Take indirect branch into account as well when folding.

We may not be able to rewrite indirect branch target, but we also want to take it into
account when folding, i.e. if it and all its successor's predecessors go to the same
destination, we can fold, i.e. no need to thread.

llvm-svn: 301816

1 files changed, 10 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Scalar/JumpThreading.cpp b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
index 55b556bb59c..7dacaba1193 100644
--- a/llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/llvm/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1253,16 +1253,12 @@ bool JumpThreadingPass::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
   Constant *OnlyVal = nullptr;
   Constant *MultipleVal = (Constant *)(intptr_t)~0ULL;
 
+  unsigned PredWithKnownDest = 0;
   for (const auto &PredValue : PredValues) {
     BasicBlock *Pred = PredValue.second;
     if (!SeenPreds.insert(Pred).second)
       continue;  // Duplicate predecessor entry.
 
-    // If the predecessor ends with an indirect goto, we can't change its
-    // destination.
-    if (isa<IndirectBrInst>(Pred->getTerminator()))
-      continue;
-
     Constant *Val = PredValue.first;
 
     BasicBlock *DestBB;
@@ -1294,6 +1290,14 @@ bool JumpThreadingPass::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
         OnlyVal = MultipleVal;
     }
 
+    // We know where this predecessor is going.
+    ++PredWithKnownDest;
+
+    // If the predecessor ends with an indirect goto, we can't change its
+    // destination.
+    if (isa<IndirectBrInst>(Pred->getTerminator()))
+      continue;
+
     PredToDestList.push_back(std::make_pair(Pred, DestBB));
   }
 
@@ -1305,7 +1309,7 @@ bool JumpThreadingPass::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
   // not thread. By doing so, we do not need to duplicate the current block and
   // also miss potential opportunities in case we dont/cant duplicate.
   if (OnlyDest && OnlyDest != MultipleDestSentinel) {
-    if (PredToDestList.size() ==
+    if (PredWithKnownDest ==
         (size_t)std::distance(pred_begin(BB), pred_end(BB))) {
       bool SeenFirstBranchToOnlyDest = false;
       for (BasicBlock *SuccBB : successors(BB)) {