Index: llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -6217,6 +6217,9 @@
       if (!DVI)
         continue;
 
+      if (DVI->isUndef())
+        continue;
+
       if (DVI->hasArgList())
         continue;
 
Index: llvm/test/Transforms/LoopStrengthReduce/pr51329.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopStrengthReduce/pr51329.ll
@@ -0,0 +1,54 @@
+; RUN: opt -S -loop-reduce %s | FileCheck %s
+;
+; Test that LSR SCEV-based salvaging does not crash when translating SCEVs
+; that contain integers with binary representations greater than 64-bits. 
+; Also show that no salvaging attempt is made for dbg.value that are undef
+; pre-LSR.
+;
+; CHECK: call void @llvm.dbg.value(metadata i64 undef, metadata !{{[0-9]+}}, metadata !DIExpression(DW_OP_plus_uconst, 228, DW_OP_stack_value))
+; CHECK: call void @llvm.dbg.value(metadata i64 %var2, metadata !{{[0-9]+}}, metadata !DIExpression(DW_OP_plus_uconst, 228, DW_OP_stack_value))
+
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: nofree nosync nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+; Function Attrs: nounwind
+define hidden void @reproducer() local_unnamed_addr !dbg !5 {
+init:
+  %0 = lshr i128 undef, 64
+  %var1 = trunc i128 %0 to i64
+  %1 = add nuw i64 undef, %var1
+  %var2 = lshr i64 %1, 12
+  br label %Label_d0
+
+Label_d0:                                         ; preds = %Label_d0, %init
+  %var3 = phi i64 [ %var2, %init ], [ %var4, %Label_d0 ]
+  call void @llvm.dbg.value(metadata i64 undef, metadata !11, metadata !DIExpression(DW_OP_plus_uconst, 228, DW_OP_stack_value)), !dbg !12
+  call void @llvm.dbg.value(metadata i64 %var2, metadata !11, metadata !DIExpression(DW_OP_plus_uconst, 228, DW_OP_stack_value)), !dbg !12
+  %var4 = add i64 %var3, -1
+  %var5 = icmp eq i64 %var4, 0
+  br i1 %var5, label %Label_1bc, label %Label_d0
+
+Label_1bc:                                        ; preds = %Label_d0
+  ret void
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "frontend", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "source", directory: "")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = distinct !DISubprogram(name: "reproducer", scope: !1, file: !1, line: 904320, type: !6, scopeLine: 904320, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !10)
+!6 = !DISubroutineType(types: !7)
+!7 = !{null, !8, !9, !9, !9, !9, !9, !9}
+!8 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+!9 = !DIBasicType(name: "my_type", size: 64, encoding: DW_ATE_unsigned)
+!10 = !{!11}
+!11 = !DILocalVariable(name: "my_var", arg: 1, scope: !5, file: !1, line: 904320, type: !8)
+!12 = !DILocation(line: 904544, scope: !5)