[PATCH] D113073: [lld-macho] Cache library paths from findLibrary

[Vy Nguyen via Phabricator via llvm-commits]

oontvoo added a comment.

In D113073#3106528 <https://reviews.llvm.org/D113073#3106528>, @keith wrote:

> In D113073#3106474 <https://reviews.llvm.org/D113073#3106474>, @oontvoo wrote:
>
>> In D113073#3105039 <https://reviews.llvm.org/D113073#3105039>, @keith wrote:
>>
>>> In D113073#3104904 <https://reviews.llvm.org/D113073#3104904>, @int3 wrote:
>>>
>>>> By the way, thanks for contributing all these optimizations! I was quite surprised to hear that ld64 was faster, given that LLD is typically much faster for our own workloads, but I guess you have rather different inputs. Hopefully we can make LLD the fastest Mach-O linker for all builds :)
>>>
>>> Thanks for all the reviews! For context our project is a huge iOS application with on the order of thousands of static libraries, and many iOS system framework + system library dependencies. Is this a case you've benchmarked? If so I'd be interested to dig a bit deeper into the differences to try and understand why it has been slower for us.
>>
>> For one of our largest ios apps that I've measured(different from int3's ):
>>
>> - ~7100 archives
>> - 56 frameworks  (including system ones)
>> - 12 weak frameworks
>
> Thanks for the info! What's your bottleneck at this point? After all my changes here our biggest area is we now spend 20+ seconds in `lld::macho::readFile`

*With* all of the patches improving load input applied, linking the app above is only slightly faster than our optimised LD64:
(cross-linking, on Linux - Broadwell (yeah, kind of old) RAM 32GB)

  x ./LLD_with_cache_patches.txt
  + ./LD64_local_imprv.txt
  +-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  |x     *           x  *x  x  * *          +      +   +                         +                                                                +                      +|
  |        |_|________A__M______|__________________M____________A____________________________________________________|                                                    |
  +-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
      N           Min           Max        Median           Avg        Stddev
  x  10         23.64         23.89         23.82        23.799   0.077667382
  +  10         23.69         25.01         24.04        24.146     0.4379041
  Difference at 95.0% confidence
  	0.347 +/- 0.295482
  	1.45804% +/- 1.24157%
  	(Student's t, pooled s = 0.314478)

Looking at the trace, the bottleneck is still in loading input and writing output. 
It seems it could be improved further ...

F20184452: Screen Shot 2021-11-09 at 10.20.13 AM.png <https://reviews.llvm.org/F20184452>


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