coverage: Treat each match arm as a "branch" for branch coverage

Author: Zalathar

compiler/rustc_codegen_llvm/src/coverageinfo/map_data.rs

@@ -203,11 +203,7 @@ impl<'tcx> FunctionCoverage<'tcx> {
     /// Return the source hash, generated from the HIR node structure, and used to indicate whether
     /// or not the source code structure changed between different compilations.
     pub(crate) fn source_hash(&self) -> u64 {
-        if self.is_used {
-            self.function_coverage_info.function_source_hash
-        } else {
-            0
-        }
+        if self.is_used { self.function_coverage_info.function_source_hash } else { 0 }
     }
 
     /// Returns an iterator over all filenames used by this function's mappings.
@@ -251,11 +247,7 @@ impl<'tcx> FunctionCoverage<'tcx> {
     }
 
     fn counter_for_term(&self, term: CovTerm) -> Counter {
-        if self.is_zero_term(term) {
-            Counter::ZERO
-        } else {
-            Counter::from_term(term)
-        }
+        if self.is_zero_term(term) { Counter::ZERO } else { Counter::from_term(term) }
     }
 
     fn is_zero_term(&self, term: CovTerm) -> bool {

compiler/rustc_middle/src/mir/pretty.rs

@@ -1743,13 +1743,12 @@ pub fn write_allocation_bytes<'tcx, Prov: Provenance, Extra, Bytes: AllocBytes>(
             }
         } else if let Some(prov) = alloc.provenance().get(i, &tcx) {
             // Memory with provenance must be defined
-            assert!(alloc
-                .init_mask()
-                .is_range_initialized(alloc_range(i, Size::from_bytes(1)))
-                .is_ok());
+            assert!(
+                alloc.init_mask().is_range_initialized(alloc_range(i, Size::from_bytes(1))).is_ok()
+            );
             ascii.push('━'); // HEAVY HORIZONTAL
-                             // We have two characters to display this, which is obviously not enough.
-                             // Format is similar to "oversized" above.
+            // We have two characters to display this, which is obviously not enough.
+            // Format is similar to "oversized" above.
             let j = i.bytes_usize();
             let c = alloc.inspect_with_uninit_and_ptr_outside_interpreter(j..j + 1)[0];
             write!(w, "╾{c:02x}{prov:#?} (1 ptr byte)╼")?;

compiler/rustc_mir_build/src/build/coverageinfo.rs

@@ -43,6 +43,12 @@ struct NotInfo {
     is_flipped: bool,
 }
 
+pub(crate) struct MatchArm {
+    pub(crate) source_info: SourceInfo,
+    pub(crate) pre_binding_block: Option<BasicBlock>,
+    pub(crate) arm_block: BasicBlock,
+}
+
 #[derive(Default)]
 struct BlockMarkerGen {
     num_block_markers: usize,
@@ -169,6 +175,34 @@ impl CoverageInfoBuilder {
         }
     }
 
+    pub(crate) fn add_match_arms(&mut self, cfg: &mut CFG<'_>, arms: &[MatchArm]) {
+        // Match expressions with 0-1 arms don't have any branches for their arms.
+        if arms.len() < 2 {
+            return;
+        }
+
+        // FIXME(#124118) The current implementation of branch coverage for
+        // match arms can't handle or-patterns.
+        if arms.iter().any(|arm| arm.pre_binding_block.is_none()) {
+            return;
+        }
+
+        let branch_arms = arms
+            .iter()
+            .map(|&MatchArm { source_info, pre_binding_block, arm_block }| {
+                let pre_guard_marker =
+                    self.markers.inject_block_marker(cfg, source_info, pre_binding_block.unwrap());
+                let arm_taken_marker =
+                    self.markers.inject_block_marker(cfg, source_info, arm_block);
+                BranchArm { span: source_info.span, pre_guard_marker, arm_taken_marker }
+            })
+            .collect::<Vec<_>>();
+
+        if let Some(branch_info) = self.branch_info.as_mut() {
+            branch_info.branch_arm_lists.push(branch_arms);
+        }
+    }
+
     pub(crate) fn into_done(self) -> Box<CoverageInfoHi> {
         let Self { nots: _, markers: BlockMarkerGen { num_block_markers }, branch_info, mcdc_info } =
             self;

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

@@ -22,7 +22,7 @@ use crate::build::ForGuard::{self, OutsideGuard, RefWithinGuard};
 use crate::build::expr::as_place::PlaceBuilder;
 use crate::build::scope::DropKind;
 use crate::build::{
-    BlockAnd, BlockAndExtension, Builder, GuardFrame, GuardFrameLocal, LocalsForNode,
+    BlockAnd, BlockAndExtension, Builder, GuardFrame, GuardFrameLocal, LocalsForNode, coverageinfo,
 };
 
 // helper functions, broken out by category:
@@ -416,7 +416,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     where
         'tcx: 'pat,
     {
-        let arm_end_blocks: Vec<BasicBlock> = arms
+        let mut coverage_match_arms = self.coverage_info.is_some().then_some(vec![]);
+
+        let arm_end_blocks: Vec<_> = arms
             .into_iter()
             .zip(built_match_tree.branches)
             .map(|(arm, branch)| {
@@ -451,6 +453,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         opt_scrutinee_place,
                     );
 
+                    // FIXME: Propagate this info down to codegen
+                    let pre_binding_block = branch.sub_branches[0].otherwise_block;
+
                     let arm_block = this.bind_pattern(
                         outer_source_info,
                         branch,
@@ -460,6 +465,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         EmitStorageLive::Yes,
                     );
 
+                    if let Some(coverage_match_arms) = coverage_match_arms.as_mut() {
+                        coverage_match_arms.push(coverageinfo::MatchArm {
+                            source_info: this.source_info(arm.pattern.span),
+                            pre_binding_block: Some(pre_binding_block),
+                            arm_block,
+                        })
+                    }
+
                     this.fixed_temps_scope = old_dedup_scope;
 
                     if let Some(source_scope) = scope {
@@ -472,6 +485,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             })
             .collect();
 
+        if let Some(coverage_match_arms) = coverage_match_arms {
+            self.coverage_info
+                .as_mut()
+                .expect("checked when creating `coverage_match_arms`")
+                .add_match_arms(&mut self.cfg, &coverage_match_arms);
+        }
+
         // all the arm blocks will rejoin here
         let end_block = self.cfg.start_new_block();
 

compiler/rustc_mir_transform/src/coverage/mappings.rs

@@ -3,9 +3,7 @@ use std::collections::BTreeSet;
 use rustc_data_structures::graph::DirectedGraph;
 use rustc_index::IndexVec;
 use rustc_index::bit_set::BitSet;
-use rustc_middle::mir::coverage::{
-    BlockMarkerId, ConditionInfo, CoverageInfoHi, CoverageKind,
-};
+use rustc_middle::mir::coverage::{BlockMarkerId, ConditionInfo, CoverageInfoHi, CoverageKind};
 use rustc_middle::mir::{self, BasicBlock, StatementKind};
 use rustc_middle::ty::TyCtxt;
 use rustc_span::Span;

tests/coverage/branch/guard-simple.cov-map

@@ -1,24 +1,35 @@
 Function name: guard_simple::never_taken
-Raw bytes (56): 0x[01, 01, 04, 01, 05, 11, 09, 0f, 0d, 05, 09, 08, 01, 08, 01, 02, 1e, 20, 05, 02, 02, 0e, 00, 1e, 05, 00, 22, 00, 24, 11, 01, 0e, 00, 1e, 20, 09, 06, 00, 0e, 00, 1e, 09, 00, 22, 00, 24, 0d, 01, 0e, 00, 10, 0b, 02, 01, 00, 02]
+Raw bytes (80): 0x[01, 01, 09, 07, 01, 17, 05, 0d, 09, 01, 05, 17, 11, 0d, 09, 11, 09, 23, 0d, 05, 09, 0a, 01, 08, 01, 02, 1e, 20, 01, 02, 02, 09, 00, 0a, 20, 05, 0e, 00, 0e, 00, 1e, 05, 00, 22, 00, 24, 20, 11, 12, 01, 09, 00, 0a, 11, 00, 0e, 00, 1e, 20, 09, 1a, 00, 0e, 00, 1e, 09, 00, 22, 00, 24, 0d, 01, 0e, 00, 10, 1f, 02, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 4
-- expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(4), rhs = Counter(2)
-- expression 2 operands: lhs = Expression(3, Add), rhs = Counter(3)
-- expression 3 operands: lhs = Counter(1), rhs = Counter(2)
-Number of file 0 mappings: 8
+Number of expressions: 9
+- expression 0 operands: lhs = Expression(1, Add), rhs = Counter(0)
+- expression 1 operands: lhs = Expression(5, Add), rhs = Counter(1)
+- expression 2 operands: lhs = Counter(3), rhs = Counter(2)
+- expression 3 operands: lhs = Counter(0), rhs = Counter(1)
+- expression 4 operands: lhs = Expression(5, Add), rhs = Counter(4)
+- expression 5 operands: lhs = Counter(3), rhs = Counter(2)
+- expression 6 operands: lhs = Counter(4), rhs = Counter(2)
+- expression 7 operands: lhs = Expression(8, Add), rhs = Counter(3)
+- expression 8 operands: lhs = Counter(1), rhs = Counter(2)
+Number of file 0 mappings: 10
 - Code(Counter(0)) at (prev + 8, 1) to (start + 2, 30)
-- Branch { true: Counter(1), false: Expression(0, Sub) } at (prev + 2, 14) to (start + 0, 30)
+- Branch { true: Counter(0), false: Expression(0, Sub) } at (prev + 2, 9) to (start + 0, 10)
+    true  = c0
+    false = (((c3 + c2) + c1) - c0)
+- Branch { true: Counter(1), false: Expression(3, Sub) } at (prev + 0, 14) to (start + 0, 30)
     true  = c1
     false = (c0 - c1)
 - Code(Counter(1)) at (prev + 0, 34) to (start + 0, 36)
-- Code(Counter(4)) at (prev + 1, 14) to (start + 0, 30)
-- Branch { true: Counter(2), false: Expression(1, Sub) } at (prev + 0, 14) to (start + 0, 30)
+- Branch { true: Counter(4), false: Expression(4, Sub) } at (prev + 1, 9) to (start + 0, 10)
+    true  = c4
+    false = ((c3 + c2) - c4)
+- Code(Counter(4)) at (prev + 0, 14) to (start + 0, 30)
+- Branch { true: Counter(2), false: Expression(6, Sub) } at (prev + 0, 14) to (start + 0, 30)
     true  = c2
     false = (c4 - c2)
 - Code(Counter(2)) at (prev + 0, 34) to (start + 0, 36)
 - Code(Counter(3)) at (prev + 1, 14) to (start + 0, 16)
-- Code(Expression(2, Add)) at (prev + 2, 1) to (start + 0, 2)
+- Code(Expression(7, Add)) at (prev + 2, 1) to (start + 0, 2)
     = ((c1 + c2) + c3)
 

tests/coverage/branch/guard-simple.coverage

@@ -10,11 +10,13 @@
    LL|      1|        _ if black_box(false) => {}
                                                ^0
   ------------------
+  |  Branch (LL:9): [True: 1, False: 0]
   |  Branch (LL:14): [True: 0, False: 1]
   ------------------
    LL|      1|        _ if black_box(false) => {}
                                                ^0
   ------------------
+  |  Branch (LL:9): [True: 1, False: 0]
   |  Branch (LL:14): [True: 0, False: 1]
   ------------------
    LL|      1|        _ => {}

tests/coverage/branch/guard.cov-map

@@ -1,32 +1,48 @@
 Function name: guard::branch_match_guard
-Raw bytes (85): 0x[01, 01, 06, 19, 0d, 05, 09, 0f, 15, 13, 11, 17, 0d, 05, 09, 0d, 01, 0c, 01, 01, 10, 1d, 03, 0b, 00, 0c, 15, 01, 14, 02, 0a, 0d, 03, 0e, 00, 0f, 19, 00, 14, 00, 19, 20, 0d, 02, 00, 14, 00, 1e, 0d, 00, 1d, 02, 0a, 11, 03, 0e, 00, 0f, 1d, 00, 14, 00, 19, 20, 11, 09, 00, 14, 00, 1e, 11, 00, 1d, 02, 0a, 17, 03, 0e, 02, 0a, 0b, 04, 01, 00, 02]
+Raw bytes (120): 0x[01, 01, 0d, 1b, 0d, 33, 11, 05, 09, 03, 19, 19, 0d, 1b, 1d, 33, 11, 05, 09, 05, 09, 2b, 15, 2f, 11, 33, 0d, 05, 09, 10, 01, 0c, 01, 01, 10, 1d, 03, 0b, 00, 0c, 20, 15, 03, 01, 09, 00, 10, 15, 00, 14, 02, 0a, 20, 19, 0e, 03, 09, 00, 10, 0d, 00, 0e, 00, 0f, 19, 00, 14, 00, 19, 20, 0d, 12, 00, 14, 00, 1e, 0d, 00, 1d, 02, 0a, 20, 1d, 16, 03, 09, 00, 10, 11, 00, 0e, 00, 0f, 1d, 00, 14, 00, 19, 20, 11, 09, 00, 14, 00, 1e, 11, 00, 1d, 02, 0a, 33, 03, 0e, 02, 0a, 27, 04, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 6
-- expression 0 operands: lhs = Counter(6), rhs = Counter(3)
-- expression 1 operands: lhs = Counter(1), rhs = Counter(2)
-- expression 2 operands: lhs = Expression(3, Add), rhs = Counter(5)
-- expression 3 operands: lhs = Expression(4, Add), rhs = Counter(4)
-- expression 4 operands: lhs = Expression(5, Add), rhs = Counter(3)
-- expression 5 operands: lhs = Counter(1), rhs = Counter(2)
-Number of file 0 mappings: 13
+Number of expressions: 13
+- expression 0 operands: lhs = Expression(6, Add), rhs = Counter(3)
+- expression 1 operands: lhs = Expression(12, Add), rhs = Counter(4)
+- expression 2 operands: lhs = Counter(1), rhs = Counter(2)
+- expression 3 operands: lhs = Expression(0, Add), rhs = Counter(6)
+- expression 4 operands: lhs = Counter(6), rhs = Counter(3)
+- expression 5 operands: lhs = Expression(6, Add), rhs = Counter(7)
+- expression 6 operands: lhs = Expression(12, Add), rhs = Counter(4)
+- expression 7 operands: lhs = Counter(1), rhs = Counter(2)
+- expression 8 operands: lhs = Counter(1), rhs = Counter(2)
+- expression 9 operands: lhs = Expression(10, Add), rhs = Counter(5)
+- expression 10 operands: lhs = Expression(11, Add), rhs = Counter(4)
+- expression 11 operands: lhs = Expression(12, Add), rhs = Counter(3)
+- expression 12 operands: lhs = Counter(1), rhs = Counter(2)
+Number of file 0 mappings: 16
 - Code(Counter(0)) at (prev + 12, 1) to (start + 1, 16)
 - Code(Counter(7)) at (prev + 3, 11) to (start + 0, 12)
-- Code(Counter(5)) at (prev + 1, 20) to (start + 2, 10)
-- Code(Counter(3)) at (prev + 3, 14) to (start + 0, 15)
+- Branch { true: Counter(5), false: Expression(0, Add) } at (prev + 1, 9) to (start + 0, 16)
+    true  = c5
+    false = (((c1 + c2) + c4) + c3)
+- Code(Counter(5)) at (prev + 0, 20) to (start + 2, 10)
+- Branch { true: Counter(6), false: Expression(3, Sub) } at (prev + 3, 9) to (start + 0, 16)
+    true  = c6
+    false = ((((c1 + c2) + c4) + c3) - c6)
+- Code(Counter(3)) at (prev + 0, 14) to (start + 0, 15)
 - Code(Counter(6)) at (prev + 0, 20) to (start + 0, 25)
-- Branch { true: Counter(3), false: Expression(0, Sub) } at (prev + 0, 20) to (start + 0, 30)
+- Branch { true: Counter(3), false: Expression(4, Sub) } at (prev + 0, 20) to (start + 0, 30)
     true  = c3
     false = (c6 - c3)
 - Code(Counter(3)) at (prev + 0, 29) to (start + 2, 10)
-- Code(Counter(4)) at (prev + 3, 14) to (start + 0, 15)
+- Branch { true: Counter(7), false: Expression(5, Sub) } at (prev + 3, 9) to (start + 0, 16)
+    true  = c7
+    false = (((c1 + c2) + c4) - c7)
+- Code(Counter(4)) at (prev + 0, 14) to (start + 0, 15)
 - Code(Counter(7)) at (prev + 0, 20) to (start + 0, 25)
 - Branch { true: Counter(4), false: Counter(2) } at (prev + 0, 20) to (start + 0, 30)
     true  = c4
     false = c2
 - Code(Counter(4)) at (prev + 0, 29) to (start + 2, 10)
-- Code(Expression(5, Add)) at (prev + 3, 14) to (start + 2, 10)
+- Code(Expression(12, Add)) at (prev + 3, 14) to (start + 2, 10)
     = (c1 + c2)
-- Code(Expression(2, Add)) at (prev + 4, 1) to (start + 0, 2)
+- Code(Expression(9, Add)) at (prev + 4, 1) to (start + 0, 2)
     = ((((c1 + c2) + c3) + c4) + c5)
 

tests/coverage/branch/guard.coverage

@@ -14,17 +14,22 @@
    LL|       |
    LL|      1|    match x {
    LL|      1|        Some(0) => {
+  ------------------
+  |  Branch (LL:9): [True: 1, False: 3]
+  ------------------
    LL|      1|            println!("zero");
    LL|      1|        }
    LL|      3|        Some(x) if x % 2 == 0 => {
                            ^2
   ------------------
+  |  Branch (LL:9): [True: 3, False: 0]
   |  Branch (LL:20): [True: 2, False: 1]
   ------------------
    LL|      2|            println!("is nonzero and even");
    LL|      2|        }
    LL|      1|        Some(x) if x % 3 == 0 => {
   ------------------
+  |  Branch (LL:9): [True: 1, False: 0]
   |  Branch (LL:20): [True: 1, False: 0]
   ------------------
    LL|      1|            println!("is nonzero and odd, but divisible by 3");