implement feedback

Author: ro-i

llvm/include/llvm/Transforms/Scalar/JumpThreading.h

@@ -147,6 +147,9 @@ class JumpThreadingPass : public PassInfoMixin<JumpThreadingPass> {
 
   Constant *evaluateOnPredecessorEdge(BasicBlock *BB, BasicBlock *PredPredBB,
                                       Value *cond, const DataLayout &DL);
+  Constant *evaluateOnPredecessorEdge(BasicBlock *BB, BasicBlock *PredPredBB,
+                                      Value *cond, const DataLayout &DL,
+                                      SmallPtrSet<Value *, 8> &Visited);
   bool maybethreadThroughTwoBasicBlocks(BasicBlock *BB, Value *Cond);
   void threadThroughTwoBasicBlocks(BasicBlock *PredPredBB, BasicBlock *PredBB,
                                    BasicBlock *BB, BasicBlock *SuccBB);

llvm/lib/Transforms/Scalar/JumpThreading.cpp

@@ -1498,6 +1498,15 @@ Constant *JumpThreadingPass::evaluateOnPredecessorEdge(BasicBlock *BB,
                                                        BasicBlock *PredPredBB,
                                                        Value *V,
                                                        const DataLayout &DL) {
+  SmallPtrSet<Value *, 8> Visited;
+  return evaluateOnPredecessorEdge(BB, PredPredBB, V, DL, Visited);
+}
+
+Constant *JumpThreadingPass::evaluateOnPredecessorEdge(
+    BasicBlock *BB, BasicBlock *PredPredBB, Value *V, const DataLayout &DL,
+    SmallPtrSet<Value *, 8> &Visited) {
+  Visited.insert(V);
+
   BasicBlock *PredBB = BB->getSinglePredecessor();
   assert(PredBB && "Expected a single predecessor");
 
@@ -1525,14 +1534,16 @@ Constant *JumpThreadingPass::evaluateOnPredecessorEdge(BasicBlock *BB,
   // instructions in unreachable code and check before going into recursion.
   if (CmpInst *CondCmp = dyn_cast<CmpInst>(V)) {
     if (CondCmp->getParent() == BB) {
-      Constant *Op0 = CondCmp->getOperand(0) == CondCmp
-                          ? nullptr
-                          : evaluateOnPredecessorEdge(
-                                BB, PredPredBB, CondCmp->getOperand(0), DL);
-      Constant *Op1 = CondCmp->getOperand(1) == CondCmp
-                          ? nullptr
-                          : evaluateOnPredecessorEdge(
-                                BB, PredPredBB, CondCmp->getOperand(1), DL);
+      Constant *Op0 =
+          Visited.contains(CondCmp->getOperand(0))
+              ? nullptr
+              : evaluateOnPredecessorEdge(BB, PredPredBB,
+                                          CondCmp->getOperand(0), DL, Visited);
+      Constant *Op1 =
+          Visited.contains(CondCmp->getOperand(1))
+              ? nullptr
+              : evaluateOnPredecessorEdge(BB, PredPredBB,
+                                          CondCmp->getOperand(1), DL, Visited);
       if (Op0 && Op1) {
         return ConstantFoldCompareInstOperands(CondCmp->getPredicate(), Op0,
                                                Op1, DL);