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Compiler Explorer @compiler-explorer.com · 2d

And we're back. A temporary misconfiguration - we have fixed it and all is well..sorry for the problem! -mg

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Compiler Explorer @compiler-explorer.com · 2d

Investigating why Windows compilers are down! Watch this space, and sorry for any inconvenience -mg

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Matt Godbolt @matt.godbolt.org · 17d

LLM-explanation is now live in @compiler-explorer.com - An example: compiler-explorer.com/z/rvvx7MxKq

* LLMs make mistakes and are overconfident
* We'll never force LLMs or AI on you, it's opt in (like clang-tidy, PVS Studio or other tools)
* It is *beta* quality

Initial results are promising(1/3)

Compiler Explorer - C++ (x86-64 clang 21.1.0)

// setup constexpr auto valid_chars = "0123456789abcdef"; bool is_valid_id(std::string_view maybe_id) { if (maybe_id.size() != 16) { return false; } if (maybe_id.find_first_not_of(valid_ch...

explain.compiler-explorer.com

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Matt Godbolt @matt.godbolt.org · 27d

@compiler-explorer.com is now running with a completely new storage mechanism in the back end. It's taken me quite a long time to get to the point where I felt confident enough to switch over to it and it seems like it's gone without a hitch. Details:
xania.org/202509/cefs

CEFS: Finally Solving CE's Mount(ing) Problems — Matt Godbolt’s blog

In which CE's boot times are finally brought under control

xania.org

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Matt Godbolt @matt.godbolt.org · Aug 22

Hey folks! @compiler-explorer.com is free & open for everyone, but if you're planning to use our API for bulk executions though, please ping us! CE is a shared resource and heavy use can slow things down for the whole community. DM me to chat - happy to help figure out what works for everyone! :)

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Compiler Explorer @compiler-explorer.com · Aug 22

Support friend of the site Jason by going to one of his excellent courses! Jason was instrumental in publicising CE in the early days and his courses are awesome too! -mg

Jason Turner @lefticus.bsky.social · Aug 22

Come to one of my highly interactive and dynamic C++ Best Practices conference workshops this year at CppCon (Sept 13-14) or NDC TechTown (Sept 22-23)

Only about 4 weeks left!

ndctechtown.com/workshops/c-...

cppcon.org/class-2025-b...

C++ Best Practices | NDC TechTown 2025

This is a 2-day workshop that explores Best Practices as they apply to C++.

ndctechtown.com

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Compiler Explorer @compiler-explorer.com · Jul 23

CE relies on your support! How you can help:

* Submit PRs & report issues: github.com/compiler-exp...
* Become a Patron: patreon.com/mattgodbolt
* Sponsor us: github.com/sponsors/com...
* Buy CE swag: shop.compiler-explorer.com
* Join our Discord: discord.gg/B5WacA7

github.com

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Matt Godbolt @matt.godbolt.org · Jul 19

I've been getting more anecdotal reports that @compiler-explorer.com is slow. Seems to be folks' simple code taking a while, likely queued up behind a longer compile. We've done some digging and it seems to have gotten worse since December last year. Doesn't seem to be bot traffic. Have you noticed?

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Compiler Explorer @compiler-explorer.com · Jun 30

Huge news! AWS has approved Compiler Explorer for their Open Source Credits program, covering our infrastructure costs for the next year!
Thank you AWS for supporting open source! This means faster compiles, better queuing & more improvements coming. Exciting times ahead!

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Matt Godbolt @matt.godbolt.org · Jun 11

I'm frequently asked "how much does @compiler-explorer.com cost to run". I've done some digging and posted xania.org/202506/compi... which is a high-level breakdown of the costs (and revenue); and links to a more in depth report if you want all the gory details.

Compiler Explorer Cost Transparency — Matt Godbolt’s blog

In which I try and show how we spend your kind Patreon donations

xania.org

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Matt Godbolt @matt.godbolt.org · Jun 8

I'm half way through my career break, and taking stock. Plan was to do conf talks (check), work on @compiler-explorer.com (check), spend time with family (sort of) and even do some hobby code (also sort of). Higher level goal still is to get CE "on its feet" a bit...

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Matt Godbolt @matt.godbolt.org · Jun 5

A fantastic walk through of some @compiler-explorer.com features by one of our core maintainers @ofekshilon.bsky.social . Thanks Ofek!

youtu.be/_9sGKcvT-TA

Get More Out of Compiler-Explorer ('godbolt') :: Ofek Shilon

YouTube video by CoreCppIL

youtu.be

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Matt Godbolt @matt.godbolt.org · Jun 3

It's been a while since I've written about the innards of @compiler-explorer.com. xania.org/202506/how-c... has the details, some statistics and some fun war stories.

How Compiler Explorer Works in 2025 — Matt Godbolt’s blog

How we handle 92 million compilations a year without everything catching fire

xania.org

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Matt Godbolt @matt.godbolt.org · May 28

On @compiler-explorer.com URLs and another Google product sunsetting: xania.org/202505/compi...

Compiler Explorer and the Promise of URLs That Last Forever — Matt Godbolt’s blog

How we're preserving 12,000 legacy links as Google's URL shortener rides into the sunset

xania.org

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Matt Godbolt @matt.godbolt.org · May 23

Experimenting with something like this for @compiler-explorer.com - wondering what your thoughts are? AI is getting everywhere, and can be divisive. I'm hoping something like this - so long as I can get the output quality high enough - is a net benefit to help folks learn more about their code.

$A screenshot of Compiler Explorer showing an "AI Explain this" view. The source code is: bool isspc(char c) { return c == '\n' || c == '\r' || c == '\t' || c == ' '; } The asm is: isspc(char): mov ecx, edi cmp cl, 33 setb dl movabs rax, 4294977024 shr rax, cl and al, dl ret Below is a "Claude Explain" window with: The function isspc(char) is compiled to an efficient bit manipulation technique to check for whitespace characters. Let's break down the assembly instructions: mov ecx, edi Copies the input character from the edi register (first function argument) to ecx cl will contain the lowest 8 bits (the character) cmp cl, 33 Compares the character against decimal 33 This is a preliminary check to quickly filter out non-whitespace characters setb dl Sets the dl register to 1 if the character is below 33 (space, tab, newline, etc.) Uses a conditional set instruction movabs rax, 4294977024 Loads a pre-computed 64-bit constant This constant represents a bit mask for whitespace detection shr rax, cl Shifts the bit mask right by the character's value This dynamically positions the mask based on the input character and al, dl Performs a bitwise AND between the shifted mask and the previous condition Produces the final boolean result in al ret Returns the result (0 or 1) in al This implementation is a highly optimized branchless method for checking whitespace characters, using bit manipulation instead of multiple comparisons. It avoids conditional jumps, which can be slower on modern CPUs. The code checks for space (' '), newline ('\n'), carriage return ('\r'), and tab ('\t') in a single, efficient operation.$

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Matt Godbolt @matt.godbolt.org · Apr 23

Thrilled to share that @compiler-explorer.com has received a $10K grant from NVIDIA's FOSS Fund! This support will help keep our GPU instances running and allow developers worldwide to experiment with CUDA code. Thank you NVIDIA AI Dev for supporting open source tools! #NVIDIAGrant

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Shafik Yaghmour @shafik.bsky.social · Feb 8

Once again

#programming

Bernie once again meme with

I am once again asking

you to remember that if turning on optimizations changes the behavior of your program, it is likely you are missing some undefined behavior

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Compiler Explorer @compiler-explorer.com · Feb 6

Does passing `-m32` to generate 32-bit code work? -mg

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Compiler Explorer @compiler-explorer.com · Feb 6

This is what I'm seeing anyway, as I'd expect. -mg

A screenshot of the site showing all the x86 gccs

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Compiler Explorer @compiler-explorer.com · Feb 6

I see them; can you elaborate on what you're seeing?

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Compiler Explorer @compiler-explorer.com · Feb 6

First I've heard that it's not there

...taking a look -mg

Compiler Explorer @compiler-explorer.com · Jan 6

We just blocked a TW-based IPv6 address from making many many back-to-back requests, most of which seemed to hit our caches (and thus were duplicates). If this affected you, please DM us or reply and we can help diagnose what went wrong. -mg

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Compiler Explorer @compiler-explorer.com · Dec 31

Compiler Explorer in 2024!

0.017 cents per compilation for 190M compilations. Tons of new features, Matt takes stock:

www.patreon.com/posts/compil...

Compiler Explorer in 2024 | Matt Godbolt

Get more from Matt Godbolt on Patreon

www.patreon.com

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Matt Godbolt @matt.godbolt.org · Dec 7

Sent my first proper Patreon/GitHub sponsor update for @compiler-explorer.com work today. Surreal experience, I'm kinda giving my first update to my new boss(es) :-)

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Slang Shading Language and Compiler @shader-slang.bsky.social · Dec 5

Godbolt now has Slang support!

godbolt.org
@compiler-explorer.com

Compiler Explorer

Compiler Explorer is an interactive online compiler which shows the assembly output of compiled C++, Rust, Go (and many more) code.

godbolt.org

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