[PM] Don't run the machinery of invalidating all the analysis passes

when all are being preserved.

We want to short-circuit this for a couple of reasons. One, I don't
really want passes to grow a dependency on actually receiving their
invalidate call when they've been preserved. I'm thinking about removing
this entirely. But more importantly, preserving everything is likely to
be the common case in a lot of scenarios, and it would be really good to
bypass all of the invalidation and preservation machinery there.
Avoiding calling N opaque functions to try to invalidate things that are
by definition still valid seems important. =]

This wasn't really inpsired by much other than seeing the spam in the
logging for analyses, but it seems better ot get it checked in rather
than forgetting about it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225163 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/CGSCCPassManager.cpp

@@ -92,6 +92,10 @@ void CGSCCAnalysisManager::invalidateImpl(void *PassID, LazyCallGraph::SCC &C) {
 
 void CGSCCAnalysisManager::invalidateImpl(LazyCallGraph::SCC &C,
                                           const PreservedAnalyses &PA) {
+  // Short circuit for a common case of all analyses being preserved.
+  if (PA.areAllPreserved())
+    return;
+
   if (DebugPM)
     dbgs() << "Invalidating all non-preserved analyses for SCC: " << C.getName()
            << "\n";