[PM/LCG] Teach LCG to support spurious reference edges.

Somewhat amazingly, this only requires teaching it to clean them up when
deleting a dead function from the graph. And we already have exactly the
necessary data structures to do that in the parent RefSCCs.

This allows ArgPromote to work in a much simpler way be merely letting
reference edges linger in the graph after the causing IR is deleted. We
will clean up these edges when we run any function pass over the IR, but
don't remove them eagerly.

This avoids all of the quadratic update issues both in the current pass
manager and in my previous attempt with the new pass manager.

Differential Revision: https://reviews.llvm.org/D29579

llvm-svn: 294663

1 files changed, 8 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/LazyCallGraph.cpp b/llvm/lib/Analysis/LazyCallGraph.cpp
index 879a59196d7..a98ef2d8e00 100644
--- a/llvm/lib/Analysis/LazyCallGraph.cpp
+++ b/llvm/lib/Analysis/LazyCallGraph.cpp
@@ -1607,7 +1607,14 @@ void LazyCallGraph::removeDeadFunction(Function &F) {
   // Validate these properties first.
   assert(C.size() == 1 && "Dead functions must be in a singular SCC");
   assert(RC.size() == 1 && "Dead functions must be in a singular RefSCC");
-  assert(RC.Parents.empty() && "Cannot have parents of a dead RefSCC!");
+
+  // Clean up any remaining reference edges. Note that we walk an unordered set
+  // here but are just removing and so the order doesn't matter.
+  for (RefSCC &ParentRC : RC.parents())
+    for (SCC &ParentC : ParentRC)
+      for (Node &ParentN : ParentC)
+        if (ParentN)
+          ParentN->removeEdgeInternal(N);
 
   // Now remove this RefSCC from any parents sets and the leaf list.
   for (Edge &E : *N)