[DWARF] Fix mixing -g with DWARF .file directives

[probinson]

Summary

This combination was emitting the assembler source filename as file 1,
instead of the filename specified by the '.file 1' directive.

Fixes PR36636.

[dblaikie]

Seems OK - maybe could use some more comments explaining what is going on in enableGenDwarfForAssembly

[probinson]

Added more commentary. Now back to round 3 of getting the "file 0" patch in...

llvm/trunk/lib/MC/MCParser/AsmParser.cpp

private:
   void printMacroInstantiations();
   void printMessage(SMLoc Loc, SourceMgr::DiagKind Kind, const Twine &Msg,
                     SMRange Range = None) const {
     ArrayRef<SMRange> Ranges(Range);
     SrcMgr.PrintMessage(Loc, Kind, Msg, Ranges);
   }
   static void DiagHandler(const SMDiagnostic &Diag, void *Context);
 
+  /// Should we emit DWARF describing this assembler source?  (Returns false if
+  /// the source has .file directives, which means we don't want to generate
+  /// info describing the assembler source itself.)
+  bool enabledGenDwarfForAssembly();
+
   /// \brief Enter the specified file. This returns true on failure.
   bool enterIncludeFile(const std::string &Filename);
 
   /// \brief Process the specified file for the .incbin directive.
   /// This returns true on failure.
   bool processIncbinFile(const std::string &Filename, int64_t Skip = 0,
                          const MCExpr *Count = nullptr, SMLoc Loc = SMLoc());
 
if (ParentIncludeLoc != SMLoc()) {
       jumpToLoc(ParentIncludeLoc);
       return Lex();
     }
   }
 
   return *tok;
 }
 
+bool AsmParser::enabledGenDwarfForAssembly() {
+  // Check whether the user specified -g.
+  if (!getContext().getGenDwarfForAssembly())
+    return false;
+  // If we haven't encountered any .file directives (which would imply that
+  // the assembler source was produced with debug info already) then emit one
+  // describing the assembler source file itself.
+  if (getContext().getGenDwarfFileNumber() == 0)
+    getContext().setGenDwarfFileNumber(getStreamer().EmitDwarfFileDirective(
+        0, StringRef(), getContext().getMainFileName()));
+  return true;
+}
+
 bool AsmParser::Run(bool NoInitialTextSection, bool NoFinalize) {
   // Create the initial section, if requested.
   if (!NoInitialTextSection)
     Out.InitSections(false);
 
   // Prime the lexer.
   Lex();
 
   HadError = false;
   AsmCond StartingCondState = TheCondState;
   SmallVector<AsmRewrite, 4> AsmStrRewrites;
 
   // If we are generating dwarf for assembly source files save the initial text
-  // section and generate a .file directive.
+  // section.  (Don't use enabledGenDwarfForAssembly() here, as we aren't
+  // emitting any actual debug info yet and haven't had a chance to parse any
+  // embedded .file directives.)
   if (getContext().getGenDwarfForAssembly()) {
     MCSection *Sec = getStreamer().getCurrentSectionOnly();
     if (!Sec->getBeginSymbol()) {
       MCSymbol *SectionStartSym = getContext().createTempSymbol();
       getStreamer().EmitLabel(SectionStartSym);
       Sec->setBeginSymbol(SectionStartSym);
     }
     bool InsertResult = getContext().addGenDwarfSection(Sec);
     assert(InsertResult && ".text section should not have debug info yet");
     (void)InsertResult;
-    getContext().setGenDwarfFileNumber(getStreamer().EmitDwarfFileDirective(
-        0, StringRef(), getContext().getMainFileName()));
   }
 
   // While we have input, parse each statement.
   while (Lexer.isNot(AsmToken::Eof)) {
     ParseStatementInfo Info(&AsmStrRewrites);
     if (!parseStatement(Info, nullptr))
       continue;
 
case AsmToken::Colon: {
     }
 
     // Emit the label.
     if (!getTargetParser().isParsingInlineAsm())
       Out.EmitLabel(Sym, IDLoc);
 
     // If we are generating dwarf for assembly source files then gather the
     // info to make a dwarf label entry for this label if needed.
-    if (getContext().getGenDwarfForAssembly())
+    if (enabledGenDwarfForAssembly())
       MCGenDwarfLabelEntry::Make(Sym, &getStreamer(), getSourceManager(),
                                  IDLoc);
 
     getTargetParser().onLabelParsed(Sym);
 
     return false;
   }
 
bool AsmParser::parseStatement(ParseStatementInfo &Info,
   }
 
   // Fail even if ParseInstruction erroneously returns false.
   if (hasPendingError() || ParseHadError)
     return true;
 
   // If we are generating dwarf for the current section then generate a .loc
   // directive for the instruction.
-  if (!ParseHadError && getContext().getGenDwarfForAssembly() &&
+  if (!ParseHadError && enabledGenDwarfForAssembly() &&
       getContext().getGenDwarfSectionSyms().count(
           getStreamer().getCurrentSectionOnly())) {
     unsigned Line;
     if (ActiveMacros.empty())
       Line = SrcMgr.FindLineNumber(IDLoc, CurBuffer);
     else
       Line = SrcMgr.FindLineNumber(ActiveMacros.front()->InstantiationLoc,
                                    ActiveMacros.front()->ExitBuffer);
else {
     }
     if (HasSource) {
       char *SourceBuf = static_cast<char *>(Ctx.allocate(SourceString.size()));
       memcpy(SourceBuf, SourceString.data(), SourceString.size());
       Source = StringRef(SourceBuf, SourceString.size());
     }
     // If there is -g option as well as debug info from directive file,
     // we turn off -g option, directly use the existing debug info instead.
-    if (getContext().getGenDwarfForAssembly())
-      getContext().setGenDwarfForAssembly(false);
-    else {
-      Expected<unsigned> FileNumOrErr = getStreamer().tryEmitDwarfFileDirective(
-          FileNumber, Directory, Filename, CKMem, Source);
-      if (!FileNumOrErr)
-        return Error(DirectiveLoc, toString(FileNumOrErr.takeError()));
-      FileNumber = FileNumOrErr.get();
-    }
-  }
 
   return false;
 }
 
 /// parseDirectiveLine
 /// ::= .line [number]
 bool AsmParser::parseDirectiveLine() {
   int64_t LineNumber;

llvm/trunk/test/MC/AsmParser/directive_file-2.s

-// RUN: llvm-mc -triple i386-unknown-unknown %s | FileCheck %s
+// RUN: llvm-mc -g -triple i386-unknown-unknown %s | FileCheck %s
 // Test for Bug 11740
 // This testcase has two directive files,
 // when compiled with -g, this testcase will not report error,
 // but keep the debug info existing in the assembly file.
 
         .file "hello"
         .file 1 "world"
 
 // CHECK: .file "hello"
 // CHECK: .file 1 "world"