Index: llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
+++ llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
@@ -158,7 +158,7 @@
     const char *getPassName() const override { return "CodeGen Prepare"; }
 
     void getAnalysisUsage(AnalysisUsage &AU) const override {
-      AU.addPreserved<DominatorTreeWrapperPass>();
+      // FIXME: When we can selectively preserve passes, preserve the domtree.
       AU.addRequired<TargetLibraryInfoWrapperPass>();
       AU.addRequired<TargetTransformInfoWrapperPass>();
     }
@@ -5277,6 +5277,7 @@
     for (auto &I : reverse(BB)) {
       if (makeBitReverse(I, *DL, *TLI)) {
         MadeBitReverse = MadeChange = true;
+        ModifiedDT = true;
         break;
       }
     }
Index: llvm/trunk/test/Transforms/CodeGenPrepare/dom-tree.ll
===================================================================
--- llvm/trunk/test/Transforms/CodeGenPrepare/dom-tree.ll
+++ llvm/trunk/test/Transforms/CodeGenPrepare/dom-tree.ll
@@ -0,0 +1,41 @@
+; RUN: opt -S -loop-unroll -codegenprepare < %s -domtree -analyze | FileCheck %s
+;
+; Checks that the dom tree is properly invalidated after an operation that will
+; invalidate it in CodeGenPrepare. If the domtree isn't properly invalidated,
+; this will likely segfault, or print badref.
+
+; CHECK-NOT: <badref>
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv7--linux-gnueabihf"
+
+define i32 @f(i32 %a) #0 {
+entry:
+  br label %for.body
+
+for.cond.cleanup:
+  ret i32 %or
+
+for.body:
+  %i.08 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  %b.07 = phi i32 [ 0, %entry ], [ %or, %for.body ]
+  %shr = lshr i32 %a, %i.08
+  %and = and i32 %shr, 1
+  %sub = sub nuw nsw i32 31, %i.08
+  %shl = shl i32 %and, %sub
+  %or = or i32 %shl, %b.07
+  %inc = add nuw nsw i32 %i.08, 1
+  %exitcond = icmp eq i32 %inc, 32
+  br i1 %exitcond, label %for.cond.cleanup, label %for.body, !llvm.loop !3
+}
+
+attributes #0 = { norecurse nounwind readnone "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="cortex-a8" "target-features"="+dsp,+neon,+vfp3" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.module.flags = !{!0, !1}
+!llvm.ident = !{!2}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 1, !"min_enum_size", i32 4}
+!2 = !{!"clang version 3.8.0 (http://llvm.org/git/clang.git b7441a0f42c43a8eea9e3e706be187252db747fa)"}
+!3 = distinct !{!3, !4}
+!4 = !{!"llvm.loop.unroll.full"}