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coverage: Clean up creation of MC/DC condition bitmaps by Zalathar · Pull Request #124555 · rust-lang/rust

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Apr 30, 2024

@Zalathar 

Because this now always takes place at the start of the function, we can just
use the normal `alloca` method and then initialize each bitmap immediately.

This patch also moves bitmap setup out of the `mcdc_parameters` method, because
there is no longer any particular reason for it to be there.
This clearly distinguishes individual decision-depth indices from the total
number of condition bitmaps to allocate.

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and removed S-waiting-on-review

Status: Awaiting review from the assignee but also interested parties.

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May 3, 2024

bors added a commit to rust-lang-ci/rust that referenced this pull request

May 3, 2024 
…iaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#122492 (Implement ptr_as_ref_unchecked)
 - rust-lang#123815 (Fix cannot usage in time.rs)
 - rust-lang#124059 (default_alloc_error_hook: explain difference to default __rdl_oom in alloc)
 - rust-lang#124510 (Add raw identifier in a typo suggestion)
 - rust-lang#124555 (coverage: Clean up creation of MC/DC condition bitmaps)
 - rust-lang#124593 (Describe and use CStr literals in CStr and CString docs)
 - rust-lang#124630 (CI: remove `env-x86_64-apple-tests` YAML anchor)

r? `@ghost`
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rust-timer added a commit to rust-lang-ci/rust that referenced this pull request

May 3, 2024 
Rollup merge of rust-lang#124555 - Zalathar:init-coverage, r=nnethercote

coverage: Clean up creation of MC/DC condition bitmaps

This PR improves the code for creating and initializing [MC/DC](https://en.wikipedia.org/wiki/Modified_condition/decision_coverage) condition bitmap variables, as introduced by rust-lang#123409 and modified by rust-lang#124255.

- The condition bitmap variables are now created eagerly at the start of per-function codegen, via a new `init_coverage` method in `CoverageInfoBuilderMethods`. This avoids having to retroactively create the bitmaps while doing codegen for an individual coverage statement.
- As a result, we can now create and initialize those bitmaps using existing safe APIs, instead of having to perform our own unsafe call to `llvm::LLVMBuildAlloca`.
- This PR also tweaks the way we count the number of condition bitmaps needed, by tracking the total number of bitmaps needed (max depth + 1), instead of only tracking the maximum depth. This reduces the potential for subtle off-by-one confusion.