[llvm] [InstCombine] lshr (mul (X, 2^N + 1)), N -> add (X, lshr(X, N)) (PR #90295)

[via llvm-commits]

AtariDreams wrote:

> > > > > > A generalization of the proposed x * 3/2 -> x + (x >> 1) transformation.
> > > 
> > > 
> > > > >
> > > 
> > > 
> > > > >
> > > 
> > > 
> > > > > Proposed where?
> > > 
> > > 
> > > > 
> > > 
> > > 
> > > > This question was not answered. The way this is written implies there was some discussion separate from this PR that proposed something. There should be a link to that proposal or this commit message should be rephrased.
> > > 
> > > 
> > > A variant of this PR was originally part of #88193. What was "proposed" is that these unrelated changes be removed from that PR.
> > 
> > 
> > And those unrelated changes were removed!
> 
> Great. But that doesn't change the fact that the description of this PR needs to be modified. It will become a commit message that will live in the LLVM repo forever. It doesn't look like the fact that this code was previously part of a different PR is relevant to understanding this PR so the sentence should just be deleted.



> > > > > > A generalization of the proposed x * 3/2 -> x + (x >> 1) transformation.
> > > 
> > > 
> > > > >
> > > 
> > > 
> > > > >
> > > 
> > > 
> > > > > Proposed where?
> > > 
> > > 
> > > > 
> > > 
> > > 
> > > > This question was not answered. The way this is written implies there was some discussion separate from this PR that proposed something. There should be a link to that proposal or this commit message should be rephrased.
> > > 
> > > 
> > > A variant of this PR was originally part of #88193. What was "proposed" is that these unrelated changes be removed from that PR.
> > 
> > 
> > And those unrelated changes were removed!
> 
> Great. But that doesn't change the fact that the description of this PR needs to be modified. It will become a commit message that will live in the LLVM repo forever. It doesn't look like the fact that this code was previously part of a different PR is relevant to understanding this PR so the sentence should just be deleted.



> > > > > > A generalization of the proposed x * 3/2 -> x + (x >> 1) transformation.
> > > 
> > > 
> > > > >
> > > 
> > > 
> > > > >
> > > 
> > > 
> > > > > Proposed where?
> > > 
> > > 
> > > > 
> > > 
> > > 
> > > > This question was not answered. The way this is written implies there was some discussion separate from this PR that proposed something. There should be a link to that proposal or this commit message should be rephrased.
> > > 
> > > 
> > > A variant of this PR was originally part of #88193. What was "proposed" is that these unrelated changes be removed from that PR.
> > 
> > 
> > And those unrelated changes were removed!
> 
> Great. But that doesn't change the fact that the description of this PR needs to be modified. It will become a commit message that will live in the LLVM repo forever. It doesn't look like the fact that this code was previously part of a different PR is relevant to understanding this PR so the sentence should just be deleted.

Fixed!

https://github.com/llvm/llvm-project/pull/90295