[llvm] [TableGen] Implement a preprocessor (PR #120113)

[Ivan Kosarev via llvm-commits]

================
@@ -77,12 +77,65 @@ static cl::opt<bool> NoWarnOnUnusedTemplateArgs(
     "no-warn-on-unused-template-args",
     cl::desc("Disable unused template argument warnings."));
 
+static cl::opt<bool> Preprocess("E", cl::desc("Write preprocessed output"));
+
 static int reportError(const char *ProgName, Twine Msg) {
   errs() << ProgName << ": " << Msg;
   errs().flush();
   return 1;
 }
 
+/// Encapsulate file, line and column numbers from SourceMgr.
+struct SMCoords {
+  unsigned Buf = 0;
+  unsigned Line = 0;
+  unsigned Col = 0;
+  SMCoords() = default;
+  SMCoords(const SourceMgr &Mgr, SMLoc Loc) {
+    Buf = Mgr.FindBufferContainingLoc(Loc);
+    // TODO: SourceMgr::getLineAndColumn is not a fast method. Find a better way
+    // to do this. For example we don't need the column number for every token,
+    // only the first token on each output line.
+    std::tie(Line, Col) = Mgr.getLineAndColumn(Loc, Buf);
+  }
+};
+
+/// Create preprocessed output for `-E` option.
+static int preprocessInput(raw_ostream &OS) {
+  TGLexer Lex(SrcMgr, MacroNames);
+  SMCoords Last;
+  bool Any = false;
----------------
kosarev wrote:

```suggestion
  bool EmptyOutput = true;
```

https://github.com/llvm/llvm-project/pull/120113