Index: lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- lib/CodeGen/CodeGenPrepare.cpp
+++ lib/CodeGen/CodeGenPrepare.cpp
@@ -292,7 +292,7 @@
     ValueToSExts ValToSExtendedUses;
 
     /// True if CFG is modified in any way.
-    bool ModifiedDT;
+    bool DTModified;
 
     /// True if optimizing for size.
     bool OptSize;
@@ -354,7 +354,7 @@
     bool optimizeExt(Instruction *&I);
     bool optimizeExtUses(Instruction *I);
     bool optimizeLoadExt(LoadInst *Load);
-    bool optimizeSelectInst(SelectInst *SI);
+    bool optimizeSelectInst(SelectInst *SI, bool &ModifiedDT);
     bool optimizeShuffleVectorInst(ShuffleVectorInst *SVI);
     bool optimizeSwitchInst(SwitchInst *SI);
     bool optimizeExtractElementInst(Instruction *Inst);
@@ -402,7 +402,7 @@
   InsertedInsts.clear();
   PromotedInsts.clear();
 
-  ModifiedDT = false;
+  DTModified = false;
   if (auto *TPC = getAnalysisIfAvailable<TargetPassConfig>()) {
     TM = &TPC->getTM<TargetMachine>();
     SubtargetInfo = TM->getSubtargetImpl(F);
@@ -2042,7 +2042,7 @@
 
     // Duplicate the return into CallBB.
     (void)FoldReturnIntoUncondBranch(RetI, BB, CallBB);
-    ModifiedDT = Changed = true;
+    DTModified = Changed = true;
     ++NumRetsDup;
   }
 
@@ -5863,7 +5863,7 @@
 
 /// If we have a SelectInst that will likely profit from branch prediction,
 /// turn it into a branch.
-bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) {
+bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI, bool &ModifiedDT) {
   // If branch conversion isn't desirable, exit early.
   if (DisableSelectToBranch || OptSize || !TLI)
     return false;
@@ -5905,6 +5905,7 @@
     return false;
 
   ModifiedDT = true;
+  DTModified = true;
 
   // Transform a sequence like this:
   //    start:
@@ -6957,7 +6958,7 @@
     return optimizeCallInst(CI, ModifiedDT);
 
   if (SelectInst *SI = dyn_cast<SelectInst>(I))
-    return optimizeSelectInst(SI);
+    return optimizeSelectInst(SI, ModifiedDT);
 
   if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(I))
     return optimizeShuffleVectorInst(SVI);
@@ -7250,7 +7251,7 @@
 
     // Note: No point in getting fancy here, since the DT info is never
     // available to CodeGenPrepare.
-    ModifiedDT = true;
+    DTModified = true;
 
     MadeChange = true;
 
Index: test/CodeGen/X86/codegen-prepare-DT.ll
===================================================================
--- test/CodeGen/X86/codegen-prepare-DT.ll
+++ test/CodeGen/X86/codegen-prepare-DT.ll
@@ -0,0 +1,51 @@
+; RUN: llc -o - -verify-machineinstrs %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @foo(i64 %i0, i64 %i1, i1 %i2, i64 %i3) !prof !1 {
+entry:
+  switch i64 %i0, label %def1 [
+    i64  -8, label %sw1
+    i64 -16, label %sw1
+    i64   0, label %sw1
+  ]
+
+def1:
+  unreachable
+
+sw1:
+  switch i64 %i1, label %def2 [
+    i64  -8, label %sw2
+    i64 -16, label %sw2
+    i64   0, label %sw2
+  ]
+
+def2:
+  unreachable
+
+sw2:
+  %v1 = select i1 %i2 , i64 %i3, i64 100, !prof !3
+  %v2 = add nsw i64 %v1, -1
+  %0 = icmp ult i64 %v2, 9223372036854775804
+  br label %if1
+
+if1:
+  br i1 %0, label %then1, label %else1
+
+then1:
+  unreachable
+
+else1:
+  %cmp = icmp eq i64 %v1, 0
+  %spec = select i1 %cmp, i64 0, i64 undef
+  ret void
+}
+
+attributes #0 = { "use-soft-float"="false" }
+
+!1 = !{!"function_entry_count", i64 10562721}
+!2 = !{!"branch_weights", i32 10562721, i32 0, i32 0, i32 0}
+!3 = !{!"branch_weights", i32 15714, i32 4352144}
+!4 = !{!"branch_weights", i32 0, i32 24913}
+!5 = !{!"branch_weights", i32 0, i32 19483}