[Bug target/65837] [arm-linux-gnueabihf] lto1 target specific builtin not available

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65837

--- Comment #21 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to prathamesh3492 from comment #18)
> Created attachment 35420 [details]
> patch to override default options by options in object file
> 
> Hi,
> 
> The following untested patch gives preference to option value in object file.
> In run_gcc(),
> options from COLLECT_GCC_OPTIONS which are taken from command line are
> stored in decoded_options.
> options from object file are stored in fdecoded_options.
> so override the option in decoded_options if it is present in
> fdecoded_options.
> 
> With the patch this works:
> arm-linux-gnueabihf-gcc test.c -mfpu=neon -flto -c
> arm-linux-gnueabihf-gcc test.o -flto 
> only passes -mfpu=neon to lto1
> 
> However the patch doesn't work when same option is passed different values
> at compile and link-time:
> arm-linux-gnuebihf-gcc test.c -mfpu=neon -flto -c
> arm-linux-gnueabihf-gcc test.o -mfpu=vfpv3-d16 -flto
> 
> In this case, -mfpu=neon is still passed to lto1, since the patch prefers
> option value from object file.
> Without the patch, the option from the command line was given preference.
> 
> for both the following cases: 
> arm-linux-gnueabihf-gcc test.o -flto
> arm-linux-gnueabihf-gcc test.o -flto -mfpu=vfpv3-d16
> 
> COLLECT_GCC_OPTIONS contains "-mfpu=vfpv3-d16", however in the first case it
> isn't explictly passed by user, so passing -mfpu=neon
> would be correct. In the second case, since -mfpu=vfpv3-d16 is passed
> intentionally by user, should it be considered
> as an error - "conflicting options" ?
> 
> Unfortunately, it looks like there is no way to distinguish between options
> defined by default and explicitly passed options from COLLECT_GCC_OPTIONS
> and that's the only way command line options are passed to lto-wrapper from
> the driver. One way would be to modify COLLECT_GCC_OPTIONS in the driver to
> indicate which options were explicitly passed from command line.
> For instance, additionally COLLECT_GCC_OPTIONS would contain 
> "-mfpu=vfpv3-d16-explicit" to indiciate that -mfpu=vfpv3-d16 was
> passed from command line and not set by default. In lto-wrapper the options
> could be parsed to check if they have "explicit" suffix and thus distinguish
> between explicit and defualt defined options.
> Does that sound reasonable ? I would be grateful for suggestions.
> 
> Thank you,
> Prathamesh

As said the patch is wrong.