[PATCH] D20423: [Clang][LLVMGold] Passing LLVM arguments to gold plugin

[Teresa Johnson via llvm-commits]

On Tue, May 31, 2016 at 9:47 AM, Mehdi Amini <mehdi.amini at apple.com> wrote:

>
> On May 31, 2016, at 9:42 AM, Teresa Johnson <tejohnson at google.com> wrote:
>
>
>
> On Tue, May 24, 2016 at 4:01 PM, Duncan P. N. Exon Smith <
> dexonsmith at apple.com> wrote:
>
>> This seems strange to me.  For example, it breaks the otherwise very
>> convenient:
>> --
>> $ clang -flto t.c -mllvm -some-internal-option-for-cc1
>> --
>>
>
> What is an example mllvm option that is passed to cc1 that would be
> illegal to pass via the gold-plugin - it isn't just ignored?
>
>
> I believe it is not about being "illegal" but rather being surprised by
> some unintended behavior, and losing the ability to control what options is
> applied during link compared to the cc1-optimizations phase.
>

But if I did a vanilla -O2 build and passed -mllvm it would be passed down
to the optimization pipeline. I find the reverse (it isn't when I do -O2
-flto) more surprising.


>
>
>
>>
>> I don't understand how it's better.
>>
>
> Another issue with the current situation is that in order to pass these to
> llvm in LTO builds (at least for gold) you have to do
> -Wl,-plugin-opt,-mllvm,-some-option, and gold gives a fatal error if it
> sees a -plugin-opt without -plugin. So for example in a clang LTO bootstrap
> I cannot set it up to pass any -mllvm option via plugin-opt because there
> are link steps that create intermediate shared libraries but don't invoke
> the plugin, so I get a fatal error (this affects all plugin-opt, but -mllvm
> is probably a likely one that I would want to pass for debugging or
> analysis).
>
>
> I'm surprised that you are building intermediate shared library during a
> bootstrap of clang, and even more that they're not built out of bitcode?
>

Looks like it is compiler-rt asan code (libclang_rt.asan-i386.so) that is
not being built with LTO, which I think makes sense given that it is linked
into user code not into the compiler.


> --
> Mehdi
>
>
>
>
>> > On 2016-May-20, at 08:14, Mehdi AMINI via llvm-commits <
>> llvm-commits at lists.llvm.org> wrote:
>> >
>> > joker.eph added a comment.
>> >
>> > I'm don't have a strong opinion, let me ask what Duncan think of that.
>> >
>> >
>> > http://reviews.llvm.org/D20423
>> >
>> >
>> >
>> > _______________________________________________
>> > llvm-commits mailing list
>> > llvm-commits at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>>
>>
>
>
> --
> Teresa Johnson |  Software Engineer |  tejohnson at google.com |
> 408-460-2413
>
>
>


-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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