[IR] Add Instruction::isLifetimeStartOrEnd, NFC

Instruction::isLifetimeStartOrEnd() checks whether an Instruction is an
llvm.lifetime.start or an llvm.lifetime.end intrinsic.

This was suggested as a cleanup in D55967.

Differential Revision: https://reviews.llvm.org/D56019

llvm-svn: 349964
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index 92a60fa..2dd961b 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -919,8 +919,7 @@
       continue;
     }
     if (const IntrinsicInst *IT = dyn_cast<IntrinsicInst>(U))
-      if (IT->getIntrinsicID() == Intrinsic::lifetime_start ||
-          IT->getIntrinsicID() == Intrinsic::lifetime_end)
+      if (IT->isLifetimeStartOrEnd())
         continue;
 
     if (U != C && U != cpy)