llvm/llvm-project

[X86] computeKnownBitsForTargetNode - add X86ISD::GF2P8AFFINEQB handling

Open

#190,520 opened on 2026年4月5日

GitHub で見る
 (13 comments) (0 reactions) (2 assignees)C++ (26,378 stars) (10,782 forks)batch import
backend:X86good first issue

説明

X86ISD::GF2P8AFFINEQB nodes are being used for many shift/rotate style expansions, it'd be very useful if we can access the known bits to attempt additional folding afterward (e.g #190502).

This should only be attempted by somebody with access to a CPU with GFNI support to allow them to actually test this properly (although constexpr testing can help now that GFNI intrinsics support it).

Reference: https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html#ig_expand=172,3053,2650,3028,3046,849,3516,3630,3054,3053,3054,4389,2239,2239,4602,205,196,4461,3954,1601,2140,417,2873,2851,2571,5840,2571,2927,3639&text=VGF2P8AFFINEQB

(see also GFNIAffine() in llvm-project\clang\lib\AST\ExprConstant.cpp)

コントリビューターガイド

技術スタック
cpp
領域
tooling
Issue 種別
feature
難度新しい貢献者にとっての実装難度です。1 は非常に小さな変更、5 は専門的な作業です。
5
推定時間経験ある貢献者が調査、実装、テスト、pull request 準備にかけるおおよその時間範囲です。
over 1 week
活動状況Issue が今どれだけ取り組みやすいかを示します。新しい、活発、古い、ブロック中、またはメンテナー入力待ちなどです。
active
明確さ期待される変更、受け入れ条件、次の手順がどれだけ明確かを示します。
clear
前提条件
LLVM codegen infrastructureX86 backend knowledgeknown bits analysisGFNI intrinsics
初心者向け度初回貢献者にどれだけ取り組みやすいかを 1-100 で推定したスコアです。
15
調査方針
The issue requests adding handling for X86ISD::GF2P8AFFINEQB in the computeKnownBitsForTargetNode function. Start by studying the existing implementations for other X86ISD nodes in the X86 backend's target specific lowering. The reference implementation for GFNI intrinsics in clang's ExprConstant.cpp (GFNIAffine) can provide insight. The Intel intrinsics guide details the behavior of the VGF2P8AFFINEQB instruction. Ensure testing is done either on a CPU with GFNI support or using constexpr evaluation as mentioned.