[PM] Improve the API and comments around the analysis manager proxies.

These are really handles that ensure the analyses get cleared at
appropriate places, and as such copying doesn't really make sense.
Instead, they should look more like unique ownership objects. Make that
the case.

Relatedly, if you create a temporary of one and move out of it
its destructor shouldn't actually clear anything. I don't think there is
any code that can trigger this currently, but it seems like a more
robust implementation.

If folks want, I can add a unittest that forces this to be exercised,
but that seems somewhat pointless -- whether a temporary is ever created
in the innards of AnalysisManager is not really something we should be
adding a reliance on, but I didn't want to leave a timebomb in the code
here.

If anyone has a cleaner way to represent this, I'm all ears, but
I wanted to assure myself that this wasn't in fact responsible for
another bug I'm chasing down (it wasn't) and figured I'd commit that.

llvm-svn: 261594

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/IR/PassManager.cpp b/llvm/lib/IR/PassManager.cpp
index a5f407c00e8..f55db9c1e64 100644
--- a/llvm/lib/IR/PassManager.cpp
+++ b/llvm/lib/IR/PassManager.cpp
@@ -22,6 +22,10 @@ FunctionAnalysisManagerModuleProxy::run(Module &M) {
 }
 
 FunctionAnalysisManagerModuleProxy::Result::~Result() {
+  // FAM is cleared in a moved from state where there is nothing to do.
+  if (!FAM)
+    return;
+
   // Clear out the analysis manager if we're being destroyed -- it means we
   // didn't even see an invalidate call when we got invalidated.
   FAM->clear();