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[beta] Backport #74085

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wants to merge 4 commits into from
Closed

[beta] Backport #74085

wants to merge 4 commits into from

Commits on Jul 6, 2020

  1. Perform obligation deduplication to avoid buggy ExistentialMismatch 

    Fix #59326.
    @estebank @Elinvynia
    estebank authored and Elinvynia committed Jul 6, 2020
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  2. rustc_lexer: Simplify shebang parsing once more

    @petrochenkov @Elinvynia
    petrochenkov authored and Elinvynia committed Jul 6, 2020
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  3. rustdoc: Fix doc aliases with crate filtering 

    Fix a crash when searching for an alias contained in the currently selected filter crate.

Also remove alias search results for crates that should be filtered out.

The test suite needed to be fixed to actually take into account the crate filtering and check that there are no results when none are expected.
    @ollie27 @Elinvynia
    ollie27 authored and Elinvynia committed Jul 6, 2020
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  4. Change how compiler-builtins gets many CGUs 

    This commit intends to fix an accidental regression from #70846. The
goal of #70846 was to build compiler-builtins with a maximal number of
CGUs to ensure that each module in the source corresponds to an object
file. This high degree of control for compiler-builtins is desirable to
ensure that there's at most one exported symbol per CGU, ideally
enabling compiler-builtins to not conflict with the system libgcc as
often.

In #70846, however, only part of the compiler understands that
compiler-builtins is built with many CGUs. The rest of the compiler
thinks it's building with `sess.codegen_units()`. Notably the
calculation of `sess.lto()` consults `sess.codegen_units()`, which when
there's only one CGU it disables ThinLTO. This means that
compiler-builtins is built without ThinLTO, which is quite harmful to
performance! This is the root of the cause from #73135 where intrinsics
were found to not be inlining trivial functions.

The fix applied in this commit is to remove the special-casing of
compiler-builtins in the compiler. Instead the build system is now
responsible for special-casing compiler-builtins. It doesn't know
exactly how many CGUs will be needed but it passes a large number that
is assumed to be much greater than the number of source-level modules
needed. After reading the various locations in the compiler source, this
seemed like the best solution rather than adding more and more special
casing in the compiler for compiler-builtins.

Closes #73135
    @alexcrichton @Elinvynia
    alexcrichton authored and Elinvynia committed Jul 6, 2020
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