coverage: Detect unused local file IDs to avoid an LLVM assertion

[Zalathar]

Each function's coverage metadata contains a local file table that maps local file IDs (used by the function's mapping regions) to global file IDs (shared by all functions in the same CGU).

LLVM requires all local file IDs to have at least one mapping region, and has an assertion that will fail if it detects a local file ID with no regions. To make sure that assertion doesn't fire, we need to detect and skip functions whose metadata would trigger it.

(This can't actually happen yet, because currently all of a function's spans must belong to the same file and expansion. But this will be an important edge case when adding expansion region support.)

[rustbot]

r? @SparrowLii

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[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[SparrowLii]

@bors r+

[bors]

📌 Commit 078144f has been approved by SparrowLii

It is now in the queue for this repository.

[bors]

⌛ Testing commit 078144f with merge 1e8d54d...

[rust-log-analyzer]

The job x86_64-mingw-1 failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [run-make] tests\run-make\rustdoc-dep-info stdout ----

error: rmake recipe failed to complete
status: exit code: 1
command: "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\test\\run-make\\rustdoc-dep-info\\rmake.exe"
stdout: none
--- stderr -------------------------------
command failed at line 10
Command { cmd: "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\stage2\\bin\\rustdoc.exe" "lib.rs" "-Zunstable-options" "--emit=dep-info", stdin_buf: None, stdin: None, stdout: None, stderr: None, drop_bomb: DropBomb { command: "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\stage2\\bin\\rustdoc.exe", defused: true, armed_location: Location { file: "D:\\a\\rust\\rust\\tests\\run-make\\rustdoc-dep-info\\rmake.rs", line: 10, col: 5 } }, already_executed: true }
output status: `exit code: 0xc00000fd`
=== STDOUT ===



=== STDERR ===

---
test result: FAILED. 284 passed; 1 failed; 110 ignored; 0 measured; 6 filtered out; finished in 205.58s

Some tests failed in compiletest suite=run-make mode=run-make host=x86_64-pc-windows-gnu target=x86_64-pc-windows-gnu
Build completed unsuccessfully in 2:25:45
make: *** [Makefile:124: ci-mingw-x] Error 1
  local time: Mon May 19 05:38:19 CUT 2025
  network time: Mon, 19 May 2025 05:38:19 GMT
##[error]Process completed with exit code 2.
Post job cleanup.
[command]"C:\Program Files\Git\bin\git.exe" version

[bors]

💔 Test failed - checks-actions

[Zalathar]

@bors retry (mingw)