1 files changed, 89 insertions, 0 deletions
diff --git a/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs b/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs
new file mode 100644
index 00000000000..1791ce4b315
--- /dev/null
+++ b/compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs
@@ -0,0 +1,89 @@
+use rustc_middle::mir::coverage::{CounterValueReference, MappedExpressionIndex};
+
+/// Must match the layout of `LLVMRustCounterKind`.
+#[derive(Copy, Clone, Debug)]
+#[repr(C)]
+pub enum CounterKind {
+    Zero = 0,
+    CounterValueReference = 1,
+    Expression = 2,
+}
+
+/// A reference to an instance of an abstract "counter" that will yield a value in a coverage
+/// report. Note that `id` has different interpretations, depending on the `kind`:
+///   * For `CounterKind::Zero`, `id` is assumed to be `0`
+///   * For `CounterKind::CounterValueReference`,  `id` matches the `counter_id` of the injected
+///     instrumentation counter (the `index` argument to the LLVM intrinsic
+///     `instrprof.increment()`)
+///   * For `CounterKind::Expression`, `id` is the index into the coverage map's array of
+///     counter expressions.
+///
+/// Corresponds to struct `llvm::coverage::Counter`.
+///
+/// Must match the layout of `LLVMRustCounter`.
+#[derive(Copy, Clone, Debug)]
+#[repr(C)]
+pub struct Counter {
+    // Important: The layout (order and types of fields) must match its C++ counterpart.
+    pub kind: CounterKind,
+    id: u32,
+}
+
+impl Counter {
+    /// Constructs a new `Counter` of kind `Zero`. For this `CounterKind`, the
+    /// `id` is not used.
+    pub fn zero() -> Self {
+        Self { kind: CounterKind::Zero, id: 0 }
+    }
+
+    /// Constructs a new `Counter` of kind `CounterValueReference`, and converts
+    /// the given 1-based counter_id to the required 0-based equivalent for
+    /// the `Counter` encoding.
+    pub fn counter_value_reference(counter_id: CounterValueReference) -> Self {
+        Self { kind: CounterKind::CounterValueReference, id: counter_id.zero_based_index() }
+    }
+
+    /// Constructs a new `Counter` of kind `Expression`.
+    pub fn expression(mapped_expression_index: MappedExpressionIndex) -> Self {
+        Self { kind: CounterKind::Expression, id: mapped_expression_index.into() }
+    }
+
+    /// Returns true if the `Counter` kind is `Zero`.
+    pub fn is_zero(&self) -> bool {
+        matches!(self.kind, CounterKind::Zero)
+    }
+
+    /// An explicitly-named function to get the ID value, making it more obvious
+    /// that the stored value is now 0-based.
+    pub fn zero_based_id(&self) -> u32 {
+        debug_assert!(!self.is_zero(), "`id` is undefined for CounterKind::Zero");
+        self.id
+    }
+}
+
+/// Corresponds to enum `llvm::coverage::CounterExpression::ExprKind`.
+///
+/// Must match the layout of `LLVMRustCounterExprKind`.
+#[derive(Copy, Clone, Debug)]
+#[repr(C)]
+pub enum ExprKind {
+    Subtract = 0,
+    Add = 1,
+}
+
+/// Corresponds to struct `llvm::coverage::CounterExpression`.
+///
+/// Must match the layout of `LLVMRustCounterExpression`.
+#[derive(Copy, Clone, Debug)]
+#[repr(C)]
+pub struct CounterExpression {
+    pub kind: ExprKind,
+    pub lhs: Counter,
+    pub rhs: Counter,
+}
+
+impl CounterExpression {
+    pub fn new(lhs: Counter, kind: ExprKind, rhs: Counter) -> Self {
+        Self { kind, lhs, rhs }
+    }
+}