2 files changed, 59 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/LowerSwitch.cpp b/llvm/lib/Transforms/Utils/LowerSwitch.cpp
index 76ad35832dc..e99ecfef19c 100644
--- a/llvm/lib/Transforms/Utils/LowerSwitch.cpp
+++ b/llvm/lib/Transforms/Utils/LowerSwitch.cpp
@@ -74,7 +74,7 @@ namespace {
 
     LowerSwitch() : FunctionPass(ID) {
       initializeLowerSwitchPass(*PassRegistry::getPassRegistry());
-    } 
+    }
 
     bool runOnFunction(Function &F) override;
 
@@ -327,7 +327,7 @@ BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
     } else if (Leaf.Low->isZero()) {
       // Val >= 0 && Val <= Hi --> Val <=u Hi
       Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High,
-                          "SwitchLeaf");      
+                          "SwitchLeaf");
     } else {
       // Emit V-Lo <=u Hi-Lo
       Constant* NegLo = ConstantExpr::getNeg(Leaf.Low);
@@ -354,7 +354,7 @@ BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
     for (uint64_t j = 0; j < Range; ++j) {
       PN->removeIncomingValue(OrigBlock);
     }
-    
+
     int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
     assert(BlockIdx != -1 && "Switch didn't go to this successor??");
     PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
@@ -495,6 +495,10 @@ void LowerSwitch::processSwitchInst(SwitchInst *SI,
     }
 #endif
 
+    // As the default block in the switch is unreachable, update the PHI nodes
+    // (remove the entry to the default block) to reflect this.
+    Default->removePredecessor(OrigBlock);
+
     // Use the most popular block as the new default, reducing the number of
     // cases.
     assert(MaxPop > 0 && PopSucc);
@@ -508,6 +512,10 @@ void LowerSwitch::processSwitchInst(SwitchInst *SI,
     if (Cases.empty()) {
       BranchInst::Create(Default, CurBlock);
       SI->eraseFromParent();
+      // As all the cases have been replaced with a single branch, only keep
+      // one entry in the PHI nodes.
+      for (unsigned I = 0 ; I < (MaxPop - 1) ; ++I)
+        PopSucc->removePredecessor(OrigBlock);
       return;
     }
   }
diff --git a/llvm/test/Transforms/Util/lowerswitch.ll b/llvm/test/Transforms/Util/lowerswitch.ll
index 70e1e239b3d..5f5134e71a2 100644
--- a/llvm/test/Transforms/Util/lowerswitch.ll
+++ b/llvm/test/Transforms/Util/lowerswitch.ll
@@ -242,3 +242,51 @@ cleanup:                                          ; preds = %for.body7, %if.then
 unreachable:                                      ; preds = %cleanup
   unreachable
 }
+
+; Test that the PHI node in cleanup17 is removed as the switch default block is
+; not reachable.
+define void @test4() {
+; CHECK-LABEL: @test4
+entry:
+  switch i32 undef, label %cleanup17 [
+    i32 0, label %return
+    i32 9, label %return
+  ]
+
+cleanup17:
+; CHECK: cleanup17:
+; CHECK-NOT: phi i16 [ undef, %entry ]
+; CHECK: return:
+
+  %retval.4 = phi i16 [ undef, %entry ]
+  unreachable
+
+return:
+  ret void
+}
+
+; Test that the PHI node in for.inc is updated correctly as the switch is
+; replaced with a single branch to for.inc
+define void @test5() {
+; CHECK-LABEL: @test5
+entry:
+  br i1 undef, label %cleanup10, label %cleanup10.thread
+
+cleanup10.thread:
+  br label %for.inc
+
+cleanup10:
+  switch i32 undef, label %unreachable [
+    i32 0, label %for.inc
+    i32 4, label %for.inc
+  ]
+
+for.inc:
+; CHECK: for.inc:
+; CHECK-NEXT: phi i16 [ 0, %cleanup10.thread ], [ undef, %cleanup10 ]
+%0 = phi i16 [ undef, %cleanup10 ], [ 0, %cleanup10.thread ], [ undef, %cleanup10 ]
+  unreachable
+
+unreachable:
+  unreachable
+}