Index: include/llvm/Transforms/Utils/BasicBlockUtils.h
===================================================================
--- include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -116,6 +116,7 @@
   bool MergeIdenticalEdges = false;
   bool KeepOneInputPHIs = false;
   bool PreserveLCSSA = false;
+  bool IgnoreUnreachableDests = false;
 
   CriticalEdgeSplittingOptions(DominatorTree *DT = nullptr,
                                LoopInfo *LI = nullptr,
@@ -137,6 +138,11 @@
     PreserveLCSSA = true;
     return *this;
   }
+
+  CriticalEdgeSplittingOptions &setIgnoreUnreachableDests() {
+    IgnoreUnreachableDests = true;
+    return *this;
+  }
 };
 
 /// If this edge is a critical edge, insert a new node to split the critical
Index: lib/Transforms/Instrumentation/SanitizerCoverage.cpp
===================================================================
--- lib/Transforms/Instrumentation/SanitizerCoverage.cpp
+++ lib/Transforms/Instrumentation/SanitizerCoverage.cpp
@@ -535,7 +535,7 @@
       isAsynchronousEHPersonality(classifyEHPersonality(F.getPersonalityFn())))
     return false;
   if (Options.CoverageType >= SanitizerCoverageOptions::SCK_Edge)
-    SplitAllCriticalEdges(F);
+    SplitAllCriticalEdges(F, CriticalEdgeSplittingOptions().setIgnoreUnreachableDests());
   SmallVector<Instruction *, 8> IndirCalls;
   SmallVector<BasicBlock *, 16> BlocksToInstrument;
   SmallVector<Instruction *, 8> CmpTraceTargets;
Index: lib/Transforms/Utils/BreakCriticalEdges.cpp
===================================================================
--- lib/Transforms/Utils/BreakCriticalEdges.cpp
+++ lib/Transforms/Utils/BreakCriticalEdges.cpp
@@ -153,6 +153,10 @@
   if (isa<CallBrInst>(TI) && SuccNum > 0)
     return nullptr;
 
+  if (Options.IgnoreUnreachableDests &&
+      isa<UnreachableInst>(DestBB->getFirstNonPHIOrDbgOrLifetime()))
+    return nullptr;
+
   // Create a new basic block, linking it into the CFG.
   BasicBlock *NewBB = BasicBlock::Create(TI->getContext(),
                       TIBB->getName() + "." + DestBB->getName() + "_crit_edge");
Index: test/Instrumentation/SanitizerCoverage/unreachable-critedge.ll
===================================================================
--- /dev/null
+++ test/Instrumentation/SanitizerCoverage/unreachable-critedge.ll
@@ -0,0 +1,46 @@
+; RUN: opt < %s -S -sancov -sanitizer-coverage-level=3 | FileCheck %s
+
+; The critical edges to unreachable_bb should not be split.
+define i32 @foo(i32 %c, i32 %d) {
+; CHECK-LABEL: @foo(
+; CHECK:         switch i32 [[C:%.*]], label [[UNREACHABLE_BB:%.*]] [
+; CHECK-NEXT:    i32 0, label %exit0
+; CHECK-NEXT:    i32 1, label %exit1
+; CHECK-NEXT:    i32 2, label %cont
+; CHECK-NEXT:    ]
+; CHECK:       cont:
+; CHECK:         switch i32 [[D:%.*]], label [[UNREACHABLE_BB]] [
+; CHECK-NEXT:    i32 0, label %exit2
+; CHECK-NEXT:    i32 1, label %exit3
+; CHECK-NEXT:    i32 2, label %exit4
+; CHECK-NEXT:    ]
+; CHECK:       unreachable_bb:
+; CHECK-NEXT:    unreachable
+;
+  switch i32 %c, label %unreachable_bb [i32 0, label %exit0
+  i32 1, label %exit1
+  i32 2, label %cont]
+
+cont:
+  switch i32 %d, label %unreachable_bb [i32 0, label %exit2
+  i32 1, label %exit3
+  i32 2, label %exit4]
+
+exit0:
+  ret i32 0
+
+exit1:
+  ret i32 1
+
+exit2:
+  ret i32 2
+
+exit3:
+  ret i32 3
+
+exit4:
+  ret i32 4
+
+unreachable_bb:
+  unreachable
+}