mcdc-coverage: Get decision_depth from THIR lowring

Author: RenjiSann

compiler/rustc_codegen_llvm/src/coverageinfo/mod.rs

@@ -204,7 +204,8 @@ fn ensure_mcdc_parameters<'ll, 'tcx>(
     let fn_name = bx.get_pgo_func_name_var(instance);
     let hash = bx.const_u64(function_coverage_info.function_source_hash);
     let bitmap_bytes = bx.const_u32(function_coverage_info.mcdc_bitmap_bytes);
-    let cond_bitmap = bx.mcdc_parameters(fn_name, hash, bitmap_bytes, 1_u32);
+    let max_decision_depth = function_coverage_info.mcdc_max_decision_depth;
+    let cond_bitmap = bx.mcdc_parameters(fn_name, hash, bitmap_bytes, max_decision_depth as u32);
     bx.coverage_context()
         .expect("already checked above")
         .mcdc_condition_bitmap_map

compiler/rustc_middle/src/mir/coverage.rs

@@ -269,6 +269,9 @@ pub struct FunctionCoverageInfo {
     pub mcdc_bitmap_bytes: u32,
     pub expressions: IndexVec<ExpressionId, Expression>,
     pub mappings: Vec<Mapping>,
+    /// The depth of the deepest decision is used to know how many
+    /// temp condbitmaps should be allocated for the function.
+    pub mcdc_max_decision_depth: u16,
 }
 
 /// Branch information recorded during THIR-to-MIR lowering, and stored in MIR.

compiler/rustc_mir_build/src/build/coverageinfo.rs

@@ -106,8 +106,9 @@ impl BranchInfoBuilder {
         tcx: TyCtxt<'_>,
         true_marker: BlockMarkerId,
         false_marker: BlockMarkerId,
-    ) -> Option<ConditionInfo> {
+    ) -> Option<(u16, ConditionInfo)> {
         let mcdc_state = self.mcdc_state.as_mut()?;
+        let decision_depth = mcdc_state.decision_depth;
         let (mut condition_info, decision_result) =
             mcdc_state.take_condition(true_marker, false_marker);
         if let Some(decision) = decision_result {
@@ -141,7 +142,7 @@ impl BranchInfoBuilder {
                 }
             }
         }
-        condition_info
+        condition_info.map(|cond_info| (decision_depth, cond_info))
     }
 
     fn next_block_marker_id(&mut self) -> BlockMarkerId {
@@ -183,13 +184,18 @@ struct MCDCState {
     /// To construct condition evaluation tree.
     decision_stack: VecDeque<ConditionInfo>,
     processing_decision: Option<MCDCDecisionSpan>,
+    decision_depth: u16,
 }
 
 impl MCDCState {
     fn new_if_enabled(tcx: TyCtxt<'_>) -> Option<Self> {
         tcx.sess
             .instrument_coverage_mcdc()
-            .then(|| Self { decision_stack: VecDeque::new(), processing_decision: None })
+            .then(|| Self {
+                decision_stack: VecDeque::new(),
+                processing_decision: None,
+                decision_depth: 0,
+            })
     }
 
     // At first we assign ConditionIds for each sub expression.
@@ -356,15 +362,15 @@ impl Builder<'_, '_> {
         let true_marker = inject_branch_marker(then_block);
         let false_marker = inject_branch_marker(else_block);
 
-        if let Some(condition_info) =
+        if let Some((decision_depth, condition_info)) =
             branch_info.fetch_condition_info(self.tcx, true_marker, false_marker)
         {
             branch_info.mcdc_branch_spans.push(MCDCBranchSpan {
                 span: source_info.span,
                 condition_info,
                 true_marker,
                 false_marker,
-                decision_depth: 0,
+                decision_depth,
             });
         } else {
             branch_info.branch_spans.push(BranchSpan {
@@ -380,4 +386,20 @@ impl Builder<'_, '_> {
             branch_info.record_conditions_operation(logical_op, span);
         }
     }
+
+    pub(crate) fn mcdc_increment_depth_if_enabled(&mut self) {
+        if let Some(branch_info) = self.coverage_branch_info.as_mut()
+            && let Some(mcdc_state) = branch_info.mcdc_state.as_mut()
+        {
+            mcdc_state.decision_depth += 1;
+        };
+    }
+
+    pub(crate) fn mcdc_decrement_depth_if_enabled(&mut self) {
+        if let Some(branch_info) = self.coverage_branch_info.as_mut()
+            && let Some(mcdc_state) = branch_info.mcdc_state.as_mut()
+        {
+            mcdc_state.decision_depth -= 1;
+        };
+    }
 }

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -151,8 +151,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let mut block = block;
                 let temp_scope = args.temp_scope_override.unwrap_or_else(|| this.local_scope());
                 let mutability = Mutability::Mut;
+
+                // Increment the decision depth, in case we encounter boolean expressions
+                // further down.
+                this.mcdc_increment_depth_if_enabled();
                 let place =
                     unpack!(block = this.as_temp(block, Some(temp_scope), expr_id, mutability));
+                this.mcdc_decrement_depth_if_enabled();
+
                 let operand = Operand::Move(Place::from(place));
 
                 let then_block = this.cfg.start_new_block();

compiler/rustc_mir_transform/src/coverage/mod.rs

@@ -102,12 +102,22 @@ fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir:
 
     inject_mcdc_statements(mir_body, &basic_coverage_blocks, &coverage_spans);
 
+    let mcdc_max_decision_depth = coverage_spans
+        .all_bcb_mappings()
+        .filter_map(|bcb_mapping| match bcb_mapping.kind {
+            BcbMappingKind::MCDCDecision { decision_depth, .. } => Some(decision_depth),
+            _ => None,
+        })
+        .max()
+        .unwrap_or(0);
+
     mir_body.function_coverage_info = Some(Box::new(FunctionCoverageInfo {
         function_source_hash: hir_info.function_source_hash,
         num_counters: coverage_counters.num_counters(),
         mcdc_bitmap_bytes: coverage_spans.test_vector_bitmap_bytes(),
         expressions: coverage_counters.into_expressions(),
         mappings,
+        mcdc_max_decision_depth,
     }));
 }