Index: llvm/lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/JumpThreading.cpp
+++ llvm/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/test/Transforms/JumpThreading/branch-debug-info.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/JumpThreading/branch-debug-info.ll
@@ -0,0 +1,34 @@
+; RUN: opt %s -debugify -jump-threading -S | FileCheck %s
+; Tests Bug 37966
+
+define dso_local void @bar(i32 %cc) local_unnamed_addr {
+; CHECK-LABEL: @bar(
+; CHECK: while.body:
+; CHECK-NEXT: br label %while.body, !dbg ![[DBG:[0-9]+]]
+; CHECK: ![[DBG]] = !DILocation(
+
+entry:
+  %dd = alloca [3 x i32], align 4
+  %tobool = icmp eq i32 %cc, 0
+  br i1 %tobool, label %while.end, label %while.body.lr.ph
+
+while.body.lr.ph:                                 ; preds = %entry
+  %idxprom = sext i32 %cc to i64
+  %arrayidx = getelementptr inbounds [3 x i32], [3 x i32]* %dd, i64 0, i64 %idxprom
+  br label %while.body
+
+while.cond:                                       ; preds = %while.body
+  store i32 2, i32* %arrayidx, align 4
+  br label %while.end
+
+; The jump threading pass will replace this branch with an unconditional branch:
+; br label %while.body
+; The debug information for the existing branch instruction should be reused
+; for the new instruction.
+while.body:                                       ; preds = %while.body.lr.ph, %while.body
+  br i1 %tobool, label %while.cond, label %while.body
+
+while.end:                                        ; preds = %entry, %while.cond
+  ret void
+}
+