[PATCH] D102726: [IR][AutoUpgrade] Drop alignment from non-pointer parameters and returns

Sat May 22 11:30:39 PDT 2021

nikic added a comment.

In D102726#2774689 <https://reviews.llvm.org/D102726#2774689>, @jdoerfert wrote:

> In D102726#2774657 <https://reviews.llvm.org/D102726#2774657>, @nikic wrote:
>
>> FYI, this change causes a non-trivial compile-time regression in LTO builds: https://llvm-compile-time-tracker.com/compare.php?from=136ced498ba84f6b6126051626e319f18ba740f5&to=5b6cae5524905bc43cfc21a515f828528d1f2e68&stat=instructions (Worst regression seems to be the ThinLTO kc.link step, which is up 4%.)
>>
>> LLVM attributes are optimized for immutable usage, and it's hard to overstate just how slow the mutable APIs on them are...
>
> I suggested not to check for attributes just to remove them. I still think that's the right thing *but* we can check for them in the remove functions.
> @nikic you think that will resolve the compile time issue?

I've added two optimizations along those lines in https://github.com/llvm/llvm-project/commit/fd46ed3f397d6cf41bc6c5a04ab2089f585afe44 and https://github.com/llvm/llvm-project/commit/05738ffcb87b76c6f166f965ba9b2db3257a4338.

The remaining impact from this change is now https://llvm-compile-time-tracker.com/compare.php?stat=instructions&from=9530d41b3106a8bdc619f7bf4dd6e2e645bb2b07&to=05738ffcb87b76c6f166f965ba9b2db3257a4338, which seems acceptable.

Repository:
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  https://reviews.llvm.org/D102726/new/

https://reviews.llvm.org/D102726