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Diffstat (limited to 'src/doc/rustc-dev-guide')
| -rw-r--r-- | src/doc/rustc-dev-guide/src/mir/optimizations.md | 23 |
1 files changed, 0 insertions, 23 deletions
diff --git a/src/doc/rustc-dev-guide/src/mir/optimizations.md b/src/doc/rustc-dev-guide/src/mir/optimizations.md index 7b987e7015b..93eeb9a372f 100644 --- a/src/doc/rustc-dev-guide/src/mir/optimizations.md +++ b/src/doc/rustc-dev-guide/src/mir/optimizations.md @@ -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 |