Index: llvm/lib/Transforms/Scalar/EarlyCSE.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/EarlyCSE.cpp
+++ llvm/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -1136,8 +1136,12 @@
             LLVM_DEBUG(dbgs() << "Skipping due to debug counter\n");
             continue;
           }
-          if (!Inst.use_empty())
+          if (!Inst.use_empty()) {
+            // Salvage debug info early to be compatible with
+            // removeRedundantDbgInstrsUsingBackwardScan() used in SimplfyCFG.
+            salvageDebugInfoOrMarkUndef(Inst);
             Inst.replaceAllUsesWith(Op);
+          }
           salvageKnowledge(&Inst, &AC);
           removeMSSA(Inst);
           Inst.eraseFromParent();
Index: llvm/test/DebugInfo/X86/earlycse-load-marks-undef.ll
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/X86/earlycse-load-marks-undef.ll
@@ -0,0 +1,65 @@
+; RUN: opt -mtriple=x86_64-- %s -S --early-cse  -o - | FileCheck %s
+; Ensure that the second dbg.value is undef as RemoveRedundantDbgInstrs
+; will remove the first dbg.value.
+; Bugzilla #46114
+
+@a = dso_local global i32 1, align 4, !dbg !0
+@c = dso_local global i8 0, align 1, !dbg !9
+@b = dso_local global i16 0, align 2, !dbg !6
+
+define dso_local void @main() #0 !dbg !15 {
+entry:
+  %0 = load i32, i32* @a, align 4
+  call void @llvm.dbg.value(metadata i32 0, metadata !20, metadata !DIExpression()), !dbg !24
+  %1 = load i32, i32* @a, align 4, !dbg !25, !tbaa !26
+; CHECK: call void @llvm.dbg.value(metadata i32 undef
+  call void @llvm.dbg.value(metadata i32 %1, metadata !20, metadata !DIExpression()), !dbg !24
+  %sub = sub nsw i32 %1, 0
+  %conv1 = trunc i32 %sub to i16
+  store i16 %conv1, i16* @b, align 2, !dbg !30, !tbaa !31
+  %tobool = icmp ne i32 %0, 0
+  unreachable
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { "use-soft-float"="false" }
+attributes #1 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!13, !14}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "a", scope: !2, file: !3, line: 1, type: !12, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 11.0.0 (https://github.com/llvm/llvm-project.git 20c9bb44ec1a4a795215ff6964d264219f9b05f2)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "earlycse-load-marks-undef.ll", directory: "/temp/bz46114")
+!4 = !{}
+!5 = !{!0, !6, !9}
+!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = distinct !DIGlobalVariable(name: "b", scope: !2, file: !3, line: 2, type: !8, isLocal: false, isDefinition: true)
+!8 = !DIBasicType(name: "short", size: 16, encoding: DW_ATE_signed)
+!9 = !DIGlobalVariableExpression(var: !10, expr: !DIExpression())
+!10 = distinct !DIGlobalVariable(name: "c", scope: !2, file: !3, line: 3, type: !11, isLocal: false, isDefinition: true)
+!11 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!12 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!13 = !{i32 2, !"Debug Info Version", i32 3}
+!14 = !{i32 1, !"wchar_size", i32 4}
+!15 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 4, type: !16, scopeLine: 4, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !18)
+!16 = !DISubroutineType(types: !17)
+!17 = !{!12}
+!18 = !{!19, !20, !21}
+!19 = !DILocalVariable(name: "d", scope: !15, file: !3, line: 5, type: !12)
+!20 = !DILocalVariable(name: "l_52", scope: !15, file: !3, line: 5, type: !12)
+!21 = !DILocalVariable(name: "e", scope: !22, file: !3, line: 8, type: !12)
+!22 = distinct !DILexicalBlock(scope: !23, file: !3, line: 7, column: 10)
+!23 = distinct !DILexicalBlock(scope: !15, file: !3, line: 7, column: 7)
+!24 = !DILocation(line: 0, scope: !15)
+!25 = !DILocation(line: 6, column: 15, scope: !15)
+!26 = !{!27, !27, i64 0}
+!27 = !{!"int", !28, i64 0}
+!28 = !{!"omnipotent char", !29, i64 0}
+!29 = !{!"Simple C/C++ TBAA"}
+!30 = !DILocation(line: 6, column: 5, scope: !15)
+!31 = !{!32, !32, i64 0}
+!32 = !{!"short", !28, i64 0}