clang/lib/Serialization/TemplateArgumentHasher.h

   1 //===- TemplateArgumentHasher.h - Hash Template Arguments -------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "clang/AST/TemplateBase.h"
  10
  11 namespace clang {
  12 namespace serialization {
  13
  14 /// Calculate a stable hash value for template arguments. We guarantee that
  15 /// the same template arguments must have the same hashed values. But we don't
  16 /// guarantee that the template arguments with the same hashed value are the
  17 /// same template arguments.
  18 ///
  19 /// ODR hashing may not be the best mechanism to hash the template
  20 /// arguments. ODR hashing is (or perhaps, should be) about determining whether
  21 /// two things are spelled the same way and have the same meaning (as required
  22 /// by the C++ ODR), whereas what we want here is whether they have the same
  23 /// meaning regardless of spelling. Maybe we can get away with reusing ODR
  24 /// hashing anyway, on the basis that any canonical, non-dependent template
  25 /// argument should have the same (invented) spelling in every translation
  26 /// unit, but it is not sure that's true in all cases. There may still be cases
  27 /// where the canonical type includes some aspect of "whatever we saw first",
  28 /// in which case the ODR hash can differ across translation units for
  29 /// non-dependent, canonical template arguments that are spelled differently
  30 /// but have the same meaning. But it is not easy to raise examples.
  31 unsigned StableHashForTemplateArguments(llvm::ArrayRef<TemplateArgument> Args);
  32
  33 } // namespace serialization
  34 } // namespace clang