llvm/llvm-project

[DAG] computeKnownFPClass - add ISD::SQRT handling + test coverage

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#189583 opened on Mar 31, 2026

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good first issuellvm:SelectionDAG

Description

This will need to be based off the implementation in computeKnownFPClass in ValueTracking.cpp.

This should be tested with IR tests and not unit tests

Contributor guide

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.
4
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.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++ knowledgeLLVM IR basicscompiler backend concepts
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Study the existing computeKnownFPClass in ValueTracking.cpp (likely in llvm/lib/Analysis/ValueTracking.cpp). Find the counterpart in DAGCombiner (likely in llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp). Add handling for ISD::SQRT similar to the IR version. Write IR tests to verify the new handling. Check the comments and any related discussions in the issue for additional details.