[PATCH] [asan-asm-instrumentation] Prologue and epilogue are moved out from InstrumentMemOperand().

[Evgeniy Stepanov]

LGTM w/ nit

================
Comment at: lib/Target/X86/AsmParser/X86AsmInstrumentation.cpp:552
@@ +551,3 @@
+
+  virtual void InstrumentMemOperandEpilogue(unsigned AccessSize,
+                                            const RegisterContext &RegCtx,
----------------
Is it possible to remove accesssize argument here and in prologue, and instead pass an invalid/zero value for the scratch register?
And check in instrumentmemoperandsmall that a scratch register is available, for sanity.

http://reviews.llvm.org/D4923