diff --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -598,6 +598,11 @@
 
   auto *ParentBB = SI.getParent();
 
+  // The same check must be used both for the default and the exit cases. We
+  // should never leave edges from the switch instruction to a basic block that
+  // we are unswitching, hence the condition used to determine the default case
+  // needs to also be used to populate ExitCaseIndices, which is then used to
+  // remove cases from the switch.
   auto IsTriviallyUnswitchableExitBlock = [&](BasicBlock &BBToCheck) {
     // BBToCheck is not an exit block if it is inside loop L.
     if (L.contains(&BBToCheck))
@@ -615,12 +620,9 @@
   };
 
   SmallVector<int, 4> ExitCaseIndices;
-  for (auto Case : SI.cases()) {
-    auto *SuccBB = Case.getCaseSuccessor();
-    if (!L.contains(SuccBB) &&
-        areLoopExitPHIsLoopInvariant(L, *ParentBB, *SuccBB))
+  for (auto Case : SI.cases())
+    if (IsTriviallyUnswitchableExitBlock(*Case.getCaseSuccessor()))
       ExitCaseIndices.push_back(Case.getCaseIndex());
-  }
   BasicBlock *DefaultExitBB = nullptr;
   SwitchInstProfUpdateWrapper::CaseWeightOpt DefaultCaseWeight =
       SwitchInstProfUpdateWrapper::getSuccessorWeight(SI, 0);
diff --git a/llvm/test/Transforms/SimpleLoopUnswitch/trivial-unswitch.ll b/llvm/test/Transforms/SimpleLoopUnswitch/trivial-unswitch.ll
--- a/llvm/test/Transforms/SimpleLoopUnswitch/trivial-unswitch.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/trivial-unswitch.ll
@@ -1274,14 +1274,67 @@
 ; CHECK-NEXT:  %cleanup.dest.slot.0 = select i1 undef, i32 5, i32 undef
 ; CHECK-NEXT:  switch i32 %cleanup.dest.slot.0, label %NonEmptyUnreachableBlock [
 ; CHECK-NEXT:    i32 1, label %NonEmptyUnreachableBlock
-; CHECK-NEXT:    i32 2, label %loop.loopexit
 ; CHECK-NEXT:    i32 0, label %loop.split
+; CHECK-NEXT:    i32 2, label %loop.split
+; CHECK-NEXT:  ]
+
+; CHECK:loop.split:
+; CHECK-NEXT:  br label %for.cond
+
+; CHECK:for.cond:
+; CHECK-NEXT:  switch i32 %cleanup.dest.slot.0, label %loop.loopexit [
+; CHECK-NEXT:    i32 0, label %for.cond
+; CHECK-NEXT:  ]
+
+; CHECK:loop.loopexit:
+; CHECK-NEXT:  unreachable
+
+; CHECK:NonEmptyUnreachableBlock:
+; CHECK-NEXT:  call void @f()
+; CHECK-NEXT:  call void @g()
+; CHECK-NEXT:  unreachable
+}
+
+define void @test_unswitch_switch_with_nonempty_unreachable2() {
+; CHECK-LABEL: @test_unswitch_switch_with_nonempty_unreachable2()
+entry:
+  br label %loop
+
+loop:
+  %cleanup.dest.slot.0 = select i1 undef, i32 5, i32 undef
+  br label %for.cond
+
+for.cond:
+  switch i32 %cleanup.dest.slot.0, label %for.cond [
+    i32 0, label %for.cond
+    i32 1, label %NonEmptyUnreachableBlock
+    i32 2, label %loop.loopexit
+  ]
+
+loop.loopexit:
+  unreachable
+
+NonEmptyUnreachableBlock:
+  call void @f()
+  call void @g()
+  unreachable
+
+; CHECK:loop:
+; CHECK-NEXT:  %cleanup.dest.slot.0 = select i1 undef, i32 5, i32 undef
+; CHECK-NEXT:  switch i32 %cleanup.dest.slot.0, label %loop.split [
+; CHECK-NEXT:    i32 1, label %NonEmptyUnreachableBlock
 ; CHECK-NEXT:  ]
 
 ; CHECK:loop.split:
 ; CHECK-NEXT:  br label %for.cond
 
 ; CHECK:for.cond:
+; CHECK-NEXT:  switch i32 %cleanup.dest.slot.0, label %for.cond.backedge [
+; CHECK-NEXT:    i32 0, label %for.cond.backedge
+; CHECK-NEXT:    i32 2, label %loop.loopexit
+; CHECK-NEXT:  ]
+
+; CHECK:for.cond.backedge:
 ; CHECK-NEXT:  br label %for.cond
 
 ; CHECK:loop.loopexit:
@@ -1292,3 +1345,34 @@
 ; CHECK-NEXT:  call void @g()
 ; CHECK-NEXT:  unreachable
 }
+
+; PR45355
+define void @test_unswitch_switch_with_duplicate_edge() {
+; CHECK-LABEL: @test_unswitch_switch_with_duplicate_edge()
+entry:
+  br label %lbl1
+
+lbl1:                                             ; preds = %entry
+  %cleanup.dest.slot.0 = select i1 undef, i32 5, i32 undef
+  br label %for.cond1
+
+for.cond1:                                        ; preds = %for.cond1, %lbl1
+  switch i32 %cleanup.dest.slot.0, label %UnifiedUnreachableBlock [
+    i32 0, label %for.cond1
+    i32 5, label %UnifiedUnreachableBlock
+    i32 2, label %lbl1.loopexit
+  ]
+
+UnifiedUnreachableBlock:                          ; preds = %for.cond1, %for.cond1
+  unreachable
+
+lbl1.loopexit:                                    ; preds = %for.cond1
+  unreachable
+
+; CHECK: for.cond1:
+; CHECK-NEXT:  switch i32 %cleanup.dest.slot.0, label %UnifiedUnreachableBlock [
+; CHECK-NEXT:    i32 0, label %for.cond1
+; CHECK-NEXT:    i32 5, label %UnifiedUnreachableBlock
+; CHECK-NEXT:    i32 2, label %lbl1.loopexit
+; CHECK-NEXT:  ]
+}