libstdc++:

        Add memory barriers to the double-checked locking used for static
        initialization.
        * libsupc++/guard.cc (__test_and_acquire): Define default.
        (_GLIBCXX_GUARD_TEST_AND_ACQUIRE, __set_and_release)
        (_GLIBCXX_GUARD_SET_AND_RELEASE): Likewise.
        (recursion_push, recursion_pop): New abstraction functions.
        (__cxa_guard_acquire): Use _GLIBCXX_GUARD_TEST_AND_ACQUIRE.
        (__cxa_guard_release): Use _GLIBCXX_GUARD_SET_AND_RELEASE.
        * config/cpu/generic/cxxabi_tweaks.h (_GLIBCXX_GUARD_TEST): Rename
        from _GLIBCXX_GUARD_ACQUIRE and reverse sense.
        (_GLIBCXX_GUARD_SET): Rename from _GLIBCXX_GUARD_RELEASE.
        * config/cpu/arm/cxxabi_tweaks.h: Likewise.
        * config/cpu/alpha/atomic_word.h (_GLIBCXX_READ_MEM_BARRIER)
        (_GLIBCXX_WRITE_MEM_BARRIER): Define.
        * config/cpu/powerpc/atomic_word.h: Likewise.
        * config/cpu/sparc/atomic_word.h: Likewise.
        * config/cpu/generic/atomic_word.h: Define them, commented out.
        * include/bits/atomicity.h: Define defaults.
        * config/cpu/ia64/atomic_word.h (__test_and_acquire)
        (__set_and_release): New inlines.
        (_GLIBCXX_GUARD_TEST_AND_ACQUIRE): Define.
        (_GLIBCXX_GUARD_SET_AND_RELEASE): Define.

        * libsupc++/guard.cc (acquire_1): Use __builtin_trap instead of
        abort();

gcc:
        * doc/tm.texi (TARGET_RELAXED_ORDERING): Document.
        * target.h (struct gcc_target): Add relaxed_ordering field.
        * target-def.h (TARGET_RELAXED_ORDERING): Define default.
        (TARGET_INITIALIZER): Add it.
        * config/alpha/alpha.c (TARGET_RELAXED_ORDERING): Define.
        * config/ia64/ia64.c (TARGET_RELAXED_ORDERING): Define.
        * config/rs6000/rs6000.c (TARGET_RELAXED_ORDERING): Define.
        * config/sparc/sparc.c (TARGET_RELAXED_ORDERING): Define.
        * cp/decl.c (expand_static_init): Don't use shortcut if
        targetm.relaxed_ordering.


git-svn-id: https://gcc.gnu.org/svn/gcc/trunk@92659 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 18 insertions, 9 deletions

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 991996bc3f5..7a839d7f3bf 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -5313,8 +5313,8 @@ expand_static_init (tree decl, tree init)
   if (DECL_FUNCTION_SCOPE_P (decl))
     {
       /* Emit code to perform this initialization but once.  */
-      tree if_stmt, inner_if_stmt = NULL_TREE;
-      tree then_clause, inner_then_clause = NULL_TREE;
+      tree if_stmt = NULL_TREE, inner_if_stmt = NULL_TREE;
+      tree then_clause = NULL_TREE, inner_then_clause = NULL_TREE;
       tree guard, guard_addr, guard_addr_list;
       tree acquire_fn, release_fn, abort_fn;
       tree flag, begin;
@@ -5353,10 +5353,16 @@ expand_static_init (tree decl, tree init)
       /* Create the guard variable.  */
       guard = get_guard (decl);
 
-      /* Begin the conditional initialization.  */
-      if_stmt = begin_if_stmt ();
-      finish_if_stmt_cond (get_guard_cond (guard), if_stmt);
-      then_clause = begin_compound_stmt (BCS_NO_SCOPE);
+      /* This optimization isn't safe on targets with relaxed memory
+	 consistency.  On such targets we force synchronization in
+	 __cxa_guard_acquire.  */
+      if (!targetm.relaxed_ordering || !flag_threadsafe_statics)
+	{
+	  /* Begin the conditional initialization.  */
+	  if_stmt = begin_if_stmt ();
+	  finish_if_stmt_cond (get_guard_cond (guard), if_stmt);
+	  then_clause = begin_compound_stmt (BCS_NO_SCOPE);
+	}
 
       if (flag_threadsafe_statics)
 	{
@@ -5419,9 +5425,12 @@ expand_static_init (tree decl, tree init)
 	  finish_if_stmt (inner_if_stmt);
 	}
 
-      finish_compound_stmt (then_clause);
-      finish_then_clause (if_stmt);
-      finish_if_stmt (if_stmt);
+      if (!targetm.relaxed_ordering || !flag_threadsafe_statics)
+	{
+	  finish_compound_stmt (then_clause);
+	  finish_then_clause (if_stmt);
+	  finish_if_stmt (if_stmt);
+	}
     }
   else
     static_aggregates = tree_cons (init, decl, static_aggregates);