Index: llvm/lib/CodeGen/GlobalISel/Localizer.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/Localizer.cpp
+++ llvm/lib/CodeGen/GlobalISel/Localizer.cpp
@@ -124,6 +124,12 @@
         MachineInstr *LocalizedMI = MF.CloneMachineInstr(&MI);
         LocalizedInstrs.insert(LocalizedMI);
         MachineInstr &UseMI = *MOUse.getParent();
+        if (UseMI.getParent() != LocalizedMI->getParent())
+          // Attach the source location of the insertion point to the
+          // localized instruction, if it comes from a different basic
+          // block. Preserving the original source location would
+          // create a misleading line table.
+          LocalizedMI->setDebugLoc(UseMI.getDebugLoc());
         if (MRI->hasOneUse(Reg) && !UseMI.isPHI())
           InsertMBB->insert(InsertMBB->SkipPHIsAndLabels(UseMI), LocalizedMI);
         else
Index: llvm/test/DebugInfo/MIR/AArch64/localizer.mir
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/MIR/AArch64/localizer.mir
@@ -0,0 +1,117 @@
+# Test that Localizer attaches a debug location to instructions sunk into a new basic block.
+# RUN: llc -O0 -mtriple=aarch64-apple-ios -run-pass=localizer -verify-machineinstrs %s -o - | FileCheck %s -check-prefix=CHECK
+--- |
+  ; clang -target arm64-apple-macos11 -mllvm -stop-before=localizer -c -gline-tables-only 
+  ; extern int j, k;
+  ; void f(int i) {
+  ;   i = 1;
+  ;   if (j)
+  ;     k += 1;
+  ; }
+
+  source_filename = "/tmp/t.c"
+  target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
+  target triple = "arm64-apple-macosx11.0.0"
+  
+  @j = external global i32, align 4
+  @k = external global i32, align 4
+  
+  ; Function Attrs: noinline nounwind optnone ssp uwtable
+  define void @f(i32 %i) #0 !dbg !14 {
+  entry:
+    %i.addr = alloca i32, align 4
+    store i32 %i, i32* %i.addr, align 4
+    store i32 1, i32* %i.addr, align 4, !dbg !17
+    %0 = load i32, i32* @j, align 4, !dbg !18
+    %tobool = icmp ne i32 %0, 0, !dbg !18
+    br i1 %tobool, label %if.then, label %if.end, !dbg !18
+  
+  if.then:                                          ; preds = %entry
+    %1 = load i32, i32* @k, align 4, !dbg !19
+    %add = add nsw i32 %1, 1, !dbg !19
+    store i32 %add, i32* @k, align 4, !dbg !19
+    br label %if.end, !dbg !20
+  
+  if.end:                                           ; preds = %if.then, %entry
+    ret void, !dbg !21
+  }
+  
+  attributes #0 = { noinline nounwind optnone ssp uwtable }
+  
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!3, !4}
+  
+  !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", emissionKind: LineTablesOnly, sysroot: "/")
+  !1 = !DIFile(filename: "t.c", directory: "/tmp")
+  !2 = !{}
+  !3 = !{i32 7, !"Dwarf Version", i32 4}
+  !4 = !{i32 2, !"Debug Info Version", i32 3}
+  !14 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 2, type: !16, scopeLine: 2, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+  !16 = !DISubroutineType(types: !2)
+  !17 = !DILocation(line: 5, column: 5, scope: !14)
+  !18 = !DILocation(line: 6, column: 7, scope: !14)
+  !19 = !DILocation(line: 7, column: 7, scope: !14)
+  !20 = !DILocation(line: 7, column: 5, scope: !14)
+  !21 = !DILocation(line: 8, column: 1, scope: !14)
+
+...
+---
+name:            f
+registers:
+  - { id: 0, class: gpr, preferred-register: '' }
+  - { id: 1, class: gpr, preferred-register: '' }
+  - { id: 2, class: gpr, preferred-register: '' }
+  - { id: 3, class: gpr, preferred-register: '' }
+  - { id: 4, class: gpr, preferred-register: '' }
+  - { id: 5, class: gpr, preferred-register: '' }
+  - { id: 6, class: gpr, preferred-register: '' }
+  - { id: 7, class: gpr, preferred-register: '' }
+  - { id: 8, class: gpr, preferred-register: '' }
+  - { id: 9, class: gpr, preferred-register: '' }
+  - { id: 10, class: _, preferred-register: '' }
+  - { id: 11, class: _, preferred-register: '' }
+  - { id: 12, class: gpr, preferred-register: '' }
+liveins:
+  - { reg: '$w0', virtual-reg: '' }
+fixedStack:      []
+stack:
+  - { id: 0, name: i.addr, type: default, offset: 0, size: 4, alignment: 4, 
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true, 
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:             |
+  bb.1.entry:
+    successors: %bb.2(0x40000000), %bb.3(0x40000000)
+    liveins: $w0
+  
+    %0:gpr(s32) = COPY $w0
+    %2:gpr(s32) = G_CONSTANT i32 1
+    %4:gpr(p0) = G_GLOBAL_VALUE @j, debug-location !DILocation(line: 0, scope: !14)
+    %5:gpr(s32) = G_CONSTANT i32 0
+    %8:gpr(p0) = G_GLOBAL_VALUE @k, debug-location !DILocation(line: 0, scope: !14)
+    %1:gpr(p0) = G_FRAME_INDEX %stack.0.i.addr
+    G_STORE %0(s32), %1(p0) :: (store 4 into %ir.i.addr)
+    G_STORE %2(s32), %1(p0), debug-location !17 :: (store 4 into %ir.i.addr)
+    %3:gpr(s32) = G_LOAD %4(p0), debug-location !18 :: (dereferenceable load 4 from @j)
+    %12:gpr(s32) = G_ICMP intpred(eq), %3(s32), %5, debug-location !18
+    %6:gpr(s1) = G_TRUNC %12(s32), debug-location !18
+    G_BRCOND %6(s1), %bb.3, debug-location !18
+    G_BR %bb.2, debug-location !18
+  
+  bb.2.if.then:
+    successors: %bb.3(0x80000000)
+    ; CHECK-LABEL: bb.1.if.then:
+    ; CHECK:         %13:gpr(p0) = G_GLOBAL_VALUE @k, debug-location ![[DBG:[0-9]+]]
+    ; CHECK-NEXT:    %7:gpr(s32) = G_LOAD %13(p0), debug-location ![[DBG]]
+    ; CHECK-NEXT:    %14:gpr(s32) = G_CONSTANT i32 1, debug-location ![[DBG]]
+    ; CHECK-NEXT:    %9:gpr(s32) = nsw G_ADD %7, %14, debug-location ![[DBG]]
+    ; CHECK-NEXT:    G_STORE %9(s32), %13(p0), debug-location ![[DBG]]
+    ; CHECK-LABEL: if.end:
+
+    %7:gpr(s32) = G_LOAD %8(p0), debug-location !19 :: (dereferenceable load 4 from @k)
+    %9:gpr(s32) = nsw G_ADD %7, %2, debug-location !19
+    G_STORE %9(s32), %8(p0), debug-location !19 :: (store 4 into @k)
+  
+  bb.3.if.end:
+    RET_ReallyLR debug-location !21
+
+...