sparc: Add -mmemory-model command-line option.

	* config/sparc/sparc-opts.h (enum sparc_memory_model_type): New.
	* config/sparc/sparc.opt (mmemory-model=): New option.
	* doc/invoke.texi (Sparc Options): Document it.
	* config/sparc/sparc.c (sparc_option_override): Provide default
	for sparc_memory_model.
	(sparc_emit_membar_for_model): Omit barrier combinations that are
	implied by the memory model.

From-SVN: r181853

3 files changed, 80 insertions, 1 deletions

diff --git a/gcc/config/sparc/sparc-opts.h b/gcc/config/sparc/sparc-opts.h
index 266cb14..7682eb9 100644
--- a/gcc/config/sparc/sparc-opts.h
+++ b/gcc/config/sparc/sparc-opts.h
@@ -47,4 +47,14 @@ enum processor_type {
   PROCESSOR_NATIVE
 };
 
+/* Sparc system memory model.  See Appendix D in the Sparc V9 manual
+   for formal specification, and Appendix J for more discussion.  */
+enum sparc_memory_model_type {
+  SMM_DEFAULT,	/* Uninitialized.  */
+  SMM_RMO,	/* Relaxed Memory Order.  */
+  SMM_PSO,	/* Partial Store Order.  */
+  SMM_TSO,	/* Total Store Order.  */
+  SMM_SC	/* Sequential Consistency.  */
+};
+
 #endif
diff --git a/gcc/config/sparc/sparc.c b/gcc/config/sparc/sparc.c
index 7db216a..713db26 100644
--- a/gcc/config/sparc/sparc.c
+++ b/gcc/config/sparc/sparc.c
@@ -1160,6 +1160,17 @@ sparc_option_override (void)
       gcc_unreachable ();
     };
 
+  if (sparc_memory_model == SMM_DEFAULT)
+    {
+      /* Choose the most relaxed model for the processor.  */
+      if (TARGET_V9)
+	sparc_memory_model = SMM_RMO;
+      else if (TARGET_V8)
+	sparc_memory_model = SMM_PSO;
+      else
+	sparc_memory_model = SMM_SC;
+    }
+
 #ifdef TARGET_DEFAULT_LONG_DOUBLE_128
   if (!(target_flags_explicit & MASK_LONG_DOUBLE_128))
     target_flags |= MASK_LONG_DOUBLE_128;
@@ -10863,7 +10874,40 @@ sparc_emit_membar_for_model (enum memmodel model,
   const int LoadStore = 4;
   const int StoreStore = 8;
 
-  int mm = 0;
+  int mm = 0, implied = 0;
+
+  switch (sparc_memory_model)
+    {
+    case SMM_SC:
+      /* Sequential Consistency.  All memory transactions are immediately
+	 visible in sequential execution order.  No barriers needed.  */
+      implied = LoadLoad | StoreLoad | LoadStore | StoreStore;
+      break;
+
+    case SMM_TSO:
+      /* Total Store Ordering: all memory transactions with store semantics
+	 are followed by an implied StoreStore.  */
+      implied |= StoreStore;
+      /* FALLTHRU */
+
+    case SMM_PSO:
+      /* Partial Store Ordering: all memory transactions with load semantics
+	 are followed by an implied LoadLoad | LoadStore.  */
+      implied |= LoadLoad | LoadStore;
+
+      /* If we're not looking for a raw barrer (before+after), then atomic
+	 operations get the benefit of being both load and store.  */
+      if (load_store == 3 && before_after == 2)
+	implied |= StoreLoad | StoreStore;
+      /* FALLTHRU */
+
+    case SMM_RMO:
+      /* Relaxed Memory Ordering: no implicit bits.  */
+      break;
+
+    default:
+      gcc_unreachable ();
+    }
 
   if (before_after & 1)
     {
@@ -10890,6 +10934,9 @@ sparc_emit_membar_for_model (enum memmodel model,
 	}
     }
 
+  /* Remove the bits implied by the system memory model.  */
+  mm &= ~implied;
+
   /* For raw barriers (before+after), always emit a barrier.
      This will become a compile-time barrier if needed.  */
   if (mm || before_after == 3)
diff --git a/gcc/config/sparc/sparc.opt b/gcc/config/sparc/sparc.opt
index cb807fd..01f3d43 100644
--- a/gcc/config/sparc/sparc.opt
+++ b/gcc/config/sparc/sparc.opt
@@ -215,3 +215,25 @@ Mask(V9)
 Mask(DEPRECATED_V8_INSNS)
 ;; Generate code that uses the V8 instructions deprecated
 ;; in the V9 architecture.
+
+mmemory-model=
+Target RejectNegative Joined Var(sparc_memory_model) Enum(sparc_memory_model) Init(SMM_DEFAULT)
+Specify the memory model in effect for the program.
+
+Enum
+Name(sparc_memory_model) Type(enum sparc_memory_model_type)
+
+EnumValue
+Enum(sparc_memory_model) String(default) Value(SMM_DEFAULT)
+
+EnumValue
+Enum(sparc_memory_model) String(rmo) Value(SMM_RMO)
+
+EnumValue
+Enum(sparc_memory_model) String(pso) Value(SMM_PSO)
+
+EnumValue
+Enum(sparc_memory_model) String(tso) Value(SMM_TSO)
+
+EnumValue
+Enum(sparc_memory_model) String(sc) Value(SMM_SC)