[PATCH] D123803: [WIP][llvm] A Unified LTO Bitcode Frontend

Fri Apr 15 11:27:27 PDT 2022

mehdi_amini added inline comments.

================
Comment at: llvm/lib/Passes/PassBuilder.cpp:1144
+      if (!PTO.UnifiedLTO)
+        MPM.addPass(buildThinLTODefaultPipeline(L, nullptr));
+      else
----------------
tejohnson wrote:
> mehdi_amini wrote:
> > It is concerning to me that we add one mode different code path / behavior to maintain instead of unifying everything.
> > 
> > If UnifiedLTO is able to use the LTO pipeline effectively, what would be the reason for ThinLTO to not align?
> > If UnifiedLTO is able to use the LTO pipeline effectively, what would be the reason for ThinLTO to not align?
> 
> Perhaps it can eventually, but I would not want to make a major change to the ThinLTO pipelines without a lot of experimentation. I don't personally have the bandwidth to do that right now, but if this was in as an alternative mode under an option, it could be done more easily at some point on a wider range of applications. I'd be concerned for example of side effects on importing behavior which is based on instruction count thresholds.
Right, but your objection is exactly the root of my concerned with this new mode in the first place right now.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D123803/new/

https://reviews.llvm.org/D123803