PPC: Experimental support for RegExp lookbehind.

Port 906903ac

R=yangguo@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=v8:4545
LOG=N

Review URL: https://codereview.chromium.org/1454783002

Cr-Commit-Position: refs/heads/master@{#32056}

src/regexp/ppc/regexp-macro-assembler-ppc.h

@@ -34,9 +34,11 @@ class RegExpMacroAssemblerPPC : public NativeRegExpMacroAssembler {
   // A "greedy loop" is a loop that is both greedy and with a simple
   // body. It has a particularly simple implementation.
   virtual void CheckGreedyLoop(Label* on_tos_equals_current_position);
-  virtual void CheckNotAtStart(Label* on_not_at_start);
-  virtual void CheckNotBackReference(int start_reg, Label* on_no_match);
+  virtual void CheckNotAtStart(int cp_offset, Label* on_not_at_start);
+  virtual void CheckNotBackReference(int start_reg, bool read_backward,
+                                     Label* on_no_match);
   virtual void CheckNotBackReferenceIgnoreCase(int start_reg,
+                                               bool read_backward,
                                                Label* on_no_match);
   virtual void CheckNotCharacter(unsigned c, Label* on_not_equal);
   virtual void CheckNotCharacterAfterAnd(unsigned c, unsigned mask,
@@ -112,9 +114,9 @@ class RegExpMacroAssemblerPPC : public NativeRegExpMacroAssembler {
   // When adding local variables remember to push space for them in
   // the frame in GetCode.
   static const int kSuccessfulCaptures = kInputString - kPointerSize;
-  static const int kInputStartMinusOne = kSuccessfulCaptures - kPointerSize;
+  static const int kStringStartMinusOne = kSuccessfulCaptures - kPointerSize;
   // First register address. Following registers are below it on the stack.
-  static const int kRegisterZero = kInputStartMinusOne - kPointerSize;
+  static const int kRegisterZero = kStringStartMinusOne - kPointerSize;
 
   // Initial size of code buffer.
   static const size_t kRegExpCodeSize = 1024;