mirror
/
rustc-dev-guide
mirror of https://github.com/rust-lang/rustc-dev-guide.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Document CGU partioning in case of generic and inline functions

This commit is contained in:
Aman Arora 2020-09-03 22:46:56 -04:00 committed by Joshua Nelson
parent d117002719
commit d8db731a4a
1 changed files with 20 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
src/backend/monomorph.md
View File

@ -55,8 +55,28 @@ The monomorphization collector is run just before MIR lowering and codegen.
collection and then partitions them into [codegen
units](../appendix/glossary.md#codegen-unit).
## Codegen Unit (CGU) partitioning
For better incremental build times, the CGU partitioner creates two CGU for each source level
modules. One is for "stable" i.e. non-generic code and the other is more volatile code i.e.
monoporphized/specialized instances.
For depenencies, consider Crate A and Crate B, such that Crate B depends on Crate A.
The following table lists different scenarios for a function in Crate A that might be used by one
or more modules in Crate B.
| Crate A function | Behavior |
| - | - |
| Non-generic function | Crate A function doesn't appear in any codegen units of Crate B |
| Non-generic `#[inline]` function | Crate A function appears with in a single CGU of Crate B, and exists even after post-inlining stage|
| Generic function | Regardless of inlining, all monoporphized (specialized) functions <br> from Crate A appear within a single codegen unit for Crate B. <br> The codegen unit exists even after the post inlining stage.|
| Generic `#[inline]` function | - same - |
For more details about the partitioner read the module level [documentation].
[mono]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir/monomorphize/partitioning/fn.collect_and_partition_mono_items.html
[codegen1]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/base/fn.codegen_crate.html
[documentation]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_mir/monomorphize/partitioning/index.html
## Polymorphization