DebugInfo: Use debug_line.dwo for debug_macro.dwo

[dblaikie]

Summary

This is an alternative proposal to D81476 (and D82084) - the details were sufficiently confusing to me it seemed easier to write some code and see how it looks.

[SouraVX]

Thank you so much @dblaikie for this. Admittedly, for all the direction I've been digging, missed this one :)
The catch here is that getDwoLineTable(U)->getFile(... this will enable the line table through MCDwarf interface, so we don't have/need to rely in DwarfTypeUnit interface for enabling line table.
Anyways, I'm planning to abandon all the revisions associated with this. IMHO D82084 is also not needed(since you did it without touching that) so we can leave it until there is actual need/situation ?

A side note: Do you also plan to put this in LLVM11 branch. AFAIK -gdwarf-5 -gsplit-dwarf -fdebug-macro still produces same error(Relocation in DWO object). This patch solves that.

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

#include "llvm/BinaryFormat/Dwarf.def"
   // We are setting Offset and line offset flags unconditionally here,
   // since we're only supporting DWARF32 and line offset should be mostly
   // present.
   // FIXME: Add support for DWARF64.
   Flags |= MACRO_FLAG_DEBUG_LINE_OFFSET;
   Asm->OutStreamer->AddComment("Flags: 32 bit, debug_line_offset present");
   Asm->emitInt8(Flags);
   Asm->OutStreamer->AddComment("debug_line_offset");
+  if (DD.useSplitDwarf())
+    Asm->OutStreamer->emitIntValue(0, /*Size=*/4);
+  else
     Asm->OutStreamer->emitSymbolValue(CU.getLineTableStartSym(), /*Size=*/4);
 }
 
 void DwarfDebug::handleMacroNodes(DIMacroNodeArray Nodes, DwarfCompileUnit &U) {
   for (auto *MN : Nodes) {
     if (auto *M = dyn_cast<DIMacro>(MN))
       emitMacro(*M);
     else if (auto *F = dyn_cast<DIMacroFile>(MN))
       emitMacroFile(*F, U);
if (!Value.empty()) {
       Asm->OutStreamer->AddComment("Macro Value=");
       Asm->OutStreamer->emitBytes(Value);
     }
     Asm->emitInt8('\0');
   }
 }
 
 void DwarfDebug::emitMacroFileImpl(
-    DIMacroFile &F, DwarfCompileUnit &U, unsigned StartFile, unsigned EndFile,
+    DIMacroFile &MF, DwarfCompileUnit &U, unsigned StartFile, unsigned EndFile,
     StringRef (*MacroFormToString)(unsigned Form)) {
 
   Asm->OutStreamer->AddComment(MacroFormToString(StartFile));
   Asm->emitULEB128(StartFile);
   Asm->OutStreamer->AddComment("Line Number");
-  Asm->emitULEB128(F.getLine());
+  Asm->emitULEB128(MF.getLine());
   Asm->OutStreamer->AddComment("File Number");
-  Asm->emitULEB128(U.getOrCreateSourceID(F.getFile()));
-  handleMacroNodes(F.getElements(), U);
+  DIFile &F = *MF.getFile();
+  if (useSplitDwarf())
+    Asm->emitULEB128(getDwoLineTable(U)->getFile(
+        F.getDirectory(), F.getFilename(), getMD5AsBytes(&F),
+        Asm->OutContext.getDwarfVersion(), F.getSource()));
+  else
+    Asm->emitULEB128(U.getOrCreateSourceID(&F));
+  handleMacroNodes(MF.getElements(), U);
   Asm->OutStreamer->AddComment(MacroFormToString(EndFile));
   Asm->emitULEB128(EndFile);
 }
 
 void DwarfDebug::emitMacroFile(DIMacroFile &F, DwarfCompileUnit &U) {
   // DWARFv5 macro and DWARFv4 macinfo share some common encodings,
   // so for readibility/uniformity, We are explicitly emitting those.
   assert(F.getMacinfoType() == dwarf::DW_MACINFO_start_file);

llvm/test/DebugInfo/X86/debug-macro-dwo.ll

 ; This test checks emission of .debug_macro.dwo section when
 ; -gdwarf-5 -gsplit-dwarf -fdebug-macro is specified.
 
 ; RUN: %llc_dwarf -dwarf-version=5 -O0 -filetype=obj \
-; RUN: -split-dwarf-file=foo.dwo < %s | llvm-dwarfdump -v - | FileCheck %s
+; RUN: -split-dwarf-file=foo.dwo < %s | llvm-dwarfdump -debug-macro -debug-info -debug-line -v - | FileCheck %s
 
 ; CHECK-LABEL:  .debug_info contents:
 ; CHECK: DW_AT_macros [DW_FORM_sec_offset] (0x00000000)
 
 ; CHECK-LABEL:  .debug_macro.dwo contents:
 ; CHECK-NEXT: 0x00000000:
-; CHECK-NEXT: macro header: version = 0x0005, flags = 0x02, format = DWARF32
+; CHECK-NEXT: macro header: version = 0x0005, flags = 0x02, format = DWARF32, debug_line_offset = 0x00000000
 ; CHECK-NEXT: DW_MACRO_start_file - lineno: 0 filenum: 0
-; FIXME: This should be filenum 1 (and 2 below) if this was using debug_loc.dwo
-;        (rather than currently incorrectly using debug_loc)
-; CHECK-NEXT:   DW_MACRO_start_file - lineno: 1 filenum: 2
+; CHECK-NEXT:   DW_MACRO_start_file - lineno: 1 filenum: 1
 ; CHECK-NEXT:     DW_MACRO_define_strx - lineno: 1 macro: FOO 5
 ; CHECK-NEXT:   DW_MACRO_end_file
-; CHECK-NEXT:   DW_MACRO_start_file - lineno: 2 filenum: 3
+; CHECK-NEXT:   DW_MACRO_start_file - lineno: 2 filenum: 2
 ; CHECK-NEXT:     DW_MACRO_undef_strx - lineno: 14 macro: YEA
 ; CHECK-NEXT:   DW_MACRO_end_file
 ; CHECK-NEXT:   DW_MACRO_undef_strx - lineno: 14 macro: YEA
 ; CHECK-NEXT: DW_MACRO_end_file
 
+; CHECK-LABEL: .debug_line.dwo contents:
+; CHECK: file_names[  0]:
+; CHECK:            name: "test.c"
+; CHECK: file_names[  1]:
+; CHECK:            name: "foo.h"
+; CHECK: file_names[  2]:
+; CHECK:            name: "bar.h"
+
+
+
 ; ModuleID = 'test.c'
 source_filename = "test.c"
 target datalayout = "e-m:e-p200:32:32-p201:32:32-p202:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!14, !15, !16}
 !llvm.ident = !{!17}