[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@349964 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/BasicBlock.cpp

@@ -206,10 +206,8 @@ const Instruction* BasicBlock::getFirstNonPHIOrDbgOrLifetime() const {
     if (isa<PHINode>(I) || isa<DbgInfoIntrinsic>(I))
       continue;
 
-    if (auto *II = dyn_cast<IntrinsicInst>(&I))
-      if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
-          II->getIntrinsicID() == Intrinsic::lifetime_end)
-        continue;
+    if (I.isLifetimeStartOrEnd())
+      continue;
 
     return &I;
   }