On Thu, Oct 26, 2023 at 07:41:09PM +0100, Richard Sandiford wrote:
> Andrew Carlotti <andrew.carlo...@arm.com> writes:
> > This patch adds support for the "target_version" attribute to the middle
> > end and the C++ frontend, which will be used to implement function
> > multiversioning in the aarch64 backend.
> >
> > Note that C++ is currently the only frontend which supports
> > multiversioning using the "target" attribute, whereas the
> > "target_clones" attribute is additionally supported in C, D and Ada.
> > Support for the target_version attribute will be extended to C at a
> > later date.
> >
> > Targets that currently use the "target" attribute for function
> > multiversioning (i.e. i386 and rs6000) are not affected by this patch.
> >
> >
> > I could have implemented the target hooks slightly differently, by reusing
> > the
> > valid_attribute_p hook and adding attribute name checks to each backend
> > implementation (c.f. the aarch64 implementation in patch 2/3). Would this
> > be
> > preferable?
>
> Having as much as possible in target-independent code seems better
> to me FWIW. On that basis:
>
> >
> > Otherwise, is this ok for master?
> >
> >
> > gcc/c-family/ChangeLog:
> >
> > * c-attribs.cc (handle_target_version_attribute): New.
> > (c_common_attribute_table): Add target_version.
> > (handle_target_clones_attribute): Add conflict with
> > target_version attribute.
> >
> > gcc/ChangeLog:
> >
> > * attribs.cc (is_function_default_version): Update comment to
> > specify incompatibility with target_version attributes.
> > * cgraphclones.cc (cgraph_node::create_version_clone_with_body):
> > Call valid_version_attribute_p for target_version attributes.
> > * target.def (valid_version_attribute_p): New hook.
> > (expanded_clones_attribute): New hook.
> > * doc/tm.texi.in: Add new hooks.
> > * doc/tm.texi: Regenerate.
> > * multiple_target.cc (create_dispatcher_calls): Remove redundant
> > is_function_default_version check.
> > (expand_target_clones): Use target hook for attribute name.
> > * targhooks.cc (default_target_option_valid_version_attribute_p):
> > New.
> > * targhooks.h (default_target_option_valid_version_attribute_p):
> > New.
> > * tree.h (DECL_FUNCTION_VERSIONED): Update comment to include
> > target_version attributes.
> >
> > gcc/cp/ChangeLog:
> >
> > * decl2.cc (check_classfn): Update comment to include
> > target_version attributes.
> >
> >
> > diff --git a/gcc/attribs.cc b/gcc/attribs.cc
> > index
> > b1300018d1e8ed8e02ded1ea721dc192a6d32a49..a3c4a81e8582ea4fd06b9518bf51fad7c998ddd6
> > 100644
> > --- a/gcc/attribs.cc
> > +++ b/gcc/attribs.cc
> > @@ -1233,8 +1233,9 @@ make_dispatcher_decl (const tree decl)
> > return func_decl;
> > }
> >
> > -/* Returns true if decl is multi-versioned and DECL is the default
> > function,
> > - that is it is not tagged with target specific optimization. */
> > +/* Returns true if DECL is multi-versioned using the target attribute, and
> > this
> > + is the default version. This function can only be used for targets
> > that do
> > + not support the "target_version" attribute. */
> >
> > bool
> > is_function_default_version (const tree decl)
> > diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
> > index
> > 072cfb69147bd6b314459c0bd48a0c1fb92d3e4d..1a224c036277d51ab4dc0d33a403177bd226e48a
> > 100644
> > --- a/gcc/c-family/c-attribs.cc
> > +++ b/gcc/c-family/c-attribs.cc
> > @@ -148,6 +148,7 @@ static tree handle_alloc_align_attribute (tree *, tree,
> > tree, int, bool *);
> > static tree handle_assume_aligned_attribute (tree *, tree, tree, int, bool
> > *);
> > static tree handle_assume_attribute (tree *, tree, tree, int, bool *);
> > static tree handle_target_attribute (tree *, tree, tree, int, bool *);
> > +static tree handle_target_version_attribute (tree *, tree, tree, int, bool
> > *);
> > static tree handle_target_clones_attribute (tree *, tree, tree, int, bool
> > *);
> > static tree handle_optimize_attribute (tree *, tree, tree, int, bool *);
> > static tree ignore_attribute (tree *, tree, tree, int, bool *);
> > @@ -480,6 +481,8 @@ const struct attribute_spec c_common_attribute_table[] =
> > handle_error_attribute, NULL },
> > { "target", 1, -1, true, false, false, false,
> > handle_target_attribute, NULL },
> > + { "target_version", 1, -1, true, false, false, false,
> > + handle_target_version_attribute, NULL },
> > { "target_clones", 1, -1, true, false, false, false,
> > handle_target_clones_attribute, NULL },
> > { "optimize", 1, -1, true, false, false, false,
> > @@ -5569,6 +5572,45 @@ handle_target_attribute (tree *node, tree name, tree
> > args, int flags,
> > return NULL_TREE;
> > }
> >
> > +/* Handle a "target_version" attribute. */
> > +
> > +static tree
> > +handle_target_version_attribute (tree *node, tree name, tree args, int
> > flags,
> > + bool *no_add_attrs)
> > +{
> > + /* Ensure we have a function type. */
> > + if (TREE_CODE (*node) != FUNCTION_DECL)
> > + {
> > + warning (OPT_Wattributes, "%qE attribute ignored", name);
> > + *no_add_attrs = true;
> > + }
> > + else if (lookup_attribute ("target_clones", DECL_ATTRIBUTES (*node)))
> > + {
> > + warning (OPT_Wattributes, "%qE attribute ignored due to conflict "
> > + "with %qs attribute", name, "target_clones");
> > + *no_add_attrs = true;
> > + }
> > + else if (!targetm.target_option.valid_version_attribute_p (*node, name,
> > args,
> > + flags))
> > + *no_add_attrs = true;
> > +
> > + /* Check that there's no empty string in values of the attribute. */
> > + for (tree t = args; t != NULL_TREE; t = TREE_CHAIN (t))
> > + {
> > + tree value = TREE_VALUE (t);
> > + if (TREE_CODE (value) == STRING_CST
> > + && TREE_STRING_LENGTH (value) == 1
> > + && TREE_STRING_POINTER (value)[0] == '\0')
> > + {
> > + warning (OPT_Wattributes,
> > + "empty string in attribute %<target_version%>");
> > + *no_add_attrs = true;
> > + }
> > + }
>
> would it make sense to do the empty string test first, and only pass
> the vetted arguments to the target hook? Also, a Google search suggests
> that there aren't any pre-existing, conflicting uses of "target_version"
> that take multiple arguments. So could this code check that there
> is exactly one argument (by changing 1, -1 to 1, 1 in the spec above)
> and then require it to be a nonempty string? It could then pass the
> string itself to the target hook (probably as a const char *).
>
> (FWIW, it doesn't look like the Clang documentation has kept the door
> open to multiple arguments.)
>
> I wonder if we could use attribute_spec::exclusions to describe the
> mutual exclusion with "target_clones". It doesn't look like the
> existing code does, though, so maybe not.
>
> I couldn't see anything that forbids a combination of "target" and
> "target_version". Should that combination be allowed? In some ways
> it makes conceptual sense, since using "target" is like changing the
> command-line options. But I suppose we'd then need to diagnose conflicts
> and deal with ordering issues. So perhaps "target" should be made
> mutually exclusive as well.
My aarch64 backend pass deals with backend issues by always applying
target_version attribute changes after target_attribute changes. I don't think
there's any additional conflicts to worry about, since adding a target_version
is simply equivalent to enabling extra features in the target string.
A similar thing would work for target_clones, but I didn't initially do that
because it would require making the frontend exclusions target dependant.
However, I think it's just a case of checking the backend hook to see whether
target_clones gets expanded to target attributes or not.
Clang currently disallows combining target attributes with either
target_version or target_clones. However, I think it's worth being able to
combine these attributes. For example, it could be useful to use the target
attribute to select different tuning for an sve target_version.
> Thanks,
> Richard
>
> > +
> > + return NULL_TREE;
> > +}
> > +
> > /* Handle a "target_clones" attribute. */
> >
> > static tree
> > @@ -5601,6 +5643,12 @@ handle_target_clones_attribute (tree *node, tree
> > name, tree ARG_UNUSED (args),
> > "with %qs attribute", name, "target");
> > *no_add_attrs = true;
> > }
> > + else if (lookup_attribute ("target_version", DECL_ATTRIBUTES
> > (*node)))
> > + {
> > + warning (OPT_Wattributes, "%qE attribute ignored due to conflict "
> > + "with %qs attribute", name, "target_version");
> > + *no_add_attrs = true;
> > + }
> > else if (get_target_clone_attr_len (args) == -1)
> > {
> > warning (OPT_Wattributes,
> > diff --git a/gcc/cgraphclones.cc b/gcc/cgraphclones.cc
> > index
> > 29d28ef895a73a223695cbb86aafbc845bbe7688..8af6b23d8c0306920e0fdcb3559ef047a16689f4
> > 100644
> > --- a/gcc/cgraphclones.cc
> > +++ b/gcc/cgraphclones.cc
> > @@ -78,6 +78,7 @@ along with GCC; see the file COPYING3. If not see
> > #include "tree-eh.h"
> > #include "tree-cfg.h"
> > #include "tree-inline.h"
> > +#include "attribs.h"
> > #include "dumpfile.h"
> > #include "gimple-pretty-print.h"
> > #include "alloc-pool.h"
> > @@ -1048,7 +1049,17 @@ cgraph_node::create_version_clone_with_body
> > location_t saved_loc = input_location;
> > tree v = TREE_VALUE (target_attributes);
> > input_location = DECL_SOURCE_LOCATION (new_decl);
> > - bool r = targetm.target_option.valid_attribute_p (new_decl, NULL, v,
> > 1);
> > + bool r;
> > + tree name_id = get_attribute_name (target_attributes);
> > + const char* name_str = IDENTIFIER_POINTER (name_id);
> > + if (strcmp (name_str, "target") == 0)
> > + r = targetm.target_option.valid_attribute_p (new_decl, name_id, v, 1);
> > + else if (strcmp (name_str, "target_version") == 0)
> > + r = targetm.target_option.valid_version_attribute_p (new_decl, name_id,
> > + v, 1);
> > + else
> > + gcc_assert(false);
> > +
> > input_location = saved_loc;
> > if (!r)
> > return NULL;
> > diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
> > index
> > 9594be4092c3c00fddc9d4c6da5931ea3b7e8792..ec78d5a5440bedd360ac8e5bc44e164da3dab410
> > 100644
> > --- a/gcc/cp/decl2.cc
> > +++ b/gcc/cp/decl2.cc
> > @@ -829,8 +829,8 @@ check_classfn (tree ctype, tree function, tree
> > template_parms)
> > tree c2 = get_constraints (fndecl);
> >
> > /* While finding a match, same types and params are not enough
> > - if the function is versioned. Also check version ("target")
> > - attributes. */
> > + if the function is versioned. Also check for different target
> > + specific attributes. */
> > if (same_type_p (TREE_TYPE (TREE_TYPE (function)),
> > TREE_TYPE (TREE_TYPE (fndecl)))
> > && compparms (p1, p2)
> > diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
> > index
> > 33e7ffc8af5a9d48430145ef9b8e7924613b7dd7..97b3e9c31631a943d95f1cf7739716a574afcfb7
> > 100644
> > --- a/gcc/doc/tm.texi
> > +++ b/gcc/doc/tm.texi
> > @@ -10507,6 +10507,23 @@ the function declaration to hold a pointer to a
> > target-specific
> > @code{struct cl_target_option} structure.
> > @end deftypefn
> >
> > +@deftypefn {Target Hook} bool TARGET_OPTION_VALID_VERSION_ATTRIBUTE_P
> > (tree @var{fndecl}, tree @var{name}, tree @var{args}, int @var{flags})
> > +This hook is called to parse @code{attribute(target_version("..."))},
> > +which allows setting target-specific options on individual function
> > versions.
> > +These function-specific options may differ
> > +from the options specified on the command line. The hook should return
> > +@code{true} if the options are valid.
> > +
> > +The hook should set the @code{DECL_FUNCTION_SPECIFIC_TARGET} field in
> > +the function declaration to hold a pointer to a target-specific
> > +@code{struct cl_target_option} structure.
> > +@end deftypefn
> > +
> > +@deftypevr {Target Hook} {const char *}
> > TARGET_OPTION_EXPANDED_CLONES_ATTRIBUTE
> > +Contains the name of the attribute used for the version description string
> > +when expanding clones for a function with the target_clones attribute.
> > +@end deftypevr
> > +
> > @deftypefn {Target Hook} void TARGET_OPTION_SAVE (struct cl_target_option
> > *@var{ptr}, struct gcc_options *@var{opts}, struct gcc_options
> > *@var{opts_set})
> > This hook is called to save any additional target-specific information
> > in the @code{struct cl_target_option} structure for function-specific
> > diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
> > index
> > c98b2447e28aa17996b1cbf8af7ed02d70db54f2..56fa3de6bba06bc0ac124bb3a41324be1997e209
> > 100644
> > --- a/gcc/doc/tm.texi.in
> > +++ b/gcc/doc/tm.texi.in
> > @@ -6979,6 +6979,10 @@ on this implementation detail.
> >
> > @hook TARGET_OPTION_VALID_ATTRIBUTE_P
> >
> > +@hook TARGET_OPTION_VALID_VERSION_ATTRIBUTE_P
> > +
> > +@hook TARGET_OPTION_EXPANDED_CLONES_ATTRIBUTE
> > +
> > @hook TARGET_OPTION_SAVE
> >
> > @hook TARGET_OPTION_RESTORE
> > diff --git a/gcc/multiple_target.cc b/gcc/multiple_target.cc
> > index
> > a2ed048d7dd28ec470953fcd8a0dc86817e4b7dc..3db57c2b13d612a37240d9dcf58ad21b2286633c
> > 100644
> > --- a/gcc/multiple_target.cc
> > +++ b/gcc/multiple_target.cc
> > @@ -66,10 +66,6 @@ create_dispatcher_calls (struct cgraph_node *node)
> > {
> > ipa_ref *ref;
> >
> > - if (!DECL_FUNCTION_VERSIONED (node->decl)
> > - || !is_function_default_version (node->decl))
> > - return;
> > -
> > if (!targetm.has_ifunc_p ())
> > {
> > error_at (DECL_SOURCE_LOCATION (node->decl),
> > @@ -377,6 +373,7 @@ expand_target_clones (struct cgraph_node *node, bool
> > definition)
> > return false;
> > }
> >
> > + const char *new_attr_name =
> > targetm.target_option.expanded_clones_attribute;
> > cgraph_function_version_info *decl1_v = NULL;
> > cgraph_function_version_info *decl2_v = NULL;
> > cgraph_function_version_info *before = NULL;
> > @@ -392,7 +389,7 @@ expand_target_clones (struct cgraph_node *node, bool
> > definition)
> > char *attr = attrs[i];
> >
> > /* Create new target clone. */
> > - tree attributes = make_attribute ("target", attr,
> > + tree attributes = make_attribute (new_attr_name, attr,
> > DECL_ATTRIBUTES (node->decl));
> >
> > char *suffix = XNEWVEC (char, strlen (attr) + 1);
> > @@ -430,7 +427,7 @@ expand_target_clones (struct cgraph_node *node, bool
> > definition)
> > XDELETEVEC (attr_str);
> >
> > /* Setting new attribute to initial function. */
> > - tree attributes = make_attribute ("target", "default",
> > + tree attributes = make_attribute (new_attr_name, "default",
> > DECL_ATTRIBUTES (node->decl));
> > DECL_ATTRIBUTES (node->decl) = attributes;
> > node->local = false;
> > diff --git a/gcc/target.def b/gcc/target.def
> > index
> > cda6c51e5167f85625168c7c26b777d6c8ccad82..39acea04db01ebaf918910b7dd73d397de6a84ec
> > 100644
> > --- a/gcc/target.def
> > +++ b/gcc/target.def
> > @@ -6492,6 +6492,31 @@ the function declaration to hold a pointer to a
> > target-specific\n\
> > bool, (tree fndecl, tree name, tree args, int flags),
> > default_target_option_valid_attribute_p)
> >
> > +/* Function to validate the attribute((target_version(...))) strings. If
> > + the option is validated, the hook should also fill in
> > + DECL_FUNCTION_SPECIFIC_TARGET in the function decl node. */
> > +DEFHOOK
> > +(valid_version_attribute_p,
> > + "This hook is called to parse
> > @code{attribute(target_version(\"...\"))},\n\
> > +which allows setting target-specific options on individual function
> > versions.\n\
> > +These function-specific options may differ\n\
> > +from the options specified on the command line. The hook should return\n\
> > +@code{true} if the options are valid.\n\
> > +\n\
> > +The hook should set the @code{DECL_FUNCTION_SPECIFIC_TARGET} field in\n\
> > +the function declaration to hold a pointer to a target-specific\n\
> > +@code{struct cl_target_option} structure.",
> > + bool, (tree fndecl, tree name, tree args, int flags),
> > + default_target_option_valid_version_attribute_p)
> > +
> > +/* Attribute to be used when expanding clones for functions with
> > + target_clones attribute. */
> > +DEFHOOKPOD
> > +(expanded_clones_attribute,
> > + "Contains the name of the attribute used for the version description
> > string\n\
> > +when expanding clones for a function with the target_clones attribute.",
> > + const char *, "target")
> > +
> > /* Function to save any extra target state in the target options
> > structure. */
> > DEFHOOK
> > (save,
> > diff --git a/gcc/targhooks.h b/gcc/targhooks.h
> > index
> > 1a0db8dddd594d9b1fb04ae0d9a66ad6b7a396dc..0efc993d82ef59b581a1df74ee0de71135a28703
> > 100644
> > --- a/gcc/targhooks.h
> > +++ b/gcc/targhooks.h
> > @@ -192,6 +192,7 @@ extern bool default_hard_regno_scratch_ok (unsigned
> > int);
> > extern bool default_mode_dependent_address_p (const_rtx, addr_space_t);
> > extern bool default_new_address_profitable_p (rtx, rtx_insn *, rtx);
> > extern bool default_target_option_valid_attribute_p (tree, tree, tree,
> > int);
> > +extern bool default_target_option_valid_version_attribute_p (tree, tree,
> > tree, int);
> > extern bool default_target_option_pragma_parse (tree, tree);
> > extern bool default_target_can_inline_p (tree, tree);
> > extern bool default_update_ipa_fn_target_info (unsigned int &, const
> > gimple *);
> > diff --git a/gcc/targhooks.cc b/gcc/targhooks.cc
> > index
> > e190369f87a92e6a92372dc348d9374c3a965c0a..7fc7bf455e80c333cced1bac7085210c2b108f8d
> > 100644
> > --- a/gcc/targhooks.cc
> > +++ b/gcc/targhooks.cc
> > @@ -1787,7 +1787,19 @@ default_target_option_valid_attribute_p (tree
> > ARG_UNUSED (fndecl),
> > int ARG_UNUSED (flags))
> > {
> > warning (OPT_Wattributes,
> > - "target attribute is not supported on this machine");
> > + "%<target%> attribute is not supported on this machine");
> > +
> > + return false;
> > +}
> > +
> > +bool
> > +default_target_option_valid_version_attribute_p (tree ARG_UNUSED (fndecl),
> > + tree ARG_UNUSED (name),
> > + tree ARG_UNUSED (args),
> > + int ARG_UNUSED (flags))
> > +{
> > + warning (OPT_Wattributes,
> > + "%<target_version%> attribute is not supported on this machine");
> >
> > return false;
> > }
> > diff --git a/gcc/tree.h b/gcc/tree.h
> > index
> > 0b72663e6a1a94406127f6253460f498b7a3ea9c..ebd89ce79566c350eaaab210c0dca3cc1ac2048e
> > 100644
> > --- a/gcc/tree.h
> > +++ b/gcc/tree.h
> > @@ -3438,8 +3438,8 @@ extern vec<tree, va_gc> **decl_debug_args_insert
> > (tree);
> > (FUNCTION_DECL_CHECK
> > (NODE)->function_decl.function_specific_optimization)
> >
> > /* In FUNCTION_DECL, this is set if this function has other versions
> > generated
> > - using "target" attributes. The default version is the one which does
> > not
> > - have any "target" attribute set. */
> > + to support different architecture feature sets, e.g. using "target" or
> > + "target_version" attributes. */
> > #define DECL_FUNCTION_VERSIONED(NODE)\
> > (FUNCTION_DECL_CHECK (NODE)->function_decl.versioned_function)
> >
