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

Remove -Zfuel. (#2032)

This commit is contained in:
Camille Gillot 2024-11-27 11:31:58 +01:00 committed by GitHub
parent c4737a8d01
commit 0962f0e058
1 changed files with 0 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
src/mir/optimizations.md
View File

@ -110,26 +110,3 @@ current level using [`tcx.sess.opts.unstable_opts.mir_opt_level`][mir_opt_level]
[compiler MCP]: https://github.com/rust-lang/compiler-team/issues/319
[mir_opt_level]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_session/config/struct.UnstableOptions.html#structfield.mir_opt_level
## Optimization fuel
Optimization fuel is a compiler option (`-Z fuel=<crate>=<value>`) that allows for fine grained
control over which optimizations can be applied during compilation: each optimization reduces
fuel by 1, and when fuel reaches 0 no more optimizations are applied. The primary use of fuel
is debugging optimizations that may be incorrect or misapplied. By changing the fuel
value, you can bisect a compilation session down to the exact incorrect optimization
(this behaves like a kind of binary search through the optimizations).
MIR optimizations respect fuel, and in general each pass should check fuel by calling
[`tcx.consider_optimizing`][consideroptimizing] and skipping the optimization if fuel
is empty. There are a few considerations:
1. If the pass is considered "guaranteed" (for example, it should always be run because it is
needed for correctness), then fuel should not be used. An example of this is `PromoteTemps`.
2. In some cases, an initial pass is performed to gather candidates, which are then iterated to
perform optimizations. In these situations, we should allow for the initial gathering pass
and then check fuel as close to the mutation as possible. This allows for the best
debugging experience, because we can determine where in the list of candidates an optimization
may have been misapplied. Examples of this are `InstSimplify` and `ConstantPropagation`.
[consideroptimizing]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/context/struct.TyCtxt.html#method.consider_optimizing