diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3954,21 +3954,15 @@
     // Recursively visit successors.  If this is a branch or switch on a
     // constant, only visit the reachable successor.
     Instruction *TI = BB->getTerminator();
-    if (BranchInst *BI = dyn_cast<BranchInst>(TI); BI && BI->isConditional()) {
-      if (isa<UndefValue>(BI->getCondition()))
-        // Branch on undef is UB.
-        continue;
-      if (auto *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
-        bool CondVal = Cond->getZExtValue();
+    if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+      if (BI->isConditional() && isa<ConstantInt>(BI->getCondition())) {
+        bool CondVal = cast<ConstantInt>(BI->getCondition())->getZExtValue();
         BasicBlock *ReachableBB = BI->getSuccessor(!CondVal);
         Worklist.push_back(ReachableBB);
         continue;
       }
     } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
-      if (isa<UndefValue>(SI->getCondition()))
-        // Switch on undef is UB.
-        continue;
-      if (auto *Cond = dyn_cast<ConstantInt>(SI->getCondition())) {
+      if (ConstantInt *Cond = dyn_cast<ConstantInt>(SI->getCondition())) {
         Worklist.push_back(SI->findCaseValue(Cond)->getCaseSuccessor());
         continue;
       }
diff --git a/llvm/test/Transforms/InstCombine/unreachable-code.ll b/llvm/test/Transforms/InstCombine/unreachable-code.ll
--- a/llvm/test/Transforms/InstCombine/unreachable-code.ll
+++ b/llvm/test/Transforms/InstCombine/unreachable-code.ll
@@ -52,8 +52,10 @@
 ; CHECK-SAME: (i1 [[X:%.*]]) {
 ; CHECK-NEXT:    br i1 undef, label [[IF:%.*]], label [[ELSE:%.*]]
 ; CHECK:       if:
+; CHECK-NEXT:    call void @dummy()
 ; CHECK-NEXT:    ret void
 ; CHECK:       else:
+; CHECK-NEXT:    call void @dummy()
 ; CHECK-NEXT:    ret void
 ;
   %c = xor i1 %x, undef
@@ -127,8 +129,10 @@
 ; CHECK-NEXT:    i32 0, label [[CASE0:%.*]]
 ; CHECK-NEXT:    ]
 ; CHECK:       case0:
+; CHECK-NEXT:    call void @dummy()
 ; CHECK-NEXT:    ret void
 ; CHECK:       default:
+; CHECK-NEXT:    call void @dummy()
 ; CHECK-NEXT:    ret void
 ;
   %v = xor i32 %x, undef