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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204027 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 10 insertions, 5 deletions

diff --git a/include/llvm/MC/MCContext.h b/include/llvm/MC/MCContext.h
index b3df225210..b51a5a589f 100644
--- a/include/llvm/MC/MCContext.h
+++ b/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; }
diff --git a/include/llvm/MC/MCDwarf.h b/include/llvm/MC/MCDwarf.h
index abd2f7a2d6..3b60450614 100644
--- a/include/llvm/MC/MCDwarf.h
+++ b/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;
diff --git a/include/llvm/MC/MCStreamer.h b/include/llvm/MC/MCStreamer.h
index 18f0e772ef..fc7a3b8648 100644
--- a/include/llvm/MC/MCStreamer.h
+++ b/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.