[Migrated] `OpConvertUToPtr` support

Issue automatically imported from old repo: https://github.com/EmbarkStudios/rust-gpu/issues/767
Old labels: t: enhancement,s: qptr may fix
Originally creatd by expenses on 2021-10-13T09:10:25Z

I started looking into how OpConvertUToPtr can be implemented - initially for RuntimeArrays. Something like this works well, but is not generic:

unsafe fn load_f32_runtime_array_from_handle(handle: u64) -> &'static mut RuntimeArray<f32> {
    asm!(
        "%f32 = OpTypeFloat 32",
        "%runtime_array = OpTypeRuntimeArray %f32",
        "%runtime_array_ptr = OpTypePointer Generic %runtime_array",
        "%result = OpConvertUToPtr %runtime_array_ptr {handle}",
        "OpReturnValue %result",
        handle = in(reg) handle,
        options(noreturn)
    )
}

I know that @msiglreith implemented loading resources from handles in https://github.com/EmbarkStudios/rust-gpu/compare/main...msiglreith:glace, but it looks like that requires a lot of codegen changes - ideally we should keep things at the asm! layer if possible.

Is there a way to make the above function generic over T, or will this require a few codegen changes?

Issue の asm! の例とリンクされている glace の比較から始めて、リソースハンドルと OpConvertUToPtr が現在どのように扱われているかを理解します。汎用サポートを asm! 層にとどめられるか、または codegen の変更が必要かを判断します。この範囲が確定し、要求されたサポートが実装された時点で作業は完了です。