Poor code gen for packed struct bitfields

[lassade]

Zig Version

0.14.0

Steps to Reproduce and Observed Behavior

https://godbolt.org/z/nrs4Eje5G

Expected Behavior

The godbolt link have 2 function elementC and elementZig they do the same thing by checking if some bits are on beased on the input ascii char. The elementC does in the c style and generates optimal assembly, while elementZig does not.

I also noticed a regression if compared with 0.13, for some odd reason 0.14 does some weird thing with the stack in both functions.

[190n]

I also noticed a regression if compared with 0.13, for some odd reason 0.14 does some weird thing with the stack in both functions.

This is because since #22180, Zig uses a frame pointer in all modes but ReleaseSmall. On x86_64 this entails push rbp; mov rbp, rsp at the start and pop rbp at the end of a function. If you want to shorten Godbolt output you can use -fomit-frame-pointer.