llvm/llvm-project

[Flang] IARGC can't be used in a range loop

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#158,438 opened on Sep 13, 2025

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flang:frontendgood first issue

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Description

Trying to compile https://github.com/loriab/dftd3/blob/8e5463eafbaa0130a1aa26b8ee8ed57b1c3ffef0/dftd3.f#L268C14-L268C19 with Flang 21 I get the following error:

/usr/local/bin/flang21   -O -O3 -c /wrkdirs/usr/ports/science/dftd3/work/dftd3-3.2.0-3-g8e5463e/dftd3.f -o CMakeFiles/dftd3.dir/dftd3.f.o
error: Semantic errors in /wrkdirs/usr/ports/science/dftd3/work/dftd3-3.2.0-3-g8e5463e/dftd3.f
/wrkdirs/usr/ports/science/dftd3/work/dftd3-3.2.0-3-g8e5463e/dftd3.f:268:14: error: No explicit type declared for 'iargc'
        do i=1,iargc()
               ^^^^^

Contributor guide

Research direction
Investigate why the intrinsic IARGC is not recognized in a DO loop context. Look into Flang's intrinsic handling and implicit type rules.
Tech stack
None
Domain
frontend
Issue type
Bug
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
GitC++
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50