39ee3aaa13
Introduce unsafe offset_from on pointers
Adds intrinsics::exact_div to take advantage of the unsafe, which reduces the implementation from
```asm
sub rcx, rdx
mov rax, rcx
sar rax, 63
shr rax, 62
lea rax, [rax + rcx]
sar rax, 2
ret
```
down to
```asm
sub rcx, rdx
sar rcx, 2
mov rax, rcx
ret
```
(for `*const i32`)
See discussion on the `offset_to` tracking issue https://github.com/rust-lang/rust/issues/41079
Some open questions
- Would you rather I split the intrinsic PR from the library PR?
- Do we even want the safe version of the API? https://github.com/rust-lang/rust/issues/41079#issuecomment-374426786 I've added some text to its documentation that even if it's not UB, it's useless to use it between pointers into different objects.
and todos
- [x] ~~I need to make a codegen test~~ Done
- [x] ~~Can the subtraction use nsw/nuw?~~ No, it can't https://github.com/rust-lang/rust/pull/49297#discussion_r176697574
- [x] ~~Should there be `usize` variants of this, like there are now `add` and `sub` that you almost always want over `offset`? For example, I imagine `sub_ptr` that returns `usize` and where it's UB if the distance is negative.~~ Can wait for later; C gives a signed result https://github.com/rust-lang/rust/issues/41079#issuecomment-375842235, so we might as well, and this existing to go with `offset` makes sense.
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| .. | ||
| bootstrap | ||
| build_helper | ||
| ci | ||
| dlmalloc@9b2dcac06c | ||
| doc | ||
| etc | ||
| grammar | ||
| jemalloc@1f5a28755e | ||
| liballoc | ||
| liballoc_jemalloc | ||
| liballoc_system | ||
| libarena | ||
| libbacktrace | ||
| libcompiler_builtins@266ea0740a | ||
| libcore | ||
| libfmt_macros | ||
| libgraphviz | ||
| liblibc@ed04152aac | ||
| libpanic_abort | ||
| libpanic_unwind | ||
| libproc_macro | ||
| libprofiler_builtins | ||
| librustc | ||
| librustc_allocator | ||
| librustc_apfloat | ||
| librustc_asan | ||
| librustc_back | ||
| librustc_borrowck | ||
| librustc_const_eval | ||
| librustc_const_math | ||
| librustc_cratesio_shim | ||
| librustc_data_structures | ||
| librustc_driver | ||
| librustc_errors | ||
| librustc_incremental | ||
| librustc_lint | ||
| librustc_llvm | ||
| librustc_lsan | ||
| librustc_metadata | ||
| librustc_mir | ||
| librustc_msan | ||
| librustc_passes | ||
| librustc_platform_intrinsics | ||
| librustc_plugin | ||
| librustc_privacy | ||
| librustc_resolve | ||
| librustc_save_analysis | ||
| librustc_traits | ||
| librustc_trans | ||
| librustc_trans_utils | ||
| librustc_tsan | ||
| librustc_typeck | ||
| librustdoc | ||
| libserialize | ||
| libstd | ||
| libstd_unicode | ||
| libsyntax | ||
| libsyntax_ext | ||
| libsyntax_pos | ||
| libterm | ||
| libtest | ||
| libunwind | ||
| llvm@6ceaaa4b01 | ||
| llvm-emscripten@2717444753 | ||
| rtstartup | ||
| rustc | ||
| rustllvm | ||
| stdsimd@bcb720e558 | ||
| test | ||
| tools | ||
| Cargo.lock | ||
| Cargo.toml | ||
| README.md | ||
| stage0.txt | ||
This directory contains the source code of the rust project, including:
rustcand its testslibstd- Various submodules for tools, like rustdoc, rls, etc.
For more information on how various parts of the compiler work, see the rustc guide.
Their is also useful content in the following READMEs, which are gradually being moved over to the guide:
- https://github.com/rust-lang/rust/tree/master/src/librustc/ty/maps
- https://github.com/rust-lang/rust/tree/master/src/librustc/dep_graph
- https://github.com/rust-lang/rust/blob/master/src/librustc/infer/region_constraints
- https://github.com/rust-lang/rust/tree/master/src/librustc/infer/higher_ranked
- https://github.com/rust-lang/rust/tree/master/src/librustc/infer/lexical_region_resolve