alias.c (nonlocal_reference_p): Take a care for CALL_INSNS's fusage field.

	* alias.c (nonlocal_reference_p): Take a care for
	CALL_INSNS's fusage field.
	* calls.c (ECF_PURE): New flag.
	(emit_call_1): Handle ECF_PURE calls.
	(initialize_argument_information): Unset ECF_PURE flag too.
	(precompute_arguments): Precompute for ECF_PURE too.
	(expand_call): Handle ECF_PURE calls too.
	(emit_library_call_value_1): Rename no_queue argument to
	fn_type, accept value of 2 as pure function.
	(emit_library_call_value, emit_library_call): Rename no_queue argument
	to fn_type.
	* optabs.c (prepare_cmp_insn): Pass fn_type 2 to memcmp call.

	* tree.h (DECL_IS_PURE): New macro.
	(struct tree_decl): Add pure_flag.
	* c-common.c (enum attrs): Add attribute "pure".
	(init_attributes): Initialize attribute "pure"
	(decl_attributes): Handle attribute "pure".
	* extend.texi (Attribute "pure"): Document.
	* calls.c (expand_call): Add (mem:BLK (scratch)) to "equal from"
	in pure function.
	(flags_from_decl_or_type): Support attribute "pure".

From-SVN: r33138

gcc/ChangeLog

+Thu Apr 13 15:55:08 MET DST 2000  Jan Hubicka  <jh@suse.cz>
+
+	* alias.c (nonlocal_reference_p): Take a care for
+	CALL_INSNS's fusage field.
+	* calls.c (ECF_PURE): New flag.
+	(emit_call_1): Handle ECF_PURE calls.
+	(initialize_argument_information): Unset ECF_PURE flag too.
+	(precompute_arguments): Precompute for ECF_PURE too.
+	(expand_call): Handle ECF_PURE calls too.
+	(emit_library_call_value_1): Rename no_queue argument to
+	fn_type, accept value of 2 as pure function.
+	(emit_library_call_value, emit_library_call): Rename no_queue argument
+	to fn_type.
+	* optabs.c (prepare_cmp_insn): Pass fn_type 2 to memcmp call.
+
+	* tree.h (DECL_IS_PURE): New macro.
+	(struct tree_decl): Add pure_flag.
+	* c-common.c (enum attrs): Add attribute "pure".
+	(init_attributes): Initialize attribute "pure"
+	(decl_attributes): Handle attribute "pure".
+	* extend.texi (Attribute "pure"): Document.
+	* calls.c (expand_call): Add (mem:BLK (scratch)) to "equal from"
+	in pure function.
+	(flags_from_decl_or_type): Support attribute "pure".
+
 2000-04-13  Jason Merrill  <jason@casey.cygnus.com>
 
 	* cpplex.c (_cpp_lex_token): Handle digraphs.  Don't null-terminate

gcc/alias.c

@@ -1424,10 +1424,15 @@ nonlocal_reference_p (x)
 
   if (GET_RTX_CLASS (code) == 'i')
     {
-      /* Constant functions are constant.  */
+      /* Constant functions can be constant if they don't use
+         scratch memory used to mark function w/o side effects.  */
       if (code == CALL_INSN && CONST_CALL_P (x))
-	return 0;
-      x = PATTERN (x);
+        {
+	  x = CALL_INSN_FUNCTION_USAGE (x);
+	  if (!x) return 0;
+        }
+      else
+        x = PATTERN (x);
       code = GET_CODE (x);
     }
 
@@ -1520,7 +1525,7 @@ nonlocal_reference_p (x)
     
     for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
       {
-	if (fmt[i] == 'e')
+	if (fmt[i] == 'e' && XEXP (x, i))
 	  {
 	    if (nonlocal_reference_p (XEXP (x, i)))
 	      return 1;

gcc/c-common.c

@@ -145,7 +145,7 @@ enum attrs {A_PACKED, A_NOCOMMON, A_COMMON, A_NORETURN, A_CONST, A_T_UNION,
 	    A_NO_CHECK_MEMORY_USAGE, A_NO_INSTRUMENT_FUNCTION,
 	    A_CONSTRUCTOR, A_DESTRUCTOR, A_MODE, A_SECTION, A_ALIGNED,
 	    A_UNUSED, A_FORMAT, A_FORMAT_ARG, A_WEAK, A_ALIAS, A_MALLOC,
-	    A_NO_LIMIT_STACK};
+	    A_NO_LIMIT_STACK, A_PURE};
 
 enum format_type { printf_format_type, scanf_format_type,
 		   strftime_format_type };
@@ -457,6 +457,7 @@ init_attributes ()
   add_attribute (A_NO_CHECK_MEMORY_USAGE, "no_check_memory_usage", 0, 0, 1);
   add_attribute (A_MALLOC, "malloc", 0, 0, 1);
   add_attribute (A_NO_LIMIT_STACK, "no_stack_limit", 0, 0, 1);
+  add_attribute (A_PURE, "pure", 0, 0, 1);
 }
 
 /* Default implementation of valid_lang_attribute, below.  By default, there
@@ -596,6 +597,7 @@ decl_attributes (node, attributes, prefix_attributes)
 	case A_MALLOC:
 	  if (TREE_CODE (decl) == FUNCTION_DECL)
 	    DECL_IS_MALLOC (decl) = 1;
+	  /* ??? TODO: Support types.  */
 	  else
 	    warning ("`%s' attribute ignored", IDENTIFIER_POINTER (name));
 	  break;
@@ -625,6 +627,15 @@ decl_attributes (node, attributes, prefix_attributes)
 	    warning ( "`%s' attribute ignored", IDENTIFIER_POINTER (name));
 	  break;
 
+	case A_PURE:
+	  if (TREE_CODE (decl) == FUNCTION_DECL)
+	    DECL_IS_PURE (decl) = 1;
+	  /* ??? TODO: Support types.  */
+	  else
+	    warning ("`%s' attribute ignored", IDENTIFIER_POINTER (name));
+	  break;
+
+
 	case A_T_UNION:
 	  if (is_type
 	      && TREE_CODE (type) == UNION_TYPE

gcc/extend.texi

@@ -1379,22 +1379,44 @@ typedef void voidfn ();
 volatile voidfn fatal;
 @end smallexample
 
-@cindex @code{const} function attribute
-@item const
-Many functions do not examine any values except their arguments, and
-have no effects except the return value.  Such a function can be subject
+@cindex @code{pure} function attribute
+@item pure
+Many functions have no effects except the return value and their
+return value and depends only on the parameters and/or global variables.
+Such a function can be subject
 to common subexpression elimination and loop optimization just as an
 arithmetic operator would be.  These functions should be declared
-with the attribute @code{const}.  For example,
+with the attribute @code{pure}.  For example,
 
 @smallexample
-int square (int) __attribute__ ((const));
+int square (int) __attribute__ ((pure));
 @end smallexample
 
 @noindent
 says that the hypothetical function @code{square} is safe to call
 fewer times than the program says.
 
+Some of common examples of pure functions are @code{strlen} or @code{memcmp}.
+Interesting non-pure functions are functions with infinite loops or those
+depending on volatile memory or other system resource, that may change between
+two consetuctive calls (such as @code{feof} in multithreding environment).
+
+The attribute @code{pure} is not implemented in GNU C versions earlier
+than 2.96.
+@cindex @code{const} function attribute
+@item const
+Many functions do not examine any values except their arguments, and
+have no effects except the return value.  Basically this is just slightly
+more strict class than the "pure" attribute above, since function is not
+alloved to read global memory.
+
+@cindex pointer arguments
+Note that a function that has pointer arguments and examines the data
+pointed to must @emph{not} be declared @code{const}.  Likewise, a
+function that calls a non-@code{const} function usually must not be
+@code{const}.  It does not make sense for a @code{const} function to
+return @code{void}.
+
 The attribute @code{const} is not implemented in GNU C versions earlier
 than 2.5.  An alternative way to declare that a function has no side
 effects, which works in the current version and in some older versions,
@@ -1409,12 +1431,6 @@ extern const intfn square;
 This approach does not work in GNU C++ from 2.6.0 on, since the language
 specifies that the @samp{const} must be attached to the return value.
 
-@cindex pointer arguments
-Note that a function that has pointer arguments and examines the data
-pointed to must @emph{not} be declared @code{const}.  Likewise, a
-function that calls a non-@code{const} function usually must not be
-@code{const}.  It does not make sense for a @code{const} function to
-return @code{void}.
 
 @item format (@var{archetype}, @var{string-index}, @var{first-to-check})
 @cindex @code{format} function attribute

gcc/optabs.c

@@ -3020,14 +3020,14 @@ prepare_cmp_insn (px, py, pcomparison, size, pmode, punsignedp, align,
 #endif
 	{
 #ifdef TARGET_MEM_FUNCTIONS
-	  emit_library_call (memcmp_libfunc, 0,
+	  emit_library_call (memcmp_libfunc, 2,
 			     TYPE_MODE (integer_type_node), 3,
 			     XEXP (x, 0), Pmode, XEXP (y, 0), Pmode,
 			     convert_to_mode (TYPE_MODE (sizetype), size,
 					      TREE_UNSIGNED (sizetype)),
 			     TYPE_MODE (sizetype));
 #else
-	  emit_library_call (bcmp_libfunc, 0,
+	  emit_library_call (bcmp_libfunc, 2,
 			     TYPE_MODE (integer_type_node), 3,
 			     XEXP (x, 0), Pmode, XEXP (y, 0), Pmode,
 			     convert_to_mode (TYPE_MODE (integer_type_node),

gcc/tree.h

@@ -1253,6 +1253,10 @@ struct tree_type
    not an alias.  */
 #define DECL_IS_MALLOC(NODE) (FUNCTION_DECL_CHECK (NODE)->decl.malloc_flag)
 
+/* Nonzero in a FUNCTION_DECL means this function should be treated
+   as "pure" function (like const function, but may read global memory).  */
+#define DECL_IS_PURE(NODE) (FUNCTION_DECL_CHECK (NODE)->decl.pure_flag)
+
 /* Nonzero in a FIELD_DECL means it is a bit field, and must be accessed
    specially.  */
 #define DECL_BIT_FIELD(NODE) (FIELD_DECL_CHECK (NODE)->decl.bit_field_flag)
@@ -1392,6 +1396,7 @@ struct tree_decl
   unsigned comdat_flag : 1;
   unsigned malloc_flag : 1;
   unsigned no_limit_stack : 1;
+  unsigned pure_flag : 1;
 #ifdef ONLY_INT_FIELDS
   unsigned int built_in_class : 2;
 #else