[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

llvm/lib/Transforms/Utils/CodeExtractor.cpp

@@ -332,8 +332,7 @@ bool CodeExtractor::isLegalToShrinkwrapLifetimeMarkers(
       default: {
         IntrinsicInst *IntrInst = dyn_cast<IntrinsicInst>(&II);
         if (IntrInst) {
-          if (IntrInst->getIntrinsicID() == Intrinsic::lifetime_start ||
-              IntrInst->getIntrinsicID() == Intrinsic::lifetime_end)
+          if (IntrInst->isLifetimeStartOrEnd())
             break;
           return false;
         }