Re: [PATCH 1/2] Fix -fno-lto (PR lto/46905)

[Richard Guenther <richard.guenther@gmail.com>]

On Thu, Dec 16, 2010 at 5:56 PM, Andi Kleen <andi@firstfloor.org> wrote:
> On Thu, Dec 16, 2010 at 03:39:33PM +0000, Joseph S. Myers wrote:
>> On Thu, 16 Dec 2010, Richard Guenther wrote:
>>
>> > > I also tried to do it without opts.c, but setting an 0 initialization
>> > > value for the -fno-lto entry, but that didn't work either.
>> >
>> > Huh, that's strange.  Joseph, do you have any idea why?  Is it because
>> > of how flags get passed to collect2?
>>
>> Having both flto and fno-lto in common.opt seems dodgy.  Try making the
>> code in opts.c that handles OPT_flto check "value" (value == 0 meaning
>> -fno-lto) instead.
>
> That worked. Here's an updated version. Ok now?

Ok.

Can you check if you also need to update the linker plugin to not
claim object files if -fno-lto is in effect?

Btw, what happens with -flto -fno-lto -flto?

Thanks,
Richard.

> From: Andi Kleen <ak@linux.intel.com>
> Date: Wed, 15 Dec 2010 20:10:22 +0100
> Subject: [PATCH] Fix -fno-lto (PR lto/46905)
>
> This fixes PR lto/46905.
>
> It's sometimes convenient in large Makefiles to globally enable LTO
> in CFLAGS, but disable it again for specific files. The simplest
> way to do that is appending -fno-lto, but that didn't work.
> Add explicit code to handle this case.
>
> gcc/
>
> 2010-12-15  Andi Kleen  <ak@linux.intel.com>
>
>        PR lto/46905
>        * collect2.c (main): Handle -fno-lto.
>        * common.opt (fno-lto): Add.
>        * opts.c (common_handle_option): Handle OPT_fno_lto.
>
> diff --git a/gcc/collect2.c b/gcc/collect2.c
> index 89b21d5..77f794f 100644
> --- a/gcc/collect2.c
> +++ b/gcc/collect2.c
> @@ -1211,6 +1211,8 @@ main (int argc, char **argv)
>         else if ((! strncmp (argv[i], "-flto=", 6)
>                  || ! strcmp (argv[i], "-flto")) && ! use_plugin)
>          lto_mode = LTO_MODE_WHOPR;
> +       else if (!strncmp (argv[i], "-fno-lto", 8))
> +         lto_mode = LTO_MODE_NONE;
>         else if (! strcmp (argv[i], "-plugin"))
>          {
>            use_plugin = true;
> diff --git a/gcc/opts.c b/gcc/opts.c
> index 2c8e767..cc4181e 100644
> --- a/gcc/opts.c
> +++ b/gcc/opts.c
> @@ -1670,7 +1670,7 @@ common_handle_option (struct gcc_options *opts,
>       break;
>
>     case OPT_flto:
> -      opts->x_flag_lto = "";
> +      opts->x_flag_lto = value ? "" : NULL;
>       break;
>
>     case OPT_w:
>