clang bug affecting greenfly - Mailing list pgsql-hackers

From John Naylor
Subject clang bug affecting greenfly
Date
Msg-id CANWCAZY7aFogEvXk+o1vZ6GdXKEA9_ctu1ycBi=E4atPTbqB7g@mail.gmail.com
Whole thread
In response to Re: Add RISC-V Zbb popcount optimization  ("Greg Burd" <greg@burd.me>)
Responses Re: clang bug affecting greenfly
Re: clang bug affecting greenfly
List pgsql-hackers
[new subject]

On Sat, Mar 28, 2026 at 3:22 AM Greg Burd <greg@burd.me> wrote:

> 0001 - This is a bug fix for DES/RISC-V/Clang DES initialization.
>
> ------> Join me in "the rabbit hole" on this issue if you care to...
>
> The existing software DES (as shown by the build-farm animal "greenfly" [1]) fails because Clang 20 has an
auto-vectorizationbug that we trigger in the DES initialization code (des_init() function), not the DES encryption
algorithmitself. 

> [disable vectorization entirely]
> While that might also fix the other intermittent bug we'd been seeing on greenfly (not tested) disablnig all RVV
optimizationsseems to heavy handed to me. 

The first thing I notice is that not very long ago the buildfarm had 3
gcc RISC-V members, but not anymore. If you care about having coverage
for this hardware, I'd suggest picking up gcc again if that's still
working, and wait and see about clang. Clang has shipped broken code
generation for obscure platforms in the past, and it seems here we're
not even sure of the extent of the breakage.

--
John Naylor
Amazon Web Services



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