[Inliner] Remove -update-return-attrs flag

[aeubanks]

Summary

This is by default on and I don't see any reason to turn it off. There's also no testing of it.

[aeubanks]

update

[nikic]

LG

llvm/lib/Transforms/Utils/InlineFunction.cpp

 // Disabled by default, because the added alignment assumptions may increase
 // compile-time and block optimizations. This option is not suitable for use
 // with frontends that emit comprehensive parameter alignment annotations.
 static cl::opt<bool>
 PreserveAlignmentAssumptions("preserve-alignment-assumptions-during-inlining",
   cl::init(false), cl::Hidden,
   cl::desc("Convert align attributes to assumptions during inlining."));
 
-static cl::opt<bool> UpdateReturnAttributes(
-        "update-return-attrs", cl::init(true), cl::Hidden,
-            cl::desc("Update return attributes on calls within inlined body"));
-
 static cl::opt<unsigned> InlinerAttributeWindow(
     "max-inst-checked-for-throw-during-inlining", cl::Hidden,
     cl::desc("the maximum number of instructions analyzed for may throw during "
              "attribute inference in inlined body"),
     cl::init(4));
 
 namespace {
 
static AttrBuilder IdentifyValidAttributes(CallBase &CB) {
   if (AB.contains(Attribute::NoAlias))
     Valid.addAttribute(Attribute::NoAlias);
   if (AB.contains(Attribute::NonNull))
     Valid.addAttribute(Attribute::NonNull);
   return Valid;
 }
 
 static void AddReturnAttributes(CallBase &CB, ValueToValueMapTy &VMap) {
-  if (!UpdateReturnAttributes)
-    return;
-
   AttrBuilder Valid = IdentifyValidAttributes(CB);
   if (!Valid.hasAttributes())
     return;
   auto *CalledFunction = CB.getCalledFunction();
   auto &Context = CalledFunction->getContext();
 
   for (auto &BB : *CalledFunction) {
     auto *RI = dyn_cast<ReturnInst>(BB.getTerminator());