[Bug jit/95415] Add support for thread-local variables

["dmalcolm at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95415

--- Comment #1 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
Perhaps, but it looks non-trivial.

Notes to self:

c/c-tree.h: struct c_declspecs has:
  /* Whether "__thread" or "_Thread_local" was specified.  */
  BOOL_BITFIELD thread_p : 1;
  /* Whether "__thread" rather than "_Thread_local" was specified.  */
  BOOL_BITFIELD thread_gnu_p : 1;

tree.h has:

/* In a VAR_DECL, the model to use if the data should be allocated from
   thread-local storage.  */
#define DECL_TLS_MODEL(NODE) decl_tls_model (NODE)

/* In a VAR_DECL, nonzero if the data should be allocated from
   thread-local storage.  */
#define DECL_THREAD_LOCAL_P(NODE) \
  ((TREE_STATIC (NODE) || DECL_EXTERNAL (NODE)) && decl_tls_model (NODE) >=
TLS_MODEL_REAL)

decl_tls_model/set_decl_tls_model get/set a field of the varpool_node, based on
this enum in coretypes.h:

/* The thread-local storage model associated with a given VAR_DECL
   or SYMBOL_REF.  This isn't used much, but both trees and RTL refer
   to it, so it's here.  */
enum tls_model {
  TLS_MODEL_NONE,
  TLS_MODEL_EMULATED,
  TLS_MODEL_REAL,
  TLS_MODEL_GLOBAL_DYNAMIC = TLS_MODEL_REAL,
  TLS_MODEL_LOCAL_DYNAMIC,
  TLS_MODEL_INITIAL_EXEC,
  TLS_MODEL_LOCAL_EXEC
};