extend.texi: Document Function Multiversioning and "default" parameter string to target...

	* doc/extend.texi: Document Function Multiversioning and "default"
	parameter string to target attribute.
	* g++.dg/ext/mv12.C: New test.
	* g++.dg/ext/mv12.h: New file.
	* g++.dg/ext/mv12-aux.C: New file.
	* g++.dg/ext/mv13.C: New test.
	* config/i386/i386.c (get_builtin_code_for_version): Return 0 if
	target attribute parameter is "default".
	(ix86_compare_version_priority): Remove checks for target attribute.
	(ix86_mangle_function_version_assembler_name): Change error to sorry.
	Remove check for target attribute equal to NULL. Add assert.
	(ix86_generate_version_dispatcher_body): Change error to sorry.

From-SVN: r195967

gcc/ChangeLog

+2013-02-11  Sriraman Tallam  <tmsriramgoogle.com>
+
+	* doc/extend.texi: Document Function Multiversioning and "default"
+	parameter string to target attribute.
+	* config/i386/i386.c (get_builtin_code_for_version): Return 0 if
+	target attribute parameter is "default".
+	(ix86_compare_version_priority): Remove checks for target attribute.
+	(ix86_mangle_function_version_assembler_name): Change error to sorry.
+	Remove check for target attribute equal to NULL. Add assert.
+	(ix86_generate_version_dispatcher_body): Change error to sorry.
+
 2013-02-11  Iain Sandoe  <iain@codesourcery.com>
 	    Jack Howarth  <howarth@bromo.med.uc.edu>
 	    Patrick Marlier  <patrick.marlier@gmail.com>

gcc/config/i386/i386.c

@@ -28696,6 +28696,9 @@ get_builtin_code_for_version (tree decl, tree *predicate_list)
   gcc_assert (TREE_CODE (attrs) == STRING_CST);
   attrs_str = TREE_STRING_POINTER (attrs);
 
+  /* Return priority zero for default function.  */
+  if (strcmp (attrs_str, "default") == 0)
+    return 0;
 
   /* Handle arch= if specified.  For priority, set it to be 1 more than
      the best instruction set the processor can handle.  For instance, if
@@ -28828,14 +28831,8 @@ get_builtin_code_for_version (tree decl, tree *predicate_list)
 static int
 ix86_compare_version_priority (tree decl1, tree decl2)
 {
-  unsigned int priority1 = 0;
-  unsigned int priority2 = 0;
-
-  if (lookup_attribute ("target", DECL_ATTRIBUTES (decl1)) != NULL)
-    priority1 = get_builtin_code_for_version (decl1, NULL);
-
-  if (lookup_attribute ("target", DECL_ATTRIBUTES (decl2)) != NULL)
-    priority2 = get_builtin_code_for_version (decl2, NULL);
+  unsigned int priority1 = get_builtin_code_for_version (decl1, NULL);
+  unsigned int priority2 = get_builtin_code_for_version (decl2, NULL);
 
   return (int)priority1 - (int)priority2;
 }
@@ -29065,14 +29062,12 @@ ix86_mangle_function_version_assembler_name (tree decl, tree id)
 
   if (DECL_VIRTUAL_P (decl)
       || DECL_VINDEX (decl))
-    error_at (DECL_SOURCE_LOCATION (decl),
-	      "Virtual function versioning not supported\n");
+    sorry ("Virtual function multiversioning not supported");
 
   version_attr = lookup_attribute ("target", DECL_ATTRIBUTES (decl));
 
-  /* target attribute string is NULL for default functions.  */
-  if (version_attr == NULL_TREE)
-    return id;
+  /* target attribute string cannot be NULL.  */
+  gcc_assert (version_attr != NULL_TREE);
 
   orig_name = IDENTIFIER_POINTER (id);
   version_string
@@ -29512,8 +29507,8 @@ ix86_generate_version_dispatcher_body (void *node_p)
 	 virtual methods in base classes but are not explicitly marked as
 	 virtual.  */
       if (DECL_VINDEX (versn->symbol.decl))
-        error_at (DECL_SOURCE_LOCATION (versn->symbol.decl),
-		  "Virtual function multiversioning not supported");
+	sorry ("Virtual function multiversioning not supported");
+
       fn_ver_vec.safe_push (versn->symbol.decl);
     }
 

gcc/doc/extend.texi

@@ -3655,6 +3655,11 @@ Enable/disable the generation of the advanced bit instructions.
 @cindex @code{target("aes")} attribute
 Enable/disable the generation of the AES instructions.
 
+@item default
+@cindex @code{target("default")} attribute
+@xref{Function Multiversioning}, where it is used to specify the
+default function version.
+
 @item mmx
 @itemx no-mmx
 @cindex @code{target("mmx")} attribute
@@ -15215,6 +15220,7 @@ Predefined Macros,cpp,The GNU C Preprocessor}).
 * Bound member functions:: You can extract a function pointer to the
                         method denoted by a @samp{->*} or @samp{.*} expression.
 * C++ Attributes::      Variable, function, and type attributes for C++ only.
+* Function Multiversioning::   Declaring multiple function versions.
 * Namespace Association:: Strong using-directives for namespace association.
 * Type Traits::         Compiler support for type traits
 * Java Exceptions::     Tweaking exception handling to work with Java.
@@ -15744,6 +15750,64 @@ interface table mechanism, instead of regular virtual table dispatch.
 
 See also @ref{Namespace Association}.
 
+@node Function Multiversioning
+@section Function Multiversioning
+@cindex function versions
+
+With the GNU C++ front end, for target i386, you may specify multiple
+versions of a function, where each function is specialized for a
+specific target feature.  At runtime, the appropriate version of the
+function is automatically executed depending on the characteristics of
+the execution platform.  Here is an example.
+
+@smallexample
+__attribute__ ((target ("default")))
+int foo ()
+@{
+  // The default version of foo.
+  return 0;
+@}
+
+__attribute__ ((target ("sse4.2")))
+int foo ()
+@{
+  // foo version for SSE4.2
+  return 1;
+@}
+
+__attribute__ ((target ("arch=atom")))
+int foo ()
+@{
+  // foo version for the Intel ATOM processor
+  return 2;
+@}
+
+__attribute__ ((target ("arch=amdfam10")))
+int foo ()
+@{
+  // foo version for the AMD Family 0x10 processors.
+  return 3;
+@}
+
+int main ()
+@{
+  int (*p)() = &foo;
+  assert ((*p) () == foo ());
+  return 0;
+@}
+@end smallexample
+
+In the above example, four versions of function foo are created. The
+first version of foo with the target attribute "default" is the default
+version.  This version gets executed when no other target specific
+version qualifies for execution on a particular platform. A new version
+of foo is created by using the same function signature but with a
+different target string.  Function foo is called or a pointer to it is
+taken just like a regular function.  GCC takes care of doing the
+dispatching to call the right version at runtime.  Refer to the
+@uref{http://gcc.gnu.org/wiki/FunctionMultiVersioning, GCC wiki on
+Function Multiversioning} for more details.
+
 @node Namespace Association
 @section Namespace Association
 

gcc/testsuite/ChangeLog

+2013-02-11  Sriraman Tallam  <tmsriramgoogle.com>
+
+	* g++.dg/ext/mv12.C: New test.
+	* g++.dg/ext/mv12.h: New file.
+	* g++.dg/ext/mv12-aux.C: New file.
+	* g++.dg/ext/mv13.C: New test.
+
 2013-02-11  Sebastian Huber  <sebastian.huber@embedded-brains.de>
 
 	* lib/target-supports.exp

gcc/testsuite/g++.dg/ext/mv12-aux.C

+// Test case to check if multiversioning works as expected when the versions
+// are defined in different files. Auxiliary file for mv12.C.
+// { dg-do compile }
+
+#include "mv12.h"
+
+__attribute__ ((target ("sse4.2")))
+int foo ()
+{
+  return 1;
+}

gcc/testsuite/g++.dg/ext/mv12.C

+// Test case to check if multiversioning works as expected when the versions
+// are defined in different files.
+
+// { dg-do run { target i?86-*-* x86_64-*-* } }
+// { dg-require-ifunc "" }
+// { dg-options "-O2" }
+// { dg-additional-sources "mv12-aux.C" }
+
+#include "mv12.h"
+
+int main ()
+{
+  if (__builtin_cpu_supports ("sse4.2"))
+    return foo () - 1;
+  return foo ();
+}
+
+__attribute__ ((target ("default")))
+int foo ()
+{
+  return 0;
+}

gcc/testsuite/g++.dg/ext/mv12.h

+// Header file used by mv12.C and mv12-aux.C.
+// { dg-do compile { target i?86-*-* x86_64-*-* } }
+// { dg-options "" }
+
+int foo () __attribute__ ((target ("default")));
+int foo () __attribute__ ((target ("sse4.2")));

gcc/testsuite/g++.dg/ext/mv13.C

+// Test case to check if multiversioning functions that are extern "C"
+// generates errors.
+
+// { dg-do compile { target i?86-*-* x86_64-*-* } }
+
+extern "C"
+__attribute__ ((target ("default")))
+int foo ()  // { dg-error "previously defined here" }
+{
+  return 0;
+}
+
+extern "C"
+__attribute__ ((target ("sse4.2")))
+int foo () // { dg-error "redefinition" }
+{
+  return 1;
+}