openmp: Improve expand_omp_atomic_pipeline

When __atomic_* builtins were introduced, omp-expand.c (omp-low.c
at that point) has been adjusted in several spots so that it uses
the atomic builtins instead of sync builtins, but
expand_omp_atomic_pipeline has not because the __atomic_compare_exchange_*
APIs take address of the argument, so it kept using __sync_val_compare_swap_*.
That means it always uses seq_cst though.
This patch changes it to use the ATOMIC_COMPARE_EXCHANGE ifn which gimple-fold
folds __atomic_compare_exchange_* into - that ifn also passes expected
directly.

2021-09-03  Jakub Jelinek  <jakub@redhat.com>

	* omp-expand.c (expand_omp_atomic_pipeline): Use
	IFN_ATOMIC_COMPARE_EXCHANGE instead of
	BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_? so that memory order
	can be provided.

diff --git a/gcc/omp-expand.c b/gcc/omp-expand.c
index a0e9e61..f2b6f6f 100644 (file)
--- a/gcc/omp-expand.c
+++ b/gcc/omp-expand.c
@@ -8807,8 +8807,6 @@ expand_omp_atomic_pipeline (basic_block load_bb, basic_block store_bb,
   edge e;
   enum built_in_function fncode;
 
-  /* ??? We need a non-pointer interface to __atomic_compare_exchange in
-     order to use the RELAXED memory model effectively.  */
   fncode = (enum built_in_function)((int)BUILT_IN_SYNC_VAL_COMPARE_AND_SWAP_N
                                    + index + 1);
   cmpxchg = builtin_decl_explicit (fncode);
@@ -8825,6 +8823,15 @@ expand_omp_atomic_pipeline (basic_block load_bb, basic_block store_bb,
   /* Load the initial value, replacing the GIMPLE_OMP_ATOMIC_LOAD.  */
   si = gsi_last_nondebug_bb (load_bb);
   gcc_assert (gimple_code (gsi_stmt (si)) == GIMPLE_OMP_ATOMIC_LOAD);
+  location_t loc = gimple_location (gsi_stmt (si));
+  enum omp_memory_order omo = gimple_omp_atomic_memory_order (gsi_stmt (si));
+  enum memmodel imo = omp_memory_order_to_memmodel (omo);
+  tree mo = build_int_cst (NULL, imo);
+  if (imo == MEMMODEL_RELEASE)
+    imo = MEMMODEL_RELAXED;
+  else if (imo == MEMMODEL_ACQ_REL)
+    imo = MEMMODEL_ACQUIRE;
+  tree fmo = build_int_cst (NULL, imo);
 
   /* For floating-point values, we'll need to view-convert them to integers
      so that we can perform the atomic compare and swap.  Simplify the
@@ -8921,7 +8928,15 @@ expand_omp_atomic_pipeline (basic_block load_bb, basic_block store_bb,
                                  GSI_SAME_STMT);
 
   /* Build the compare&swap statement.  */
-  new_storedi = build_call_expr (cmpxchg, 3, iaddr, loadedi, storedi);
+  tree ctype = build_complex_type (itype);
+  int flag = int_size_in_bytes (itype);
+  new_storedi = build_call_expr_internal_loc (loc, IFN_ATOMIC_COMPARE_EXCHANGE,
+                                             ctype, 6, iaddr, loadedi,
+                                             storedi,
+                                             build_int_cst (integer_type_node,
+                                                            flag),
+                                             mo, fmo);
+  new_storedi = build1 (REALPART_EXPR, itype, new_storedi);
   new_storedi = force_gimple_operand_gsi (&si,
                                          fold_convert (TREE_TYPE (loadedi),
                                                        new_storedi),