[Migrated] Large array variable initialization (`let arr = [0; 32 * 1024];`) compiles very slowly.

Issue automatically imported from old repo: https://github.com/EmbarkStudios/rust-gpu/issues/1132
Old labels: t: bug
Originally creatd by pyranota on 2024-02-11T13:28:58Z

EDIT(@eddyb): while there are reasons to avoid such arrays, the slowdown is the immediate Rust-GPU bug - I've left unchanged the original text, but used strikethrough for parts that don't apply, IMO.

User should not be able to create large sized arrays in rust-gpu shaders.
Stack is limited, and large sized data-structures should be moved in buffers.
Plus it makes compilation incredibly slow (I assume this syntax [0; SIZE] translates to spirv's [0, 0, 0, 0, 0, ... SIZE])

Expected Behaviour

spirv-builder should throw an error, when user creates large array in stack

Example & Steps To Reproduce

1. Setup basic rust-gpu shader
2. let arr = [0; 32 * 1024];
3. cargo build

System Info

• Rust: rustc 1.75.0 (82e1608df 2023-12-21)
• OS: Pop!_OS
• GPU: nvidia 1060
• SPIR-V: SPIRV-Tools v2022.2-dev unknown hash, 2022-02-16T16:37:15

The issue names no source file or test; begin with the minimal rust-gpu shader reproducer using let arr = [0; 32 * 1024];, then run cargo build and trace the compilation path responsible for the slowdown. Done means this large array initializer no longer makes compilation incredibly slow, with a regression test if the relevant test location can be identified.