[PM] Rework a loop in the CGSCC update logic to be more conservative and

clear. The current RefSCC can occur in exactly one position so we should
just enforce that and leverage the property rather than checking for it
anywhere.

This addresses review comments made on another patch.

llvm-svn: 290162

1 files changed, 11 insertions, 7 deletions

diff --git a/llvm/lib/Analysis/CGSCCPassManager.cpp b/llvm/lib/Analysis/CGSCCPassManager.cpp
index b2bee0258d1..5c1485d02de 100644
--- a/llvm/lib/Analysis/CGSCCPassManager.cpp
+++ b/llvm/lib/Analysis/CGSCCPassManager.cpp
@@ -329,13 +329,17 @@ LazyCallGraph::SCC &llvm::updateCGAndAnalysisManagerForFunctionPass(
       assert(G.lookupSCC(N) == C && "Changed the SCC when splitting RefSCCs!");
       RC = &C->getOuterRefSCC();
       assert(G.lookupRefSCC(N) == RC && "Failed to update current RefSCC!");
-      for (RefSCC *NewRC : reverse(NewRefSCCs))
-        if (NewRC != RC) {
-          UR.RCWorklist.insert(NewRC);
-          if (DebugLogging)
-            dbgs() << "Enqueuing a new RefSCC in the update worklist: "
-                   << *NewRC << "\n";
-        }
+      assert(NewRefSCCs.front() == RC &&
+             "New current RefSCC not first in the returned list!");
+      for (RefSCC *NewRC : reverse(
+               make_range(std::next(NewRefSCCs.begin()), NewRefSCCs.end()))) {
+        assert(NewRC != RC && "Should not encounter the current RefSCC further "
+                              "in the postorder list of new RefSCCs.");
+        UR.RCWorklist.insert(NewRC);
+        if (DebugLogging)
+          dbgs() << "Enqueuing a new RefSCC in the update worklist: " << *NewRC
+                 << "\n";
+      }
     }
   }