Fix argument passing to generated regexp code in Win64.

src/x64/regexp-macro-assembler-x64.h

Index: src/x64/regexp-macro-assembler-x64.h
diff --git a/src/x64/regexp-macro-assembler-x64.h b/src/x64/regexp-macro-assembler-x64.h
index 5dfd288353b3eadfefbdf18366df27378d834e24..31fc8efd93629e1aad3d560d53482aa91b129569 100644
--- a/src/x64/regexp-macro-assembler-x64.h
+++ b/src/x64/regexp-macro-assembler-x64.h
@@ -156,7 +156,8 @@ class RegExpMacroAssemblerX64: public NativeRegExpMacroAssembler {
   static const int kRegisterOutput = kInputEnd + kPointerSize;
   // For the case of global regular expression, we have room to store at least
   // one set of capture results.  For the case of non-global regexp, we ignore
-  // this value.
+  // this value. NumOutputRegisters is passed as 32-bit value.  The upper
+  // 32 bit of this 64-bit stack slot may contain garbage.
   static const int kNumOutputRegisters = kRegisterOutput + kPointerSize;
   static const int kStackHighEnd = kNumOutputRegisters + kPointerSize;
   // DirectCall is passed as 32 bit int (values 0 or 1).
@@ -195,7 +196,7 @@ class RegExpMacroAssemblerX64: public NativeRegExpMacroAssembler {
   static const int kLastCalleeSaveRegister = kBackup_rbx;
 #endif
 
-  static const int kSuccessfulCaptures = kBackup_rbx - kPointerSize;
+  static const int kSuccessfulCaptures = kLastCalleeSaveRegister - kPointerSize;
   // When adding local variables remember to push space for them in
   // the frame in GetCode.
   static const int kInputStartMinusOne = kSuccessfulCaptures - kPointerSize;