Revert of [regexp] Remove remainder of native RegExpExecStub

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

Index: src/regexp/ppc/regexp-macro-assembler-ppc.cc
diff --git a/src/regexp/ppc/regexp-macro-assembler-ppc.cc b/src/regexp/ppc/regexp-macro-assembler-ppc.cc
index 5c3f8d5e39f27fa98b6f4d93e53818ebc727c2a4..d6af025f2ed8f10d69a72e0d5ce6ccb757f13847 100644
--- a/src/regexp/ppc/regexp-macro-assembler-ppc.cc
+++ b/src/regexp/ppc/regexp-macro-assembler-ppc.cc
@@ -38,7 +38,8 @@
  * Each call to a public method should retain this convention.
  *
  * The stack will have the following structure:
- *  - fp[40]  Isolate* isolate   (address of the current isolate)
+ *  - fp[44]  Isolate* isolate   (address of the current isolate)
+ *  - fp[40]  secondary link/return address used by native call.
  *  - fp[36]  lr save area (currently unused)
  *  - fp[32]  backchain    (currently unused)
  *  --- sp when called ---
@@ -80,13 +81,16 @@
  *              Address start,
  *              Address end,
  *              int* capture_output_array,
- *              int num_capture_registers,
  *              byte* stack_area_base,
- *              bool direct_call = false,
- *              Isolate* isolate);
+ *              Address secondary_return_address,  // Only used by native call.
+ *              bool direct_call = false)
  * The call is performed by NativeRegExpMacroAssembler::Execute()
  * (in regexp-macro-assembler.cc) via the CALL_GENERATED_REGEXP_CODE macro
  * in ppc/simulator-ppc.h.
+ * When calling as a non-direct call (i.e., from C++ code), the return address
+ * area is overwritten with the LR register by the RegExp code. When doing a
+ * direct call from generated code, the return address is placed there by
+ * the calling code, as in a normal exit frame.
  */
 
 #define __ ACCESS_MASM(masm_)