LGTM, but a minor suggestion below:
<alfie.richa...@arm.com> writes:
> @@ -423,61 +423,100 @@ expand_target_clones (struct cgraph_node *node, bool
> definition)
> return true;
> }
>
> -/* When NODE is a target clone, consider all callees and redirect
> - to a clone with equal target attributes. That prevents multiple
> - multi-versioning dispatches and a call-chain can be optimized.
> -
> - This optimisation might pick the wrong version in some cases, since
> knowing
> - that we meet the target requirements for a matching callee version does
> not
> - tell us that we won't also meet the target requirements for a higher
> - priority callee version at runtime. Since this is longstanding behaviour
> - for x86 and powerpc, we preserve it for those targets, but skip the
> optimisation
> - for targets that use the "target_version" attribute for multi-versioning.
> */
> +/* When NODE is part of an FMV function set, consider all callees and check
> if
> + any can provably always resolve a certain version and then call that
> version
> + directly. */
>
> static void
> redirect_to_specific_clone (cgraph_node *node)
> {
> - cgraph_function_version_info *fv = node->function_version ();
> - if (fv == NULL)
> - return;
> -
> - gcc_assert (TARGET_HAS_FMV_TARGET_ATTRIBUTE);
> - tree attr_target = lookup_attribute ("target", DECL_ATTRIBUTES
> (node->decl));
> - if (attr_target == NULL_TREE)
> + if (!targetm.compare_version_priority || !optimize)
> return;
>
> /* We need to remember NEXT_CALLER as it could be modified in the loop. */
> for (cgraph_edge *e = node->callees; e ; e = e->next_callee)
> {
> - cgraph_function_version_info *fv2 = e->callee->function_version ();
> - if (!fv2)
> + /* Only if this is a call to a dispatched symbol. */
> + if (!e->callee->dispatcher_function)
> continue;
>
> - tree attr_target2 = lookup_attribute ("target",
> - DECL_ATTRIBUTES (e->callee->decl));
> + cgraph_function_version_info *callee_v
> + = e->callee->function_version ();
> + cgraph_function_version_info *caller_v
> + = e->caller->function_version ();
> +
> + gcc_assert (callee_v);
>
> - /* Function is not calling proper target clone. */
> - if (attr_target2 == NULL_TREE
> - || !attribute_value_equal (attr_target, attr_target2))
> + /* Find the default nodes for both callee and caller (if present). */
> + cgraph_function_version_info *callee_default_v = callee_v->next;
> + cgraph_function_version_info *caller_default_v = caller_v;
> + if (caller_v)
> {
> - while (fv2->prev != NULL)
> - fv2 = fv2->prev;
> + while (caller_default_v->prev)
> + caller_default_v = caller_default_v->prev;
> + if (!is_function_default_version (caller_default_v->this_node->decl))
> + caller_default_v = NULL;
> + }
> +
> + /* If this is not the TU that contains the definition of the default
> + version we are not guaranteed to have visibility of all versions
> + so cannot reason about them. */
> + if (!callee_default_v
> + || !callee_default_v->this_node->binds_to_current_def_p ())
> + continue;
> +
> + cgraph_function_version_info *highest_callable_fn = NULL;
> + for (cgraph_function_version_info *ver = callee_v->next;
> + ver;
> + ver = ver->next)
> + if (targetm.target_option.functions_b_resolvable_from_a
> + (node->decl, ver->this_node->decl, node->decl))
> + highest_callable_fn = ver;
>
> - /* Try to find a clone with equal target attribute. */
> - for (; fv2 != NULL; fv2 = fv2->next)
> + if (!highest_callable_fn)
> + continue;
> +
> + bool inlinable = true;
> +
> + /* If there are higher priority versions of callee and caller has no
> + more version information, then not callable. */
> + if (highest_callable_fn->next)
> + {
> + /* If this is not the decl where the callee default is defined then
"the TU where ..." seems more accurate to me. That is, the callee's
default version must be defined in the current translation unit and
references to the callee must bind to this local definition.
OK with that change, thanks.
Richard
> + cannot reason about the caller versions. */
> + if (!caller_default_v
> + || !caller_default_v->this_node->binds_to_current_def_p ())
> + continue;
> +
> + /* If every higher priority version would imply a higher priority
> + version of caller would have been selected, then this is
> + callable. */
> + for (cgraph_function_version_info *callee_ver
> + = highest_callable_fn->next;
> + callee_ver; callee_ver = callee_ver->next)
> {
> - cgraph_node *callee = fv2->this_node;
> - attr_target2 = lookup_attribute ("target",
> - DECL_ATTRIBUTES (callee->decl));
> - if (attr_target2 != NULL_TREE
> - && attribute_value_equal (attr_target, attr_target2))
> + bool is_possible = true;
> + for (cgraph_function_version_info *caller_ver = caller_v->next;
> + caller_ver; caller_ver = caller_ver->next)
> + if (targetm.target_option.functions_b_resolvable_from_a
> + (callee_ver->this_node->decl, caller_ver->this_node->decl,
> + node->decl))
> + {
> + is_possible = false;
> + break;
> + }
> + if (is_possible)
> {
> - e->redirect_callee (callee);
> - cgraph_edge::redirect_call_stmt_to_callee (e);
> + inlinable = false;
> break;
> }
> }
> }
> + if (inlinable)
> + {
> + e->redirect_callee (highest_callable_fn->this_node);
> + cgraph_edge::redirect_call_stmt_to_callee (e);
> + }
> }
> }
>
