re PR target/65697 (__atomic memory barriers not strong enough for __sync builtins)

        PR target/65697
	* config/aarch64/aarch64.c (aarch64_emit_post_barrier):New.
	(aarch64_split_atomic_op): Check for __sync memory models, emit
	appropriate initial loads and final barriers.

From-SVN: r223983

gcc/ChangeLog

+2015-06-01  Matthew Wahab  <matthew.wahab@arm.com>
+
+        PR target/65697
+	* config/aarch64/aarch64.c (aarch64_emit_post_barrier):New.
+	(aarch64_split_atomic_op): Check for __sync memory models, emit
+	appropriate initial loads and final barriers.
+
 2015-06-01  Vidya Praveen  <vidya.praveen@atmel.com>
 
 	* Makefile.in: Fix gcov dependencies that should

gcc/config/aarch64/aarch64.c

@@ -9409,6 +9409,23 @@ aarch64_expand_compare_and_swap (rtx operands[])
   emit_insn (gen_rtx_SET (bval, x));
 }
 
+/* Emit a barrier, that is appropriate for memory model MODEL, at the end of a
+   sequence implementing an atomic operation.  */
+
+static void
+aarch64_emit_post_barrier (enum memmodel model)
+{
+  const enum memmodel base_model = memmodel_base (model);
+
+  if (is_mm_sync (model)
+      && (base_model == MEMMODEL_ACQUIRE
+	  || base_model == MEMMODEL_ACQ_REL
+	  || base_model == MEMMODEL_SEQ_CST))
+    {
+      emit_insn (gen_mem_thread_fence (GEN_INT (MEMMODEL_SEQ_CST)));
+    }
+}
+
 /* Split a compare and swap pattern.  */
 
 void
@@ -9471,6 +9488,8 @@ aarch64_split_atomic_op (enum rtx_code code, rtx old_out, rtx new_out, rtx mem,
 {
   machine_mode mode = GET_MODE (mem);
   machine_mode wmode = (mode == DImode ? DImode : SImode);
+  const enum memmodel model = memmodel_from_int (INTVAL (model_rtx));
+  const bool is_sync = is_mm_sync (model);
   rtx_code_label *label;
   rtx x;
 
@@ -9485,7 +9504,13 @@ aarch64_split_atomic_op (enum rtx_code code, rtx old_out, rtx new_out, rtx mem,
     old_out = new_out;
   value = simplify_gen_subreg (wmode, value, mode, 0);
 
-  aarch64_emit_load_exclusive (mode, old_out, mem, model_rtx);
+  /* The initial load can be relaxed for a __sync operation since a final
+     barrier will be emitted to stop code hoisting.  */
+ if (is_sync)
+    aarch64_emit_load_exclusive (mode, old_out, mem,
+				 GEN_INT (MEMMODEL_RELAXED));
+  else
+    aarch64_emit_load_exclusive (mode, old_out, mem, model_rtx);
 
   switch (code)
     {
@@ -9521,6 +9546,10 @@ aarch64_split_atomic_op (enum rtx_code code, rtx old_out, rtx new_out, rtx mem,
   x = gen_rtx_IF_THEN_ELSE (VOIDmode, x,
 			    gen_rtx_LABEL_REF (Pmode, label), pc_rtx);
   aarch64_emit_unlikely_jump (gen_rtx_SET (pc_rtx, x));
+
+  /* Emit any final barrier needed for a __sync operation.  */
+  if (is_sync)
+    aarch64_emit_post_barrier (model);
 }
 
 static void