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Re: User directed Function Multiversioning via Function Overloading (issue5752064)
- From: Jason Merrill <jason at redhat dot com>
- To: Sriraman Tallam <tmsriram at google dot com>
- Cc: David Li <davidxl at google dot com>, "H.J. Lu" <hjl dot tools at gmail dot com>, gcc-patches List <gcc-patches at gcc dot gnu dot org>, Jan Hubicka <jh at suse dot cz>, Diego Novillo <dnovillo at google dot com>
- Date: Tue, 06 Nov 2012 10:52:02 -0500
- Subject: Re: User directed Function Multiversioning via Function Overloading (issue5752064)
- References: <CAAs8HmxHF38ktt6syjWp-MpjiX+6NcXh7_8Xn6iKnAiF2vRymQ@mail.gmail.com> <5008708E.1030109@redhat.com> <CAAs8Hmy7h5SGkJ+D5v_DnXs-h4B2d_YWEcstufb5=SowbVBp0Q@mail.gmail.com> <CAAs8HmyKPG_LxxxP2ngkGTFAKUPXQDJsbbsrOB_oAP0ViyER3g@mail.gmail.com> <506F27AF.3070805@redhat.com> <CAAs8HmxEod=EJNyUjrD0-WaP0-cB5o_AN9oc2O2ryu--MRQf4w@mail.gmail.com> <CAAs8Hmyy9S+Ucg6rTDU3xGMg8JEaa0r3rNjbxhbjuk9H8Sb6wg@mail.gmail.com> <50816D63.3020908@google.com> <CAAs8HmzZUnGq9G3KQ-wesKOHVWJBHn1n0zyFhEOPxo+i0PBrww@mail.gmail.com> <CAAs8HmxXfBdsLOrhEnd=syUXfbo5gKa-QkdWQG=4bUeWOPrSfQ@mail.gmail.com> <20121026155447.GA4348@atrey.karlin.mff.cuni.cz> <CAAs8Hmw0KBhKp_3qe0gzVi1jw=LVg6GD1cv-++=Kh3OjThwB+A@mail.gmail.com> <50902624.3020705@redhat.com> <CAAs8Hmw09giv-5_v0irhByTjTJV=kD58rCAD2SAz7M8zrwjBOA@mail.gmail.com> <50912F66.3030707@redhat.com> <CAAs8Hmz4CNzyJHAPoRkEe5gtL3YXSqoNHGMeZdm0uJujFHkMhQ@mail.gmail.com> <CAAs8Hmz7aDcN+2YGfH8ixrgUt+A=PuTt8ZzPhUVeQTgSWGP-Ww@mail.gmail.com>
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.
+ /* 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