Xcode producing corrupt build

If I had to guess, I think that the issue is something that has worked for iOS 13 and before is no longer properly working with either iOS 15 SDK or possibly iOS 14 SDK.

Building for iOS 13 then building for iOS 15 works, because I suspect that something is actually being cached when I build for iOS 13 that should not be cached after deleting the derived files. So I fear the “correct” behavior is for it to complain about something and not successfully compile at all using the iOS 15 SDK. I’m pretty much forced to only support iOS 15 because of a severe issue that it resolved with CoreML or I would be glad to just leave it at iOS 13 and shrug it off.

The most suspicious difference is in iOS 13 Float16 was not supported yet so I am using Uint8 with a Float16 alias. 

I tried commenting out by Float16 alias (which just pointed to UInt8) and to use the SDK for Float16 instead, but it still had the same issue of taking 30 seconds to compile the shader and hanging.

Can anyone tell me what iOS uses under the hood for to represent Float16? Does it have the same alignment as UInt8?

For all of by MTLBuffers and parameters I use MemoryLayout’s Stride. Should I be using Size instead of Stride for iOS 15?

All the metal structures are defined in a C header which is suppose to enforce Metal compatibility as I understand it.

Hi 3DTOPO,

The the error message you are obtaining indicates that there is an out-of-bounds access occurring within your computeArtPointsToRender function. These problems are difficult to catch without additional instrumentation in the shader, and may explain the difference in behavior you are experiencing between iOS 13 and iOS 15, as they ultimately depend on how your resources are laid out in memory.

Shader Validation, which you are already using, instruments your shader to include additional out-of-bounds error detection. In addition to reporting the problem you copied, you can also click on the arrow next to the shader validation checkbox to enable a shader breakpoint for when the problem is detected.

An additional check you can enable is to opt you command buffers into enhanced error detection. This will allow you to verify if the problem is causing a command buffer failure, which could help explain the difference in timings you are seeing.

If you are unsure about how to accomplish this, here is a video that shows this process in detail, as well as tips and tricks for debugging these kinds of difficult errors - https://developer.apple.com/videos/play/wwdc2020/10616/

It turns out that the slow compile only occurs (intermittently) when Shader Validation is enabled. If I disable Shader Validation it compiles as expected.

When compiling for iOS 13, since Shader Validation is not supported, the slow compile would not occur since it was not being validated.

As for the runtime hang, it turns out that I was indeed accessing a buffer out-of-bounds. Why it was never an issue before I can't say, but it was my bad. I was just super suspicious of the build since it was taking abnormally long to compile.

As for the apparent bug with Shader Validation, I have updated my FeedBack Assistant report with sysdiagnose reports.