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

2015-06-29  Matthew Wahab  <matthew.wahab@arm.com>

	PR target/65697
	* config/armc/arm.c (arm_split_atomic_op): For ARMv8, replace an
	initial acquire barrier with final barrier.

From-SVN: r225132

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b07930194226250a0d1090161db2592a9c671d34..2a7ef9d10502486d8bd6ce9ce15a54746f403539 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2015-06-29  Matthew Wahab  <matthew.wahab@arm.com>
+
+       PR target/65697
+       * config/armc/arm.c (arm_split_atomic_op): For ARMv8, replace an
+       initial acquire barrier with final barrier.
+
 2015-06-29  Richard Henderson  <rth@redhat.com>
 
        * config/i386/constraints.md (Bf): New constraint.

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 9f300415ede9f48b2a2704283629ffef7e5e1db4..56677634ee01acdc0db317b4e08fa9e1b8c8a9e3 100644 (file)
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -27679,6 +27679,8 @@ arm_split_atomic_op (enum rtx_code code, rtx old_out, rtx new_out, rtx mem,
   rtx_code_label *label;
   rtx x;
 
+  bool is_armv8_sync = arm_arch8 && is_mm_sync (model);
+
   bool use_acquire = TARGET_HAVE_LDACQ
                      && !(is_mm_relaxed (model) || is_mm_consume (model)
                          || is_mm_release (model));
@@ -27687,6 +27689,11 @@ arm_split_atomic_op (enum rtx_code code, rtx old_out, rtx new_out, rtx mem,
                      && !(is_mm_relaxed (model) || is_mm_consume (model)
                          || is_mm_acquire (model));
 
+  /* For ARMv8, a load-acquire is too weak for __sync memory orders.  Instead,
+     a full barrier is emitted after the store-release.  */
+  if (is_armv8_sync)
+    use_acquire = false;
+
   /* Checks whether a barrier is needed and emits one accordingly.  */
   if (!(use_acquire || use_release))
     arm_pre_atomic_barrier (model);
@@ -27757,7 +27764,8 @@ arm_split_atomic_op (enum rtx_code code, rtx old_out, rtx new_out, rtx mem,
   emit_unlikely_jump (gen_cbranchsi4 (x, cond, const0_rtx, label));
 
   /* Checks whether a barrier is needed and emits one accordingly.  */
-  if (!(use_acquire || use_release))
+  if (is_armv8_sync
+      || !(use_acquire || use_release))
     arm_post_atomic_barrier (model);
 }
 \f