[PATCH] D64258: [InferFuncAttributes] extend 'dereferenceable' attribute based on loads

Fri Jul 5 14:37:11 PDT 2019

spatel added a comment.

In D64258#1571981 <https://reviews.llvm.org/D64258#1571981>, @jdoerfert wrote:

> The direction of this makes total sense and we will need it. However this shoulnd't be here (wrt. the file/pass).
>
> Assuming we want this right right now, it should life in FunctionAttrs.cpp. Assuming we want to do it "right" it should become part of the Attributor framework.
>
> The early prototype of the "deref-or-null" abstract attribute already had this functionality, see https://reviews.llvm.org/D59202#C1381429NL1995, and the test case https://reviews.llvm.org/D59202#change-FJbHx7N4s6ye . For the new Attributor, dereferenceable-or-null has not yet been ported and the transfer of "close by information" is not part of the new model. Both things are going to change soon.

Thanks for taking a look! I was just about to add you as a reviewer. I know you are working on a major overhaul of this functionality, but I have not gotten a chance to look at those patches.
The reason I did not put this into FunctionAttrs.cpp is because that's currently too late to catch the motivating example from PR21780 using the default opt pass pipeline. Ie, -instcombine runs before -functionattrs and kills the loads before we have a chance to update the arguments. I would like to get this in soon to make the next clang major release, so this seemed like the patch of least resistance. :)
If there's a better way, I can certainly try to make it happen.

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https://reviews.llvm.org/D64258