DebugInfo: Improve reuse of file table entries in asm debug info

The previous deduping strategy was woefully inadequate - it only
considered the most recent file used and avoided emitting a duplicate in
that case - never considering the a/b/a scenario.

It was also lacking when it came to directory paths as the previous
filename would never match the current if the filename had been split
into file and directory components.

This change builds caching functionality into the line table at the
lowest level in an optional form (a file number of 0 indicates that one
should be chosen and returned) and will eventually be reused by the
normal source level debugging DWARF emission.

llvm-svn: 204027

llvm/include/llvm/MC/MCContext.h

@@ -371,7 +371,9 @@ namespace llvm {
     bool getGenDwarfForAssembly() { return GenDwarfForAssembly; }
     void setGenDwarfForAssembly(bool Value) { GenDwarfForAssembly = Value; }
     unsigned getGenDwarfFileNumber() { return GenDwarfFileNumber; }
-    unsigned nextGenDwarfFileNumber() { return ++GenDwarfFileNumber; }
+    void setGenDwarfFileNumber(unsigned FileNumber) {
+      GenDwarfFileNumber = FileNumber;
+    }
     const MCSection *getGenDwarfSection() { return GenDwarfSection; }
     void setGenDwarfSection(const MCSection *Sec) { GenDwarfSection = Sec; }
     MCSymbol *getGenDwarfSectionStartSym() { return GenDwarfSectionStartSym; }

llvm/include/llvm/MC/MCDwarf.h

@@ -16,6 +16,7 @@
 #define LLVM_MC_MCDWARF_H
 
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Dwarf.h"
@@ -179,8 +180,9 @@ struct MCDwarfLineTableHeader {
   MCSymbol *Label;
   SmallVector<std::string, 3> MCDwarfDirs;
   SmallVector<MCDwarfFile, 3> MCDwarfFiles;
+  StringMap<unsigned> SourceIdMap;
   MCDwarfLineTableHeader() : Label(nullptr) {}
-  unsigned getFile(StringRef Directory, StringRef FileName, unsigned FileNumber);
+  unsigned getFile(StringRef Directory, StringRef FileName, unsigned FileNumber = 0);
   std::pair<MCSymbol *, MCSymbol *> Emit(MCStreamer *MCOS) const;
 };
 
@@ -195,7 +197,7 @@ public:
   // This emits the Dwarf file and the line tables for a given Compile Unit.
   const MCSymbol *EmitCU(MCStreamer *MCOS) const;
 
-  unsigned getFile(StringRef Directory, StringRef FileName, unsigned FileNumber);
+  unsigned getFile(StringRef Directory, StringRef FileName, unsigned FileNumber = 0);
 
   MCSymbol *getLabel() const {
     return Header.Label;

llvm/include/llvm/MC/MCStreamer.h

@@ -628,8 +628,9 @@ public:
   /// EmitDwarfFileDirective - Associate a filename with a specified logical
   /// file number.  This implements the DWARF2 '.file 4 "foo.c"' assembler
   /// directive.
-  virtual bool EmitDwarfFileDirective(unsigned FileNo, StringRef Directory,
-                                      StringRef Filename, unsigned CUID = 0);
+  virtual unsigned EmitDwarfFileDirective(unsigned FileNo, StringRef Directory,
+                                          StringRef Filename,
+                                          unsigned CUID = 0);
 
   /// EmitDwarfLocDirective - This implements the DWARF2
   // '.loc fileno lineno ...' assembler directive.

llvm/lib/MC/MCAsmStreamer.cpp

@@ -197,8 +197,9 @@ public:
                          unsigned char Value = 0) override;
 
   void EmitFileDirective(StringRef Filename) override;
-  bool EmitDwarfFileDirective(unsigned FileNo, StringRef Directory,
-                              StringRef Filename, unsigned CUID = 0) override;
+  unsigned EmitDwarfFileDirective(unsigned FileNo, StringRef Directory,
+                                  StringRef Filename,
+                                  unsigned CUID = 0) override;
   void EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                              unsigned Column, unsigned Flags,
                              unsigned Isa, unsigned Discriminator,
@@ -843,8 +844,10 @@ void MCAsmStreamer::EmitFileDirective(StringRef Filename) {
   EmitEOL();
 }
 
-bool MCAsmStreamer::EmitDwarfFileDirective(unsigned FileNo, StringRef Directory,
-                                           StringRef Filename, unsigned CUID) {
+unsigned MCAsmStreamer::EmitDwarfFileDirective(unsigned FileNo,
+                                               StringRef Directory,
+                                               StringRef Filename,
+                                               unsigned CUID) {
   if (!UseDwarfDirectory && !Directory.empty()) {
     if (sys::path::is_absolute(Filename))
       return EmitDwarfFileDirective(FileNo, "", Filename, CUID);

llvm/lib/MC/MCDwarf.cpp

@@ -336,7 +336,18 @@ unsigned MCDwarfLineTable::getFile(StringRef Directory, StringRef FileName,
   return Header.getFile(Directory, FileName, FileNumber);
 }
 
-unsigned MCDwarfLineTableHeader::getFile(StringRef Directory, StringRef FileName, unsigned FileNumber) {
+unsigned MCDwarfLineTableHeader::getFile(StringRef Directory,
+                                         StringRef FileName,
+                                         unsigned FileNumber) {
+  if (FileNumber == 0) {
+    FileNumber = SourceIdMap.size() + 1;
+    assert((MCDwarfFiles.empty() || FileNumber == MCDwarfFiles.size()) &&
+           "Don't mix autonumbered and explicit numbered line table usage");
+    StringMapEntry<unsigned> &Ent = SourceIdMap.GetOrCreateValue(
+        (Directory + Twine('\0') + FileName).str(), FileNumber);
+    if (Ent.getValue() != FileNumber)
+      return Ent.getValue();
+  }
   // Make space for this FileNumber in the MCDwarfFiles vector if needed.
   MCDwarfFiles.resize(FileNumber + 1);
 

llvm/lib/MC/MCNullStreamer.cpp

@@ -85,10 +85,10 @@ namespace {
                            unsigned char Value = 0) override { return false; }
 
     void EmitFileDirective(StringRef Filename) override {}
-    bool EmitDwarfFileDirective(unsigned FileNo, StringRef Directory,
+    unsigned EmitDwarfFileDirective(unsigned FileNo, StringRef Directory,
                                     StringRef Filename,
                                     unsigned CUID = 0) override {
-      return false;
+      return 0;
     }
     void EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
                                unsigned Column, unsigned Flags,

llvm/lib/MC/MCParser/AsmParser.cpp

@@ -640,9 +640,8 @@ bool AsmParser::Run(bool NoInitialTextSection, bool NoFinalize) {
     MCSymbol *SectionStartSym = getContext().CreateTempSymbol();
     getStreamer().EmitLabel(SectionStartSym);
     getContext().setGenDwarfSectionStartSym(SectionStartSym);
-    getStreamer().EmitDwarfFileDirective(getContext().nextGenDwarfFileNumber(),
-                                         StringRef(),
-                                         getContext().getMainFileName());
+    getContext().setGenDwarfFileNumber(getStreamer().EmitDwarfFileDirective(
+        0, StringRef(), getContext().getMainFileName()));
   }
 
   // While we have input, parse each statement.
@@ -1589,14 +1588,10 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info) {
     // If we previously parsed a cpp hash file line comment then make sure the
     // current Dwarf File is for the CppHashFilename if not then emit the
     // Dwarf File table for it and adjust the line number for the .loc.
-    const SmallVectorImpl<MCDwarfFile> &MCDwarfFiles =
-        getContext().getMCDwarfFiles();
     if (CppHashFilename.size() != 0) {
-      if (MCDwarfFiles[getContext().getGenDwarfFileNumber()].Name !=
-          CppHashFilename)
-        getStreamer().EmitDwarfFileDirective(
-            getContext().nextGenDwarfFileNumber(), StringRef(),
-            CppHashFilename);
+      unsigned FileNumber = getStreamer().EmitDwarfFileDirective(
+          0, StringRef(), CppHashFilename);
+      getContext().setGenDwarfFileNumber(FileNumber);
 
       // Since SrcMgr.FindLineNumber() is slow and messes up the SourceMgr's
       // cache with the different Loc from the call above we save the last
@@ -2762,7 +2757,8 @@ bool AsmParser::parseDirectiveFile(SMLoc DirectiveLoc) {
             "input can't have .file dwarf directives when -g is "
             "used to generate dwarf debug info for assembly code");
 
-    if (getStreamer().EmitDwarfFileDirective(FileNumber, Directory, Filename))
+    if (getStreamer().EmitDwarfFileDirective(FileNumber, Directory, Filename) ==
+        0)
       Error(FileNumberLoc, "file number already allocated");
   }
 

llvm/lib/MC/MCStreamer.cpp

@@ -174,10 +174,10 @@ void MCStreamer::EmitZeros(uint64_t NumBytes) {
   EmitFill(NumBytes, 0);
 }
 
-bool MCStreamer::EmitDwarfFileDirective(unsigned FileNo,
+unsigned MCStreamer::EmitDwarfFileDirective(unsigned FileNo,
                                             StringRef Directory,
                                             StringRef Filename, unsigned CUID) {
-  return getContext().GetDwarfFile(Directory, Filename, FileNo, CUID) == 0;
+  return getContext().GetDwarfFile(Directory, Filename, FileNo, CUID);
 }
 
 void MCStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,

llvm/test/MC/MachO/gen-dwarf-cpp.s

@@ -4,6 +4,7 @@
 # 100 "t.s" 1
 .globl _bar
 _bar:
+	movl	$0, %eax
 # 3 "inc/g.s"
 	movl	$0, %eax
 L1:	leave