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Update LLVM coverage mapping format version supported by rustc #1267

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Dec 3, 2021
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Update LLVM coverage mapping format version supported by rustc #1267

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20 changes: 9 additions & 11 deletions src/llvm-coverage-instrumentation.md
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Expand Up @@ -221,17 +221,15 @@ substitution combinations), `mapgen`'s `finalize()` method queries the
and `CodeRegion`s; and calls LLVM codegen APIs to generate
properly-configured variables in LLVM IR, according to very specific
details of the [_LLVM Coverage Mapping Format_][coverage-mapping-format]
(Version 4).[^llvm-and-covmap-versions]

[^llvm-and-covmap-versions]: The Rust compiler (as of
January 2021) supports _LLVM Coverage Mapping Format_ Version 4 (the most
up-to-date version of the format, at the time of this writing) for improved
compatibility with other LLVM-based compilers (like _Clang_), and to take
advantage of some format optimizations. Version 4 was introduced in _LLVM 11_,
which is currently the default LLVM version for Rust. Note that the Rust
compiler optionally supports some earlier LLVM versions, prior to _LLVM 11_. If
`rustc` is configured to use an incompatible version of LLVM, compiling with `-Z
instrument-coverage` will generate an error message.
(Version 6).[^llvm-and-covmap-versions]

[^llvm-and-covmap-versions]: The Rust compiler (as of <!-- date: 2021-12 -->
December 2021) supports _LLVM Coverage Mapping Format_ Version 5 or 6. Version 5
was introduced in _LLVM 12_, which is (as of this writing) the minimum LLVM
version supported by the current version of Rust. Version 6 was introduced in
_LLVM 13_, which is currently the default LLVM version for Rust. The Rust
compiler will automatically use the most up-to-date coverage mapping format
version that is compatible with the compiler's built-in version of LLVM.

```rust
pub fn finalize<'ll, 'tcx>(cx: &CodegenCx<'ll, 'tcx>) {
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