[lld] r222983 - [Core] Add flag to check if RoundTripPasses need to be run.

[Rui Ueyama]

I think that's arguable if that's considered as information lost. After an
atom is written to a new Native file and reloaded, it gets a new file name
because it was actually read from a different file. If a compiler outputs
an object file in Native format, it's the file name of an atom read from
the file.

On Mon, Dec 1, 2014 at 2:14 PM, Shankar Easwaran <shankare at codeaurora.org>
wrote:

> On 12/1/2014 4:02 PM, Rui Ueyama wrote:
>
>> On Mon, Dec 1, 2014 at 1:48 PM, Nick Kledzik <kledzik at apple.com> wrote:
>>
>>  On Dec 1, 2014, at 12:34 PM, Rui Ueyama <ruiu at google.com> wrote:
>>>
>>> That sounds like we really need a new property of Atom.
>>>
>>> 1. If we run LLD in Release build, the roundtrip passes don't run, so
>>> everything works fine.
>>> 2. If we run LLD in Debug build (and from the unit tests), the
>>> information
>>> is dropped during the round-trip conversion, and it fails.
>>> 3. RoundTrip tests should't drop any information.
>>>
>>> 2 and 3 conflicts.
>>>
>>>
>>> I have a different view.
>>>
>>> I think of those Passes as a quick way to exercise the YAML and native
>>> formats.  The mechanism is as if you went through the test cases and
>>> added
>>> a line which ran “ld -r” to merge all input files into one file, then ran
>>> the rest of the test with that merged input file.  That works everywhere
>>> except in tests that care about the name of the input file (which is now
>>> changed).  So, for those cases you would not do the merge step.  But
>>> since
>>> the round trip is implicit, there is no way to turn it off.  Shankar is
>>> adding a way to turn it off.
>>>
>>>  That doesn't sounds like a different view.
>>
>> If a test fails because of the difference of an input file name, not
>> because the round-trip conversion drops some information, we should
>> disable
>> the round-trip test only for that test. Now I feel I understood your
>> suggestion in a different thread. Is there any way to override the
>> environment variable in the lit test? Does it allow us to write RUN:
>> LLD_ROUNDTRIP_TEST=0 lld <args here> ?
>>
>
> The filename information of the Atom is lost in the Native format.
>
> Gnu flavor needs the filename whenever the user uses a linker script (or)
> the user decides to know the memory map of the image.
>
> So this is needed almost all the time.
>
>
> Shankar Easwaran
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by the Linux Foundation
>
>
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