Auto merge of #116046 - Zalathar:fn-cov-info, r=cjgillot

coverage: Move most per-function coverage info into `mir::Body`

Currently, all of the coverage information collected by the `InstrumentCoverage` pass is smuggled through MIR in the form of individual `StatementKind::Coverage` statements, which must then be reassembled by coverage codegen.

That's awkward for a number of reasons:
- While some of the coverage statements do care about their specific position in the MIR control-flow graph, many of them don't, and are just tacked onto the function's first BB as metadata carriers.
- MIR inlining can result in coverage statements being duplicated, so coverage codegen has to jump through hoops to avoid emitting duplicate mappings.
- MIR optimizations that would delete coverage statements need to carefully copy them into the function's first BB so as not to omit them from coverage reports.
- The order in which coverage codegen sees coverage statements is dependent on MIR optimizations/inlining, which can cause unnecessary churn in the emitted coverage mappings.
- We don't have a good way to annotate MIR-level functions with extra coverage info that doesn't belong in a statement.

---

This PR therefore takes most of the per-function coverage info and stores it in a field in `mir::Body` as `Option<Box<FunctionCoverageInfo>>`.

(This adds one pointer to the size of `mir::Body`, even when coverage is not enabled.)

Coverage statements still need to be injected into MIR in some cases, but only when they actually affect codegen (counters) or are needed to detect code that has been optimized away as unreachable (counters/expressions).

---

By the end of this PR, the information stored in `FunctionCoverageInfo` is:

- A hash of the function's source code (needed by LLVM's coverage map format)
- The number of coverage counters added by coverage instrumentation
- A table of coverage expressions, associating each expression ID with its operator (add or subtract) and its two operands
- The list of mappings, associating each covered code region with a counter/expression/zero value

---

~~This is built on top of #115301, so I'll rebase and roll a reviewer once that lands.~~
r? `@ghost`
`@rustbot` label +A-code-coverage

1 files changed, 5 insertions, 15 deletions

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 940ab190ffc..afe94d10752 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -573,24 +573,14 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    /// Returns coverage summary info for a function, after executing the `InstrumentCoverage`
-    /// MIR pass (assuming the -Cinstrument-coverage option is enabled).
-    query coverageinfo(key: ty::InstanceDef<'tcx>) -> &'tcx mir::CoverageInfo {
-        desc { |tcx| "retrieving coverage info from MIR for `{}`", tcx.def_path_str(key.def_id()) }
+    /// Summarizes coverage IDs inserted by the `InstrumentCoverage` MIR pass
+    /// (for compiler option `-Cinstrument-coverage`), after MIR optimizations
+    /// have had a chance to potentially remove some of them.
+    query coverage_ids_info(key: ty::InstanceDef<'tcx>) -> &'tcx mir::CoverageIdsInfo {
+        desc { |tcx| "retrieving coverage IDs info from MIR for `{}`", tcx.def_path_str(key.def_id()) }
         arena_cache
     }
 
-    /// Returns the `CodeRegions` for a function that has instrumented coverage, in case the
-    /// function was optimized out before codegen, and before being added to the Coverage Map.
-    query covered_code_regions(key: DefId) -> &'tcx Vec<&'tcx mir::coverage::CodeRegion> {
-        desc {
-            |tcx| "retrieving the covered `CodeRegion`s, if instrumented, for `{}`",
-            tcx.def_path_str(key)
-        }
-        arena_cache
-        cache_on_disk_if { key.is_local() }
-    }
-
     /// The `DefId` is the `DefId` of the containing MIR body. Promoteds do not have their own
     /// `DefId`. This function returns all promoteds in the specified body. The body references
     /// promoteds by the `DefId` and the `mir::Promoted` index. This is necessary, because