[DebugInfo] Fix emitting DWARF64 .debug_addr sections (15/19).

[ikudrin]

Summary

The patch fixes emitting the header of the table. The content is independent of the DWARF format.

[dblaikie]

Looks good, thanks!

llvm/lib/CodeGen/AsmPrinter/AddressPool.cpp

 }
 
 MCSymbol *AddressPool::emitHeader(AsmPrinter &Asm, MCSection *Section) {
   static const uint8_t AddrSize = Asm.getDataLayout().getPointerSize();
   StringRef Prefix = "debug_addr_";
   MCSymbol *BeginLabel = Asm.createTempSymbol(Prefix + "start");
   MCSymbol *EndLabel = Asm.createTempSymbol(Prefix + "end");
 
-  Asm.OutStreamer->AddComment("Length of contribution");
-  Asm.emitLabelDifference(EndLabel, BeginLabel,
-                          4); // TODO: Support DWARF64 format.
+  Asm.emitDwarfUnitLength(EndLabel, BeginLabel, "Length of contribution");
   Asm.OutStreamer->emitLabel(BeginLabel);
   Asm.OutStreamer->AddComment("DWARF version number");
   Asm.emitInt16(Asm.getDwarfVersion());
   Asm.OutStreamer->AddComment("Address size");
   Asm.emitInt8(AddrSize);
   Asm.OutStreamer->AddComment("Segment selector size");
   Asm.emitInt8(0); // TODO: Support non-zero segment_selector_size.
 

llvm/test/DebugInfo/X86/debug-addr-dwarf64.ll

+; This checks that .debug_addr can be generated in the DWARF64 format.
+
+; RUN: llc -mtriple=x86_64 -dwarf-version=5 -dwarf64 -filetype=obj %s -o %t
+; RUN: llvm-dwarfdump -debug-info -debug-addr %t | FileCheck %s
+
+; CHECK:      .debug_info contents:
+; CHECK:      DW_TAG_compile_unit
+; CHECK:        DW_AT_addr_base (0x0000000000000010)
+
+; CHECK:      .debug_addr contents:
+; CHECK-NEXT: Address table header: length = 0x0000000000000014, format = DWARF64, version = 0x0005, addr_size = 0x08, seg_size = 0x00
+; CHECK-NEXT: Addrs: [
+; CHECK-NEXT: 0x0000000000000000
+; CHECK-NEXT: 0x0000000000000004
+; CHECK-NEXT: ]
+
+; IR generated and reduced from:
+; $ cat foo.c
+; int foo;
+; int bar;
+; $ 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
+@bar = dso_local global i32 0, align 4, !dbg !6
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!9, !10, !11}
+!llvm.ident = !{!12}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "foo", scope: !2, file: !3, line: 1, type: !8, 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}
+!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = distinct !DIGlobalVariable(name: "bar", scope: !2, file: !3, line: 2, type: !8, isLocal: false, isDefinition: true)
+!8 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!9 = !{i32 7, !"Dwarf Version", i32 4}
+!10 = !{i32 2, !"Debug Info Version", i32 3}
+!11 = !{i32 1, !"wchar_size", i32 4}
+!12 = !{!"clang version 12.0.0"}