Splitting transform/instrument_coverage.rs into transform/coverage/...

compiler/rustc_mir/src/transform/coverage/counters.rs

@@ -0,0 +1,54 @@
+use rustc_middle::mir::coverage::*;
+
+/// Manages the counter and expression indexes/IDs to generate `CoverageKind` components for MIR
+/// `Coverage` statements.
+pub(crate) struct CoverageCounters {
+    function_source_hash: u64,
+    next_counter_id: u32,
+    num_expressions: u32,
+}
+
+impl CoverageCounters {
+    pub fn new(function_source_hash: u64) -> Self {
+        Self {
+            function_source_hash,
+            next_counter_id: CounterValueReference::START.as_u32(),
+            num_expressions: 0,
+        }
+    }
+
+    pub fn make_counter(&mut self) -> CoverageKind {
+        CoverageKind::Counter {
+            function_source_hash: self.function_source_hash,
+            id: self.next_counter(),
+        }
+    }
+
+    pub fn make_expression(
+        &mut self,
+        lhs: ExpressionOperandId,
+        op: Op,
+        rhs: ExpressionOperandId,
+    ) -> CoverageKind {
+        let id = self.next_expression();
+        CoverageKind::Expression { id, lhs, op, rhs }
+    }
+
+    /// Counter IDs start from one and go up.
+    fn next_counter(&mut self) -> CounterValueReference {
+        assert!(self.next_counter_id < u32::MAX - self.num_expressions);
+        let next = self.next_counter_id;
+        self.next_counter_id += 1;
+        CounterValueReference::from(next)
+    }
+
+    /// Expression IDs start from u32::MAX and go down because a Expression can reference
+    /// (add or subtract counts) of both Counter regions and Expression regions. The counter
+    /// expression operand IDs must be unique across both types.
+    fn next_expression(&mut self) -> InjectedExpressionId {
+        assert!(self.next_counter_id < u32::MAX - self.num_expressions);
+        let next = u32::MAX - self.num_expressions;
+        self.num_expressions += 1;
+        InjectedExpressionId::from(next)
+    }
+}