coverage: Don't create counters for code that was removed by MIR opts

Zalathar · Zalathar · commit bf1f254b13d0 · 2025-02-06T21:44:31.000+11:00
diff --git a/compiler/rustc_mir_transform/src/coverage/counters.rs b/compiler/rustc_mir_transform/src/coverage/counters.rs
@@ -80,28 +80,30 @@ fn make_node_flow_priority_list(
 pub(crate) fn transcribe_counters(
     old: &NodeCounters<BasicCoverageBlock>,
     bcb_needs_counter: &DenseBitSet<BasicCoverageBlock>,
+    bcbs_seen: &DenseBitSet<BasicCoverageBlock>,
 ) -> CoverageCounters {
     let mut new = CoverageCounters::with_num_bcbs(bcb_needs_counter.domain_size());
 
     for bcb in bcb_needs_counter.iter() {
+        if !bcbs_seen.contains(bcb) {
+            // This BCB's code was removed by MIR opts, so its counter is always zero.
+            new.set_node_counter(bcb, CovTerm::Zero);
+            continue;
+        }
+
         // Our counter-creation algorithm doesn't guarantee that a node's list
         // of terms starts or ends with a positive term, so partition the
         // counters into "positive" and "negative" lists for easier handling.
-        let (mut pos, mut neg): (Vec<_>, Vec<_>) =
-            old.counter_terms[bcb].iter().partition_map(|&CounterTerm { node, op }| match op {
+        let (mut pos, mut neg): (Vec<_>, Vec<_>) = old.counter_terms[bcb]
+            .iter()
+            // Filter out any BCBs that were removed by MIR opts;
+            // this treats them as having an execution count of 0.
+            .filter(|term| bcbs_seen.contains(term.node))
+            .partition_map(|&CounterTerm { node, op }| match op {
                 Op::Add => Either::Left(node),
                 Op::Subtract => Either::Right(node),
             });
 
-        if pos.is_empty() {
-            // If we somehow end up with no positive terms, fall back to
-            // creating a physical counter. There's no known way for this
-            // to happen, but we can avoid an ICE if it does.
-            debug_assert!(false, "{bcb:?} has no positive counter terms");
-            pos = vec![bcb];
-            neg = vec![];
-        }
-
         // These intermediate sorts are not strictly necessary, but were helpful
         // in reducing churn when switching to the current counter-creation scheme.
         // They also help to slightly decrease the overall size of the expression
@@ -119,7 +121,7 @@ pub(crate) fn transcribe_counters(
         pos.sort();
         neg.sort();
 
-        let pos_counter = new.make_sum(&pos).expect("`pos` should not be empty");
+        let pos_counter = new.make_sum(&pos).unwrap_or(CovTerm::Zero);
         let new_counter = new.make_subtracted_sum(pos_counter, &neg);
         new.set_node_counter(bcb, new_counter);
     }
diff --git a/compiler/rustc_mir_transform/src/coverage/query.rs b/compiler/rustc_mir_transform/src/coverage/query.rs
@@ -127,8 +127,12 @@ fn coverage_ids_info<'tcx>(
         }
     }
 
+    // FIXME(Zalathar): It should be possible to sort `priority_list[1..]` by
+    // `!bcbs_seen.contains(bcb)` to simplify the mappings even further, at the
+    // expense of some churn in the tests. When doing so, also consider removing
+    // the sorts in `transcribe_counters`.
     let node_counters = make_node_counters(&fn_cov_info.node_flow_data, &fn_cov_info.priority_list);
-    let coverage_counters = transcribe_counters(&node_counters, &bcb_needs_counter);
+    let coverage_counters = transcribe_counters(&node_counters, &bcb_needs_counter, &bcbs_seen);
 
     let mut counters_seen = DenseBitSet::new_empty(coverage_counters.node_counters.len());
     let mut expressions_seen = DenseBitSet::new_filled(coverage_counters.expressions.len());
diff --git a/tests/coverage/assert_not.cov-map b/tests/coverage/assert_not.cov-map
@@ -1,15 +1,13 @@
 Function name: assert_not::main
-Raw bytes (31): 0x[01, 01, 01, 0d, 00, 05, 01, 06, 01, 01, 12, 05, 02, 05, 00, 14, 09, 01, 05, 00, 14, 0d, 01, 05, 00, 16, 02, 01, 01, 00, 02]
+Raw bytes (29): 0x[01, 01, 00, 05, 01, 06, 01, 01, 12, 05, 02, 05, 00, 14, 09, 01, 05, 00, 14, 0d, 01, 05, 00, 16, 0d, 01, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 1
-- expression 0 operands: lhs = Counter(3), rhs = Zero
+Number of expressions: 0
 Number of file 0 mappings: 5
 - Code(Counter(0)) at (prev + 6, 1) to (start + 1, 18)
 - Code(Counter(1)) at (prev + 2, 5) to (start + 0, 20)
 - Code(Counter(2)) at (prev + 1, 5) to (start + 0, 20)
 - Code(Counter(3)) at (prev + 1, 5) to (start + 0, 22)
-- Code(Expression(0, Sub)) at (prev + 1, 1) to (start + 0, 2)
-    = (c3 - Zero)
+- Code(Counter(3)) at (prev + 1, 1) to (start + 0, 2)
 Highest counter ID seen: c3
 
diff --git a/tests/coverage/bad_counter_ids.cov-map b/tests/coverage/bad_counter_ids.cov-map
@@ -9,15 +9,13 @@ Number of file 0 mappings: 2
 Highest counter ID seen: c0
 
 Function name: bad_counter_ids::eq_bad_message
-Raw bytes (21): 0x[01, 01, 01, 01, 00, 03, 01, 29, 01, 02, 0f, 02, 02, 20, 00, 2b, 00, 01, 01, 00, 02]
+Raw bytes (19): 0x[01, 01, 00, 03, 01, 29, 01, 02, 0f, 01, 02, 20, 00, 2b, 00, 01, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 1
-- expression 0 operands: lhs = Counter(0), rhs = Zero
+Number of expressions: 0
 Number of file 0 mappings: 3
 - Code(Counter(0)) at (prev + 41, 1) to (start + 2, 15)
-- Code(Expression(0, Sub)) at (prev + 2, 32) to (start + 0, 43)
-    = (c0 - Zero)
+- Code(Counter(0)) at (prev + 2, 32) to (start + 0, 43)
 - Code(Zero) at (prev + 1, 1) to (start + 0, 2)
 Highest counter ID seen: c0
 
@@ -64,27 +62,23 @@ Number of file 0 mappings: 3
 Highest counter ID seen: c1
 
 Function name: bad_counter_ids::ne_good
-Raw bytes (16): 0x[01, 01, 01, 01, 00, 02, 01, 1a, 01, 02, 1f, 02, 03, 01, 00, 02]
+Raw bytes (14): 0x[01, 01, 00, 02, 01, 1a, 01, 02, 1f, 01, 03, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 1
-- expression 0 operands: lhs = Counter(0), rhs = Zero
+Number of expressions: 0
 Number of file 0 mappings: 2
 - Code(Counter(0)) at (prev + 26, 1) to (start + 2, 31)
-- Code(Expression(0, Sub)) at (prev + 3, 1) to (start + 0, 2)
-    = (c0 - Zero)
+- Code(Counter(0)) at (prev + 3, 1) to (start + 0, 2)
 Highest counter ID seen: c0
 
 Function name: bad_counter_ids::ne_good_message
-Raw bytes (21): 0x[01, 01, 01, 01, 00, 03, 01, 1f, 01, 02, 0f, 00, 02, 20, 00, 2b, 02, 01, 01, 00, 02]
+Raw bytes (19): 0x[01, 01, 00, 03, 01, 1f, 01, 02, 0f, 00, 02, 20, 00, 2b, 01, 01, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 1
-- expression 0 operands: lhs = Counter(0), rhs = Zero
+Number of expressions: 0
 Number of file 0 mappings: 3
 - Code(Counter(0)) at (prev + 31, 1) to (start + 2, 15)
 - Code(Zero) at (prev + 2, 32) to (start + 0, 43)
-- Code(Expression(0, Sub)) at (prev + 1, 1) to (start + 0, 2)
-    = (c0 - Zero)
+- Code(Counter(0)) at (prev + 1, 1) to (start + 0, 2)
 Highest counter ID seen: c0
 
diff --git a/tests/coverage/fn_sig_into_try.cov-map b/tests/coverage/fn_sig_into_try.cov-map
@@ -8,44 +8,38 @@ Number of file 0 mappings: 1
 Highest counter ID seen: c0
 
 Function name: fn_sig_into_try::b
-Raw bytes (26): 0x[01, 01, 01, 01, 00, 04, 01, 11, 01, 03, 0f, 00, 03, 0f, 00, 10, 02, 01, 05, 00, 0c, 01, 01, 01, 00, 02]
+Raw bytes (24): 0x[01, 01, 00, 04, 01, 11, 01, 03, 0f, 00, 03, 0f, 00, 10, 01, 01, 05, 00, 0c, 01, 01, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 1
-- expression 0 operands: lhs = Counter(0), rhs = Zero
+Number of expressions: 0
 Number of file 0 mappings: 4
 - Code(Counter(0)) at (prev + 17, 1) to (start + 3, 15)
 - Code(Zero) at (prev + 3, 15) to (start + 0, 16)
-- Code(Expression(0, Sub)) at (prev + 1, 5) to (start + 0, 12)
-    = (c0 - Zero)
+- Code(Counter(0)) at (prev + 1, 5) to (start + 0, 12)
 - Code(Counter(0)) at (prev + 1, 1) to (start + 0, 2)
 Highest counter ID seen: c0
 
 Function name: fn_sig_into_try::c
-Raw bytes (26): 0x[01, 01, 01, 01, 00, 04, 01, 18, 01, 03, 17, 00, 03, 17, 00, 18, 02, 01, 05, 00, 0c, 01, 01, 01, 00, 02]
+Raw bytes (24): 0x[01, 01, 00, 04, 01, 18, 01, 03, 17, 00, 03, 17, 00, 18, 01, 01, 05, 00, 0c, 01, 01, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 1
-- expression 0 operands: lhs = Counter(0), rhs = Zero
+Number of expressions: 0
 Number of file 0 mappings: 4
 - Code(Counter(0)) at (prev + 24, 1) to (start + 3, 23)
 - Code(Zero) at (prev + 3, 23) to (start + 0, 24)
-- Code(Expression(0, Sub)) at (prev + 1, 5) to (start + 0, 12)
-    = (c0 - Zero)
+- Code(Counter(0)) at (prev + 1, 5) to (start + 0, 12)
 - Code(Counter(0)) at (prev + 1, 1) to (start + 0, 2)
 Highest counter ID seen: c0
 
 Function name: fn_sig_into_try::d
-Raw bytes (26): 0x[01, 01, 01, 01, 00, 04, 01, 1f, 01, 04, 0f, 00, 04, 0f, 00, 10, 02, 01, 05, 00, 0c, 01, 01, 01, 00, 02]
+Raw bytes (24): 0x[01, 01, 00, 04, 01, 1f, 01, 04, 0f, 00, 04, 0f, 00, 10, 01, 01, 05, 00, 0c, 01, 01, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 1
-- expression 0 operands: lhs = Counter(0), rhs = Zero
+Number of expressions: 0
 Number of file 0 mappings: 4
 - Code(Counter(0)) at (prev + 31, 1) to (start + 4, 15)
 - Code(Zero) at (prev + 4, 15) to (start + 0, 16)
-- Code(Expression(0, Sub)) at (prev + 1, 5) to (start + 0, 12)
-    = (c0 - Zero)
+- Code(Counter(0)) at (prev + 1, 5) to (start + 0, 12)
 - Code(Counter(0)) at (prev + 1, 1) to (start + 0, 2)
 Highest counter ID seen: c0
 
diff --git a/tests/coverage/inline-dead.cov-map b/tests/coverage/inline-dead.cov-map
@@ -32,16 +32,13 @@ Number of file 0 mappings: 2
 Highest counter ID seen: c0
 
 Function name: inline_dead::main::{closure#0}
-Raw bytes (23): 0x[01, 01, 02, 07, 00, 01, 00, 03, 01, 07, 17, 01, 16, 00, 01, 17, 00, 18, 02, 01, 05, 00, 06]
+Raw bytes (19): 0x[01, 01, 00, 03, 01, 07, 17, 01, 16, 00, 01, 17, 00, 18, 01, 01, 05, 00, 06]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
-- expression 0 operands: lhs = Expression(1, Add), rhs = Zero
-- expression 1 operands: lhs = Counter(0), rhs = Zero
+Number of expressions: 0
 Number of file 0 mappings: 3
 - Code(Counter(0)) at (prev + 7, 23) to (start + 1, 22)
 - Code(Zero) at (prev + 1, 23) to (start + 0, 24)
-- Code(Expression(0, Sub)) at (prev + 1, 5) to (start + 0, 6)
-    = ((c0 + Zero) - Zero)
+- Code(Counter(0)) at (prev + 1, 5) to (start + 0, 6)
 Highest counter ID seen: c0
 
diff --git a/tests/coverage/issue-84561.cov-map b/tests/coverage/issue-84561.cov-map
@@ -59,10 +59,10 @@ Number of file 0 mappings: 1
 Highest counter ID seen: c0
 
 Function name: issue_84561::test3
-Raw bytes (317): 0x[01, 01, 1c, 1d, 21, 25, 29, 21, 25, 2d, 31, 21, 17, 25, 2d, 41, 45, 49, 4d, 51, 55, 33, 51, 49, 4d, 33, 37, 49, 4d, 51, 59, 55, 59, 55, 59, 47, 5d, 55, 59, 61, 65, 71, 75, 69, 6d, 69, 6d, 69, 5f, 6d, 00, 67, 79, 71, 75, 79, 7d, 7d, 81, 01, 33, 01, 08, 01, 03, 1c, 05, 04, 09, 01, 1c, 09, 02, 05, 04, 1f, 0d, 05, 05, 00, 1f, 11, 01, 05, 00, 1f, 15, 01, 09, 01, 1c, 19, 02, 05, 00, 1f, 1d, 01, 05, 00, 0f, 02, 00, 20, 00, 30, 21, 01, 05, 03, 0f, 25, 03, 20, 00, 30, 29, 00, 33, 00, 41, 06, 00, 4b, 00, 5a, 0a, 01, 05, 00, 0f, 2d, 05, 09, 03, 10, 31, 05, 0d, 00, 1b, 0e, 02, 0d, 00, 1c, 12, 04, 09, 05, 06, 35, 06, 05, 03, 06, 39, 04, 05, 03, 06, 3d, 04, 09, 04, 06, 41, 05, 08, 00, 0f, 45, 01, 09, 03, 0a, 1a, 05, 09, 03, 0a, 33, 05, 08, 00, 0f, 51, 01, 09, 00, 13, 22, 03, 0d, 00, 1d, 26, 03, 09, 00, 13, 2e, 03, 0d, 00, 1d, 47, 03, 05, 00, 0f, 47, 01, 0c, 00, 13, 5d, 01, 0d, 00, 13, 42, 02, 0d, 00, 13, 61, 04, 05, 02, 13, 65, 03, 0d, 00, 13, 4a, 02, 0d, 00, 13, 67, 03, 05, 00, 0f, 69, 01, 0c, 00, 13, 6d, 01, 0d, 03, 0e, 71, 04, 0d, 00, 13, 56, 02, 0d, 00, 17, 56, 01, 14, 00, 1b, 00, 01, 15, 00, 1b, 5a, 02, 15, 00, 1b, 75, 04, 0d, 00, 13, 62, 03, 09, 00, 19, 79, 02, 05, 00, 0f, 6a, 03, 09, 00, 22, 7d, 02, 05, 00, 0f, 6e, 03, 09, 00, 2c, 81, 01, 02, 01, 00, 02]
+Raw bytes (315): 0x[01, 01, 1b, 1d, 21, 25, 29, 21, 25, 2d, 31, 21, 17, 25, 2d, 41, 45, 49, 4d, 51, 55, 33, 51, 49, 4d, 33, 37, 49, 4d, 51, 59, 55, 59, 55, 59, 47, 5d, 55, 59, 61, 65, 71, 75, 69, 6d, 69, 6d, 69, 6d, 63, 79, 71, 75, 79, 7d, 7d, 81, 01, 33, 01, 08, 01, 03, 1c, 05, 04, 09, 01, 1c, 09, 02, 05, 04, 1f, 0d, 05, 05, 00, 1f, 11, 01, 05, 00, 1f, 15, 01, 09, 01, 1c, 19, 02, 05, 00, 1f, 1d, 01, 05, 00, 0f, 02, 00, 20, 00, 30, 21, 01, 05, 03, 0f, 25, 03, 20, 00, 30, 29, 00, 33, 00, 41, 06, 00, 4b, 00, 5a, 0a, 01, 05, 00, 0f, 2d, 05, 09, 03, 10, 31, 05, 0d, 00, 1b, 0e, 02, 0d, 00, 1c, 12, 04, 09, 05, 06, 35, 06, 05, 03, 06, 39, 04, 05, 03, 06, 3d, 04, 09, 04, 06, 41, 05, 08, 00, 0f, 45, 01, 09, 03, 0a, 1a, 05, 09, 03, 0a, 33, 05, 08, 00, 0f, 51, 01, 09, 00, 13, 22, 03, 0d, 00, 1d, 26, 03, 09, 00, 13, 2e, 03, 0d, 00, 1d, 47, 03, 05, 00, 0f, 47, 01, 0c, 00, 13, 5d, 01, 0d, 00, 13, 42, 02, 0d, 00, 13, 61, 04, 05, 02, 13, 65, 03, 0d, 00, 13, 4a, 02, 0d, 00, 13, 63, 03, 05, 00, 0f, 69, 01, 0c, 00, 13, 6d, 01, 0d, 03, 0e, 71, 04, 0d, 00, 13, 5a, 02, 0d, 00, 17, 5a, 01, 14, 00, 1b, 00, 01, 15, 00, 1b, 5a, 02, 15, 00, 1b, 75, 04, 0d, 00, 13, 5e, 03, 09, 00, 19, 79, 02, 05, 00, 0f, 66, 03, 09, 00, 22, 7d, 02, 05, 00, 0f, 6a, 03, 09, 00, 2c, 81, 01, 02, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 28
+Number of expressions: 27
 - expression 0 operands: lhs = Counter(7), rhs = Counter(8)
 - expression 1 operands: lhs = Counter(9), rhs = Counter(10)
 - expression 2 operands: lhs = Counter(8), rhs = Counter(9)
@@ -85,12 +85,11 @@ Number of expressions: 28
 - expression 19 operands: lhs = Counter(28), rhs = Counter(29)
 - expression 20 operands: lhs = Counter(26), rhs = Counter(27)
 - expression 21 operands: lhs = Counter(26), rhs = Counter(27)
-- expression 22 operands: lhs = Counter(26), rhs = Expression(23, Add)
-- expression 23 operands: lhs = Counter(27), rhs = Zero
-- expression 24 operands: lhs = Expression(25, Add), rhs = Counter(30)
-- expression 25 operands: lhs = Counter(28), rhs = Counter(29)
-- expression 26 operands: lhs = Counter(30), rhs = Counter(31)
-- expression 27 operands: lhs = Counter(31), rhs = Counter(32)
+- expression 22 operands: lhs = Counter(26), rhs = Counter(27)
+- expression 23 operands: lhs = Expression(24, Add), rhs = Counter(30)
+- expression 24 operands: lhs = Counter(28), rhs = Counter(29)
+- expression 25 operands: lhs = Counter(30), rhs = Counter(31)
+- expression 26 operands: lhs = Counter(31), rhs = Counter(32)
 Number of file 0 mappings: 51
 - Code(Counter(0)) at (prev + 8, 1) to (start + 3, 28)
 - Code(Counter(1)) at (prev + 4, 9) to (start + 1, 28)
@@ -142,26 +141,26 @@ Number of file 0 mappings: 51
 - Code(Counter(25)) at (prev + 3, 13) to (start + 0, 19)
 - Code(Expression(18, Sub)) at (prev + 2, 13) to (start + 0, 19)
     = (c24 - c25)
-- Code(Expression(25, Add)) at (prev + 3, 5) to (start + 0, 15)
+- Code(Expression(24, Add)) at (prev + 3, 5) to (start + 0, 15)
     = (c28 + c29)
 - Code(Counter(26)) at (prev + 1, 12) to (start + 0, 19)
 - Code(Counter(27)) at (prev + 1, 13) to (start + 3, 14)
 - Code(Counter(28)) at (prev + 4, 13) to (start + 0, 19)
-- Code(Expression(21, Sub)) at (prev + 2, 13) to (start + 0, 23)
+- Code(Expression(22, Sub)) at (prev + 2, 13) to (start + 0, 23)
     = (c26 - c27)
-- Code(Expression(21, Sub)) at (prev + 1, 20) to (start + 0, 27)
+- Code(Expression(22, Sub)) at (prev + 1, 20) to (start + 0, 27)
     = (c26 - c27)
 - Code(Zero) at (prev + 1, 21) to (start + 0, 27)
 - Code(Expression(22, Sub)) at (prev + 2, 21) to (start + 0, 27)
-    = (c26 - (c27 + Zero))
+    = (c26 - c27)
 - Code(Counter(29)) at (prev + 4, 13) to (start + 0, 19)
-- Code(Expression(24, Sub)) at (prev + 3, 9) to (start + 0, 25)
+- Code(Expression(23, Sub)) at (prev + 3, 9) to (start + 0, 25)
     = ((c28 + c29) - c30)
 - Code(Counter(30)) at (prev + 2, 5) to (start + 0, 15)
-- Code(Expression(26, Sub)) at (prev + 3, 9) to (start + 0, 34)
+- Code(Expression(25, Sub)) at (prev + 3, 9) to (start + 0, 34)
     = (c30 - c31)
 - Code(Counter(31)) at (prev + 2, 5) to (start + 0, 15)
-- Code(Expression(27, Sub)) at (prev + 3, 9) to (start + 0, 44)
+- Code(Expression(26, Sub)) at (prev + 3, 9) to (start + 0, 44)
     = (c31 - c32)
 - Code(Counter(32)) at (prev + 2, 1) to (start + 0, 2)
 Highest counter ID seen: c32
diff --git a/tests/coverage/loops_branches.cov-map b/tests/coverage/loops_branches.cov-map
diff --git a/tests/coverage/no_spans_if_not.cov-map b/tests/coverage/no_spans_if_not.cov-map
diff --git a/tests/coverage/tight_inf_loop.cov-map b/tests/coverage/tight_inf_loop.cov-map

Original file line number	Diff line number	Diff line change
`@@ -127,8 +127,12 @@ fn coverage_ids_info<'tcx>(`
`127`	`127`	`}`
`128`	`128`	`}`
`129`	`129`
	`130`	+ // FIXME(Zalathar): It should be possible to sort `priority_list[1..]` by
	`131`	+ // `!bcbs_seen.contains(bcb)` to simplify the mappings even further, at the
	`132`	`+ // expense of some churn in the tests. When doing so, also consider removing`
	`133`	+ // the sorts in `transcribe_counters`.
`130`	`134`	`let node_counters = make_node_counters(&fn_cov_info.node_flow_data, &fn_cov_info.priority_list);`
`131`		`- let coverage_counters = transcribe_counters(&node_counters, &bcb_needs_counter);`
	`135`	`+ let coverage_counters = transcribe_counters(&node_counters, &bcb_needs_counter, &bcbs_seen);`
`132`	`136`
`133`	`137`	`let mut counters_seen = DenseBitSet::new_empty(coverage_counters.node_counters.len());`
`134`	`138`	`let mut expressions_seen = DenseBitSet::new_filled(coverage_counters.expressions.len());`