Index: llvm/lib/CodeGen/MachineCSE.cpp
===================================================================
--- llvm/lib/CodeGen/MachineCSE.cpp
+++ llvm/lib/CodeGen/MachineCSE.cpp
@@ -831,6 +831,13 @@
           continue;
         MachineInstr &NewMI =
             TII->duplicate(*CMBB, CMBB->getFirstTerminator(), *MI);
+
+        // When hoisting, make sure we don't carry the debug location of
+        // the original instruction, as that's not correct and can cause
+        // unexpected jumps when debugging optimized code.
+        auto EmptyDL = DebugLoc();
+        NewMI.setDebugLoc(EmptyDL);
+
         NewMI.getOperand(0).setReg(NewReg);
 
         PREMap[MI] = CMBB;
Index: llvm/test/DebugInfo/X86/machinecse-wrongdebug-hoist.ll
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/X86/machinecse-wrongdebug-hoist.ll
@@ -0,0 +1,85 @@
+; RUN: llc %s -o - -print-after=machine-cse -mtriple=x86_64-- 2>&1 | FileCheck %s --match-full-lines
+
+; CHECK: %5:gr32 = SUB32ri8 %0:gr32(tied-def 0), 1, implicit-def $eflags, debug-location !24; a.c:3:13
+; CHECK-NEXT: %10:gr32 = MOVSX32rr8 %4:gr8
+; CHECK-NEXT: JCC_1 %bb.2, 15, implicit $eflags, debug-location !25; a.c:3:18
+
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.15.0"
+
+@a = local_unnamed_addr global i32 0, align 4, !dbg !0
+
+; Function Attrs: norecurse nounwind readonly ssp uwtable
+define i32 @b(i8 signext %0) local_unnamed_addr #0 !dbg !12 {
+  call void @llvm.dbg.value(metadata i8 %0, metadata !17, metadata !DIExpression()), !dbg !18
+  %2 = load i32, i32* @a, align 4, !dbg !19, !tbaa !20
+  %3 = icmp sgt i32 %2, 1, !dbg !24
+  br i1 %3, label %8, label %4, !dbg !25
+
+4:                                                ; preds = %1
+  %5 = sext i8 %0 to i32, !dbg !26
+  %6 = ashr i32 %5, %2, !dbg !27
+  %7 = icmp eq i32 %6, 0, !dbg !27
+  br i1 %7, label %10, label %8, !dbg !28
+
+8:                                                ; preds = %4, %1
+  %9 = sext i8 %0 to i32, !dbg !29
+  br label %10, !dbg !28
+
+10:                                               ; preds = %4, %8
+  %11 = phi i32 [ %9, %8 ], [ 0, %4 ], !dbg !28
+  ret i32 %11, !dbg !30
+}
+
+; Function Attrs: norecurse nounwind readonly ssp uwtable
+define i32 @main() local_unnamed_addr #0 !dbg !31 {
+  %1 = call i32 @b(i8 signext 0), !dbg !34
+  ret i32 %1, !dbg !35
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { norecurse nounwind readonly ssp uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+cx8,+fxsr,+mmx,+sahf,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!7, !8, !9, !10}
+!llvm.ident = !{!11}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "a", scope: !2, file: !3, line: 1, type: !6, 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 75cfd382201978615cca1c91c2d9f14f8b7af56d)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, nameTableKind: None, sysroot: "/")
+!3 = !DIFile(filename: "a.c", directory: "/Users/davide/work/build/bin")
+!4 = !{}
+!5 = !{!0}
+!6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!7 = !{i32 7, !"Dwarf Version", i32 4}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{i32 1, !"wchar_size", i32 4}
+!10 = !{i32 7, !"PIC Level", i32 2}
+!11 = !{!"clang version 11.0.0 (https://github.com/llvm/llvm-project 75cfd382201978615cca1c91c2d9f14f8b7af56d)"}
+!12 = distinct !DISubprogram(name: "b", scope: !3, file: !3, line: 2, type: !13, scopeLine: 2, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !16)
+!13 = !DISubroutineType(types: !14)
+!14 = !{!6, !15}
+!15 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!16 = !{!17}
+!17 = !DILocalVariable(name: "c", arg: 1, scope: !12, file: !3, line: 2, type: !15)
+!18 = !DILocation(line: 0, scope: !12)
+!19 = !DILocation(line: 3, column: 11, scope: !12)
+!20 = !{!21, !21, i64 0}
+!21 = !{!"int", !22, i64 0}
+!22 = !{!"omnipotent char", !23, i64 0}
+!23 = !{!"Simple C/C++ TBAA"}
+!24 = !DILocation(line: 3, column: 13, scope: !12)
+!25 = !DILocation(line: 3, column: 18, scope: !12)
+!26 = !DILocation(line: 3, column: 21, scope: !12)
+!27 = !DILocation(line: 3, column: 23, scope: !12)
+!28 = !DILocation(line: 3, column: 10, scope: !12)
+!29 = !DILocation(line: 4, column: 16, scope: !12)
+!30 = !DILocation(line: 3, column: 3, scope: !12)
+!31 = distinct !DISubprogram(name: "main", scope: !3, file: !3, line: 8, type: !32, scopeLine: 9, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !2, retainedNodes: !4)
+!32 = !DISubroutineType(types: !33)
+!33 = !{!6}
+!34 = !DILocation(line: 10, column: 10, scope: !31)
+!35 = !DILocation(line: 10, column: 3, scope: !31)