[llvm] [Frontend][OpenMP] Implement directive name parser (PR #146776)

[Krzysztof Parzyszek via llvm-commits]

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@@ -0,0 +1,77 @@
+//===- DirectiveNameParser.h  ------------------------------------- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_FRONTEND_OPENMP_DIRECTIVENAMEPARSER_H
+#define LLVM_FRONTEND_OPENMP_DIRECTIVENAMEPARSER_H
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Frontend/OpenMP/OMP.h"
+
+#include <memory>
+
+namespace llvm::omp {
+/// Parser class for OpenMP directive names. It only recognizes names listed
+/// in OMP.td, in particular it does not recognize Fortran's end-directives
+/// if they are not explicitly listed in OMP.td.
+///
+/// The class itself may be a singleton, once it's constructed it never
+/// changes.
+///
+/// Usage:
+/// {
+///   DirectiveNameParser Parser;   // Could be static const.
+///
+///   DirectiveNameParser::State *S = Parser.initial();
+///   for (StringRef Token : Tokens)
+///     S = Parser.apply(S, Token); // Passing nullptr is ok.
+///
+///   if (S == nullptr) {
+///     // Error: ended up in a state from which there is no possible path
+///     // to a successful parse.
+///   } else if (S->Value == OMPD_unknown) {
+///     // Parsed a sequence of tokens that are not a complete name, but
+///     // parsing more tokens could lead to a successful parse.
+///   } else {
+///     // Success.
+///     ParsedId = S->Value;
+///   }
+/// }
+struct DirectiveNameParser {
+  DirectiveNameParser(SourceLanguage L = SourceLanguage::C);
+
+  struct State {
+    Directive Value = Directive::OMPD_unknown;
+
+  private:
+    using TransitionMapTy = StringMap<State>;
+    std::unique_ptr<TransitionMapTy> Transition;
+
+    State *next(StringRef Tok);
+    const State *next(StringRef Tok) const;
+    bool isValid() const {
+      return Value != Directive::OMPD_unknown || !Transition->empty();
+    }
+    friend struct DirectiveNameParser;
+  };
+
+  const State *initial() const { return &InitialState; }
+  const State *apply(const State *Current, StringRef Tok) const;
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kparzysz wrote:

I renamed it to "consume".

https://github.com/llvm/llvm-project/pull/146776