SourceMgr: make valid buffer IDs start from one

Use 0 for the invalid buffer instead of -1/~0 and switch to unsigned
representation to enable more idiomatic usage.

Also introduce a trivial SourceMgr::getMainFileID() instead of hard-coding 0/1
to identify the main file.

llvm-svn: 212398

2 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/TableGen/TGLexer.cpp b/llvm/lib/TableGen/TGLexer.cpp
index 1ec2eea67d9..1a876232e27 100644
--- a/llvm/lib/TableGen/TGLexer.cpp
+++ b/llvm/lib/TableGen/TGLexer.cpp
@@ -27,7 +27,7 @@
 using namespace llvm;
 
 TGLexer::TGLexer(SourceMgr &SM) : SrcMgr(SM) {
-  CurBuffer = 0;
+  CurBuffer = SrcMgr.getMainFileID();
   CurBuf = SrcMgr.getMemoryBuffer(CurBuffer);
   CurPtr = CurBuf->getBufferStart();
   TokStart = nullptr;
@@ -304,7 +304,7 @@ bool TGLexer::LexInclude() {
   
   CurBuffer = SrcMgr.AddIncludeFile(Filename, SMLoc::getFromPointer(CurPtr),
                                     IncludedFile);
-  if (CurBuffer == -1) {
+  if (!CurBuffer) {
     PrintError(getLoc(), "Could not find include file '" + Filename + "'");
     return true;
   }
diff --git a/llvm/lib/TableGen/TGLexer.h b/llvm/lib/TableGen/TGLexer.h
index 1e599f84b06..cd1bb0bbe78 100644
--- a/llvm/lib/TableGen/TGLexer.h
+++ b/llvm/lib/TableGen/TGLexer.h
@@ -73,7 +73,7 @@ class TGLexer {
 
   /// CurBuffer - This is the current buffer index we're lexing from as managed
   /// by the SourceMgr object.
-  int CurBuffer;
+  unsigned CurBuffer;
 
 public:
   typedef std::map<std::string, SMLoc> DependenciesMapTy;