Rollup merge of #136053 - Zalathar:defer-counters, r=saethlin

coverage: Defer part of counter-creation until codegen

Follow-up to #135481 and #135873.

One of the pleasant properties of the new counter-assignment algorithm is that we can stop partway through the process, store the intermediate state in MIR, and then resume the rest of the algorithm during codegen. This lets it take into account which parts of the control-flow graph were eliminated by MIR opts, resulting in fewer physical counters and simpler counter expressions.

Those improvements end up completely obsoleting much larger chunks of code that were previously responsible for cleaning up the coverage metadata after MIR opts, while also doing a more thorough cleanup job.

(That change also unlocks some further simplifications that I've kept out of this PR to limit its scope.)

1 files changed, 1 insertions, 9 deletions

diff --git a/compiler/rustc_mir_transform/src/coverage/graph.rs b/compiler/rustc_mir_transform/src/coverage/graph.rs
index 392b54c8d81..6d84248ddfb 100644
--- a/compiler/rustc_mir_transform/src/coverage/graph.rs
+++ b/compiler/rustc_mir_transform/src/coverage/graph.rs
@@ -8,6 +8,7 @@ use rustc_data_structures::graph::dominators::Dominators;
 use rustc_data_structures::graph::{self, DirectedGraph, StartNode};
 use rustc_index::IndexVec;
 use rustc_index::bit_set::DenseBitSet;
+pub(crate) use rustc_middle::mir::coverage::{BasicCoverageBlock, START_BCB};
 use rustc_middle::mir::{self, BasicBlock, Terminator, TerminatorKind};
 use tracing::debug;
 
@@ -269,15 +270,6 @@ impl graph::Predecessors for CoverageGraph {
     }
 }
 
-rustc_index::newtype_index! {
-    /// A node in the control-flow graph of CoverageGraph.
-    #[orderable]
-    #[debug_format = "bcb{}"]
-    pub(crate) struct BasicCoverageBlock {
-        const START_BCB = 0;
-    }
-}
-
 /// `BasicCoverageBlockData` holds the data indexed by a `BasicCoverageBlock`.
 ///
 /// A `BasicCoverageBlock` (BCB) represents the maximal-length sequence of MIR `BasicBlock`s without