C-Reduce (@creduce) profile picture

C-Reduce

@creduce

I am C-Reduce, the shrinker of C/C++ programs.

 Salt Lake City, UT, USA
embed.cs.utah.edu/creduce/
Joined June 2012
  • Tweets289
  • Following69
  • Followers479
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Photo by C-Reduce (@creduce)Photo by C-Reduce (@creduce)Photo by C-Reduce (@creduce)
Always happy to help!
LaurieWired (@lauriewired) profile pictureLaurieWired
@lauriewired10 Jul 2025
Replying to @lauriewired
One contestant experimented with C-Reduce; a way to search for C++ programs that create unusual compiler behavior. Maximizing the fitness function for error as a reward, no templates, no pre-processor hacks. Just nested parenthesis causing exponential error output!
Image from LaurieWired (@lauriewired)
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C-Reduce retweeted
Lee Wei (@leewei666) profile picture
Lee Wei@leewei6664 Mar 2025
Learn LLVM until I find a compiler job | Day 29 Both creduce and llvm-reduce are still running. Hopefully, the can finish by tomorrow morning.
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Replying to @creduce
My favorite version of this is github.com/maleadt/creduce_j… which can take an entire tree of Julia packages and apply creduce to it . Now I just need to figure out how to use Julia's parser to do smarter rewrites.
GitHub - maleadt/creduce_julia

GitHub - maleadt/creduce_julia

Contribute to maleadt/creduce_julia development by creating an account on GitHub.

github.com
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"You can use C-Reduce for any language" by Max Bernstein. bernsteinbear.com/blog/credu…

You can use C-Reduce for any language

C-Reduce is a tool by Regehr and friends for minimizing C compiler bug reproducers. Imagine if you had a 10,000 line long C file that triggered a Clang bug. You don’t want to send a massive blob to...

bernsteinbear.com
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Running creduce to try to minimize a test case for "clang produces different binaries when building natively on i386 vs cross-building from amd64". Only reduced from 2346 to 1727 lines so far, which makes me think this bug is hard to trigger.
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I'll try anything!
Brendan Dolan-Gavitt (@moyix) profile pictureBrendan Dolan-Gavitt
@moyix9 Jan 2024
Does such a thing as CReduce for a Python script exist? (Or can CReduce be abused into working on Python code?)
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I tried creduce to reduce a segfaulting test case and it reduced it to this 👍 #creduce #screenshotsaturday
gdb disassembly output showing code for main function that basically calls itself, which is UB and causes segfault.

ALT gdb disassembly output showing code for main function that basically calls itself, which is UB and causes segfault.

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We've all been there.
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I love working the night shift. 🌜 Thanks for the shout out!
@ericniebler.bsky.social (@ericniebler) profile picture@ericniebler.bsky.social@ericniebler28 Jun 2023
Replying to @atomgalaxy
I reduce a lot of compiler bugs, so I have a system that involves a directory full of stub stdlib/system headers, creduce, and some ready-made scripts. I also have a 64-core machine. creduce takes it down to ~10k overnight, and I take it from there.
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Replying to @lemire
You should use creduce to minimize that.
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Thanks for the shout out!
furtive pygmy (parody) 💨 (@steubens7) profile picturefurtive pygmy (parody) 💨@steubens729 May 2023
Replying to @steubens7 @tom_verbeure
creduce is good to know regardless, it's just especially good at this
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Replying to @BruceDawson0xB @visualc
You can make minimal repros using creduce fairly easily. Even with msvc, just do it under WSL and take advantage of the fact you can call native win32 programs. No advanced C++ skills necessary
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creduce help text: --shaddap Suppress output about non-fatal internal errors [..] --sllooww Try harder to reduce, but perhaps take a long time to do so
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Expectation: I have a bug, let me try to use C-Reduce to reduce it Reality: Run into a bug with C-Reduce itself Happy weekend I guess... Oh wait, it's just Thursday.
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C-Reduce retweeted
Eric Eide (@eeide) profile picture
Eric Eide@eeide25 Jan 2023
Hey! Guess what came in the mail today! @sigplan @PLDI @creduce
Photograph of a glass award in box. Text: "ACM SIGPLAN / Most Influential Paper of PLDI 2012 / Awarded at PLDI 2022 / Test-Case Reduction for C Compiler Bugs / by / John Regehr, Yang Chen, Pascal Cuoq, Eric Eide, Chucky Ellison and Xuejun Yang"

ALT Photograph of a glass award in box. Text: "ACM SIGPLAN / Most Influential Paper of PLDI 2012 / Awarded at PLDI 2022 / Test-Case Reduction for C Compiler Bugs / by / John Regehr, Yang Chen, Pascal Cuoq, Eric Eide, Chucky Ellison and Xuejun Yang"

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💯 github.com/csmith-project/cr…

FYI: also reduces Dafny code! · Issue #250 · csmith-project/creduce

I managed to reduce a bug in Dafny code (https://dafny.org/). This was in macOS 13, Apple Silicon, using creduce 2.11.0 (installed with brew --HEAD), with the --not-c option.

github.com
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Replying to @Cor3ntin @creduce
creduce is magic.
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TFW the code creduce produces would probably not lead to a productive compiler bug report because it does weird things (like a null deref) that the original code doesn't do, but re-adding parts of the original code makes the bug you're trying to report not reproduce anymore...
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Replying to @stephenrkell @SreepathiPai @creduce
Thanks - for now I wrote a script that inlines specific #included files but does not actually preprocess, then I used @creduce to do a reduction on that code, and things are working nicely.
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I'm having a @creduce problem: my source file has been preprocessed using clang-14, and now gcc-11 is complaining about it with errors like: error: two or more data types in declaration specifiers 214 | typedef float _Float32; Anyone know how to solve this?
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