llvm/llvm-project

[X86] Recognise VPMADD52L/H patterns on AVX512IFMA/AVXIFMA targets

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#153,787 opened on Aug 15, 2025

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backend:X86good first issuemissed-optimization

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Description

AVX512IFMA/AVXIFMA targets should be able to fold vXi64 mul-add patterns assuming the multiplicands are known to be u52 integers

X86ISD::VPMADD52L patterns can be matched for (X * Y) + Z if the upper 12 bits of X, Y AND (X * Y) are all known zero

X86ISD::VPMADD52H patterns are trickier as we extract the upper 52 bits of the (X * Y) 104-bit mulu extended result, but at least basic matching might be achievable

Contributor guide

Research direction
Study the existing AVX512IFMA patterns in X86InstrInfo.td and X86ISelLowering.cpp, trace how similar multiply add patterns are matched, and identify the code sections that handle VPMADD52. Implement the pattern recognition following the existing conventions.
Tech stack
None
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
5
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Over 1 week
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.
Mostly clear
Prerequisites
C++
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
15