Index: llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
@@ -1316,9 +1316,12 @@
     if (Instruction *Result = foldPHIArgOpIntoPHI(PN))
       return Result;
 
+  // "catchswitch" blocks cannot have any other non-phis.
+  bool IsCatchSwitch = isa<CatchSwitchInst>(PN.getParent()->getTerminator());
+
   // If the incoming values are pointer casts of the same original value,
   // replace the phi with a single cast.
-  if (PN.getType()->isPointerTy()) {
+  if (PN.getType()->isPointerTy() && !IsCatchSwitch) {
     Value *IV0 = PN.getIncomingValue(0);
     Value *IV0Stripped = IV0->stripPointerCasts();
     // Set to keep track of values known to be equal to IV0Stripped after
Index: llvm/test/Transforms/InstCombine/phi-catchswitch.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/phi-catchswitch.ll
@@ -0,0 +1,74 @@
+; RUN: opt -passes=instcombine -S %s | FileCheck %s
+
+; Catchswitch blocks may only contain phi and catchswitch.
+; phi => bitcast transform must be suppressed in these blocks.
+
+; CHECK-LABEL: bb9:
+; CHECK: phi i8*
+; CHECK-NEXT: catchswitch
+; CHECK-LABEL: bb12:
+
+source_filename = "memory_attributes-host-x86_64-pc-windows-msvc.ii"
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.16.27045"
+
+%struct.snork = type { i8**, i8*, [24 x i8] }
+@global = external global %struct.snork
+
+; Function Attrs: argmemonly nofree nosync nounwind willreturn
+declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #0
+
+define dso_local void @main() local_unnamed_addr #1 personality i32 (...)* @__CxxFrameHandler3 {
+bb:
+  %tmp = alloca i32, align 8
+  invoke void @baz.3()
+          to label %bb1 unwind label %bb3
+
+bb1:                                              ; preds = %bb
+  invoke void @quux()
+          to label %bb2 unwind label %bb6
+
+bb2:                                              ; preds = %bb1
+  unreachable
+
+bb3:                                              ; preds = %bb
+  %tmp4 = cleanuppad within none []
+  %tmp5 = bitcast i32* %tmp to i8*
+  cleanupret from %tmp4 unwind label %bb9
+
+bb6:                                              ; preds = %bb1
+  %tmp7 = cleanuppad within none []
+  %tmp8 = bitcast i32* %tmp to i8*
+  cleanupret from %tmp7 unwind label %bb9
+
+bb9:                                              ; preds = %bb6, %bb3
+  %tmp10 = phi i8* [ %tmp8, %bb6 ], [ %tmp5, %bb3 ]
+  %tmp11 = catchswitch within none [label %bb12] unwind label %bb15
+
+bb12:                                             ; preds = %bb9
+  %tmp13 = catchpad within %tmp11 [%struct.snork* @global, i32 8, i32** undef]
+  invoke void @baz() [ "funclet"(token %tmp13) ]
+          to label %bb14 unwind label %bb15
+
+bb14:                                             ; preds = %bb12
+  unreachable
+
+bb15:                                             ; preds = %bb12, %bb9
+  %tmp16 = cleanuppad within none []
+  call void @llvm.lifetime.end.p0i8(i64 40, i8* nonnull %tmp10) #3
+  cleanupret from %tmp16 unwind to caller
+}
+
+declare dso_local void @baz() local_unnamed_addr #1
+
+; Function Attrs: nofree
+declare dso_local i32 @__CxxFrameHandler3(...) #2
+
+declare dllimport void @baz.3() unnamed_addr #1
+
+declare dso_local void @quux() unnamed_addr #1 align 2
+
+attributes #0 = { argmemonly nofree nosync nounwind willreturn }
+attributes #1 = { "unsafe-fp-math"="true" }
+attributes #2 = { nofree }
+attributes #3 = { nounwind }