Improve documentation for codegen options #141554
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| @@ -379,7 +396,7 @@ This flag controls the optimization level. | |||
| * `2`: some optimizations. | |||
| * `3`: all optimizations. | |||
| * `s`: optimize for binary size. | |||
| * `z`: optimize for binary size, but also turn off loop vectorization. | |||
| * `z`: optimize for binary size, but more aggressively. Often results in larger binaries than `s` | |||
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I took the description from https://llvm.org/doxygen/classllvm_1_1OptimizationLevel.html#a1e916712888d6a2d3952834c126460e7
The fact that it's often worse is based on experience
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I'd guess the old information was based on https://stackoverflow.com/questions/15548023/clang-optimization-levels
But that misses all the heuristics that are also affected by this flag, which are much more important (there's no way just not doing vectorization results in significantly bigger binaries)
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This adds more information to many different codegen options. It should not add any new guarantees, just document existing behavior.
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| @@ -407,6 +424,8 @@ This option lets you control what happens when the code panics. | |||
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| If not specified, the default depends on the target. | |||
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| If any crate in the crate graph uses `abort`, the final binary (`bin`, `dylib`, `cdylib`, `staticlib`) must also use `abort`. | |||
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And if libstd is used as dylib compiled with panic=unwind, the final binary must also use panic=unwind. (In that case libstd.so links against libpanic_unwind.rlib. rustc will emit an error when using panic=abort while linking libpanic_unwind.rlib)
This adds more information to many different codegen options. It should not add any new guarantees, just document existing behavior.
r? bjorn3