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note about why stage1/stage2 are different

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Niko Matsakis 2018-08-31 12:48:54 -04:00
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@ -62,6 +62,15 @@ internally. The result is the compiling `rustc` is done in stages:
compiled with the stage0 compiler to produce the stage1 compiler. compiled with the stage0 compiler to produce the stage1 compiler.
However, it was built with an older compiler (stage0), so to However, it was built with an older compiler (stage0), so to
optimize the stage1 compiler we go to next stage. optimize the stage1 compiler we go to next stage.
- (In theory, the stage1 compiler is functionally identical to the
stage2 compiler, but in practice there are subtle differences. In
particular, the stage1 compiler itself was built by stage0 and
hence not by the source in your working directory: this means that
the symbol names used in the compiler source may not match the
symbol names that would have been made by the stage1 compiler.
This can be important when using dynamic linking (e.g., with
derives. Sometimes this means that some tests don't work when run
with stage1.)
- **Stage 2:** we rebuild our stage1 compiler with itself to produce - **Stage 2:** we rebuild our stage1 compiler with itself to produce
the stage2 compiler (i.e. it builds itself) to have all the _latest the stage2 compiler (i.e. it builds itself) to have all the _latest
optimizations_. optimizations_.