2 files changed, 140 insertions, 1 deletions
diff --git a/llvm/lib/Transforms/Utils/LowerSwitch.cpp b/llvm/lib/Transforms/Utils/LowerSwitch.cpp
index b3bdae47d94..7bfb3d9f4d4 100644
--- a/llvm/lib/Transforms/Utils/LowerSwitch.cpp
+++ b/llvm/lib/Transforms/Utils/LowerSwitch.cpp
@@ -175,11 +175,16 @@ static void fixPhis(BasicBlock *SuccBB, BasicBlock *OrigBB, BasicBlock *NewBB,
 
     // Remove additional occurences coming from condensed cases and keep the
     // number of incoming values equal to the number of branches to SuccBB.
+    SmallVector<unsigned, 8> Indices;
     for (++Idx; LocalNumMergedCases > 0 && Idx < E; ++Idx)
       if (PN->getIncomingBlock(Idx) == OrigBB) {
-        PN->removeIncomingValue(Idx);
+        Indices.push_back(Idx);
         LocalNumMergedCases--;
       }
+    // Remove incoming values in the reverse order to prevent invalidating
+    // *successive* index.
+    for (auto III = Indices.rbegin(), IIE = Indices.rend(); III != IIE; ++III)
+      PN->removeIncomingValue(*III);
   }
 }
 
diff --git a/llvm/test/Transforms/Util/lowerswitch.ll b/llvm/test/Transforms/Util/lowerswitch.ll
index 17c12028705..1eddb43c1a0 100644
--- a/llvm/test/Transforms/Util/lowerswitch.ll
+++ b/llvm/test/Transforms/Util/lowerswitch.ll
@@ -52,3 +52,137 @@ bb3:
 exit:
   ret void
 }
+
+; Test that we don't crash.
+define void @test2(i32 %mode) {
+; CHECK-LABEL: @test2
+  br i1 undef, label %1, label %._crit_edge
+
+; <label>:1                                       ; preds = %0
+  switch i32 %mode, label %33 [
+    i32 2, label %2
+    i32 3, label %3
+    i32 4, label %4
+    i32 5, label %5
+    i32 6, label %6
+    i32 7, label %7
+    i32 8, label %8
+    i32 9, label %9
+    i32 10, label %10
+    i32 11, label %14
+    i32 12, label %18
+    i32 13, label %22
+    i32 14, label %26
+    i32 15, label %27
+    i32 16, label %34
+    i32 17, label %34
+    i32 18, label %34
+    i32 19, label %34
+    i32 22, label %34
+    i32 20, label %31
+    i32 21, label %32
+  ]
+
+; <label>:2                                       ; preds = %1
+  br label %34
+
+; <label>:3                                       ; preds = %1
+  br label %34
+
+; <label>:4                                       ; preds = %1
+  br label %34
+
+; <label>:5                                       ; preds = %1
+  br label %34
+
+; <label>:6                                       ; preds = %1
+  br label %34
+
+; <label>:7                                       ; preds = %1
+  br label %34
+
+; <label>:8                                       ; preds = %1
+  br label %34
+
+; <label>:9                                       ; preds = %1
+  br label %34
+
+; <label>:10                                      ; preds = %1
+  br i1 undef, label %11, label %12
+
+; <label>:11                                      ; preds = %10
+  br label %13
+
+; <label>:12                                      ; preds = %10
+  br label %13
+
+; <label>:13                                      ; preds = %12, %11
+  br label %34
+
+; <label>:14                                      ; preds = %1
+  br i1 undef, label %15, label %16
+
+; <label>:15                                      ; preds = %14
+  br label %17
+
+; <label>:16                                      ; preds = %14
+  br label %17
+
+; <label>:17                                      ; preds = %16, %15
+  br label %34
+
+; <label>:18                                      ; preds = %1
+  br i1 undef, label %19, label %20
+
+; <label>:19                                      ; preds = %18
+  br label %21
+
+; <label>:20                                      ; preds = %18
+  br label %21
+
+; <label>:21                                      ; preds = %20, %19
+  br label %34
+
+; <label>:22                                      ; preds = %1
+  br i1 undef, label %23, label %24
+
+; <label>:23                                      ; preds = %22
+  br label %25
+
+; <label>:24                                      ; preds = %22
+  br label %25
+
+; <label>:25                                      ; preds = %24, %23
+  br label %34
+
+; <label>:26                                      ; preds = %1
+  br label %34
+
+; <label>:27                                      ; preds = %1
+  br i1 undef, label %28, label %29
+
+; <label>:28                                      ; preds = %27
+  br label %30
+
+; <label>:29                                      ; preds = %27
+  br label %30
+
+; <label>:30                                      ; preds = %29, %28
+  br label %34
+
+; <label>:31                                      ; preds = %1
+  br label %34
+
+; <label>:32                                      ; preds = %1
+  br label %34
+
+; <label>:33                                      ; preds = %1
+  br label %34
+
+; <label>:34                                      ; preds = %33, %32, %31, %30, %26, %25, %21, %17, %13, %9, %8, %7, %6, %5, %4, %3, %2, %1, %1, %1, %1, %1
+  %o.0 = phi float [ undef, %33 ], [ undef, %32 ], [ undef, %31 ], [ undef, %30 ], [ undef, %26 ], [ undef, %25 ], [ undef, %21 ], [ undef, %17 ], [ undef, %13 ], [ undef, %9 ], [ undef, %8 ], [ undef, %7 ], [ undef, %6 ], [ undef, %5 ], [ undef, %4 ], [ undef, %3 ], [ undef, %2 ], [ undef, %1 ], [ undef, %1 ], [ undef, %1 ], [ undef, %1 ], [ undef, %1 ]
+  br label %._crit_edge
+
+._crit_edge:                                      ; preds = %34, %0
+  ret void
+}