coverage: Remove incorrect assertions from counter allocation

compiler/rustc_mir_transform/src/coverage/counters.rs

@@ -1,13 +1,12 @@
+use std::fmt::{self, Debug};
+
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::graph::WithNumNodes;
-use rustc_index::bit_set::BitSet;
 use rustc_index::IndexVec;
-use rustc_middle::mir::coverage::*;
+use rustc_middle::mir::coverage::{CounterId, CovTerm, Expression, ExpressionId, Op};
 
-use super::graph::{BasicCoverageBlock, CoverageGraph, TraverseCoverageGraphWithLoops};
-
-use std::fmt::{self, Debug};
+use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph, TraverseCoverageGraphWithLoops};
 
 /// The coverage counter or counter expression associated with a particular
 /// BCB node or BCB edge.
@@ -18,10 +17,6 @@ pub(super) enum BcbCounter {
 }
 
 impl BcbCounter {
-    fn is_expression(&self) -> bool {
-        matches!(self, Self::Expression { .. })
-    }
-
     pub(super) fn as_term(&self) -> CovTerm {
         match *self {
             BcbCounter::Counter { id, .. } => CovTerm::Counter(id),
@@ -60,10 +55,6 @@ pub(super) struct CoverageCounters {
     /// We currently don't iterate over this map, but if we do in the future,
     /// switch it back to `FxIndexMap` to avoid query stability hazards.
     bcb_edge_counters: FxHashMap<(BasicCoverageBlock, BasicCoverageBlock), BcbCounter>,
-    /// Tracks which BCBs have a counter associated with some incoming edge.
-    /// Only used by assertions, to verify that BCBs with incoming edge
-    /// counters do not have their own physical counters (expressions are allowed).
-    bcb_has_incoming_edge_counters: BitSet<BasicCoverageBlock>,
     /// Table of expression data, associating each expression ID with its
     /// corresponding operator (+ or -) and its LHS/RHS operands.
     expressions: IndexVec<ExpressionId, Expression>,
@@ -83,7 +74,6 @@ impl CoverageCounters {
             counter_increment_sites: IndexVec::new(),
             bcb_counters: IndexVec::from_elem_n(None, num_bcbs),
             bcb_edge_counters: FxHashMap::default(),
-            bcb_has_incoming_edge_counters: BitSet::new_empty(num_bcbs),
             expressions: IndexVec::new(),
         };
 
@@ -122,14 +112,6 @@ impl CoverageCounters {
     }
 
     fn set_bcb_counter(&mut self, bcb: BasicCoverageBlock, counter_kind: BcbCounter) -> BcbCounter {
-        assert!(
-            // If the BCB has an edge counter (to be injected into a new `BasicBlock`), it can also
-            // have an expression (to be injected into an existing `BasicBlock` represented by this
-            // `BasicCoverageBlock`).
-            counter_kind.is_expression() || !self.bcb_has_incoming_edge_counters.contains(bcb),
-            "attempt to add a `Counter` to a BCB target with existing incoming edge counters"
-        );
-
         if let Some(replaced) = self.bcb_counters[bcb].replace(counter_kind) {
             bug!(
                 "attempt to set a BasicCoverageBlock coverage counter more than once; \
@@ -146,19 +128,6 @@ impl CoverageCounters {
         to_bcb: BasicCoverageBlock,
         counter_kind: BcbCounter,
     ) -> BcbCounter {
-        // If the BCB has an edge counter (to be injected into a new `BasicBlock`), it can also
-        // have an expression (to be injected into an existing `BasicBlock` represented by this
-        // `BasicCoverageBlock`).
-        if let Some(node_counter) = self.bcb_counter(to_bcb)
-            && !node_counter.is_expression()
-        {
-            bug!(
-                "attempt to add an incoming edge counter from {from_bcb:?} \
-                when the target BCB already has {node_counter:?}"
-            );
-        }
-
-        self.bcb_has_incoming_edge_counters.insert(to_bcb);
         if let Some(replaced) = self.bcb_edge_counters.insert((from_bcb, to_bcb), counter_kind) {
             bug!(
                 "attempt to set an edge counter more than once; from_bcb: \

tests/coverage/let_else_loop.cov-map

@@ -0,0 +1,30 @@
+Function name: let_else_loop::_if (unused)
+Raw bytes (19): 0x[01, 01, 00, 03, 00, 16, 01, 01, 0c, 00, 02, 09, 00, 10, 00, 02, 09, 00, 10]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 3
+- Code(Zero) at (prev + 22, 1) to (start + 1, 12)
+- Code(Zero) at (prev + 2, 9) to (start + 0, 16)
+- Code(Zero) at (prev + 2, 9) to (start + 0, 16)
+
+Function name: let_else_loop::_loop_either_way (unused)
+Raw bytes (19): 0x[01, 01, 00, 03, 00, 0f, 01, 01, 14, 00, 01, 1c, 00, 23, 00, 01, 05, 00, 0c]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 3
+- Code(Zero) at (prev + 15, 1) to (start + 1, 20)
+- Code(Zero) at (prev + 1, 28) to (start + 0, 35)
+- Code(Zero) at (prev + 1, 5) to (start + 0, 12)
+
+Function name: let_else_loop::loopy
+Raw bytes (19): 0x[01, 01, 00, 03, 01, 09, 01, 01, 14, 00, 01, 1c, 00, 23, 05, 01, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 3
+- Code(Counter(0)) at (prev + 9, 1) to (start + 1, 20)
+- Code(Zero) at (prev + 1, 28) to (start + 0, 35)
+- Code(Counter(1)) at (prev + 1, 1) to (start + 0, 2)
+

tests/coverage/let_else_loop.coverage

@@ -0,0 +1,35 @@
+   LL|       |#![feature(coverage_attribute)]
+   LL|       |//@ edition: 2021
+   LL|       |
+   LL|       |// Regression test for <https://github.com/rust-lang/rust/issues/122738>.
+   LL|       |// These code patterns should not trigger an ICE when allocating a physical
+   LL|       |// counter to a node and also one of its in-edges, because that is allowed
+   LL|       |// when the node contains a tight loop to itself.
+   LL|       |
+   LL|      1|fn loopy(cond: bool) {
+   LL|      1|    let true = cond else { loop {} };
+                                         ^0
+   LL|      1|}
+   LL|       |
+   LL|       |// Variant that also has `loop {}` on the success path.
+   LL|       |// This isn't needed to catch the original ICE, but might help detect regressions.
+   LL|      0|fn _loop_either_way(cond: bool) {
+   LL|      0|    let true = cond else { loop {} };
+   LL|      0|    loop {}
+   LL|       |}
+   LL|       |
+   LL|       |// Variant using regular `if` instead of let-else.
+   LL|       |// This doesn't trigger the original ICE, but might help detect regressions.
+   LL|      0|fn _if(cond: bool) {
+   LL|      0|    if cond {
+   LL|      0|        loop {}
+   LL|       |    } else {
+   LL|      0|        loop {}
+   LL|       |    }
+   LL|       |}
+   LL|       |
+   LL|       |#[coverage(off)]
+   LL|       |fn main() {
+   LL|       |    loopy(true);
+   LL|       |}
+

tests/coverage/let_else_loop.rs

@@ -0,0 +1,33 @@
+#![feature(coverage_attribute)]
+//@ edition: 2021
+
+// Regression test for <https://github.com/rust-lang/rust/issues/122738>.
+// These code patterns should not trigger an ICE when allocating a physical
+// counter to a node and also one of its in-edges, because that is allowed
+// when the node contains a tight loop to itself.
+
+fn loopy(cond: bool) {
+    let true = cond else { loop {} };
+}
+
+// Variant that also has `loop {}` on the success path.
+// This isn't needed to catch the original ICE, but might help detect regressions.
+fn _loop_either_way(cond: bool) {
+    let true = cond else { loop {} };
+    loop {}
+}
+
+// Variant using regular `if` instead of let-else.
+// This doesn't trigger the original ICE, but might help detect regressions.
+fn _if(cond: bool) {
+    if cond {
+        loop {}
+    } else {
+        loop {}
+    }
+}
+
+#[coverage(off)]
+fn main() {
+    loopy(true);
+}