));
+    BranchOrBacktrack(ls, on_no_match);
+    return true;
+  case '.': {
+    // Match non-newlines (not 0x0a('\n'), 0x0d('\r'), 0x2028 and 0x2029)
+    if (check_offset) {
+      LoadCurrentCharacter(cp_offset, on_no_match, 1);
+    } else {
+      LoadCurrentCharacterUnchecked(cp_offset, 1);
+    }
+    __ eor(r0, current_character(), Operand(0x01));
+    // See if current character is '\n'^1 or '\r'^1, i.e., 0x0b or 0x0c
+    __ sub(r0, r0, Operand(0x0b));
+    __ cmp(r0, Operand(0x0c - 0x0b));
+    BranchOrBacktrack(ls, on_no_match);
+    if (mode_ == UC16) {
+      // Compare original value to 0x2028 and 0x2029, using the already
+      // computed (current_char ^ 0x01 - 0x0b). I.e., check for
+      // 0x201d (0x2028 - 0x0b) or 0x201e.
+      __ sub(r0, r0, Operand(0x2028 - 0x0b));
+      __ cmp(r0, Operand(1));
+      BranchOrBacktrack(ls, on_no_match);
+    }
+    return true;
+  }
+  case '*':
+    // Match any character.
+    if (check_offset) {
+      CheckPosition(cp_offset, on_no_match);
+    }
+    return true;
+  // No custom implementation (yet): w, W, s(UC16), S(UC16).
+  default:
+    return false;
+  }
+}
+
+
+void RegExpMacroAssemblerARM::Fail() {
+  ASSERT(FAILURE == 0);  // Return value for failure is zero.
+  __ mov(r0, Operand(0));

[Erik Corry, 2009/08/27 14:43:05]

Can't we just use Operand(FAILURE)?

[Lasse Reichstein, 2009/08/28 09:15:18]

Done.

+  __ jmp(&exit_label_);
+}
+
+
+Handle<Object> RegExpMacroAssemblerARM::GetCode(Handle<String> source) {
+  // Finalize code - write the entry point code now we know how many
+  // registers we need.
+
+  // Entry code:
+  __ bind(&entry_label_);
+  // Push Link register.
+  // Push arguments
+  // Save callee-save registers.
+  // Start new stack frame.
+  // Order here should correspond to order of offset constants in header file.
+  RegList registers_to_retain = r4.bit() | r5.bit() | r6.bit() |
+      r7.bit() | r8.bit() | r9.bit() | r10.bit() | fp.bit();
+  RegList argument_registers = r0.bit() | r1.bit() | r2.bit() | r3.bit();
+  __ stm(db_w, sp, argument_registers | registers_to_retain | lr.bit());
+  // Set frame pointer just above the arguments.
+  __ add(frame_pointer(), sp, Operand(4 * kPointerSize));
+  __ push(r0);  // Make room for "position - 1" constant (value is irrelevant).
+
+  // Check if we have space on the stack for registers.
+  Label stack_limit_hit;
+  Label stack_ok;
+
+  ExternalReference stack_guard_limit =
+      ExternalReference::address_of_stack_guard_limit();
+  __ mov(r0, Operand(stack_guard_limit));
+  __ ldr(r0, MemOperand(r0));
+  __ sub(r0, sp, r0, SetCC);
+  // Handle it if the stack pointer is already below the stack limit.
+  __ b(ls, &stack_limit_hit);
+  // Check if there is room for the variable number of registers above
+  // the stack limit.
+  __ cmp(r0, Operand(num_registers_ * kPointerSize));
+  __ b(hs, &stack_ok);
+  // Exit with OutOfMemory exception. There is not enough space on the stack
+  // for our working registers.
+  __ mov(r0, Operand(EXCEPTION));
+  __ jmp(&exit_label_);
+
+  __ bind(&stack_limit_hit);
+  CallCheckStackGuardState(r0);
+  __ cmp(r0, Operand(0));
+  // If returned value is non-zero, we exit with the returned value as result.
+  __ b(ne, &exit_label_);
+
+  __ bind(&stack_ok);
+
+  // Allocate space on stack for registers.
+  __ sub(sp, sp, Operand(num_registers_ * kPointerSize));
+  // Load string end.
+  __ ldr(end_of_input_address(), MemOperand(frame_pointer(), kInputEnd));
+  // Load input start.
+  __ ldr(r0, MemOperand(frame_pointer(), kInputStart));
+  // Find negative length (offset of start relative to end).
+  __ sub(current_input_offset(), r0, end_of_input_address());
+  // Set r0 to address of char before start of input
+  // (effectively string position -1).
+  __ sub(r0, current_input_offset(), Operand(char_size()));
+  // Store this value in a local variable, for use when clearing
+  // position registers.
+  __ str(r0, MemOperand(frame_pointer(), kInputStartMinusOne));
+  if (num_saved_registers_ > 0) {  // Always is, if generated from a regexp.
+    // Fill saved registers with initial value = start offset - 1
+    // Fill in stack push order, to avoid accessing across an unwritten
+    // page (a problem on Windows).

[Erik Corry, 2009/08/27 14:43:05]

Comment seems malplaced.

[Lasse Reichstein, 2009/08/28 09:15:18]

Gone.

+
+    // Address of register 0.
+    __ add(r1, frame_pointer(), Operand(kRegisterZero));
+    __ mov(r2, Operand(num_saved_registers_));
+    Label init_loop;
+    __ bind(&init_loop);
+    __ str(r0, MemOperand(r1, kPointerSize, NegPostIndex));
+    __ sub(r2, r2, Operand(1), SetCC);
+    __ b(ne, &init_loop);
+  }
+  // TODO(ARM) Is this necessary? Is the page size correct?

[Erik Corry, 2009/08/27 14:43:05]

I think we can just delete this on ARM.

[Lasse Reichstein, 2009/08/28 09:15:18]

Done.

+  // Ensure that we have written to each stack page, in order. Skipping a page
+  // on Windows can cause segmentation faults. Assuming page size is 4k.
+  const int kPageSize = 4096;
+  const int kRegistersPerPage = kPageSize / kPointerSize;
+  for (int i = num_saved_registers_ + kRegistersPerPage - 1;
+      i < num_registers_;
+      i += kRegistersPerPage) {
+    __ str(r0, register_location(i));  // One write every page.
+  }
+
+
+  // Initialize backtrack stack pointer.
+  __ ldr(backtrack_stackpointer(), MemOperand(frame_pointer(), kStackHighEnd));
+  // Load previous char as initial value of current-character.

[Erik Corry, 2009/08/27 14:43:05]

No-need for a hyphen-here.

+  Label at_start;
+  __ ldrb(r0, MemOperand(frame_pointer(), kAtStart));

[Erik Corry, 2009/08/27 14:43:05]

ldr

+  __ cmp(r0, Operand(0));
+  __ b(ne, &at_start);
+  LoadCurrentCharacterUnchecked(-1, 1);  // Load previous char.
+  __ jmp(&start_label_);
+  __ bind(&at_start);
+  __ mov(current_character(), Operand('\n'));
+  __ jmp(&start_label_);
+
+
+  // Exit code:
+  if (success_label_.is_linked()) {
+    // Save captures when successful.
+    __ bind(&success_label_);
+    if (num_saved_registers_ > 0) {
+      // copy captures to output
+      __ ldr(r0, MemOperand(frame_pointer(), kRegisterOutput));
+      __ ldr(r1, MemOperand(frame_pointer(), kInputStart));
+      __ sub(r1, end_of_input_address(), r1);
+      // r1 is length of input.
+      for (int i = 0; i < num_saved_registers_; i++) {
+        __ ldr(r2, register_location(i));
+        __ add(r2, r2, Operand(r1));

[Erik Corry, 2009/08/27 14:43:05]

This add and mov can be combined into one instruction! (And given that the
number of registers is always even perhaps we should unwind once).

[Lasse Reichstein, 2009/08/28 09:15:18]

Done (both combining the add and move, and unrolling).

+        if (mode_ == UC16) {
+          __ mov(r2, Operand(r2, ASR, 1));
+        }
+        __ str(r2, MemOperand(r0, kPointerSize, PostIndex));
+      }
+    }
+    __ mov(r0, Operand(SUCCESS));
+  }
+  // Exit and return r0
+  __ bind(&exit_label_);
+  // Skip sp past regexp registers and local variables..
+  __ mov(sp, frame_pointer());
+  // Restore registers r4..r11 and return (restoring lr to pc).
+  __ ldm(ia_w, sp, registers_to_retain | pc.bit());
+
+  // Backtrack code (branch target for conditional backtracks).
+  if (backtrack_label_.is_linked()) {
+    __ bind(&backtrack_label_);
+    Backtrack();
+  }
+
+  Label exit_with_exception;
+
+  // Preempt-code
+  if (check_preempt_label_.is_linked()) {
+    SafeCallTarget(&check_preempt_label_);
+
+    CallCheckStackGuardState(r0);
+    __ cmp(r0, Operand(0));
+    // If returning non-zero, we should end execution with the given
+    // result as return value.
+    __ b(ne, &exit_label_);
+
+    // String might have moved: Reload end of string from frame.
+    __ ldr(end_of_input_address(), MemOperand(frame_pointer(), kInputEnd));
+    SafeReturn();
+  }
+
+  // Backtrack stack overflow code.
+  if (stack_overflow_label_.is_linked()) {
+    SafeCallTarget(&stack_overflow_label_);
+    // Reached if the backtrack-stack limit has been hit.
+
+    Label grow_failed;
+
+    // Call GrowStack(backtrack_stackpointer())
+    int num_arguments = 2;
+    FrameAlign(num_arguments, r0);
+    __ mov(r0, backtrack_stackpointer());
+    __ add(r1, frame_pointer(), Operand(kStackHighEnd));
+    ExternalReference grow_stack =
+      ExternalReference::re_grow_stack();
+    CallCFunction(grow_stack, num_arguments);
+    // If return NULL, we have failed to grow the stack, and
+    // must exit with a stack-overflow exception.
+    __ cmp(r0, Operand(0));
+    __ b(eq, &exit_with_exception);
+    // Otherwise use return value as new stack pointer.
+    __ mov(backtrack_stackpointer(), r0);
+    // Restore saved registers and continue.
+    SafeReturn();
+  }
+
+  if (exit_with_exception.is_linked()) {
+    // If any of the code above needed to exit with an exception.
+    __ bind(&exit_with_exception);
+    // Exit with Result EXCEPTION(-1) to signal thrown exception.
+    __ mov(r0, Operand(EXCEPTION));
+    __ jmp(&exit_label_);
+  }
+
+  CodeDesc code_desc;
+  masm_->GetCode(&code_desc);
+  Handle<Code> code = Factory::NewCode(code_desc,
+                                       NULL,
+                                       Code::ComputeFlags(Code::REGEXP),
+                                       masm_->CodeObject());
+  LOG(RegExpCodeCreateEvent(*code, *source));
+  return Handle<Object>::cast(code);
+}
+
+
+void RegExpMacroAssemblerARM::GoTo(Label* to) {
+  BranchOrBacktrack(al, to);
+}
+
+
+void RegExpMacroAssemblerARM::IfRegisterGE(int reg,
+                                           int comparand,
+                                           Label* if_ge) {
+  __ ldr(r0, register_location(reg));
+  __ cmp(r0, Operand(comparand));
+  BranchOrBacktrack(ge, if_ge);
+}
+
+
+void RegExpMacroAssemblerARM::IfRegisterLT(int reg,
+                                           int comparand,
+                                           Label* if_lt) {
+  __ ldr(r0, register_location(reg));
+  __ cmp(r0, Operand(comparand));
+  BranchOrBacktrack(lt, if_lt);
+}
+
+
+void RegExpMacroAssemblerARM::IfRegisterEqPos(int reg,
+                                              Label* if_eq) {
+  __ ldr(r0, register_location(reg));
+  __ cmp(r0, Operand(current_input_offset()));
+  BranchOrBacktrack(eq, if_eq);
+}
+
+
+RegExpMacroAssembler::IrregexpImplementation
+    RegExpMacroAssemblerARM::Implementation() {
+  return kARMImplementation;
+}
+
+
+void RegExpMacroAssemblerARM::LoadCurrentCharacter(int cp_offset,
+                                                   Label* on_end_of_input,
+                                                   bool check_bounds,

[Erik Corry, 2009/08/27 14:43:05]

We don't use check_bounds.  Can that be right?

[Lasse Reichstein, 2009/08/28 09:15:18]

Doesn't seem so. We should only call CheckPosition if check_bounds is true.
Fixed both here and on ia32/x64.

+                                                   int characters) {
+  ASSERT(cp_offset >= -1);      // ^ and \b can look behind one character.
+  ASSERT(cp_offset < (1<<30));  // Be sane! (And ensure negation works)
+  CheckPosition(cp_offset + characters - 1, on_end_of_input);
+  LoadCurrentCharacterUnchecked(cp_offset, characters);
+}
+
+
+void RegExpMacroAssemblerARM::PopCurrentPosition() {
+  Pop(current_input_offset());
+}
+
+
+void RegExpMacroAssemblerARM::PopRegister(int register_index) {
+  Pop(r0);
+  __ str(r0, register_location(register_index));
+}

[Erik Corry, 2009/08/27 14:43:05]

This is as far as I got.

+
+
+void RegExpMacroAssemblerARM::PushBacktrack(Label* label) {
+  if (label->is_bound()) {
+    int target = label->pos();
+    __ mov(r0, Operand(target + Code::kHeaderSize));

[Erik Corry, 2009/08/28 09:47:03]

If the label is used in a constant pool address that is within range we should
load from there (unless we can encode the number in one instruction).  This
instruction will otherwise create a new constant pool address.  If it isn't in
range we should make a new constant pool address and put it in the label. 
Perhaps we need a subclass of Label for this.

[Lasse Reichstein, 2009/08/28 11:43:15]

It's an interesting idea, but I'll prefer to look at the code before doing a
complex rewrite to achieve this.

+  } else {
+    int constant_offset = GetBacktrackConstantPoolEntry();
+    masm_->label_at_put(label, constant_offset);
+    __ ldr(r0, MemOperand(pc, constant_offset - masm_->pc_offset() - 8));
+  }
+  Push(r0);
+  CheckStackLimit();
+}
+
+
+void RegExpMacroAssemblerARM::PushCurrentPosition() {
+  Push(current_input_offset());
+}
+
+
+void RegExpMacroAssemblerARM::PushRegister(int register_index,
+                                           StackCheckFlag check_stack_limit) {
+  __ ldr(r0, register_location(register_index));
+  Push(r0);
+  if (check_stack_limit) CheckStackLimit();
+}
+
+
+void RegExpMacroAssemblerARM::ReadCurrentPositionFromRegister(int reg) {
+  __ ldr(current_input_offset(), register_location(reg));
+}
+
+
+void RegExpMacroAssemblerARM::ReadStackPointerFromRegister(int reg) {
+  __ ldr(backtrack_stackpointer(), register_location(reg));
+  __ ldr(r0, MemOperand(frame_pointer(), kStackHighEnd));
+  __ add(backtrack_stackpointer(), backtrack_stackpointer(), Operand(r0));
+}
+
+
+void RegExpMacroAssemblerARM::SetRegister(int register_index, int to) {
+  ASSERT(register_index >= num_saved_registers_);  // Reserved for positions!
+  __ mov(r0, Operand(to));
+  __ str(r0, register_location(register_index));
+}
+
+
+void RegExpMacroAssemblerARM::Succeed() {
+  __ jmp(&success_label_);
+}
+
+
+void RegExpMacroAssemblerARM::WriteCurrentPositionToRegister(int reg,
+                                                             int cp_offset) {
+  if (cp_offset == 0) {
+    __ str(current_input_offset(), register_location(reg));
+  } else {
+    __ add(r0, current_input_offset(), Operand(cp_offset * char_size()));
+    __ str(r0, register_location(reg));
+  }
+}
+
+
+void RegExpMacroAssemblerARM::ClearRegisters(int reg_from, int reg_to) {
+  ASSERT(reg_from <= reg_to);
+  __ ldr(r0, MemOperand(frame_pointer(), kInputStartMinusOne));
+  for (int reg = reg_from; reg <= reg_to; reg++) {
+    __ str(r0, register_location(reg));
+  }
+}
+
+
+void RegExpMacroAssemblerARM::WriteStackPointerToRegister(int reg) {
+  __ ldr(r1, MemOperand(frame_pointer(), kStackHighEnd));
+  __ sub(r0, backtrack_stackpointer(), r1);
+  __ str(r0, register_location(reg));
+}
+
+
+// Private methods:
+
+void RegExpMacroAssemblerARM::CallCheckStackGuardState(Register scratch) {
+  int num_arguments = 3;
+  FrameAlign(num_arguments, scratch);
+  // RegExp code frame pointer.
+  __ mov(r2, frame_pointer());
+  // Code* of self.
+  __ mov(r1, Operand(masm_->CodeObject()));
+  // r0 becomes return address pointer.
+  ExternalReference stack_guard_check =
+      ExternalReference::re_check_stack_guard_state();
+  CallCFunctionUsingStub(stack_guard_check, num_arguments);
+}
+
+
+// Helper function for reading a value out of a stack frame.
+template <typename T>
+static T& frame_entry(Address re_frame, int frame_offset) {
+  return reinterpret_cast<T&>(Memory::int32_at(re_frame + frame_offset));
+}
+
+
+int RegExpMacroAssemblerARM::CheckStackGuardState(Address* return_address,
+                                                  Code* re_code,
+                                                  Address re_frame) {
+  if (StackGuard::IsStackOverflow()) {
+    Top::StackOverflow();
+    return EXCEPTION;
+  }
+
+  // If not real stack overflow the stack guard was used to interrupt
+  // execution for another purpose.
+
+  // Prepare for possible GC.
+  HandleScope handles;
+  Handle<Code> code_handle(re_code);
+
+  Handle<String> subject(frame_entry<String*>(re_frame, kInputString));
+  // Current string.
+  bool is_ascii = subject->IsAsciiRepresentation();
+
+  ASSERT(re_code->instruction_start() <= *return_address);
+  ASSERT(*return_address <=
+      re_code->instruction_start() + re_code->instruction_size());
+
+  Object* result = Execution::HandleStackGuardInterrupt();
+
+  if (*code_handle != re_code) {  // Return address no longer valid
+    UNIMPLEMENTED();  // TODO(ARM): Can't handle moving code yet.

[Erik Corry, 2009/08/28 09:47:03]

We need to fix this!

[Lasse Reichstein, 2009/08/28 11:43:15]

Fixed. Removed the UNIMPLEMENTED and comment. It should work.

+                      // Link register is not reified, so we can't
+                      // update it. The address in the argument is
+                      // just what the return address might be,
+                      // but we don't use it to return.
+    int delta = *code_handle - re_code;
+    // Overwrite the return address on the stack.
+    *return_address += delta;
+  }
+
+  if (result->IsException()) {
+    return EXCEPTION;
+  }
+
+  // String might have changed.
+  if (subject->IsAsciiRepresentation() != is_ascii) {
+    // If we changed between an ASCII and an UC16 string, the specialized
+    // code cannot be used, and we need to restart regexp matching from
+    // scratch (including, potentially, compiling a new version of the code).
+    return RETRY;
+  }
+
+  // Otherwise, the content of the string might have moved. It must still
+  // be a sequential or external string with the same content.
+  // Update the start and end pointers in the stack frame to the current
+  // location (whether it has actually moved or not).
+  ASSERT(StringShape(*subject).IsSequential() ||
+      StringShape(*subject).IsExternal());
+
+  // The original start address of the characters to match.
+  const byte* start_address = frame_entry<const byte*>(re_frame, kInputStart);
+
+  // Find the current start address of the same character at the current string
+  // position.
+  int start_index = frame_entry<int>(re_frame, kStartIndex);
+  const byte* new_address = StringCharacterPosition(*subject, start_index);
+
+  if (start_address != new_address) {
+    // If there is a difference, update the object pointer and start and end
+    // addresses in the RegExp stack frame to match the new value.
+    const byte* end_address = frame_entry<const byte* >(re_frame, kInputEnd);
+    int byte_length = end_address - start_address;
+    frame_entry<const String*>(re_frame, kInputString) = *subject;
+    frame_entry<const byte*>(re_frame, kInputStart) = new_address;
+    frame_entry<const byte*>(re_frame, kInputEnd) = new_address + byte_length;
+  }
+
+  return 0;
+}
+
+
+MemOperand RegExpMacroAssemblerARM::register_location(int register_index) {
+  ASSERT(register_index < (1<<30));
+  if (num_registers_ <= register_index) {
+    num_registers_ = register_index + 1;
+  }
+  return MemOperand(frame_pointer(),
+                    kRegisterZero - register_index * kPointerSize);
+}
+
+
+void RegExpMacroAssemblerARM::CheckPosition(int cp_offset,
+                                            Label* on_outside_input) {
+  __ cmp(current_input_offset(), Operand(-cp_offset * char_size()));
+  BranchOrBacktrack(ge, on_outside_input);
+}
+
+
+void RegExpMacroAssemblerARM::BranchOrBacktrack(Condition condition,
+                                                Label* to) {
+  if (condition == al) {  // Unconditional.
+    if (to == NULL) {
+      Backtrack();
+      return;
+    }
+    __ jmp(to);
+    return;
+  }
+  if (to == NULL) {
+    __ b(condition, &backtrack_label_);
+    return;
+  }
+  __ b(condition, to);
+}
+
+
+void RegExpMacroAssemblerARM::SafeCall(Label* to, Condition cond) {
+  __ bl(to, cond);
+}
+
+
+void RegExpMacroAssemblerARM::SafeReturn() {
+  __ pop(lr);
+  __ add(lr, lr, Operand(masm_->CodeObject()));

[Erik Corry, 2009/08/28 09:47:03]

Can't we just add(pc, lr...

[Lasse Reichstein, 2009/08/28 11:43:15]

Should work. Done.

+  __ bx(lr);
+}
+
+
+void RegExpMacroAssemblerARM::SafeCallTarget(Label* name) {
+  __ bind(name);
+  __ sub(lr, lr, Operand(masm_->CodeObject()));
+  __ push(lr);
+}
+
+
+void RegExpMacroAssemblerARM::Push(Register source) {
+  ASSERT(!source.is(backtrack_stackpointer()));
+  __ str(source,
+         MemOperand(backtrack_stackpointer(), kPointerSize, NegPreIndex));
+}
+
+
+void RegExpMacroAssemblerARM::Pop(Register target) {
+  ASSERT(!target.is(backtrack_stackpointer()));
+  __ ldr(target,
+         MemOperand(backtrack_stackpointer(), kPointerSize, PostIndex));
+}
+
+
+void RegExpMacroAssemblerARM::CheckPreemption() {
+  // Check for preemption.
+  ExternalReference stack_guard_limit =
+      ExternalReference::address_of_stack_guard_limit();
+  __ mov(r0, Operand(stack_guard_limit));

[Erik Corry, 2009/08/27 14:43:05]

While you were working on this patch we made a faster way to do preemption
checks.  Probably best to fix in a second patch unless you already moved up to
the latest version before starting the gcl issue.

[Lasse Reichstein, 2009/08/28 11:43:15]

If this still works, I'll leave it for a second patch.

+  __ ldr(r0, MemOperand(r0));
+  __ cmp(sp, r0);
+  SafeCall(&check_preempt_label_, ls);
+}
+
+
+void RegExpMacroAssemblerARM::CheckStackLimit() {
+  if (FLAG_check_stack) {
+    ExternalReference stack_limit =
+        ExternalReference::address_of_regexp_stack_limit();
+    __ mov(r0, Operand(stack_limit));
+    __ ldr(r0, MemOperand(r0));
+    __ cmp(backtrack_stackpointer(), Operand(r0));
+    SafeCall(&stack_overflow_label_, ls);
+  }
+}
+
+
+void RegExpMacroAssemblerARM::EmitBacktrackConstantPool() {
+  __ BlockConstPoolBefore(masm_->pc_offset() + kBacktrackConstantPoolSize);
+  backtrack_constant_pool_offset_ = masm_->pc_offset();
+  for (int i = 0; i < kBacktrackConstantPoolSize; i++) {
+    __ emit(0);
+  }
+  backtrack_constant_pool_capacity_ = kBacktrackConstantPoolSize;
+}
+
+
+int RegExpMacroAssemblerARM::GetBacktrackConstantPoolEntry() {
+  while (backtrack_constant_pool_capacity_ > 0) {
+    int offset = backtrack_constant_pool_offset_;
+    backtrack_constant_pool_offset_ += kPointerSize;
+    backtrack_constant_pool_capacity_--;
+    if (masm_->pc_offset() - offset < 4 * KB) {
+      return offset;
+    }
+  }
+  Label new_pool_skip;
+  __ jmp(&new_pool_skip);
+  EmitBacktrackConstantPool();
+  __ bind(&new_pool_skip);
+  int offset = backtrack_constant_pool_offset_;
+  backtrack_constant_pool_offset_ += kPointerSize;
+  backtrack_constant_pool_capacity_--;
+  return offset;
+}
+
+
+void RegExpMacroAssemblerARM::FrameAlign(int num_arguments, Register scratch) {
+  // Make this work!

[Erik Corry, 2009/08/28 09:47:03]

Yes!

[Lasse Reichstein, 2009/08/28 11:43:15]

Comment removed.

+  int frameAlignment = OS::ActivationFrameAlignment();
+  // Up to four simple arguments are passed in registers r0..r3.
+  int stack_passed_arguments = (num_arguments <= 4) ? 0 : num_arguments - 4;
+  if (frameAlignment != 0) {
+    // Make stack end at alignment and make room for num_arguments - 4 words
+    // and the original value of sp.
+    __ mov(scratch, sp);
+    __ sub(sp, sp, Operand((stack_passed_arguments + 1) * kPointerSize));
+    ASSERT(IsPowerOf2(frameAlignment));
+    __ and_(sp, sp, Operand(-frameAlignment));
+    __ str(scratch, MemOperand(sp, stack_passed_arguments * kPointerSize));
+  } else {
+    __ sub(sp, sp, Operand(stack_passed_arguments * kPointerSize));
+  }
+}
+
+
+void RegExpMacroAssemblerARM::CallCFunction(ExternalReference function,
+                                            int num_arguments) {
+  __ mov(r5, Operand(function));
+  // Just call directly. The function called cannot cause a GC, or
+  // allow preemption, so the return address in the link register
+  // stays correct.
+  __ Call(r5);
+  int stack_passed_arguments = (num_arguments <= 4) ? 0 : num_arguments - 4;
+  if (OS::ActivationFrameAlignment() != 0) {

[Lasse Reichstein, 2009/08/28 11:43:15]

Done

+    __ ldr(sp, MemOperand(sp, stack_passed_arguments * kPointerSize));
+  } else {
+    __ add(sp, sp, Operand(stack_passed_arguments * sizeof(kPointerSize)));
+  }
+}
+
+
+void RegExpMacroAssemblerARM::CallCFunctionUsingStub(
+    ExternalReference function,
+    int num_arguments) {
+  // Must pass all arguments in registers. The stub pushes on the stack.
+  ASSERT(num_arguments <= 4);
+  __ mov(r5, Operand(function));
+  RegExpCEntryStub stub;
+  __ CallStub(&stub);
+  if (OS::ActivationFrameAlignment() != 0) {
+    __ ldr(sp, MemOperand(sp, 0));
+  }
+}
+
+
+void RegExpMacroAssemblerARM::LoadCurrentCharacterUnchecked(int cp_offset,
+                                                            int characters) {
+  Register offset = current_input_offset();
+  if (cp_offset != 0) {
+    __ add(r0, current_input_offset(), Operand(cp_offset * char_size()));
+    offset = r0;
+  }
+  // Cannot read unaligned, so we ensure that we always load at most twice.
+  if (mode_ == ASCII) {
+    if (characters == 4) {

[Erik Corry, 2009/08/28 09:47:03]

This is unnecessary.  On a system that can't load unaligned we are never asked
to load more than one character at a time.

[Lasse Reichstein, 2009/08/28 11:43:15]

I'll assert that characters is 1, and hope the calling code knows how to handle
it.

+      Label done;
+      __ add(r0, end_of_input_address(), Operand(offset));
+      __ and_(r1, r0, Operand(3), SetCC);
+      __ ldr(current_character(), MemOperand(r0, r1, NegOffset), eq);
+      __ b(eq, &done);
+      __ sub(r0, r0, r1);
+      // Read two consecutive words into r4 and r5.
+      __ ldm(ia, r0, r4.bit() | r5.bit());
+      __ mov(r1, Operand(r1, LSL, 3));
+      __ mov(current_character(), Operand(r4, LSR, r1));
+      __ rsb(r1, r1, Operand(0x20));
+      __ add(current_character(), current_character(), Operand(r5, LSL, r1));
+      __ bind(&done);
+    } else if (characters == 2) {
+      // TODO(lrn): Optimize for case where both characters is inside same word.
+      __ add(r0, end_of_input_address(), Operand(offset));
+      __ tst(r0, Operand(1));
+      __ ldrb(current_character(), MemOperand(r0), ne);
+      __ ldrb(r1, MemOperand(r0, 1), ne);
+      __ ldrh(current_character(), MemOperand(r0), eq);
+      __ add(current_character(),
+             current_character(), Operand(r1, LSL, 8), LeaveCC, ne);
+    } else {
+      ASSERT(characters == 1);
+      __ ldrb(current_character(), MemOperand(end_of_input_address(), offset));
+    }
+  } else {
+    ASSERT(mode_ == UC16);
+    if (characters == 2) {
+      __ add(r0, end_of_input_address(), Operand(offset));
+      __ tst(r0, Operand(2));  // Low bit is always zero.
+      __ ldrh(current_character(), MemOperand(r0), ne);
+      __ ldrh(r1, MemOperand(r0, 2), ne);
+      __ ldr(current_character(), MemOperand(r0), eq);
+      __ add(current_character(),
+             current_character(), Operand(r1, LSL, 16), LeaveCC, ne);
+    } else {
+      ASSERT(characters == 1);
+      __ ldrh(current_character(), MemOperand(end_of_input_address(), offset));
+    }
+  }
+}
+
+
+void RegExpCEntryStub::Generate(MacroAssembler* masm_) {
+  int stack_alignment = OS::ActivationFrameAlignment();
+  if (stack_alignment == 0) stack_alignment = kPointerSize;
+  // Stack is already aligned for call, so decrement by alignment
+  // to make room for storing the link register.
+  __ str(lr, MemOperand(sp, stack_alignment, NegPreIndex));
+  __ mov(r0, sp);
+  __ Call(r5);
+  __ ldr(pc, MemOperand(sp, stack_alignment, PostIndex));
+}
+
+#undef __
+
+#endif  // V8_NATIVE_REGEXP
+
+}}  // namespace v8::internal