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, 0 insertions, 61 deletions

diff --git a/compiler/rustc_mir_transform/src/coverage/mappings.rs b/compiler/rustc_mir_transform/src/coverage/mappings.rs
index 8d0d92dc367..d83c0d40a7e 100644
--- a/compiler/rustc_mir_transform/src/coverage/mappings.rs
+++ b/compiler/rustc_mir_transform/src/coverage/mappings.rs
@@ -1,9 +1,7 @@
 use std::collections::BTreeSet;
 
 use rustc_data_structures::fx::FxIndexMap;
-use rustc_data_structures::graph::DirectedGraph;
 use rustc_index::IndexVec;
-use rustc_index::bit_set::DenseBitSet;
 use rustc_middle::mir::coverage::{
     BlockMarkerId, BranchSpan, ConditionId, ConditionInfo, CoverageInfoHi, CoverageKind,
 };
@@ -63,10 +61,6 @@ const MCDC_MAX_BITMAP_SIZE: usize = i32::MAX as usize;
 
 #[derive(Default)]
 pub(super) struct ExtractedMappings {
-    /// Store our own copy of [`CoverageGraph::num_nodes`], so that we don't
-    /// need access to the whole graph when allocating per-BCB data. This is
-    /// only public so that other code can still use exhaustive destructuring.
-    pub(super) num_bcbs: usize,
     pub(super) code_mappings: Vec<CodeMapping>,
     pub(super) branch_pairs: Vec<BranchPair>,
     pub(super) mcdc_bitmap_bits: usize,
@@ -118,7 +112,6 @@ pub(super) fn extract_all_mapping_info_from_mir<'tcx>(
     );
 
     ExtractedMappings {
-        num_bcbs: graph.num_nodes(),
         code_mappings,
         branch_pairs,
         mcdc_bitmap_bits,
@@ -127,60 +120,6 @@ pub(super) fn extract_all_mapping_info_from_mir<'tcx>(
     }
 }
 
-impl ExtractedMappings {
-    pub(super) fn all_bcbs_with_counter_mappings(&self) -> DenseBitSet<BasicCoverageBlock> {
-        // Fully destructure self to make sure we don't miss any fields that have mappings.
-        let Self {
-            num_bcbs,
-            code_mappings,
-            branch_pairs,
-            mcdc_bitmap_bits: _,
-            mcdc_degraded_branches,
-            mcdc_mappings,
-        } = self;
-
-        // Identify which BCBs have one or more mappings.
-        let mut bcbs_with_counter_mappings = DenseBitSet::new_empty(*num_bcbs);
-        let mut insert = |bcb| {
-            bcbs_with_counter_mappings.insert(bcb);
-        };
-
-        for &CodeMapping { span: _, bcb } in code_mappings {
-            insert(bcb);
-        }
-        for &BranchPair { true_bcb, false_bcb, .. } in branch_pairs {
-            insert(true_bcb);
-            insert(false_bcb);
-        }
-        for &MCDCBranch { true_bcb, false_bcb, .. } in mcdc_degraded_branches
-            .iter()
-            .chain(mcdc_mappings.iter().map(|(_, branches)| branches.into_iter()).flatten())
-        {
-            insert(true_bcb);
-            insert(false_bcb);
-        }
-
-        // MC/DC decisions refer to BCBs, but don't require those BCBs to have counters.
-        if bcbs_with_counter_mappings.is_empty() {
-            debug_assert!(
-                mcdc_mappings.is_empty(),
-                "A function with no counter mappings shouldn't have any decisions: {mcdc_mappings:?}",
-            );
-        }
-
-        bcbs_with_counter_mappings
-    }
-
-    /// Returns the set of BCBs that have one or more `Code` mappings.
-    pub(super) fn bcbs_with_ordinary_code_mappings(&self) -> DenseBitSet<BasicCoverageBlock> {
-        let mut bcbs = DenseBitSet::new_empty(self.num_bcbs);
-        for &CodeMapping { span: _, bcb } in &self.code_mappings {
-            bcbs.insert(bcb);
-        }
-        bcbs
-    }
-}
-
 fn resolve_block_markers(
     coverage_info_hi: &CoverageInfoHi,
     mir_body: &mir::Body<'_>,