1 files changed, 15 insertions, 10 deletions
diff --git a/gnu/llvm/lib/Transforms/Scalar/NewGVN.cpp b/gnu/llvm/lib/Transforms/Scalar/NewGVN.cpp
index 6043e04bb8c..57e6e3ddad9 100644
--- a/gnu/llvm/lib/Transforms/Scalar/NewGVN.cpp
+++ b/gnu/llvm/lib/Transforms/Scalar/NewGVN.cpp
@@ -85,6 +85,8 @@ STATISTIC(NumGVNLeaderChanges, "Number of leader changes");
 STATISTIC(NumGVNSortedLeaderChanges, "Number of sorted leader changes");
 STATISTIC(NumGVNAvoidedSortedLeaderChanges,
           "Number of avoided sorted leader changes");
+STATISTIC(NumGVNNotMostDominatingLeader,
+          "Number of times a member dominated it's new classes' leader");
 
 //===----------------------------------------------------------------------===//
 //                                GVN Pass
@@ -1073,17 +1075,20 @@ void NewGVN::moveValueToNewCongruenceClass(Instruction *I,
   if (I == OldClass->NextLeader.first)
     OldClass->NextLeader = {nullptr, ~0U};
 
-  // The new instruction and new class leader may either be siblings in the
-  // dominator tree, or the new class leader should dominate the new member
-  // instruction.  We simply check that the member instruction does not properly
-  // dominate the new class leader.
-  assert(
-      !isa<Instruction>(NewClass->RepLeader) || !NewClass->RepLeader ||
-      I == NewClass->RepLeader ||
-      !DT->properlyDominates(
+  // It's possible, though unlikely, for us to discover equivalences such
+  // that the current leader does not dominate the old one.
+  // This statistic tracks how often this happens.
+  // We assert on phi nodes when this happens, currently, for debugging, because
+  // we want to make sure we name phi node cycles properly.
+  if (isa<Instruction>(NewClass->RepLeader) && NewClass->RepLeader &&
+      I != NewClass->RepLeader &&
+      DT->properlyDominates(
           I->getParent(),
-          cast<Instruction>(NewClass->RepLeader)->getParent()) &&
-          "New class for instruction should not be dominated by instruction");
+          cast<Instruction>(NewClass->RepLeader)->getParent())) {
+    ++NumGVNNotMostDominatingLeader;
+    assert(!isa<PHINode>(I) &&
+           "New class for instruction should not be dominated by instruction");
+  }
 
   if (NewClass->RepLeader != I) {
     auto DFSNum = InstrDFS.lookup(I);