llvm/llvm-project

getNegatedExpression should handle FP16_TO_FP and FP_TO_FP16

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#177,448 opened on Jan 22, 2026

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floating-pointgood first issuellvm:SelectionDAGmissed-optimization

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Description

getNegatedExpression does not handle the opcodes FP16_TO_FP and FP_TO_FP16, but it could. This could improve use of source modifiers on AMDGPU with illegal f16.

I started implementing it in this patch, but it requires additional work to avoid regressions.

0001-DAG-Implement-getNegatedExpression-for-FP16_TO_FP.patch

Contributor guide

Research direction
Examine the existing getNegatedExpression implementation in TargetLowering.cpp and the FP16 TO FP/FP TO FP16 opcodes. Apply the provided patch and verify no regressions by running the relevant LLVM test suite.
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.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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
C++LLVM
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60