TableGen: support #ifndef in addition to #ifdef

[t.p.northover]

Summary

TableGen's preprocessor currently only supports #ifdef, but we have a situation where #ifndef would be more convenient. So this patch adds support.

[nhaehnle]

LGTM

[t.p.northover]

Thanks for the quick review Nicolai. Committed as r360670.

llvm/lib/TableGen/TGLexer.h

enum TokKind {
     // bits given.
     BinaryIntVal,
 
     // String valued tokens.
     Id, StrVal, VarName, CodeFragment,
 
     // Preprocessing tokens for internal usage by the lexer.
     // They are never returned as a result of Lex().
-    Ifdef, Else, Endif, Define
+    Ifdef, Ifndef, Else, Endif, Define
   };
 }
 
 /// TGLexer - TableGen Lexer class.
 class TGLexer {
   SourceMgr &SrcMgr;
 
   const char *CurPtr;

llvm/lib/TableGen/TGLexer.cpp

 namespace {
 // A list of supported preprocessing directives with their
 // internal token kinds and names.
 struct {
   tgtok::TokKind Kind;
   const char *Word;
 } PreprocessorDirs[] = {
   { tgtok::Ifdef, "ifdef" },
+  { tgtok::Ifndef, "ifndef" },
   { tgtok::Else, "else" },
   { tgtok::Endif, "endif" },
   { tgtok::Define, "define" }
 };
 } // end anonymous namespace
 
 TGLexer::TGLexer(SourceMgr &SM, ArrayRef<std::string> Macros) : SrcMgr(SM) {
   CurBuffer = SrcMgr.getMainFileID();

 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");
 
-  if (Kind == tgtok::Ifdef) {
+  if (Kind == tgtok::Ifdef || Kind == tgtok::Ifndef) {
     StringRef MacroName = prepLexMacroName();
+    StringRef IfTokName = Kind == tgtok::Ifdef ? "#ifdef" : "#ifndef";
     if (MacroName.empty())
-      return ReturnError(TokStart, "Expected macro name after #ifdef");
+      return ReturnError(TokStart, "Expected macro name after " + IfTokName);
 
     bool MacroIsDefined = DefinedMacros.count(MacroName) != 0;
 
+    // Canonicalize ifndef to ifdef equivalent
+    if (Kind == tgtok::Ifndef) {
+      MacroIsDefined = !MacroIsDefined;
+      Kind = tgtok::Ifdef;
+    }
+
     // Regardless of whether we are processing tokens or not,
     // we put the #ifdef control on stack.
     PrepIncludeStack.back()->push_back(
         {Kind, MacroIsDefined, SMLoc::getFromPointer(TokStart)});
 
     if (!prepSkipDirectiveEnd())
-      return ReturnError(CurPtr,
-                         "Only comments are supported after #ifdef NAME");
+      return ReturnError(CurPtr, "Only comments are supported after " +
+                                     IfTokName + " NAME");
 
     // If we were not processing tokens before this #ifdef,
     // then just return back to the lines skipping code.
     if (!ReturnNextLiveToken)
       return Kind;
 
     // If we were processing tokens before this #ifdef,
     // and the macro is defined, then just return the next token.
     if (MacroIsDefined)
       return LexToken();
 
     // We were processing tokens before this #ifdef, and the macro
     // is not defined, so we have to start skipping the lines.
     // If the skipping is successful, it will return the token following
     // either #else or #endif corresponding to this #ifdef.
     if (prepSkipRegion(ReturnNextLiveToken))
       return LexToken();
 
     return tgtok::Error;
   } else if (Kind == tgtok::Else) {
     // Check if this #else is correct before calling prepSkipDirectiveEnd(),
     // which will move CurPtr away from the beginning of #else.
     if (PrepIncludeStack.back()->empty())
-      return ReturnError(TokStart, "#else without #ifdef");
+      return ReturnError(TokStart, "#else without #ifdef or #ifndef");
 
     PreprocessorControlDesc IfdefEntry = PrepIncludeStack.back()->back();
 
     if (IfdefEntry.Kind != tgtok::Ifdef) {
       PrintError(TokStart, "double #else");
       return ReturnError(IfdefEntry.SrcPos, "Previous #else is here");
     }
 

llvm/test/TableGen/prep-diag5.td

 // RUN: not llvm-tblgen -I %p %s 2>&1 | FileCheck %s
 
-// CHECK: error: #else without #ifdef
+// CHECK: error: #else without #ifdef or #ifndef
 #else
 #else
 #endif

llvm/test/TableGen/prep-ifndef-diag-1.td

+// RUN: not llvm-tblgen %s 2>&1 | FileCheck %s
+
+// CHECK: error: Expected macro name after #ifndef
+#ifndef 1

llvm/test/TableGen/prep-ifndef-diag-2.td

+// RUN: not llvm-tblgen %s 2>&1 | FileCheck %s
+
+// CHECK: error: Only comments are supported after #ifndef NAME
+#ifndef MACRO 42

llvm/test/TableGen/prep-ifndef.td

+// RUN: llvm-tblgen %s -DMACRO | FileCheck %s
+// RUN: llvm-tblgen %s | FileCheck %s --check-prefix=CHECK-NOMACRO
+
+#ifndef MACRO
+// CHECK-NOMACRO: def nomacro
+def nomacro;
+#else
+// CHECK: def macro
+def macro;
+#endif