craig.topper added a comment.

In D63638#1560846 <https://reviews.llvm.org/D63638#1560846>, @spatel wrote:

> I skimmed D63174 <https://reviews.llvm.org/D63174> but haven't applied either 
> of these patches to test locally, so I may not have the full picture.
>
> IMO, we do not want clang regression tests running 
> -instcombine/-instsimplify. That can cause clang tests to break when an 
> underlying LLVM change is made. Forcing LLVM devs to depend on clang and fix 
> the resulting breakage is backwards and unexpected extra work. This has 
> happened to me several times.
>
> As a compromise to the -O0 IR explosion, we do have precedent for running the 
> optimizer's -mem2reg pass since that doesn't change frequently at this point.
>
> And I haven't tried this, but we do have utils/update_cc_test_checks.py - 
> this is supposed to take the manual labor out of generating assertions in the 
> same way that we do in the optimizer and codegen regression tests with 
> utils/update_test_checks.py and utils/update_llc_test_checks.py. Can you 
> start with that and remove the irrelevant CHECK lines, so only the 
> common/important lines remain? Or just use independent FileCheck 
> '--check-prefixes'?


I definitely agree running -instcombine would be bad since it can replace 
squences with other sequences. -instsimplify is a little less scary because our 
intrinsic tests shouldn't really have a lot of things that are trivially 
reducible. Though that may not be as true as I want it to be. The main issue we 
seemed to need -instsimplify for with the new pass manager is to merge 
redundant bitcasts. The inliner in the old pass manager seemed to do that 
itself, but the new pass manager's always inliner doesn't.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63638/new/

https://reviews.llvm.org/D63638



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