llvm/llvm-project

scalbln(x, n), scalbn(x, n), ldexp(x, n) are not folded at the compilation time when (x, n) is constant

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#112,631 opened on Oct 16, 2024

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floating-pointgood first issuellvm:optimizationsmissed-optimization

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Description

Consider the following example. https://godbolt.org/z/54xsG8WTr

#include <cmath>

double f1() {
  return std::scalbln(3.0, 4);
}

double f2() {
  return std::scalbn(3.0, 4);
}

double f3() {
  return std::ldexp(3.0, 4);
}

Contributor guide

Research direction
Investigate why LLVM's constant folding pass does not fold std::scalbln, std::scalbn, and std::ldexp with constant arguments. Trace the handling of these math functions in the InstCombine or SelectionDAG passes.
Tech stack
c
Domain
backend
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
C++LLVM
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40