[llvm-dev] RFC: LTO should use -disable-llvm-verifier

[Duncan P. N. Exon Smith via llvm-dev]

> On 2015-Sep-16, at 10:51, Mehdi Amini <mehdi.amini at apple.com> wrote:
> 
>> 
>> On Sep 16, 2015, at 10:46 AM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
>> 
>> 
>>> On 2015-Sep-16, at 10:09, Mehdi Amini <mehdi.amini at apple.com> wrote:
>>> 
>>>> 
>>>> On Sep 16, 2015, at 9:45 AM, Teresa Johnson via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>>> 
>>>> On Wed, Sep 16, 2015 at 7:47 AM, Teresa Johnson <tejohnson at google.com> wrote:
>>>>> On Tue, Sep 15, 2015 at 3:31 PM, Duncan P. N. Exon Smith via llvm-dev
>>>>> <llvm-dev at lists.llvm.org> wrote:
>>>>>> 
>>>>>>> On 2015-Sep-02, at 19:31, Peter Collingbourne <peter at pcc.me.uk> wrote:
>>>>>>> 
>>>>>>> On Thu, Sep 03, 2015 at 01:10:42AM +0000, Eric Christopher wrote:
>>>>>>>> On Tue, Sep 1, 2015 at 10:43 AM Duncan P. N. Exon Smith <
>>>>>>>> dexonsmith at apple.com> wrote:
>>>>>>>> 
>>>>>>>>> 
>>>>>>>>>> On 2015-Aug-31, at 18:09, Eric Christopher <echristo at gmail.com> wrote:
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> On Mon, Aug 31, 2015 at 5:50 PM Duncan P. N. Exon Smith <
>>>>>>>>> dexonsmith at apple.com> wrote:
>>>>>>>>>> 
>>>>>>>>>>> On 2015-Aug-31, at 12:21, Eric Christopher <echristo at gmail.com> wrote:
>>>>>>>>>>> Yep. This is where I was going :)
>>>>>>>>>> 
>>>>>>>>>> Glad I found consensus, but I want to double-check that this makes
>>>>>>>>>> sense to add to the driver.  I didn't quite think through the
>>>>>>>>>> implications myself.
>>>>>>>>>> 
>>>>>>>>>> Since the driver doesn't know if there's any bitcode, or if LTO is
>>>>>>>>>> going to be invoked, it seems like I'll have to change the noasserts
>>>>>>>>>> driver to *always* pass the option to the linker just in case we are
>>>>>>>>>> doing LTO.  Is this reasonable?
>>>>>>>>>> 
>>>>>>>>>> Also, I realized that passing `-mllvm -disable-llvm-verifier` to ld64
>>>>>>>>>> is redundant... so I'm thinking `-mllvm -disable-verify`.  Make
>>>>>>>>>> sense?
>>>>>>>>>> 
>>>>>>>>>> *sigh* Reasons to hate the driver interface again...
>>>>>>>>>> 
>>>>>>>>>> I guess this is ok. Could possibly add it to the existing terrible
>>>>>>>>> "enable this pass" interface on liblto as well.
>>>>>>>>> 
>>>>>>>>> The linker doesn't know whether clang was built with asserts, though.
>>>>>>>>> 
>>>>>>>>> We could just make it implicit: move the decision to libLTO itself.  Given
>>>>>>>>> that clang and libLTO.dylib are different executables anyway -- and you
>>>>>>>>> might be interposing an asserts libLTO.dylib to use with an installed clang
>>>>>>>>> -- maybe it's even better?
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>> *nod* We could do that. Seems better than the alternative.
>>>>>>> 
>>>>>>> +1
>>>>>> 
>>>>>> Finally got back to this.  Done in r247729.
>>>>>> 
>>>>>> I didn't modify gold-plugin.cpp, as I don't have a good way to test it,
>>>>>> but someone else should be able to do it pretty easily.
>>>>> 
>>>>> I can do this for gold (presumably also controlled via an option, but
>>>>> set default based on NDEBUG).
>>>>> 
>>>>> Couple questions:
>>>>> - For your patch the default is set based on NDEBUG for lto.cpp, but
>>>>> in llvm-lto it always defaults to false. Is that intentional?
>>>> 
>>>> After writing a test for my gold-plugin changes, I think I know the
>>>> answer to the above question. It is presumably because you don't want
>>>> the behavior of new test ./test/LTO/X86/disable-verify.ll which uses
>>>> llvm-lto to change based on whether the compiler is built NDEBUG or
>>>> not, since you are also testing the default behavior without
>>>> -disable-verify in this test.
>>>> 
>>>> Since gold-plugin isn't a testing tool, I think we do want the default
>>>> controlled by NDEBUG. So presumably my new gold-plugin-based test
>>>> cannot test the default behavior, just the behavior with the new
>>>> disable-verify plugin option.
>>> 
>>> Note sure if it would help but you can add “REQUIRE: assert” in a test to only run it when NDEBUG is enabled.
>>> 
>>> There is no “REQUIRE: noassert” though.
>> 
>> It would be possible, but I like that llvm-lto (as a testing tool) behaves
>> consistently regardless of assertions.
> 
> It was a suggestion to be able to test gold, not for llvm-lto.

Ah.

This would be possible for tools/lto as well, FWIW.