coverage. Add discard end blocks for decisions to reset condbitmap without updating global bitmap

Author: zhuyunxing

compiler/rustc_middle/src/mir/coverage.rs

@@ -331,12 +331,20 @@ pub struct DecisionInfo {
 #[derive(TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
 pub struct MCDCDecisionSpan {
     pub span: Span,
-    pub end_markers: Vec<BlockMarkerId>,
+    // Blocks where update test vectors of the decision.
+    pub update_end_markers: Vec<BlockMarkerId>,
+    // Block where discard written condition bitmap of the decision.
+    pub discard_end_markers: Vec<BlockMarkerId>,
     pub decision_depth: u16,
 }
 
 impl MCDCDecisionSpan {
     pub fn new(span: Span) -> Self {
-        Self { span, end_markers: Vec::new(), decision_depth: 0 }
+        Self {
+            span,
+            update_end_markers: Vec::new(),
+            discard_end_markers: Vec::new(),
+            decision_depth: 0,
+        }
     }
 }

compiler/rustc_middle/src/mir/pretty.rs

@@ -513,12 +513,20 @@ fn write_coverage_info_hi(
         did_print = true;
     }
 
-    for (coverage::MCDCDecisionSpan { span, end_markers, decision_depth }, conditions) in mcdc_spans
+    for (
+        coverage::MCDCDecisionSpan {
+            span,
+            update_end_markers: end_markers,
+            discard_end_markers: discard_markers,
+            decision_depth,
+        },
+        conditions,
+    ) in mcdc_spans
     {
         let num_conditions = conditions.len();
         writeln!(
             w,
-            "{INDENT}coverage mcdc decision {{ num_conditions: {num_conditions:?}, end: {end_markers:?}, depth: {decision_depth:?} }} => {span:?}"
+            "{INDENT}coverage mcdc decision {{ num_conditions: {num_conditions:?}, end: {end_markers:?}, discard_markers: {discard_markers:?} depth: {decision_depth:?} }} => {span:?}"
         )?;
         for coverage::MCDCBranchSpan { span, condition_info, true_markers, false_markers } in
             conditions

compiler/rustc_mir_build/src/build/coverageinfo/mcdc.rs

@@ -148,10 +148,10 @@ impl BooleanDecisionCtx {
             false_next_id: None,
         });
         if condition_info.true_next_id.is_none() {
-            self.decision_info.end_markers.push(true_marker);
+            self.decision_info.update_end_markers.push(true_marker);
         }
         if condition_info.false_next_id.is_none() {
-            self.decision_info.end_markers.push(false_marker);
+            self.decision_info.update_end_markers.push(false_marker);
         }
 
         self.conditions.push(MCDCBranchSpan {

compiler/rustc_mir_transform/src/coverage/mappings.rs

@@ -1,6 +1,4 @@
-use std::collections::BTreeSet;
-
-use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::graph::DirectedGraph;
 use rustc_index::bit_set::BitSet;
 use rustc_index::IndexVec;
@@ -51,7 +49,8 @@ pub(super) struct MCDCBranch {
 #[derive(Debug)]
 pub(super) struct MCDCDecision {
     pub(super) span: Span,
-    pub(super) end_bcbs: BTreeSet<BasicCoverageBlock>,
+    pub(super) update_end_bcbs: FxIndexSet<BasicCoverageBlock>,
+    pub(super) discard_end_bcbs: FxIndexSet<BasicCoverageBlock>,
     pub(super) bitmap_idx: usize,
     pub(super) num_test_vectors: usize,
     pub(super) decision_depth: u16,
@@ -308,11 +307,16 @@ pub(super) fn extract_mcdc_mappings(
         }
         let decision_span = unexpand_into_body_span(decision.span, body_span)?;
 
-        let end_bcbs = decision
-            .end_markers
+        let update_end_bcbs = decision
+            .update_end_markers
+            .iter()
+            .filter_map(|&marker| bcb_from_marker(marker))
+            .collect();
+        let discard_end_bcbs = decision
+            .discard_end_markers
             .iter()
-            .map(|&marker| bcb_from_marker(marker))
-            .collect::<Option<_>>()?;
+            .filter_map(|&marker| bcb_from_marker(marker))
+            .collect();
 
         let mut branch_mappings: Vec<_> =
             branches.into_iter().filter_map(extract_condition_mapping).collect();
@@ -344,7 +348,8 @@ pub(super) fn extract_mcdc_mappings(
         Some((
             MCDCDecision {
                 span,
-                end_bcbs,
+                update_end_bcbs,
+                discard_end_bcbs,
                 bitmap_idx,
                 num_test_vectors,
                 decision_depth: decision.decision_depth,
@@ -403,7 +408,10 @@ fn calc_test_vectors_index(conditions: &mut Vec<MCDCBranch>) -> usize {
             }
         }
     }
-    assert!(next_conditions.is_empty(), "the decision tree has untouched nodes");
+    assert!(
+        next_conditions.is_empty(),
+        "the decision tree has untouched nodes, next_conditions: {next_conditions:?}"
+    );
     let mut cur_idx = 0;
     // LLVM hopes the end nodes are sorted in descending order by `num_paths` so that it can
     // optimize bitmap size for decisions in tree form such as `a && b && c && d && ...`.

compiler/rustc_mir_transform/src/coverage/mod.rs

@@ -351,7 +351,7 @@ fn inject_mcdc_statements<'tcx>(
 ) {
     for (decision, conditions) in &extracted_mappings.mcdc_mappings {
         // Inject test vector update first because `inject_statement` always insert new statement at head.
-        for &end in &decision.end_bcbs {
+        for &end in &decision.update_end_bcbs {
             let end_bb = basic_coverage_blocks[end].leader_bb();
             inject_statement(
                 mir_body,
@@ -363,6 +363,15 @@ fn inject_mcdc_statements<'tcx>(
             );
         }
 
+        for &discard in &decision.discard_end_bcbs {
+            let discard_bb = basic_coverage_blocks[discard].leader_bb();
+            inject_statement(
+                mir_body,
+                CoverageKind::CondBitmapReset { decision_depth: decision.decision_depth },
+                discard_bb,
+            );
+        }
+
         for mappings::MCDCBranch {
             span: _,
             true_bcbs,