[LVer][profcheck] explicitly set unknown branch weights for the versioned/unversioned selector

Author: mtrofin

llvm/lib/Transforms/Utils/LoopVersioning.cpp

@@ -23,6 +23,7 @@
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/PassManager.h"
+#include "llvm/IR/ProfDataUtils.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
@@ -109,8 +110,12 @@ void LoopVersioning::versionLoop(
   // Insert the conditional branch based on the result of the memchecks.
   Instruction *OrigTerm = RuntimeCheckBB->getTerminator();
   Builder.SetInsertPoint(OrigTerm);
-  Builder.CreateCondBr(RuntimeCheck, NonVersionedLoop->getLoopPreheader(),
+  auto *BI = Builder.CreateCondBr(RuntimeCheck, NonVersionedLoop->getLoopPreheader(),
                        VersionedLoop->getLoopPreheader());
+  // We don't know what the probability of executing the versioned vs the
+  // unversioned variants is.
+  setExplicitlyUnknownBranchWeightsIfProfiled(
+      *BI, *BI->getParent()->getParent(), DEBUG_TYPE);
   OrigTerm->eraseFromParent();
 
   // The loops merge in the original exit block.  This is now dominated by the