[XCOFF][DWARF] XCOFF64 should be able to select the dwarf format in intergrated-as mode.

[Esme]

Summary

DWARF32 is not supported for XCOFF64 under non integrated-as mode, because system assembler will fill the debug section lengths according to DWARF64 format.
While in intergrated-as mode, XCOFF64 should be able to select the DWARF version.

[shchenz]

I think this is correct. DWARF spec indicates that DWARF64 should not be set as default. So it is right to change to DWARF32 by default for integrated-as mode for XCOFF64.

LGTM with one nit.

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

403

Nit: Maybe we can use a variable to contain the value for TT.isOSBinFormatXCOFF().

[Esme]

Update test cases.

clang/lib/Driver/ToolChains/Clang.cpp

static void renderDwarfFormat(const Driver &D, const llvm::Triple &T,
 
   if (DwarfFormatArg->getOption().matches(options::OPT_gdwarf64)) {
     if (DwarfVersion < 3)
       D.Diag(diag::err_drv_argument_only_allowed_with)
           << DwarfFormatArg->getAsString(Args) << "DWARFv3 or greater";
     else if (!T.isArch64Bit())
       D.Diag(diag::err_drv_argument_only_allowed_with)
           << DwarfFormatArg->getAsString(Args) << "64 bit architecture";
-    else if (!T.isOSBinFormatELF())
+    else if (!(T.isOSBinFormatELF() || T.isOSBinFormatXCOFF()))
       D.Diag(diag::err_drv_argument_only_allowed_with)
-          << DwarfFormatArg->getAsString(Args) << "ELF platforms";
+          << DwarfFormatArg->getAsString(Args) << "ELF/XCOFF platforms";
   }
 
   DwarfFormatArg->render(Args, CmdArgs);
 }
 
 static void renderDebugOptions(const ToolChain &TC, const Driver &D,
                                const llvm::Triple &T, const ArgList &Args,
                                bool EmitCodeView, bool IRInput,

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

DwarfDebug::DwarfDebug(AsmPrinter *A)
 
   unsigned DwarfVersionNumber = Asm->TM.Options.MCOptions.DwarfVersion;
   unsigned DwarfVersion = DwarfVersionNumber ? DwarfVersionNumber
                                     : MMI->getModule()->getDwarfVersion();
   // Use dwarf 4 by default if nothing is requested. For NVPTX, use dwarf 2.
   DwarfVersion =
       TT.isNVPTX() ? 2 : (DwarfVersion ? DwarfVersion : dwarf::DWARF_VERSION);
 
+  bool UseIntegratedAs = Asm->OutStreamer->isIntegratedAssemblerRequired();
   bool Dwarf64 = DwarfVersion >= 3 && // DWARF64 was introduced in DWARFv3.
                  TT.isArch64Bit();    // DWARF64 requires 64-bit relocations.
 
   // Support DWARF64
   // 1: For ELF when requested.
   // 2: For XCOFF64: the AIX assembler will fill in debug section lengths
   //    according to the DWARF64 format for 64-bit assembly, so we must use
-  //    DWARF64 in the compiler too for 64-bit mode.
+  //    DWARF64 in the compiler for 64-bit mode on non-integrated-as mode.
   Dwarf64 &=
-      ((Asm->TM.Options.MCOptions.Dwarf64 || MMI->getModule()->isDwarf64()) &&
-       TT.isOSBinFormatELF()) ||
-      TT.isOSBinFormatXCOFF();
-
-  if (!Dwarf64 && TT.isArch64Bit() && TT.isOSBinFormatXCOFF())
-    report_fatal_error("XCOFF requires DWARF64 for 64-bit mode!");
+      ((TT.isOSBinFormatELF() ||
+        (TT.isOSBinFormatXCOFF() && UseIntegratedAs)) &&
+       (Asm->TM.Options.MCOptions.Dwarf64 || MMI->getModule()->isDwarf64())) ||
+      (TT.isOSBinFormatXCOFF() && !UseIntegratedAs);
+
+  if (!Dwarf64 && TT.isArch64Bit() && TT.isOSBinFormatXCOFF() &&
+      !UseIntegratedAs)
+    report_fatal_error(
+        "XCOFF requires DWARF64 for 64-bit mode on non-integrated-as mode!");
   
   UseRangesSection = !NoDwarfRangesSection && !TT.isNVPTX();
 
   // Use sections as references. Force for NVPTX.
   if (DwarfSectionsAsReferences == Default)
     UseSectionsAsReferences = TT.isNVPTX();
   else
     UseSectionsAsReferences = DwarfSectionsAsReferences == Enable;
 

llvm/test/DebugInfo/XCOFF/dwarf-format.ll

+; RUN: llc -mtriple powerpc64-ibm-aix-xcoff -filetype=obj %s -o - \
+; RUN:   | llvm-dwarfdump -debug-line - | FileCheck %s --check-prefixes=CHECK
+
+; RUN: llc -mtriple powerpc64-ibm-aix-xcoff -filetype=obj -dwarf64 %s -o - \
+; RUN:   | llvm-dwarfdump -debug-line - | FileCheck %s --check-prefixes=CHECK64
+
+; CHECK: file format aix5coff64-rs6000
+; CHECK: format: DWARF32
+
+; CHECK64: file format aix5coff64-rs6000
+; CHECK64: format: DWARF64
+
+source_filename = "1.c"
+target datalayout = "E-m:a-p:32:32-Fi32-i64:64-n32"
+
+@foo = global i32 0, align 4, !dbg !0
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!6, !7, !8, !9, !10}
+!llvm.ident = !{!11}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "foo", scope: !2, file: !3, line: 1, type: !5, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 17.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "1.c", directory: "llvm-project")
+!4 = !{!0}
+!5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!6 = !{i32 7, !"Dwarf Version", i32 3}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{i32 1, !"wchar_size", i32 2}
+!9 = !{i32 8, !"PIC Level", i32 2}
+!10 = !{i32 7, !"frame-pointer", i32 2}
+!11 = !{!"clang version 17.0.0"}