Auto merge of #114791 - Zalathar:bcb-counter, r=cjgillot

coverage: Give the instrumentor its own counter type, separate from MIR

Within the MIR representation of coverage data, `CoverageKind` is an important part of `StatementKind::Coverage`, but the `InstrumentCoverage` pass also uses it heavily as an internal data structure. This means that any change to `CoverageKind` also needs to update all of the internal parts of `InstrumentCoverage` that manipulate it directly, making the MIR representation difficult to modify.

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This change fixes that by giving the instrumentor its own `BcbCounter` type for internal use, which is then converted to a `CoverageKind` when injecting coverage information into MIR.

The main change is mostly mechanical, because the initial `BcbCounter` is drop-in compatible with `CoverageKind`, minus the unnecessary `CoverageKind::Unreachable` variant.

I've then removed the `function_source_hash` field from `BcbCounter::Counter`, as a small example of how the two types can now usefully differ from each other. Every counter in a MIR-level function should have the same source hash, so we can supply the hash during the conversion to `CoverageKind::Counter` instead.

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*Background:* BCB stands for “basic coverage block”, which is a node in the simplified control-flow graph used by coverage instrumentation. The instrumentor pass uses the function's actual MIR control-flow graph to build a simplified BCB graph, then assigns coverage counters and counter expressions to various nodes/edges in that simplified graph, and then finally injects corresponding coverage information into the underlying MIR.

1 files changed, 4 insertions, 5 deletions

diff --git a/compiler/rustc_mir_transform/src/coverage/tests.rs b/compiler/rustc_mir_transform/src/coverage/tests.rs
index d797a6057a7..4a066ed3abd 100644
--- a/compiler/rustc_mir_transform/src/coverage/tests.rs
+++ b/compiler/rustc_mir_transform/src/coverage/tests.rs
@@ -34,7 +34,6 @@ use itertools::Itertools;
 use rustc_data_structures::graph::WithNumNodes;
 use rustc_data_structures::graph::WithSuccessors;
 use rustc_index::{Idx, IndexVec};
-use rustc_middle::mir::coverage::CoverageKind;
 use rustc_middle::mir::*;
 use rustc_middle::ty;
 use rustc_span::{self, BytePos, Pos, Span, DUMMY_SP};
@@ -675,8 +674,8 @@ fn test_make_bcb_counters() {
                 ));
             }
         }
-        let mut coverage_counters = counters::CoverageCounters::new(0, &basic_coverage_blocks);
-        let () = coverage_counters
+        let mut coverage_counters = counters::CoverageCounters::new(&basic_coverage_blocks);
+        coverage_counters
             .make_bcb_counters(&mut basic_coverage_blocks, &coverage_spans)
             .expect("should be Ok");
         assert_eq!(coverage_counters.intermediate_expressions.len(), 0);
@@ -685,7 +684,7 @@ fn test_make_bcb_counters() {
         assert_eq!(
             0, // bcb1 has a `Counter` with id = 0
             match coverage_counters.bcb_counter(bcb1).expect("should have a counter") {
-                CoverageKind::Counter { id, .. } => id,
+                counters::BcbCounter::Counter { id, .. } => id,
                 _ => panic!("expected a Counter"),
             }
             .as_u32()
@@ -695,7 +694,7 @@ fn test_make_bcb_counters() {
         assert_eq!(
             1, // bcb2 has a `Counter` with id = 1
             match coverage_counters.bcb_counter(bcb2).expect("should have a counter") {
-                CoverageKind::Counter { id, .. } => id,
+                counters::BcbCounter::Counter { id, .. } => id,
                 _ => panic!("expected a Counter"),
             }
             .as_u32()