llvm/llvm-project

[DAG] Add computeKnownBits(FREEZE(X)) handling

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#161,642 opened on Oct 2, 2025

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Description

Similar to #161507 - add FREEZE handling to allow us to analyze demanded elements of a node through a FREEZE

The tricky bit will be to add test coverage - you will need a FREEZE node that can't be removed due to some elements possibly being undef/poison, but other elements that are not and have useful known bits data for a dependent node.

This might be easier once #161512 has landed.

Contributor guide

Research direction
Study the existing computeKnownBits implementations for other nodes in SelectionDAG, understand FREEZE semantics, and write code to handle FREEZE in computeKnownBits. Ensure to add test cases where FREEZE cannot be eliminated due to undef/poison elements.
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.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
C++LLVM
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20