Index: llvm/trunk/lib/Transforms/Utils/BasicBlockUtils.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ llvm/trunk/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -149,10 +149,11 @@
         return false;
 
   // Begin by getting rid of unneeded PHIs.
-  SmallVector<Value *, 4> IncomingValues;
+  SmallVector<AssertingVH<Value>, 4> IncomingValues;
   if (isa<PHINode>(BB->front())) {
     for (PHINode &PN : BB->phis())
-      if (PN.getIncomingValue(0) != &PN)
+      if (!isa<PHINode>(PN.getIncomingValue(0)) ||
+          cast<PHINode>(PN.getIncomingValue(0))->getParent() != BB)
         IncomingValues.push_back(PN.getIncomingValue(0));
     FoldSingleEntryPHINodes(BB, MemDep);
   }
@@ -168,8 +169,8 @@
   PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
 
   // Eliminate duplicate dbg.values describing the entry PHI node post-splice.
-  for (auto *Incoming : IncomingValues) {
-    if (isa<Instruction>(Incoming)) {
+  for (auto Incoming : IncomingValues) {
+    if (isa<Instruction>(*Incoming)) {
       SmallVector<DbgValueInst *, 2> DbgValues;
       SmallDenseSet<std::pair<DILocalVariable *, DIExpression *>, 2>
           DbgValueSet;
Index: llvm/trunk/test/Transforms/SimplifyCFG/fold-debug-info.ll
===================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/fold-debug-info.ll
+++ llvm/trunk/test/Transforms/SimplifyCFG/fold-debug-info.ll
@@ -0,0 +1,102 @@
+;; Check that we don't crash. PR37300.
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt %s -S -simplifycfg | FileCheck %s
+
+define void @patatino() {
+; CHECK-LABEL: @patatino(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    ret void
+;
+bb:
+  %tmp = icmp eq i32 7, 0
+  br label %bb3
+bb3:                                              ; preds = %bb2, %bb
+  br label %bb36
+bb5:                                              ; preds = %bb4
+  %tmp7 = icmp ne i32 7, 0
+  %tmp8 = and i1 true, %tmp7
+  br i1 %tmp8, label %bb16, label %bb14
+bb9:                                              ; preds = %bb33, %bb10
+  br label %bb18
+bb10:                                             ; preds = %bb19, %bb13
+  %tmp11 = add nsw i32 2, 1
+  %tmp12 = icmp eq i32 %tmp11, 0
+  br i1 %tmp12, label %bb17, label %bb9
+bb13:                                             ; preds = %bb18, %bb13
+  br label %bb10
+bb14:                                             ; preds = %bb17, %bb6, %bb5
+  br label %bb35
+bb16:                                             ; preds = %bb6
+  br label %bb31
+bb17:                                             ; preds = %bb32, %bb10
+  br label %bb14
+bb18:                                             ; preds = %bb9
+  br label %bb13
+bb21:                                             ; preds = %bb31, %bb23
+  %tmp22 = phi i32 [ 0, %bb23 ], [ 0, %bb31 ]
+  br label %bb27
+bb23:                                             ; preds = %bb29, %bb28, %bb26
+  %tmp24 = add nsw i32 %tmp22, 1
+  %tmp25 = icmp eq i32 %tmp24, 0
+  br i1 %tmp25, label %bb32, label %bb21
+bb27:                                             ; preds = %bb21
+  br label %bb30
+bb28:                                             ; preds = %bb30
+  br label %bb23
+bb30:                                             ; preds = %bb30, %bb27
+  br label %bb28
+bb31:                                             ; preds = %bb16
+  br label %bb21
+bb32:                                             ; preds = %bb23
+  br label %bb17
+bb35:                                             ; preds = %bb14
+  br label %bb3
+bb36:                                             ; preds = %bb3, %bb3
+  br label %bb37
+bb37:                                             ; preds = %bb36
+  %tmp39 = and i1 %tmp, true
+  br i1 %tmp39, label %bb40, label %bb67
+bb40:                                             ; preds = %bb38
+  br i1 %tmp, label %bb42, label %bb41
+bb41:                                             ; preds = %bb40
+  br label %bb43
+bb42:                                             ; preds = %bb40
+  br label %bb66
+bb43:                                             ; preds = %bb41
+  br label %bb44
+bb44:                                             ; preds = %bb61, %bb43
+  %tmp45 = phi i32 [ 0, %bb61 ], [ 0, %bb43 ]
+  %tmp46 = phi i32 [ %tmp62, %bb61 ], [ 0, %bb43 ]
+  br label %bb51
+bb48:                                             ; preds = %bb47
+  br label %bb49
+bb49:                                             ; preds = %bb48
+  %tmp50 = phi i32 [ 0, %bb48 ]
+  br label %bb61
+bb51:                                             ; preds = %bb44
+  br label %bb52
+bb52:                                             ; preds = %bb55, %bb51
+  %tmp53 = phi i32 [ %tmp46, %bb51 ], [ 0, %bb55 ]
+  br label %bb55
+bb54:                                             ; preds = %bb52
+  br label %bb55
+bb55:                                             ; preds = %bb54, %bb52
+  %tmp56 = phi i32 [ 0, %bb54 ], [ 0, %bb52 ]
+  %tmp57 = shl i32 %tmp56, 16
+  br i1 false, label %bb52, label %bb58
+bb58:                                             ; preds = %bb55
+  %tmp59 = phi i32 [ 0, %bb55 ]
+  %tmp60 = phi i32 [ %tmp53, %bb55 ]
+  br label %bb61
+bb61:                                             ; preds = %bb58, %bb49
+  %tmp62 = phi i32 [ %tmp59, %bb58 ], [ %tmp50, %bb49 ]
+  %tmp63 = add nsw i32 %tmp45, 1
+  %tmp64 = icmp eq i32 %tmp63, 0
+  br i1 %tmp64, label %bb65, label %bb44
+bb65:                                             ; preds = %bb61
+  br label %bb66
+bb66:                                             ; preds = %bb65, %bb42
+  br label %bb67
+bb67:                                             ; preds = %bb66, %bb38
+  ret void
+}