introduce const_memory opcode flag and is_irn_const_memory()

include/libfirm/irnode.h

@@ -472,6 +472,10 @@ FIRM_API int is_fragile_op(const ir_node *node);
  *  operation: Cond. */
 FIRM_API int is_irn_forking(const ir_node *node);
 
+/** Returns true if the operation does not change anymemory contents although
+ * it has a memory input/output. */
+FIRM_API int is_irn_const_memory(const ir_node *node);
+
 /**
  * Copies attributes stored in the old node to a new node.
  * Assumes both have the same opcode and sufficient size.

include/libfirm/irop.h

@@ -61,6 +61,10 @@ typedef enum {
 	 * conservative aproximation in this case. You cannot change the destination
 	 * of an unknown_jump */
 	irop_flag_unknown_jump = 1U << 11,
+	/** The opcode has a memory input/output but does not actually change the
+	 * contents of any memory block known to the program. The input/output is
+	 * just necessary for scheduling reasons. Implies irop_flag_uses_memory. */
+	irop_flag_const_memory = 1U << 12,
 } irop_flags;
 ENUM_BITSET(irop_flags)
 

ir/ir/irnode.c

@@ -948,6 +948,56 @@ int (is_irn_forking)(const ir_node *node)
 	return is_irn_forking_(node);
 }
 
+static bool is_call_no_write(const ir_node *node)
+{
+	ir_type *call_tp = get_Call_type(node);
+	unsigned prop    = get_method_additional_properties(call_tp);
+
+	/* check first the call type */
+	if ((prop & (mtp_property_const|mtp_property_pure)) == 0) {
+		/* try the called entity */
+		ir_entity *callee = get_Call_callee(node);
+		if (callee != NULL) {
+			prop = get_entity_additional_properties(callee);
+		}
+	}
+	return prop & (mtp_property_const|mtp_property_pure);
+}
+
+int is_irn_const_memory(const ir_node *node)
+{
+	const ir_op *op = get_irn_op(node);
+	if (get_op_flags(op) & irop_flag_const_memory)
+		return true;
+	if (is_Builtin(node)) {
+		switch (get_Builtin_kind(node)) {
+		case ir_bk_trap:
+		case ir_bk_debugbreak:
+		case ir_bk_compare_swap:
+			return false;
+		case ir_bk_return_address:
+		case ir_bk_frame_address:
+		case ir_bk_prefetch:
+		case ir_bk_ffs:
+		case ir_bk_clz:
+		case ir_bk_ctz:
+		case ir_bk_popcount:
+		case ir_bk_parity:
+		case ir_bk_bswap:
+		case ir_bk_inport:
+		case ir_bk_outport:
+		case ir_bk_inner_trampoline:
+		case ir_bk_saturating_increment:
+		case ir_bk_may_alias:
+			return true;
+		}
+		panic("invalid Builtin %+F", node);
+	}
+	if (is_Call(node))
+		return is_call_no_write(node);
+	return false;
+}
+
 void (copy_node_attr)(ir_graph *irg, const ir_node *old_node, ir_node *new_node)
 {
 	copy_node_attr_(irg, old_node, new_node);

scripts/ir_spec.py

@@ -78,7 +78,7 @@ class Alloc:
 		Attribute("alignment", type="unsigned",
 		          comment="alignment of the memory block (must be a power of 2)"),
 	]
-	flags       = [ "uses_memory" ]
+	flags       = [ "uses_memory", "const_memory" ]
 	pinned      = "yes"
 	attr_struct = "alloc_attr"
 
@@ -433,7 +433,7 @@ class Div:
 		("X_regular", "control flow when no exception occurs"),
 		("X_except",  "control flow when exception occured"),
 	]
-	flags = [ "fragile", "uses_memory" ]
+	flags = [ "fragile", "uses_memory", "const_memory" ]
 	attrs = [
 		Attribute("resmode", type="ir_mode*",
 		          comment="mode of the result value"),
@@ -482,7 +482,7 @@ class Free:
 		("ptr", "pointer to the object to free"),
 	]
 	mode   = "mode_M"
-	flags  = [ "uses_memory" ]
+	flags  = [ "uses_memory", "const_memory" ]
 	pinned = "yes"
 
 @op
@@ -530,7 +530,7 @@ class Load:
 		("X_regular", "control flow when no exception occurs"),
 		("X_except",  "control flow when exception occured"),
 	]
-	flags    = [ "fragile", "uses_memory" ]
+	flags    = [ "fragile", "uses_memory", "const_memory" ]
 	pinned   = "exception"
 	attrs    = [
 		Attribute("mode", type="ir_mode*",
@@ -583,7 +583,7 @@ class Mod:
 		("X_regular", "control flow when no exception occurs"),
 		("X_except",  "control flow when exception occured"),
 	]
-	flags = [ "fragile", "uses_memory" ]
+	flags = [ "fragile", "uses_memory", "const_memory" ]
 	attrs = [
 		Attribute("resmode", type="ir_mode*", comment="mode of the result"),
 	]