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(DRAFT) Combined draft branch for coverage work #115428

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wants to merge 13 commits into from
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(DRAFT) Combined draft branch for coverage work #115428

wants to merge 13 commits into from

Commits on Oct 21, 2023

  1. coverage: Emit mappings for unused functions without generating stubs

    @Zalathar
    Zalathar committed Oct 21, 2023
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  2. coverage: Move unused-function helpers closer to where they are used

    @Zalathar
    Zalathar committed Oct 21, 2023
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  3. coverage: Change query codegened_and_inlined_items to a plain function 

    This query has a name that sounds general-purpose, but in fact it has
coverage-specific semantics, and (fortunately) is only used by coverage code.

Because it is only ever called once, it doesn't need to be a query, and we can
change it to a regular function instead.
    @Zalathar
    Zalathar committed Oct 21, 2023
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  4. coverage: Force -Copt-level=2 in the unreachable-code test 

    This test is mainly for detecting problems triggered by MIR optimizations, but
the run-coverage tests don't enable optimization by default.

(The coverage-map tests do enable optimization by default, but I'm updating the
test anyway so that the two `unreachable.rs` files don't drift out of sync.)
    @Zalathar
    Zalathar committed Oct 21, 2023
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  5. coverage: Repair instrumented functions that have lost all their coun… 

    …ters

If a function has been instrumented for coverage, but MIR optimizations
subsequently remove all of its counter-increment statements, then we won't emit
LLVM counter-increment intrinsics. LLVM will think the function is not
instrumented, and it will disappear from coverage mappings and coverage
reports.

This new MIR pass detects when that has happened, and re-inserts a dummy
counter-increment statement so that LLVM knows to treat the function as
instrumented.
    @Zalathar
    Zalathar committed Oct 21, 2023
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  6. Allow MIR pass UnreachableProp when coverage is enabled

    @Zalathar
    Zalathar committed Oct 21, 2023
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  7. coverage: Split FunctionCoverage into distinct collector/finished p… 

    …hases
    @Zalathar
    Zalathar committed Oct 21, 2023
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  8. coverage: Fetch expressions and mappings separately

    @Zalathar
    Zalathar committed Oct 21, 2023
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  9. coverage: Build the global file table ahead of time

    @Zalathar
    Zalathar committed Oct 21, 2023
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  10. coverage: Encapsulate local-to-global file mappings

    @Zalathar
    Zalathar committed Oct 21, 2023
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  11. coverage: Encode function mappings without re-sorting them

    @Zalathar
    Zalathar committed Oct 21, 2023
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  12. coverage: Emit the filenames section before encoding per-function map… 

    …pings

Most coverage metadata is encoded into two sections in the final executable.
The `__llvm_covmap` section mostly just contains a list of filenames, while the
`__llvm_covfun` section contains encoded coverage maps for each instrumented
function.

The catch is that each per-function record also needs to contain a hash of the
filenames list that it refers to. Historically this was handled by assembling
most of the per-function data into a temporary list, then assembling the
filenames buffer, then using the filenames hash to emit the per-function data,
and then finally emitting the filenames table itself.

However, now that we build the filenames table up-front (via a separate
traversal of the per-function data), we can hash and emit that part first, and
then emit each of the per-function records immediately after building. This
removes the awkwardness of having to temporarily store nearly-complete
per-function records.
    @Zalathar
    Zalathar committed Oct 21, 2023
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  13. coverage: Consolidate creation of __llvm_covmap records 

    The code for creating these records was spread across multiple functions and
multiple files, so this change moves as much of it as possible into one place.
    @Zalathar
    Zalathar committed Oct 21, 2023
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