User directed Function Multiversioning via Function Overloading (issue5752064)
Sriraman Tallam
tmsriram@google.com
Tue Nov 6 18:17:00 GMT 2012
On Tue, Nov 6, 2012 at 7:52 AM, Jason Merrill <jason@redhat.com> wrote:
> On 11/05/2012 09:38 PM, Sriraman Tallam wrote:
>>
>> + /* For multi-versioned functions, more than one match is just fine.
>>
>> + Call decls_match to make sure they are different because they are
>> + versioned. */
>> + if (DECL_FUNCTION_VERSIONED (fn))
>> + {
>> + for (match = TREE_CHAIN (matches); match; match = TREE_CHAIN
>> (match))
>> + if (!DECL_FUNCTION_VERSIONED (TREE_PURPOSE (match))
>> + || decls_match (fn, TREE_PURPOSE (match)))
>> + break;
>> + }
>
>
> I still don't understand what this code is supposed to be doing. Please
> remove it and instead modify the other loop to allow mismatches that are
> versions of the same function.
Ok, will do. I was trying to do for versioned functions what the other
loop was doing thought I could not come up with a test case to
exercise this code.
I will make all the other changes and get back asap.
Thanks,
-Sri.
>
>> + /* If the olddecl is a version, so is the newdecl. */
>> + if (TREE_CODE (newdecl) == FUNCTION_DECL
>> + && DECL_FUNCTION_VERSIONED (olddecl))
>> + {
>> + DECL_FUNCTION_VERSIONED (newdecl) = 1;
>> + /* newdecl will be purged and is no longer a version. */
>> + delete_function_version (newdecl);
>> + }
>
>
> Please make the comment clearer that the reason we're setting the flag on
> the newdecl is so that it'll be copied back into the olddecl; otherwise it
> seems odd to say it's a version and then it isn't a version.
>
>> + /* If a pointer to a function that is multi-versioned is requested, the
>> + pointer to the dispatcher function is returned instead. This works
>> + well because indirectly calling the function will dispatch the right
>> + function version at run-time. */
>>
>> + if (DECL_FUNCTION_VERSIONED (fn))
>> + {
>> + tree dispatcher_decl = NULL;
>> + gcc_assert (targetm.get_function_versions_dispatcher);
>> + dispatcher_decl = targetm.get_function_versions_dispatcher (fn);
>> + if (!dispatcher_decl)
>> + {
>> + error_at (input_location, "Pointer to a multiversioned function"
>> + " without a default is not allowed");
>> + return error_mark_node;
>> + }
>> + retrofit_lang_decl (dispatcher_decl);
>> + fn = dispatcher_decl;
>
>
> This code should use the get_function_version_dispatcher function in
> cp/call.c.
>
> Jason
>
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