Don't trivially delete unused calls to llvm.invariant.start. This allows

llvm.invariant.start to be used without necessarily being paired with a call
to llvm.invariant.end.  If you run the entire optimization pipeline then such
calls are in fact deleted (adce does it), but that's actually a good thing since
we probably do want them to be zapped late in the game.  There should really be
an integration test that checks that the llvm.invariant.start call lasts long
enough that all passes that do interesting things with it get to do their stuff
before it is deleted.  But since no passes do anything interesting with it yet
this will have to wait for later.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@86840 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/Local.cpp

@@ -252,6 +252,9 @@ bool llvm::isInstructionTriviallyDead(Instruction *I) {
   // We don't want debug info removed by anything this general.
   if (isa<DbgInfoIntrinsic>(I)) return false;
 
+  // Likewise for memory use markers.
+  if (isa<MemoryUseIntrinsic>(I)) return false;
+
   if (!I->mayHaveSideEffects()) return true;
 
   // Special case intrinsics that "may have side effects" but can be deleted