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

1 files changed, 7 insertions, 11 deletions

diff --git a/llvm/lib/MC/MCParser/AsmParser.cpp b/llvm/lib/MC/MCParser/AsmParser.cpp
index f3cf8f2d1c7..fbbd4365bcb 100644
--- a/llvm/lib/MC/MCParser/AsmParser.cpp
+++ b/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");
   }