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Subject: [Bug bootstrap/100186] lto-wrapper.c assumes std::thread
Date: Wed, 21 Apr 2021 17:19:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100186

--- Comment #5 from David Edelsohn <dje at gcc dot gnu.org> ---
For example, in GCC 6:

#if defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1)

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   * @defgroup threads Threads
   * @ingroup concurrency
   *
   * Classes for thread support.
   * @{
   */

  /// thread
  class thread
  {

If we are going to support bootstrap with releases of GCC back to GCC 6 or =
GCC
4.8, the source code cannot assume that std::thread exists.

However, it's probably reasonable to assume hardware_concurrency of 1 when
compiling in a mode without GTHREADS.=