[TableGen] Use assert instead of PrintFatalError in TGLexer. NFC. (llvm#122303)

Do not use the PrintFatalError diagnostic machinery for conditions that
can never happen with any input.

Author: jayfoad

llvm/lib/TableGen/TGLexer.cpp

@@ -235,8 +235,7 @@ tgtok::TokKind TGLexer::LexToken(bool FileOrLineStart) {
     return tgtok::dot;
 
   case '\r':
-    PrintFatalError("getNextChar() must never return '\r'");
-    return tgtok::Error;
+    llvm_unreachable("getNextChar() must never return '\r'");
 
   case ' ':
   case '\t':
@@ -664,11 +663,10 @@ bool TGLexer::prepExitInclude(bool IncludeStackMustBeEmpty) {
   PrepIncludeStack.pop_back();
 
   if (IncludeStackMustBeEmpty) {
-    if (!PrepIncludeStack.empty())
-      PrintFatalError("preprocessor include stack is not empty");
+    assert(PrepIncludeStack.empty() &&
+           "preprocessor include stack is not empty");
   } else {
-    if (PrepIncludeStack.empty())
-      PrintFatalError("preprocessor include stack is empty");
+    assert(!PrepIncludeStack.empty() && "preprocessor include stack is empty");
   }
 
   return true;
@@ -718,27 +716,25 @@ tgtok::TokKind TGLexer::prepIsDirective() const {
   return tgtok::Error;
 }
 
-bool TGLexer::prepEatPreprocessorDirective(tgtok::TokKind Kind) {
+void TGLexer::prepEatPreprocessorDirective(tgtok::TokKind Kind) {
   TokStart = CurPtr;
 
-  for (const auto [PKind, PWord] : PreprocessorDirs)
+  for (const auto [PKind, PWord] : PreprocessorDirs) {
     if (PKind == Kind) {
       // Advance CurPtr to the end of the preprocessing word.
       CurPtr += PWord.size();
-      return true;
+      return;
     }
+  }
 
-  PrintFatalError("unsupported preprocessing token in "
-                  "prepEatPreprocessorDirective()");
-  return false;
+  llvm_unreachable(
+      "unsupported preprocessing token in prepEatPreprocessorDirective()");
 }
 
 tgtok::TokKind TGLexer::lexPreprocessor(tgtok::TokKind Kind,
                                         bool ReturnNextLiveToken) {
   // We must be looking at a preprocessing directive.  Eat it!
-  if (!prepEatPreprocessorDirective(Kind))
-    PrintFatalError("lexPreprocessor() called for unknown "
-                    "preprocessor directive");
+  prepEatPreprocessorDirective(Kind);
 
   if (Kind == tgtok::Ifdef || Kind == tgtok::Ifndef) {
     StringRef MacroName = prepLexMacroName();
@@ -820,11 +816,9 @@ tgtok::TokKind TGLexer::lexPreprocessor(tgtok::TokKind Kind,
 
     auto &IfdefOrElseEntry = PrepIncludeStack.back().back();
 
-    if (IfdefOrElseEntry.Kind != tgtok::Ifdef &&
-        IfdefOrElseEntry.Kind != tgtok::Else) {
-      PrintFatalError("invalid preprocessor control on the stack");
-      return tgtok::Error;
-    }
+    assert((IfdefOrElseEntry.Kind == tgtok::Ifdef ||
+            IfdefOrElseEntry.Kind == tgtok::Else) &&
+           "invalid preprocessor control on the stack");
 
     if (!prepSkipDirectiveEnd())
       return ReturnError(CurPtr, "only comments are supported after #endif");
@@ -852,21 +846,17 @@ tgtok::TokKind TGLexer::lexPreprocessor(tgtok::TokKind Kind,
       return ReturnError(CurPtr,
                          "only comments are supported after #define NAME");
 
-    if (!ReturnNextLiveToken) {
-      PrintFatalError("#define must be ignored during the lines skipping");
-      return tgtok::Error;
-    }
+    assert(ReturnNextLiveToken &&
+           "#define must be ignored during the lines skipping");
 
     return LexToken();
   }
 
-  PrintFatalError("preprocessing directive is not supported");
-  return tgtok::Error;
+  llvm_unreachable("preprocessing directive is not supported");
 }
 
 bool TGLexer::prepSkipRegion(bool MustNeverBeFalse) {
-  if (!MustNeverBeFalse)
-    PrintFatalError("invalid recursion.");
+  assert(MustNeverBeFalse && "invalid recursion.");
 
   do {
     // Skip all symbols to the line end.
@@ -902,20 +892,17 @@ bool TGLexer::prepSkipRegion(bool MustNeverBeFalse) {
     if (ProcessedKind == tgtok::Error)
       return false;
 
-    if (Kind != ProcessedKind)
-      PrintFatalError("prepIsDirective() and lexPreprocessor() "
-                      "returned different token kinds");
+    assert(Kind == ProcessedKind && "prepIsDirective() and lexPreprocessor() "
+                                    "returned different token kinds");
 
     // If this preprocessing directive enables tokens processing,
     // then return to the lexPreprocessor() and get to the next token.
     // We can move from line-skipping mode to processing tokens only
     // due to #else or #endif.
     if (prepIsProcessingEnabled()) {
-      if (Kind != tgtok::Else && Kind != tgtok::Endif) {
-        PrintFatalError("tokens processing was enabled by an unexpected "
-                        "preprocessing directive");
-        return false;
-      }
+      assert((Kind == tgtok::Else || Kind == tgtok::Endif) &&
+             "tokens processing was enabled by an unexpected preprocessing "
+             "directive");
 
       return true;
     }
@@ -1053,10 +1040,6 @@ bool TGLexer::prepIsProcessingEnabled() {
 }
 
 void TGLexer::prepReportPreprocessorStackError() {
-  if (PrepIncludeStack.back().empty())
-    PrintFatalError("prepReportPreprocessorStackError() called with "
-                    "empty control stack");
-
   auto &PrepControl = PrepIncludeStack.back().back();
   PrintError(CurBuf.end(), "reached EOF without matching #endif");
   PrintError(PrepControl.SrcPos, "the latest preprocessor control is here");

llvm/lib/TableGen/TGLexer.h

@@ -347,14 +347,13 @@ class TGLexer {
   tgtok::TokKind prepIsDirective() const;
 
   // Given a preprocessing token kind, adjusts CurPtr to the end
-  // of the preprocessing directive word.  Returns true, unless
-  // an unsupported token kind is passed in.
+  // of the preprocessing directive word.
   //
   // We use look-ahead prepIsDirective() and prepEatPreprocessorDirective()
   // to avoid adjusting CurPtr before we are sure that '#' is followed
   // by a preprocessing directive.  If it is not, then we fall back to
   // tgtok::paste interpretation of '#'.
-  bool prepEatPreprocessorDirective(tgtok::TokKind Kind);
+  void prepEatPreprocessorDirective(tgtok::TokKind Kind);
 
   // The main "exit" point from the token parsing to preprocessor.
   //