[DEBUGINFO] Add option that allows to disable emission of flags in .loc directives.

[ABataev]

Summary

Some targets do not support extended format of .loc directive and
support only simple format: .loc <FileID> <Line> <Column>. Patch adds
MCAsmInfo flag and option that allows emit .loc directive without
additional flags.

[echristo]

Sure. LGTM for now.

include/llvm/MC/MCAsmInfo.h

protected:
   /// True if dwarf register numbers are printed instead of symbolic register
   /// names in .cfi_* directives.  Defaults to false.
   bool DwarfRegNumForCFI = false;
 
   /// True if target uses parens to indicate the symbol variant instead of @.
   /// For example, foo(plt) instead of foo@plt.  Defaults to false.
   bool UseParensForSymbolVariant = false;
 
+  /// True if the target supports flags in ".loc" directive, false if only
+  /// location is allowed.
+  bool SupportsExtendedDwarfLocDirective = true;
+
   //===--- Prologue State ----------------------------------------------===//
 
   std::vector<MCCFIInstruction> InitialFrameState;
 
   //===--- Integrated Assembler Information ----------------------------===//
 
   /// Should we use the integrated assembler?
   /// The integrated assembler should be enabled by default (by the
public:
 
   bool doesDwarfUseRelocationsAcrossSections() const {
     return DwarfUsesRelocationsAcrossSections;
   }
 
   bool doDwarfFDESymbolsUseAbsDiff() const { return DwarfFDESymbolsUseAbsDiff; }
   bool useDwarfRegNumForCFI() const { return DwarfRegNumForCFI; }
   bool useParensForSymbolVariant() const { return UseParensForSymbolVariant; }
+  bool supportsExtendedDwarfLocDirective() const {
+    return SupportsExtendedDwarfLocDirective;
+  }
 
   void addInitialFrameState(const MCCFIInstruction &Inst) {
     InitialFrameState.push_back(Inst);
   }
 
   const std::vector<MCCFIInstruction> &getInitialFrameState() const {
     return InitialFrameState;
   }

lib/MC/MCAsmInfo.cpp

 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCStreamer.h"
+#include "llvm/Support/CommandLine.h"
 
 using namespace llvm;
 
+enum DefaultOnOff { Default, Enable, Disable };
+static cl::opt<DefaultOnOff> DwarfExtendedLoc(
+    "dwarf-extended-loc", cl::Hidden,
+    cl::desc("Disable emission of the extended flags in .loc directives."),
+    cl::values(clEnumVal(Default, "Default for platform"),
+               clEnumVal(Enable, "Enabled"), clEnumVal(Disable, "Disabled")),
+    cl::init(Default));
+
 MCAsmInfo::MCAsmInfo() {
   SeparatorString = ";";
   CommentString = "#";
   LabelSuffix = ":";
   PrivateGlobalPrefix = "L";
   PrivateLabelPrefix = PrivateGlobalPrefix;
   LinkerPrivateGlobalPrefix = "";
   InlineAsmStart = "APP";
   InlineAsmEnd = "NO_APP";
   Code16Directive = ".code16";
   Code32Directive = ".code32";
   Code64Directive = ".code64";
   ZeroDirective = "\t.zero\t";
   AsciiDirective = "\t.ascii\t";
   AscizDirective = "\t.asciz\t";
   Data8bitsDirective = "\t.byte\t";
   Data16bitsDirective = "\t.short\t";
   Data32bitsDirective = "\t.long\t";
   Data64bitsDirective = "\t.quad\t";
   GlobalDirective = "\t.globl\t";
   WeakDirective = "\t.weak\t";
+  if (DwarfExtendedLoc != Default)
+    SupportsExtendedDwarfLocDirective = DwarfExtendedLoc == Enable;
 
   // FIXME: Clang's logic should be synced with the logic used to initialize
   //        this member and the two implementations should be merged.
   // For reference:
   // - Solaris always enables the integrated assembler by default
   //   - SparcELFMCAsmInfo and X86ELFMCAsmInfo are handling this case
   // - Windows always enables the integrated assembler by default
   //   - MCAsmInfoCOFF is handling this case, should it be MCAsmInfoMicrosoft?

lib/MC/MCAsmStreamer.cpp

 }
 
 void MCAsmStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                                           unsigned Column, unsigned Flags,
                                           unsigned Isa,
                                           unsigned Discriminator,
                                           StringRef FileName) {
   OS << "\t.loc\t" << FileNo << " " << Line << " " << Column;
+  if (MAI->supportsExtendedDwarfLocDirective()) {
     if (Flags & DWARF2_FLAG_BASIC_BLOCK)
       OS << " basic_block";
     if (Flags & DWARF2_FLAG_PROLOGUE_END)
       OS << " prologue_end";
     if (Flags & DWARF2_FLAG_EPILOGUE_BEGIN)
       OS << " epilogue_begin";
 
     unsigned OldFlags = getContext().getCurrentDwarfLoc().getFlags();
     if ((Flags & DWARF2_FLAG_IS_STMT) != (OldFlags & DWARF2_FLAG_IS_STMT)) {
       OS << " is_stmt ";
 
       if (Flags & DWARF2_FLAG_IS_STMT)
         OS << "1";
       else
         OS << "0";
     }
 
     if (Isa)
       OS << " isa " << Isa;
     if (Discriminator)
       OS << " discriminator " << Discriminator;
+  }
 
   if (IsVerboseAsm) {
     OS.PadToColumn(MAI->getCommentColumn());
     OS << MAI->getCommentString() << ' ' << FileName << ':'
        << Line << ':' << Column;
   }
   EmitEOL();
   this->MCStreamer::EmitDwarfLocDirective(FileNo, Line, Column, Flags,

test/DebugInfo/Generic/extended-loc-directive.ll

+; RUN: llc -filetype=asm -asm-verbose=0 -O0 -dwarf-extended-loc=Enable < %s | FileCheck %s --check-prefix ENABLED --check-prefix CHECK
+; RUN: llc -filetype=asm -asm-verbose=0 -O0 -dwarf-extended-loc=Disable < %s | FileCheck %s --check-prefix DISABLED --check-prefix CHECK
+
+; Check that the assembly output properly handles is_stmt changes. And since
+; we're testing anyway, check the integrated assembler too.
+
+; Generated with clang from multiline.c:
+; void f1();
+; void f2() {
+;   f1(); f1(); f1();
+;   f1(); f1(); f1();
+; }
+
+
+; CHECK: .loc 1 2 0{{$}}
+; CHECK-NOT: .loc{{ }}
+; ENABLED: .loc 1 3 3 prologue_end{{$}}
+; DISABLED: .loc 1 3 3{{$}}
+; CHECK-NOT: .loc
+; ENABLED: .loc 1 3 9 is_stmt 0{{$}}
+; DISABLED: .loc 1 3 9{{$}}
+; CHECK-NOT: .loc
+; CHECK: .loc 1 3 15{{$}}
+; CHECK-NOT: .loc
+; ENABLED: .loc 1 4 3 is_stmt 1{{$}}
+; DISABLED: .loc 1 4 3{{$}}
+; CHECK-NOT: .loc
+; ENABLED: .loc 1 4 9 is_stmt 0{{$}}
+; DISABLED: .loc 1 4 9{{$}}
+; CHECK-NOT: .loc
+; CHECK: .loc 1 4 15{{$}}
+; CHECK-NOT: .loc
+; ENABLED: .loc 1 5 1 is_stmt 1{{$}}
+; DISABLED: .loc 1 5 1{{$}}
+
+; Function Attrs: nounwind uwtable
+define void @f2() #0 !dbg !4 {
+entry:
+  call void (...) @f1(), !dbg !11
+  call void (...) @f1(), !dbg !12
+  call void (...) @f1(), !dbg !13
+  call void (...) @f1(), !dbg !14
+  call void (...) @f1(), !dbg !15
+  call void (...) @f1(), !dbg !16
+  ret void, !dbg !17
+}
+
+declare void @f1(...) #1
+
+attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!8, !9}
+!llvm.ident = !{!10}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang version 3.6.0 (trunk 225000) (llvm/trunk 224999)", isOptimized: false, emissionKind: FullDebug, file: !1, enums: !2, retainedTypes: !2, globals: !2, imports: !2)
+!1 = !DIFile(filename: "multiline.c", directory: "/tmp/dbginfo")
+!2 = !{}
+!4 = distinct !DISubprogram(name: "f2", line: 2, isLocal: false, isDefinition: true, isOptimized: false, unit: !0, scopeLine: 2, file: !1, scope: !5, type: !6, variables: !2)
+!5 = !DIFile(filename: "multiline.c", directory: "/tmp/dbginfo")
+!6 = !DISubroutineType(types: !7)
+!7 = !{null}
+!8 = !{i32 2, !"Dwarf Version", i32 4}
+!9 = !{i32 2, !"Debug Info Version", i32 3}
+!10 = !{!"clang version 3.6.0 (trunk 225000) (llvm/trunk 224999)"}
+!11 = !DILocation(line: 3, column: 3, scope: !4)
+!12 = !DILocation(line: 3, column: 9, scope: !4)
+!13 = !DILocation(line: 3, column: 15, scope: !4)
+!14 = !DILocation(line: 4, column: 3, scope: !4)
+!15 = !DILocation(line: 4, column: 9, scope: !4)
+!16 = !DILocation(line: 4, column: 15, scope: !4)
+!17 = !DILocation(line: 5, column: 1, scope: !4)