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add small explanation of why fuel can be useful for debugging

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cjkenn 2020-11-20 14:51:29 -05:00 committed by Joshua Nelson
parent ed89d6f643
commit 49069a0233
1 changed files with 4 additions and 2 deletions
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src/mir/optimizations.md
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@ -65,8 +65,10 @@ current level using `tcx.sess.opts.debugging_opts.mir_opt_level`.
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. This can help with debugging
and identifying problems with optimizations.
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