[llvm] r188188 - Misc enhancements to LTO:

[Shuxin Yang]

On 8/12/13 12:16 PM, Nick Lewycky wrote:
> Shuxin Yang wrote:
>> Author: shuxin_yang
>> Date: Mon Aug 12 13:29:43 2013
>> New Revision: 188188
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=188188&view=rev
>> Log:
>> Misc enhancements to LTO:
>>
>>    1. Add some helper classes for partitions. They are designed in a
>>       way such that the top-level LTO driver will not see much 
>> difference
>>       with or without partitioning.
>>
>>    2. Introduce work-dir. Now all intermediate files generated during
>>       LTO phases will be saved under work-dir. User can specify the 
>> workdir
>>       via -lto-workdir=/path/to/dir. By default the work-dir will be
>>       erased before linker exit. To keep the workdir, do -lto-keep, 
>> or -lto-keep=1.
>>
>>      TODO: Erase the workdir, if the linker exit prematurely.
>>        We are currently not able to remove directory on signal. The 
>> support
>>        routines simply ignore directory.
>>
>>    3. Add one new API lto_codegen_get_files_need_remove().
>>       Linker and LTO plugin will communicate via this API about which 
>> files
>>      (including directories) need to removed before linker exit.
>
> Please revert. Adding new flags to libLTO is the wrong direction (in 
> spite of the ones that exist -- consider those grandfathered in). 
It dose not make sense. Without flags, how do you manage to triage the 
correctness and performance problem?
Adding flags to linker instead, I think that is wrong direction. Linker 
dose not have data structure which libLTO dose.

> libLTO is intended to be used as a library, it may not get a chance to 
> parse flags.
It has to. Prior to my change, linkers (GNU linker and Apple ld) pass 
arch to linker, via a function
confusingly called, something like "add.*debug.*options".