coverage: Rearrange the code for embedding per-function coverage metadata

This is a series of refactorings to the code that prepares and embeds per-function coverage metadata records (“covfun records”) in the `__llvm_covfun` linker section of the final binary. The `llvm-cov` tool reads this metadata from the binary when preparing a coverage report.

Beyond general cleanup, a big motivation behind these changes is to pave the way for re-landing an updated version of rust-lang#133418.

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There should be no change in compiler output, as demonstrated by the absence of (meaningful) changes to coverage tests.

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try-job: x86_64-gnu
try-job: x86_64-msvc
try-job: aarch64-apple

…iaskrgr

Rollup of 6 pull requests

Successful merges:

 - rust-lang#132975 (De-duplicate and improve definition of core::ffi::c_char)
 - rust-lang#133598 (Change `GetManyMutError` to match T-libs-api decision)
 - rust-lang#134148 (add comments in check_expr_field)
 - rust-lang#134163 (coverage: Rearrange the code for embedding per-function coverage metadata)
 - rust-lang#134165 (wasm(32|64): update alignment string)
 - rust-lang#134170 (Subtree update of `rust-analyzer`)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#134163 - Zalathar:covfun, r=SparrowLii,jieyouxu

coverage: Rearrange the code for embedding per-function coverage metadata

This is a series of refactorings to the code that prepares and embeds per-function coverage metadata records (“covfun records”) in the `__llvm_covfun` linker section of the final binary. The `llvm-cov` tool reads this metadata from the binary when preparing a coverage report.

Beyond general cleanup, a big motivation behind these changes is to pave the way for re-landing an updated version of rust-lang#133418.

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There should be no change in compiler output, as demonstrated by the absence of (meaningful) changes to coverage tests.

The first patch is just moving code around, so I suggest looking at the other patches to see the actual changes.

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try-job: x86_64-gnu
try-job: x86_64-msvc
try-job: aarch64-apple

…-errors

coverage: Tidy up creation of covmap and covfun records

This is a small follow-up to rust-lang#134163 that mostly just inlines and renames some variables, and adds a few comments.

It also slightly defers the creation of the LLVM value that holds the filename table, to just before the value is needed.

coverage: Tidy up creation of covmap and covfun records

This is a small follow-up to rust-lang#134163 that mostly just inlines and renames some variables, and adds a few comments.

It also slightly defers the creation of the LLVM value that holds the filename table, to just before the value is needed.

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try-job: x86_64-mingw-2

…-errors

coverage: Tidy up creation of covmap and covfun records

This is a small follow-up to rust-lang#134163 that mostly just inlines and renames some variables, and adds a few comments.

It also slightly defers the creation of the LLVM value that holds the filename table, to just before the value is needed.

---

try-job: x86_64-mingw-2

…-errors

coverage: Tidy up creation of covmap and covfun records

This is a small follow-up to rust-lang#134163 that mostly just inlines and renames some variables, and adds a few comments.

It also slightly defers the creation of the LLVM value that holds the filename table, to just before the value is needed.

---

try-job: x86_64-mingw-2

coverage: Tidy up creation of covmap and covfun records

This is a small follow-up to rust-lang#134163 that mostly just inlines and renames some variables, and adds a few comments.

It also slightly defers the creation of the LLVM value that holds the filename table, to just before the value is needed.

---

try-job: x86_64-mingw-2
try-job: dist-x86_64-linux

…-errors

coverage: Tidy up creation of covmap and covfun records

This is a small follow-up to rust-lang#134163 that mostly just inlines and renames some variables, and adds a few comments.

It also slightly defers the creation of the LLVM value that holds the filename table, to just before the value is needed.

---

try-job: x86_64-mingw-2
try-job: dist-x86_64-linux

…-errors

coverage: Tidy up creation of covmap and covfun records

This is a small follow-up to rust-lang#134163 that mostly just inlines and renames some variables, and adds a few comments.

It also slightly defers the creation of the LLVM value that holds the filename table, to just before the value is needed.

---

try-job: x86_64-mingw-2
try-job: dist-x86_64-linux

…-errors

coverage: Tidy up creation of covmap and covfun records

This is a small follow-up to rust-lang#134163 that mostly just inlines and renames some variables, and adds a few comments.

It also slightly defers the creation of the LLVM value that holds the filename table, to just before the value is needed.

---

try-job: x86_64-mingw-2
try-job: dist-x86_64-linux

…-errors

coverage: Tidy up creation of covmap and covfun records

This is a small follow-up to rust-lang#134163 that mostly just inlines and renames some variables, and adds a few comments.

It also slightly defers the creation of the LLVM value that holds the filename table, to just before the value is needed.

---

try-job: x86_64-mingw-2
try-job: dist-x86_64-linux

Rollup merge of rust-lang#134208 - Zalathar:covmap-covfun, r=compiler-errors

coverage: Tidy up creation of covmap and covfun records

This is a small follow-up to rust-lang#134163 that mostly just inlines and renames some variables, and adds a few comments.

It also slightly defers the creation of the LLVM value that holds the filename table, to just before the value is needed.

---

try-job: x86_64-mingw-2
try-job: dist-x86_64-linux

coverage: Store coverage source regions as `Span` until codegen (take 2)

This is an attempt to re-land rust-lang#133418:

> Historically, coverage spans were converted into line/column coordinates during the MIR instrumentation pass.

> This PR moves that conversion step into codegen, so that coverage spans spend most of their time stored as Span instead.

> In addition to being conceptually nicer, this also reduces the size of coverage mappings in MIR, because Span is smaller than 4x u32.

That PR was reverted by rust-lang#133608, because in some circumstances not covered by our test suite we were emitting coverage metadata that was causing `llvm-cov` to exit with an error (rust-lang#133606).

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The implementation here is *mostly* the same, but adapted for subsequent changes in the relevant code (e.g. rust-lang#134163).

I believe that the changes in rust-lang#134163 should be sufficient to prevent the problem that required the original PR to be reverted. But I haven't been able to reproduce the original breakage in a regression test, and the `llvm-cov` error message is extremely unhelpful, so I can't completely rule out the possibility of this breaking again.

r? jieyouxu (reviewer of the original PR)

Rollup merge of rust-lang#134497 - Zalathar:spans, r=jieyouxu

coverage: Store coverage source regions as `Span` until codegen (take 2)

This is an attempt to re-land rust-lang#133418:

> Historically, coverage spans were converted into line/column coordinates during the MIR instrumentation pass.

> This PR moves that conversion step into codegen, so that coverage spans spend most of their time stored as Span instead.

> In addition to being conceptually nicer, this also reduces the size of coverage mappings in MIR, because Span is smaller than 4x u32.

That PR was reverted by rust-lang#133608, because in some circumstances not covered by our test suite we were emitting coverage metadata that was causing `llvm-cov` to exit with an error (rust-lang#133606).

---

The implementation here is *mostly* the same, but adapted for subsequent changes in the relevant code (e.g. rust-lang#134163).

I believe that the changes in rust-lang#134163 should be sufficient to prevent the problem that required the original PR to be reverted. But I haven't been able to reproduce the original breakage in a regression test, and the `llvm-cov` error message is extremely unhelpful, so I can't completely rule out the possibility of this breaking again.

r? jieyouxu (reviewer of the original PR)