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Ben Kimock bf9df97660 Remove -Zinline-in-all-cgus and clean up CGU partitioning tests		2025-01-27 23:48:47 -05:00
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README.md	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
extern-drop-glue.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
extern-generic.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
incremental-merging.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
inline-always.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
inlining-from-extern-crate.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
local-drop-glue.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
local-generic.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
local-transitive-inlining.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
methods-are-with-self-type.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
regular-modules.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
shared-generics.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
statics.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00
vtable-through-const.rs	Remove -Zinline-in-all-cgus and clean up CGU partitioning tests	2025-01-27 23:48:47 -05:00

README.md

codegen-units/partitioning tests

This test suite is designed to test that codegen unit partitioning works as intended. Note that it does not evaluate whether CGU partitioning is good. That is the job of the compiler benchmark suite.

All tests in this suite use the flag -Zprint-mono-items=lazy, which makes the compiler print a machine-readable summary of all MonoItems that were collected, which CGUs they were assigned to, and the linkage in each CGU. The output looks like:

MONO_ITEM <item> @@ <cgu name>[<linkage>] <other cgu name>[<linkage in other cgu>]

DO NOT add tests to this suite that use -Zprint-mono-items=eager. That flag changes the way that MonoItem collection works in rather fundamental ways that are otherwise only used by -Clink-dead-code, and thus the MonoItems collected and their linkage under -Zprint-mono-items=eager does not correlate very well with normal compilation behavior.

The current CGU partitioning algorithm essentially groups MonoItems by which module they are defined in, then merges small CGUs. There are a lot of inline modules in this test suite because that's the only way to observe the partitioning.

Currently, the test suite is very heavily biased towards incremental builds with -Copt-level=0. This is mostly an accident of history; the entire test suite was added as part of supporting incremental compilation in #32779. But also CGU partitioning is mostly valuable because the CGU is the unit of incrementality to the codegen backend (cached queries are the unit of incrementality for the rest of the compiler).