http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55742
--- Comment #32 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-18 14:18:58 UTC --- Created attachment 29207 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29207 gcc48-pr55742.patch This bug is open for way too long given its severity, so let's start talking over patches. This patch attempts to implement what I understand from Jason's comments, just with "default" instead of "any", because it is indeed the default target attribute (whatever you specify on the command line). Say on: void foo (); void foo () __attribute__((target ("avx"))); void foo () __attribute__((target ("default"))); __attribute__((target ("default"))) void foo () { } __attribute__((target ("avx"))) void foo () { } void (*fn) () = foo; first we merge the first two decls, because only if target attribute is present on both, we consider it for multi-versioning, for compatibility with 4.7 and older. On e.g. void foo (); void foo () __attribute__((target ("sse4"))); void foo () __attribute__((target ("default"))); void foo () { } we reject the last fn definition, because at that point foo is already known to be multi-versioned, thus it is required that target attribute is specified for foo (either "default", or some other). Unfortunately, for this case the error is reported twice for some reason. The #c0 testcase now compiles. Now, the issues I discovered with multiversioning, still unfixed by the patch: 1) the mv*.C testcases should be moved, probably to g++.dg/ext/mv*.C 2) can you please explain the mess in handle_target_attribute? /* Do not strip invalid target attributes for targets which support function multiversioning as the target string is used to determine versioned functions. */ else if (! targetm.target_option.valid_attribute_p (*node, name, args, flags) && ! targetm.target_option.supports_function_versions ()) *no_add_attrs = true; Why do you need that? Consider complete garbage in target attribute arguments, which is errored about, but the above for i386/x86_64 keeps the target attribute around anyway, leading to lots of ICEs everywhere: Consider e.g.: __attribute__((target ("default"))) void foo (void) { } __attribute__((target (128))) void foo (void) { } 3) the multiversioning code assumes that target has a single argument, but it can have more than one. Say for: __attribute__((target ("avx,popcnt"))) void foo (void) { } __attribute__((target ("popcnt","avx"))) void bar (void) { } the compiler handles those two as equivalent, but with -Dbar=foo multi-versioning only considers the first string out of that.
