[llvm-dev] RFC: Mark BasicAA as a CFG-only pass. (original) (raw)

Alina Sbirlea via llvm-dev llvm-dev at lists.llvm.org
Mon Feb 10 15:58:30 PST 2020

Got it, I updated the patch. Please let me know fi I should detail it further.

Thank you, Alina

On Mon, Feb 10, 2020 at 3:10 PM Hal Finkel <hfinkel at anl.gov> wrote:

On 2/10/20 4:09 PM, Alina Sbirlea wrote: On Mon, Feb 10, 2020 at 1:48 PM Hal Finkel <hfinkel at anl.gov> wrote:

On 2/10/20 2:35 PM, Alina Sbirlea wrote: Hi, Here's a tentative patch of the changes for this: D74353 <https://reviews.llvm.org/D74353>.

I suppose that, as expected, it's invalidated less often this way. Given that it's generally stateless, does this really represent a cost savings? -Hal I don't think there is a cost savings now, the current patch shouldn't have much or any impact. But I think this can affect future infrastructure changes. I got here by looking at MemCpyOpt, as part of a longer term goal of having the pass sequence [GVN, MemCpyOpt, DSE] use MemorySSA instead of MemDepAnalysis. Currently we're explicitly checking that, after MemCpyOpt, BasicAA is freed. This wouldn't make sense when using MemorySSA in all 3 passes, as we'd end up rebuilding MemorySSA due to invalidating BasicAA. I kept the changes needed to MemCpyOpt to preserve passes separate from this discussion. Does this clarify some of the motivation? Yes, please add this information to the patch description. I think that it makes sense to mark BasicAA as not being invalidated on non-CFG-altering IR changes if it's not. -Hal Alina

Thank you, Alina On Mon, Feb 10, 2020 at 11:34 AM Alina Sbirlea <alina.sbirlea at gmail.com> wrote: Hi, I'd like to understand if it makes sense to keep BasicAA as a not CFG-only pass, or if it can be updated to CFG-only. The change was made in D44564 <https://reviews.llvm.org/D44564>. From what I gathered the motivation was PhiValuesAnalysis not being properly updated, and BasicAA having an instance of it. PhiValuesAnalysis now uses callback values to invalidate deleted values ( r340613 <https://reviews.llvm.org/rL340613>), PhiValuesAnalysis is also being updated in MemDepAnalysis (D48489 <https://reviews.llvm.org/D48489>) and BasicAA is invalidated if PhiValuesAnalysis gets invalidated. I may not have the full context here, so I'd like some feedback: does it make sense to make BasicAA a CFG-only pass again? Thank you, Alina -- Hal Finkel Lead, Compiler Technology and Programming Languages Leadership Computing Facility Argonne National Laboratory -- Hal Finkel Lead, Compiler Technology and Programming Languages Leadership Computing Facility Argonne National Laboratory -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200210/56123356/attachment-0001.html>

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