Editing do_alloc for reducing LLVM IR

[JustForFun88]

1. I think this will speed up compilation, since one way or another everything will come down to this code (but I didn’t compare performance).

2. I don’t know if the compiler was able to optimize that old code, but it literally checked the same thing twice (due to map and map_err in a row, and roughly speaking it came down to:

   pub fn do_alloc<A: Allocator>(alloc: &A, layout: Layout) -> Result<NonNull<u8>, ()> {
       match match alloc.allocate(layout) {
           Ok(ptr) => Ok(ptr.as_non_null_ptr()),
           Err(e) => Err(e),
       } {
           Ok(ptr) => Ok(ptr),
           Err(_) => Err(()),
       }
   }

   And when the code is written explicitly, it is immediately clear that it looks strange. And why force the compiler to think beyond the need?

3. And finally, in my opinion, the readability of the code has not only not decreased, but even increased.

[Amanieu]

@bors r+

[Amanieu]

@bors r+

[bors]

📌 Commit 9d23b42 has been approved by Amanieu

[bors]

⌛ Testing commit 9d23b42 with merge 67e3f87...

[bors]

☀️ Test successful - checks-actions
Approved by: Amanieu
Pushing 67e3f87 to master...