Sign in

Compiler Explorer

@compiler-explorer.com
1.4K followers 30 following 15 posts

A website for exploring the output of compilers. aka godbolt.org Supports C, C++, Rust, Fortran, COBOL and many many more. Support us at patreon.com/mattgodbolt

PostsRepliesMedia
Reposted by Compiler Explorer
Colin Hoad @colinhoad.com · 22/06/2026
Loving my new @compiler-explorer.com desk topper! Really nice quality and a huge improvement on my old IKEA one that had seen better days 😅 Thanks, @matt.godbolt.org and team!
My desk looking unusually tidy (it won't last) with my new Compiler Explorer desk topper
0114
Reposted by Compiler Explorer
Mathieu Ropert @matropert.bsky.social · 04/07/2026
People were literally giving up on C++ before @compiler-explorer.com because they didn't trust the generated assembly would be good enough. That was only 10 years ago.
4242
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 09/06/2026
I did Compiler Explorer's monthly accounts, and for the first time in ages we only broke even. Usually we run at a small surplus (which I save) & we have a year contingency saved up. If you want to support us: * Buy stuff: shop.compiler-explorer.com * Patron/GH: "Other" menu on CE Please repost. thx
shop.compiler-explorer.com
Compiler Explorer
The official Compiler Explorer shop! Come show your support for CE and get cool gear!
55125
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 13/11/2025
This December, I'll be posting an article & video each day until Christmas in the Advent of Compiler Optimisations! #AoCO2025 Each day we'll explore a fun optimisation in C or C++; some low-level, x86 or ARM-specific, some high-level. Hope you'll join me! YT: youtube.com/mattgodbolt Blog: xania.org
xania.org
Matt Godbolt’s blog
36416
Compiler Explorer @compiler-explorer.com · 07/10/2025
Investigating why Windows compilers are down! Watch this space, and sorry for any inconvenience -mg
181
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 21/09/2025
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)
explain.compiler-explorer.com
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...
5345
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 11/09/2025
@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
xania.org
CEFS: Finally Solving CE's Mount(ing) Problems — Matt Godbolt’s blog
In which CE's boot times are finally brought under control
1306
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 22/08/2025
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! :)
1346
Compiler Explorer @compiler-explorer.com · 22/08/2025
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
011
Compiler Explorer @compiler-explorer.com · 24/07/2025
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
033
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 20/07/2025
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?
1151
Compiler Explorer @compiler-explorer.com · 30/06/2025
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!
09411
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 11/06/2025
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.
xania.org
Compiler Explorer Cost Transparency — Matt Godbolt’s blog
In which I try and show how we spend your kind Patreon donations
15214
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 08/06/2025
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...
1402
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 05/06/2025
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
youtu.be
Get More Out of Compiler-Explorer ('godbolt') :: Ofek Shilon
YouTube video by CoreCppIL
0194
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 03/06/2025
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.
xania.org
How Compiler Explorer Works in 2025 — Matt Godbolt’s blog
How we handle 92 million compilations a year without everything catching fire
35717
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 28/05/2025
On @compiler-explorer.com URLs and another Google product sunsetting: xania.org/202505/compi...
xania.org
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
38524
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 23/05/2025
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.
21486
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 23/04/2025
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
1868
Reposted by Compiler Explorer
Shafik Yaghmour @shafik.bsky.social · 08/02/2025
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
5699
Compiler Explorer @compiler-explorer.com · 06/01/2025
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
051
Compiler Explorer @compiler-explorer.com · 31/12/2024
Compiler Explorer in 2024! 0.017 cents per compilation for 190M compilations. Tons of new features, Matt takes stock: www.patreon.com/posts/compil...
patreon.com
Compiler Explorer in 2024 | Matt Godbolt
Get more from Matt Godbolt on Patreon
1194
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 07/12/2024
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) :-)
0282
Reposted by Compiler Explorer
Slang Shading Language and Compiler @shader-slang.bsky.social · 05/12/2024
Godbolt now has Slang support! godbolt.org @compiler-explorer.com
godbolt.org
Compiler Explorer
Compiler Explorer is an interactive online compiler which shows the assembly output of compiled C++, Rust, Go (and many more) code.
04113
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 22/11/2024
So, after over 5 years at Aquatic, I made the tough call to leave and try something else. I had a wonderful time there, enjoyed the work and made some great friends. I'll be taking some time between jobs and will be working on @compiler-explorer.com and other OSS projects. I'm excited!
9803
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 23/11/2024
Only 2 days left 15% off stuff at the CE shop. I just uploaded a dark-friendly logo too! Get some stuff to show off your love of CE and know you're helping the site at the same time! compiler-explorer.myspreadshop.com
compiler-explorer.myspreadshop.com
Compiler Explorer
Support Compiler Explorer by buying awesome branded kit!
0102
Compiler Explorer @compiler-explorer.com · 17/11/2024
Investigating a DDoS attack (looks like script kiddies again). Getting a bunch of weird POSTs to our noscript API. Site is handling it but it's alerting me, so have temporarily blocked some things. Apologies if you're caught in the crossfire! -mg
2251
Reposted by Compiler Explorer
Matt Godbolt @matt.godbolt.org · 12/11/2024
We have so many compilers on @compiler-explorer.com that the "configuration JSON" we send on /every pageload/ totals 60GiB/day (!!) I think we can probably do better...
4271
Compiler Explorer @compiler-explorer.com · 11/11/2024
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.spreadshirt.com/compiler-exp... * Join our Discord: discord.gg/B5WacA7
github.com
GitHub - compiler-explorer/compiler-explorer: Run compilers interactively from your web browser and interact with the assembly
Run compilers interactively from your web browser and interact with the assembly - compiler-explorer/compiler-explorer
0102