golang/go

cmd/compile: mips/mips64 floating point negation does not handle NaN correctly

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#58,466 opened on Feb 10, 2023

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Description

As discussed on https://github.com/golang/go/issues/56491#issuecomment-1426492508, on MIPS the gc compiler uses neg.d (which it calls NEGD) to negate a floating-point value. However, that instruction does not actually negate a NaN. That suggests that we should not use neg.d for floating point negation, but should instead xor with the high bit.

CC @randall77 @golang/mips @golang/runtime

Contributor guide

Research direction
Trace the MIPS floating point negation code generation in cmd/compile/internal/ssagen and replace NEGD with an XOR of the high bit.
Tech stack
go
Domain
tooling
Issue type
Bug
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.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GoMIPS assembly
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35