Index: llvm/lib/IR/BasicBlock.cpp
===================================================================
--- llvm/lib/IR/BasicBlock.cpp
+++ llvm/lib/IR/BasicBlock.cpp
@@ -332,9 +332,9 @@
 /// Update PHI nodes in this BasicBlock before removal of predecessor \p Pred.
 /// Note that this function does not actually remove the predecessor.
 ///
-/// If \p KeepOneInputPHIs is true then don't remove PHIs that are left with
-/// zero or one incoming values, and don't simplify PHIs with all incoming
-/// values the same.
+/// If \p KeepOneInputPHIs is true, then don't remove PHIs that are left with
+/// one incoming value, and don't simplify PHIs with all incoming values that
+/// are the same constant.
 void BasicBlock::removePredecessor(BasicBlock *Pred,
                                    bool KeepOneInputPHIs) {
   // Use hasNUsesOrMore to bound the cost of this assertion for complex CFGs.
@@ -349,7 +349,8 @@
   // Update all PHI nodes.
   for (iterator II = begin(); isa<PHINode>(II);) {
     PHINode *PN = cast<PHINode>(II++);
-    PN->removeIncomingValue(Pred, !KeepOneInputPHIs);
+    bool DeletePhiIfEmpty = NumPreds == 1 || !KeepOneInputPHIs;
+    PN->removeIncomingValue(Pred, DeletePhiIfEmpty);
     if (!KeepOneInputPHIs) {
       // If we have a single predecessor, removeIncomingValue erased the PHI
       // node itself.
Index: llvm/test/Transforms/LoopRotate/phi-empty.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopRotate/phi-empty.ll
@@ -0,0 +1,35 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -lcssa -loop-rotate < %s | FileCheck %s
+
+define void @PR48296(i1 %cond) {
+; CHECK-LABEL: @PR48296(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[INC:%.*]], label [[LOOP_BACKEDGE:%.*]]
+; CHECK:       loop.backedge:
+; CHECK-NEXT:    br label [[LOOP]]
+; CHECK:       dead:
+; CHECK-NEXT:    unreachable
+; CHECK:       inc:
+; CHECK-NEXT:    br label [[LOOP_BACKEDGE]]
+; CHECK:       return:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+
+loop:
+  br i1 %cond, label %inc, label %loop
+
+dead:                                        ; No predecessors!
+  br i1 %cond, label %inc, label %return
+
+inc:
+  br label %loop
+
+return:
+  %r = phi i32 [ undef, %dead ]
+  ret void
+}
+