llvm/llvm-project

[AArch64] Add SimplifyDemandedVectorEltsForTargetNode support for AArch64ISD::DUPLANE nodes

Open

#87,497 opened on Apr 3, 2024

View on GitHub
 (13 comments) (0 reactions) (1 assignee)C++ (10,782 forks)batch import
backend:AArch64good first issue

Repository metrics

Stars
 (26,378 stars)
PR merge metrics
 (Avg merge 1d 2h) (1,000 merged PRs in 30d)

Description

Noticed on #86284 - aarch64 is missing SimplifyDemandedVectorElts handling to/from AArch64ISD::DUPLANE nodes

  • Extend performDUPCombine to call SimplifyDemandedVectorElts from AArch64ISD::DUPLANE nodes as we only demand that one lane element.
  • Add AArch64TargetLowering::SimplifyDemandedVectorEltsForTargetNode to handle AArch64ISD::DUPLANE nodes (and AArch64ISD::DUP?) - if we only demand the dup lane index we might be able to remove the node entirely.
  • The hadd-combine.ll tests might be enough, but we could require some additional test coverage.

Contributor guide

Research direction
Examine the existing performDUPCombine function in AArch64ISelLowering.cpp and understand how SimplifyDemandedVectorElts is used in other targets. Then implement the changes step by step: first extend performDUPCombine to call SimplifyDemandedVectorElts, then add the target specific callback, and finally verify with the hadd combine.ll tests. Focus on how DUPLANE nodes only demand one lane element and how to remove them if only that lane is demanded.
Tech stack
cpp
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitC++
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40