Index: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1142,7 +1142,9 @@
         unsigned ToKeep = Ret == LazyValueInfo::True ? 0 : 1;
         BasicBlock *ToRemoveSucc = CondBr->getSuccessor(ToRemove);
         ToRemoveSucc->removePredecessor(BB, true);
-        BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
+        BranchInst *UncondBr =
+          BranchInst::Create(CondBr->getSuccessor(ToKeep), CondBr);
+        UncondBr->setDebugLoc(CondBr->getDebugLoc());
         CondBr->eraseFromParent();
         if (CondCmp->use_empty())
           CondCmp->eraseFromParent();
@@ -1245,7 +1247,8 @@
       BasicBlock *KeepSucc = BI->getSuccessor(*Implication ? 0 : 1);
       BasicBlock *RemoveSucc = BI->getSuccessor(*Implication ? 1 : 0);
       RemoveSucc->removePredecessor(BB);
-      BranchInst::Create(KeepSucc, BI);
+      BranchInst *UncondBI = BranchInst::Create(KeepSucc, BI);
+      UncondBI->setDebugLoc(BI->getDebugLoc());
       BI->eraseFromParent();
       DTU->applyUpdatesPermissive({{DominatorTree::Delete, BB, RemoveSucc}});
       return true;
Index: llvm/trunk/test/Transforms/JumpThreading/branch-debug-info.ll
===================================================================
--- llvm/trunk/test/Transforms/JumpThreading/branch-debug-info.ll
+++ llvm/trunk/test/Transforms/JumpThreading/branch-debug-info.ll
@@ -0,0 +1,41 @@
+; RUN: opt %s -debugify -jump-threading -S | FileCheck %s
+; Tests Bug 37966
+
+define void @test0(i32 %i) {
+; CHECK-LABEL: @test0(
+; CHECK: left:
+; CHECK: br label %left, !dbg ![[DBG0:[0-9]+]]
+ entry:
+  %c0 = icmp ult i32 %i, 5
+  br i1 %c0, label %left, label %right
+
+ left:
+  br i1 %c0, label %left, label %right
+
+ right:
+  ret void
+}
+
+define void @test1(i32 %i, i32 %len) {
+; CHECK-LABEL: @test1(
+; CHECK: left:
+; CHECK: br label %right, !dbg ![[DBG1:[0-9]+]]
+ entry:
+  %i.inc = add nuw i32 %i, 1
+  %c0 = icmp ult i32 %i.inc, %len
+  br i1 %c0, label %left, label %right
+
+ left:
+  %c1 = icmp ult i32 %i, %len
+  br i1 %c1, label %right, label %left0
+
+ left0:
+  ret void
+
+ right:
+  ret void
+}
+
+; CHECK-DAG: ![[DBG0]] = !DILocation(
+; CHECK-DAG: ![[DBG1]] = !DILocation(
+