diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -373,6 +373,11 @@
   DwarfVersion =
       TT.isNVPTX() ? 2 : (DwarfVersion ? DwarfVersion : dwarf::DWARF_VERSION);
 
+  bool Dwarf64 = Asm->TM.Options.MCOptions.Dwarf64 &&
+                 DwarfVersion >= 3 &&   // DWARF64 was introduced in DWARFv3.
+                 TT.isArch64Bit() &&    // DWARF64 requires 64-bit relocations.
+                 TT.isOSBinFormatELF(); // Support only ELF for now.
+
   UseRangesSection = !NoDwarfRangesSection && !TT.isNVPTX();
 
   // Use sections as references. Force for NVPTX.
@@ -414,6 +419,8 @@
       DwarfVersion >= 5 || (UseGNUDebugMacro && !useSplitDwarf());
 
   Asm->OutStreamer->getContext().setDwarfVersion(DwarfVersion);
+  Asm->OutStreamer->getContext().setDwarfFormat(Dwarf64 ? dwarf::DWARF64
+                                                        : dwarf::DWARF32);
 }
 
 // Define out of line so we don't have to include DwarfUnit.h in DwarfDebug.h.
diff --git a/llvm/test/DebugInfo/X86/debug-frame-dwarf64.ll b/llvm/test/DebugInfo/X86/debug-frame-dwarf64.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/debug-frame-dwarf64.ll
@@ -0,0 +1,37 @@
+; This checks that .debug_frame can be generated in the DWARF64 format.
+
+; RUN: llc -mtriple=x86_64 -dwarf64 -force-dwarf-frame-section -filetype=obj %s -o %t
+; RUN: llvm-dwarfdump -debug-frame %t | FileCheck %s
+
+; CHECK:      .debug_frame contents:
+; CHECK:      00000000 {{.+}} ffffffffffffffff CIE
+; CHECK-NEXT:   Format:                DWARF64
+; CHECK:      {{.+}} 0000000000000000 FDE cie=00000000 pc=
+; CHECK-NEXT:   Format:       DWARF64
+
+; IR generated and reduced from:
+; $ cat foo.c
+; void foo() { }
+; $ clang -g -S -emit-llvm foo.c -o foo.ll
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local void @foo() #0 !dbg !7 {
+  ret void, !dbg !10
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 12.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "foo.c", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 12.0.0"}
+!7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null}
+!10 = !DILocation(line: 1, column: 14, scope: !7)
diff --git a/llvm/test/DebugInfo/X86/debug-line-dwarf64.ll b/llvm/test/DebugInfo/X86/debug-line-dwarf64.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/debug-line-dwarf64.ll
@@ -0,0 +1,35 @@
+; This checks that .debug_line can be generated in the DWARF64 format.
+
+; RUN: llc -mtriple=x86_64 -dwarf-version=3 -dwarf64 -filetype=obj %s -o %t3
+; RUN: llvm-dwarfdump -debug-line %t3 | FileCheck %s
+
+; CHECK:        .debug_line contents:
+; CHECK-NEXT:   debug_line[0x00000000]
+; CHECK-NEXT:   Line table prologue:
+; CHECK-NEXT:       total_length:
+; CHECK-NEXT:         format: DWARF64
+
+; IR generated and reduced from:
+; $ cat foo.c
+; int foo;
+; $ clang -g -S -emit-llvm foo.c -o foo.ll
+
+target triple = "x86_64-unknown-linux-gnu"
+
+@foo = dso_local global i32 0, align 4, !dbg !0
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!7, !8, !9}
+!llvm.ident = !{!10}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "foo", scope: !2, file: !3, line: 1, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 12.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "foo.c", directory: "/tmp")
+!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 = !{!"clang version 12.0.0"}
diff --git a/llvm/test/DebugInfo/X86/dwarf64-support.ll b/llvm/test/DebugInfo/X86/dwarf64-support.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/dwarf64-support.ll
@@ -0,0 +1,59 @@
+; This checks cases when the 64-bit DWARF debug info should not be generated
+; even if '-dwarf64' is specified.
+
+; The 64-bit DWARF format was introduced in DWARFv3, so the '-dwarf64' switch
+; should be ignored for earlier versions.
+; RUN: llc -mtriple=x86_64 -dwarf-version=2 -dwarf64 -filetype=obj %s -o - | \
+; RUN:   llvm-dwarfdump -debug-line - | \
+; RUN:   FileCheck %s --check-prefixes=ELF64,CHECK
+
+; DWARF64 requires 64-bit relocations, so it is not produced for 32-bit targets.
+; RUN: llc -mtriple=i386 -dwarf-version=5 -dwarf64 -filetype=obj %s -o - | \
+; RUN:   llvm-dwarfdump -debug-line - | \
+; RUN:   FileCheck %s --check-prefixes=ELF32,CHECK
+
+; DWARF64 is enabled only for ELF targets. The switch should be ignored for COFF.
+; RUN: llc -mtriple=x86_64-windows-gnu -dwarf-version=5 -dwarf64 -filetype=obj %s -o - | \
+; RUN:   llvm-dwarfdump -debug-line - | \
+; RUN:   FileCheck %s --check-prefixes=COFF,CHECK
+
+; DWARF64 is enabled only for ELF targets. The switch should be ignored for Mach-O.
+; RUN: llc -mtriple=x86_64-apple-darwin -dwarf-version=5 -dwarf64 -filetype=obj %s -o - | \
+; RUN:   llvm-dwarfdump -debug-line - | \
+; RUN:   FileCheck %s --check-prefixes=MACHO,CHECK
+
+; ELF64:    file format elf64-x86-64
+; ELF32:    file format elf32-i386
+; COFF:     file format COFF-x86-64
+; MACHO:    file format Mach-O 64-bit x86-64
+
+; CHECK:      .debug_line contents:
+; CHECK-NEXT: debug_line[0x00000000]
+; CHECK-NEXT: Line table prologue:
+; CHECK-NEXT:     total_length:
+; CHECK-NEXT:         format: DWARF32
+
+; IR generated and reduced from:
+; $ cat foo.c
+; int foo;
+; $ clang -g -S -emit-llvm foo.c -o foo.ll
+
+target triple = "x86_64-unknown-linux-gnu"
+
+@foo = dso_local global i32 0, align 4, !dbg !0
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!7, !8, !9}
+!llvm.ident = !{!10}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "foo", scope: !2, file: !3, line: 1, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 12.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "foo.c", directory: "/tmp")
+!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 = !{!"clang version 12.0.0"}