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Specify what a CGU is #2163

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Dec 16, 2024
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Specify what a CGU is #2163

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17 changes: 8 additions & 9 deletions src/queries/incremental-compilation-in-detail.md
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Expand Up @@ -377,15 +377,14 @@ the result cache doesn't unnecessarily shrink again.
# Incremental Compilation and the Compiler Backend

The compiler backend, the part involving LLVM, is using the query system but
it is not implemented in terms of queries itself. As a consequence
it does not automatically partake in dependency tracking. However, the manual
integration with the tracking system is pretty straight-forward. The compiler
simply tracks what queries get invoked when generating the initial LLVM version
of each codegen unit, which results in a dep-node for each of them. In
subsequent compilation sessions it then tries to mark the dep-node for a CGU as
green. If it succeeds it knows that the corresponding object and bitcode files
on disk are still valid. If it doesn't succeed, the entire codegen unit has to
be recompiled.
it is not implemented in terms of queries itself. As a consequence it does not
automatically partake in dependency tracking. However, the manual integration
with the tracking system is pretty straight-forward. The compiler simply tracks
what queries get invoked when generating the initial LLVM version of each
codegen unit (CGU), which results in a dep-node for each CGU. In subsequent
compilation sessions it then tries to mark the dep-node for a CGU as green. If
it succeeds, it knows that the corresponding object and bitcode files on disk
are still valid. If it doesn't succeed, the entire CGU has to be recompiled.

This is the same approach that is used for regular queries. The main differences
are:
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