The test relies on the undefined behavior, and so may fail in some
circumstances. This can be worked around by stubbing a memory allocator
in the test, but it is a bit of work, and LLVM could still theoretically
eliminate the write of the zero byte in release mode (which is
intended).
So let's just remove the test and mark the function as inline. It
shouldn't be optimized away when inlined into the debug build of user's
code.
Don't allocate during default HashSet creation.
The following `HashMap` creation functions don't allocate heap storage for elements.
```
HashMap::new()
HashMap::default()
HashMap::with_hasher()
```
This is good, because it's surprisingly common to create a HashMap and never
use it. So that case should be cheap.
However, `HashSet` does not have the same behaviour. The corresponding creation
functions *do* allocate heap storage for the default number of non-zero
elements (which is 32 slots for 29 elements).
```
HashMap::new()
HashMap::default()
HashMap::with_hasher()
```
This commit gives `HashSet` the same behaviour as `HashMap`, by simply calling
the corresponding `HashMap` functions (something `HashSet` already does for
`with_capacity` and `with_capacity_and_hasher`). It also reformats one existing
`HashSet` construction to use a consistent single-line format.
This speeds up rustc itself by 1.01--1.04x on most of the non-tiny
rustc-benchmarks.
The following `HashMap` creation functions don't allocate heap storage for elements.
```
HashMap::new()
HashMap::default()
HashMap::with_hasher()
```
This is good, because it's surprisingly common to create a HashMap and never
use it. So that case should be cheap.
However, `HashSet` does not have the same behaviour. The corresponding creation
functions *do* allocate heap storage for the default number of non-zero
elements (which is 32 slots for 29 elements).
```
HashMap::new()
HashMap::default()
HashMap::with_hasher()
```
This commit gives `HashSet` the same behaviour as `HashMap`, by simply calling
the corresponding `HashMap` functions (something `HashSet` already does for
`with_capacity` and `with_capacity_and_hasher`). It also reformats one existing
`HashSet` construction to use a consistent single-line format.
This speeds up rustc itself by 1.01--1.04x on most of the non-tiny
rustc-benchmarks.
refactor to remove trans::adt and make rustc::ty::layout authoritative
I asked on IRC about optimizing struct layout by reordering fields from most-aligned to least-aligned and somehow ended up getting talked into doing this. The goal here is to make `layout` authoritative and to remove `adt`. The former has been accomplished by reimplementing `represent_type_uncached` and the latter is in progress. @eddyb thought I should make the PR now.
My plan is to reserve the actual optimization for a second PR, as this work is useful by itself.
