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Zig cc generated wrong executable code for switch statement when (-Ofast) is used
Zig Version
0.12.0
Steps to Reproduce and Observed Behavior
All of the steps and how to reproduce the bug is explained in detail here: https://github.com/ring-lang/ring/blob/master/marketing/articles/ZigCCisNotReadyYet.md
The bug is discovered while using Zig cc to build the Ring programming language
Expected Behavior
As in this article: https://github.com/ring-lang/ring/blob/master/marketing/articles/ZigCCisNotReadyYet.md
It would help if you could provide a small reproduction. Also, do you see the same behaviour with clang? zig cc is a wrapper for clang with a few extra features, so I would be surprised if it introduces miscompilations that clang doesn't have
Also, do you see the same behaviour with clang?
All other compilers including Clang doesn't have this bug and produce valid Ring executable
@MahmoudFayed I can reproduce this with Clang on Ubuntu 22.04, using your Clang build script. I suspect your code is triggering undefined behaviour, causing garbage optimizations in Clang. Regardless, this is not an issue in Zig.
@silversquirl I am use Clang and Zig on Windows Clang (Windows) doesn't have the problem Zig (Windows) have it I think this requires attention at Zig project level
Tested building Ring on macOS using Clang ---> The problem doesn't exist there too. Will test it now on Ubuntu (based on your feedback) to see the results.
Your clang build script for windows doesn't provide any optimization options. If you provide -O2 or -Ofast, I expect you will see the same result as zig cc
I added (-Ofast) in this commit: https://github.com/ring-lang/ring/commit/90ad2071925f8cb563d99b3e44adc5cf858a8e6d
The problem doesn't exist when using (Clang) in windows while (-Ofast) is active
I can confirm that the bug happens on MacOS using Apple clang version 15.0.0 (clang-1500.3.9.4) if -O2 is used, and does not occur if -O0 is used. This is either a clang optimizer bug or undefined behavior in your C code; it is not a zig cc bug.
@ehaas We already use -o2 on macOS and we don't have this problem: https://github.com/ring-lang/ring/blob/master/language/build/buildclang.sh
Here is a screen recording of myself compiling it with Apple system clang and reproducing the bug.
https://github.com/ziglang/zig/assets/4575/7de29a2e-0e0c-4158-9105-62ff7136765e
The warning about unsequenced modifications to nNum2 may be relevant.
The warning is related to a function implementation called Random() Doesn't have anything to do with the reported bug.
The bug doesn't appears using my old Clang version: Apple clang version 12.
I can reproduce it now using Clang (Windows) - A modern version of Clang.
We can say now it's not a Zig bug ---> Looks like a Clang bug.
Thanks
if it reproduces on the latest clang as well, we generally still track it here if it's affecting zig
@nektro I am trying to find a way (workaround) to still use Zig/Clang and (Ofast) flag and avoid this issue
Hello
I applied a workaround to avoid the problem so I can use Zig cc Or Clang & keep the -Ofast flag - The workaround is applied in this commit: https://github.com/ring-lang/ring/commit/f9abf2376e61f0eea37091095f9c2de4eebbbd1e Thanks to everyone who checked this issue. Keep up the GREAT WORK