coverage: Rename Operand to CovTerm

Later patches in this PR will use `CovTerm` to represent things that are not
expression operands.

Author: Zalathar

compiler/rustc_codegen_llvm/src/coverageinfo/ffi.rs

@@ -1,4 +1,4 @@
-use rustc_middle::mir::coverage::{CounterId, ExpressionId, Operand};
+use rustc_middle::mir::coverage::{CounterId, CovTerm, ExpressionId};
 
 /// Must match the layout of `LLVMRustCounterKind`.
 #[derive(Copy, Clone, Debug)]
@@ -43,11 +43,11 @@ impl Counter {
         Self { kind: CounterKind::Expression, id: expression_id.as_u32() }
     }
 
-    pub(crate) fn from_operand(operand: Operand) -> Self {
-        match operand {
-            Operand::Zero => Self::ZERO,
-            Operand::Counter(id) => Self::counter_value_reference(id),
-            Operand::Expression(id) => Self::expression(id),
+    pub(crate) fn from_term(term: CovTerm) -> Self {
+        match term {
+            CovTerm::Zero => Self::ZERO,
+            CovTerm::Counter(id) => Self::counter_value_reference(id),
+            CovTerm::Expression(id) => Self::expression(id),
         }
     }
 }

compiler/rustc_codegen_llvm/src/coverageinfo/map_data.rs

@@ -3,15 +3,15 @@ use crate::coverageinfo::ffi::{Counter, CounterExpression, ExprKind};
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_index::IndexVec;
 use rustc_middle::mir::coverage::{
-    CodeRegion, CounterId, ExpressionId, FunctionCoverageInfo, Op, Operand,
+    CodeRegion, CounterId, CovTerm, ExpressionId, FunctionCoverageInfo, Op,
 };
 use rustc_middle::ty::Instance;
 
 #[derive(Clone, Debug, PartialEq)]
 pub struct Expression {
-    lhs: Operand,
+    lhs: CovTerm,
     op: Op,
-    rhs: Operand,
+    rhs: CovTerm,
     code_regions: Vec<CodeRegion>,
 }
 
@@ -101,15 +101,15 @@ impl<'tcx> FunctionCoverage<'tcx> {
     /// code regions mapped to that expression.
     ///
     /// Both counters and "counter expressions" (or simply, "expressions") can be operands in other
-    /// expressions. These are tracked as separate variants of `Operand`, so there is no ambiguity
+    /// expressions. These are tracked as separate variants of `CovTerm`, so there is no ambiguity
     /// between operands that are counter IDs and operands that are expression IDs.
     #[instrument(level = "debug", skip(self))]
     pub(crate) fn add_counter_expression(
         &mut self,
         expression_id: ExpressionId,
-        lhs: Operand,
+        lhs: CovTerm,
         op: Op,
-        rhs: Operand,
+        rhs: CovTerm,
         code_regions: &[CodeRegion],
     ) {
         debug_assert!(
@@ -151,7 +151,7 @@ impl<'tcx> FunctionCoverage<'tcx> {
         // The set of expressions that either were optimized out entirely, or
         // have zero as both of their operands, and will therefore always have
         // a value of zero. Other expressions that refer to these as operands
-        // can have those operands replaced with `Operand::Zero`.
+        // can have those operands replaced with `CovTerm::Zero`.
         let mut zero_expressions = FxIndexSet::default();
 
         // For each expression, perform simplifications based on lower-numbered
@@ -168,10 +168,10 @@ impl<'tcx> FunctionCoverage<'tcx> {
             };
 
             // If an operand refers to an expression that is always zero, then
-            // that operand can be replaced with `Operand::Zero`.
-            let maybe_set_operand_to_zero = |operand: &mut Operand| match &*operand {
-                Operand::Expression(id) if zero_expressions.contains(id) => {
-                    *operand = Operand::Zero;
+            // that operand can be replaced with `CovTerm::Zero`.
+            let maybe_set_operand_to_zero = |operand: &mut CovTerm| match &*operand {
+                CovTerm::Expression(id) if zero_expressions.contains(id) => {
+                    *operand = CovTerm::Zero;
                 }
                 _ => (),
             };
@@ -181,13 +181,13 @@ impl<'tcx> FunctionCoverage<'tcx> {
             // Coverage counter values cannot be negative, so if an expression
             // involves subtraction from zero, assume that its RHS must also be zero.
             // (Do this after simplifications that could set the LHS to zero.)
-            if let Expression { lhs: Operand::Zero, op: Op::Subtract, .. } = expression {
-                expression.rhs = Operand::Zero;
+            if let Expression { lhs: CovTerm::Zero, op: Op::Subtract, .. } = expression {
+                expression.rhs = CovTerm::Zero;
             }
 
             // After the above simplifications, if both operands are zero, then
             // we know that this expression is always zero too.
-            if let Expression { lhs: Operand::Zero, rhs: Operand::Zero, .. } = expression {
+            if let Expression { lhs: CovTerm::Zero, rhs: CovTerm::Zero, .. } = expression {
                 zero_expressions.insert(id);
             }
         }
@@ -254,12 +254,12 @@ impl<'tcx> FunctionCoverage<'tcx> {
                 &Some(Expression { lhs, op, rhs, .. }) => {
                     // Convert the operands and operator as normal.
                     CounterExpression::new(
-                        Counter::from_operand(lhs),
+                        Counter::from_term(lhs),
                         match op {
                             Op::Add => ExprKind::Add,
                             Op::Subtract => ExprKind::Subtract,
                         },
-                        Counter::from_operand(rhs),
+                        Counter::from_term(rhs),
                     )
                 }
             })

compiler/rustc_middle/src/mir/coverage.rs

@@ -35,19 +35,21 @@ impl ExpressionId {
     pub const START: Self = Self::from_u32(0);
 }
 
-/// Operand of a coverage-counter expression.
+/// Enum that can hold a constant zero value, the ID of an physical coverage
+/// counter, or the ID of a coverage-counter expression.
 ///
-/// Operands can be a constant zero value, an actual coverage counter, or another
-/// expression. Counter/expression operands are referred to by ID.
+/// This was originally only used for expression operands (and named `Operand`),
+/// but the zero/counter/expression distinction is also useful for representing
+/// the value of code/gap mappings, and the true/false arms of branch mappings.
 #[derive(Copy, Clone, PartialEq, Eq)]
 #[derive(TyEncodable, TyDecodable, Hash, HashStable, TypeFoldable, TypeVisitable)]
-pub enum Operand {
+pub enum CovTerm {
     Zero,
     Counter(CounterId),
     Expression(ExpressionId),
 }
 
-impl Debug for Operand {
+impl Debug for CovTerm {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         match self {
             Self::Zero => write!(f, "Zero"),
@@ -68,9 +70,9 @@ pub enum CoverageKind {
         /// ID of this coverage-counter expression within its enclosing function.
         /// Other expressions in the same function can refer to it as an operand.
         id: ExpressionId,
-        lhs: Operand,
+        lhs: CovTerm,
         op: Op,
-        rhs: Operand,
+        rhs: CovTerm,
     },
     Unreachable,
 }

compiler/rustc_mir_transform/src/coverage/counters.rs

@@ -19,18 +19,18 @@ const NESTED_INDENT: &str = "    ";
 #[derive(Clone)]
 pub(super) enum BcbCounter {
     Counter { id: CounterId },
-    Expression { id: ExpressionId, lhs: Operand, op: Op, rhs: Operand },
+    Expression { id: ExpressionId, lhs: CovTerm, op: Op, rhs: CovTerm },
 }
 
 impl BcbCounter {
     fn is_expression(&self) -> bool {
         matches!(self, Self::Expression { .. })
     }
 
-    pub(super) fn as_operand(&self) -> Operand {
+    pub(super) fn as_term(&self) -> CovTerm {
         match *self {
-            BcbCounter::Counter { id, .. } => Operand::Counter(id),
-            BcbCounter::Expression { id, .. } => Operand::Expression(id),
+            BcbCounter::Counter { id, .. } => CovTerm::Counter(id),
+            BcbCounter::Expression { id, .. } => CovTerm::Expression(id),
         }
     }
 }
@@ -106,7 +106,7 @@ impl CoverageCounters {
         BcbCounter::Counter { id }
     }
 
-    fn make_expression(&mut self, lhs: Operand, op: Op, rhs: Operand) -> BcbCounter {
+    fn make_expression(&mut self, lhs: CovTerm, op: Op, rhs: CovTerm) -> BcbCounter {
         let id = self.next_expression();
         BcbCounter::Expression { id, lhs, op, rhs }
     }
@@ -138,22 +138,22 @@ impl CoverageCounters {
         &mut self,
         bcb: BasicCoverageBlock,
         counter_kind: BcbCounter,
-    ) -> Result<Operand, Error> {
+    ) -> Result<CovTerm, Error> {
         debug_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"
         );
-        let operand = counter_kind.as_operand();
+        let term = counter_kind.as_term();
         if let Some(replaced) = self.bcb_counters[bcb].replace(counter_kind) {
             Error::from_string(format!(
                 "attempt to set a BasicCoverageBlock coverage counter more than once; \
                 {bcb:?} already had counter {replaced:?}",
             ))
         } else {
-            Ok(operand)
+            Ok(term)
         }
     }
 
@@ -162,7 +162,7 @@ impl CoverageCounters {
         from_bcb: BasicCoverageBlock,
         to_bcb: BasicCoverageBlock,
         counter_kind: BcbCounter,
-    ) -> Result<Operand, Error> {
+    ) -> Result<CovTerm, Error> {
         if level_enabled!(tracing::Level::DEBUG) {
             // 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
@@ -175,14 +175,14 @@ impl CoverageCounters {
             }
         }
         self.bcb_has_incoming_edge_counters.insert(to_bcb);
-        let operand = counter_kind.as_operand();
+        let term = counter_kind.as_term();
         if let Some(replaced) = self.bcb_edge_counters.insert((from_bcb, to_bcb), counter_kind) {
             Error::from_string(format!(
                 "attempt to set an edge counter more than once; from_bcb: \
                 {from_bcb:?} already had counter {replaced:?}",
             ))
         } else {
-            Ok(operand)
+            Ok(term)
         }
     }
 
@@ -284,7 +284,7 @@ impl<'a> MakeBcbCounters<'a> {
         &mut self,
         traversal: &mut TraverseCoverageGraphWithLoops,
         branching_bcb: BasicCoverageBlock,
-        branching_counter_operand: Operand,
+        branching_counter_operand: CovTerm,
     ) -> Result<(), Error> {
         let branches = self.bcb_branches(branching_bcb);
         debug!(
@@ -332,7 +332,7 @@ impl<'a> MakeBcbCounters<'a> {
                         sumup_counter_operand,
                     );
                     debug!("  [new intermediate expression: {:?}]", intermediate_expression);
-                    let intermediate_expression_operand = intermediate_expression.as_operand();
+                    let intermediate_expression_operand = intermediate_expression.as_term();
                     self.coverage_counters.intermediate_expressions.push(intermediate_expression);
                     some_sumup_counter_operand.replace(intermediate_expression_operand);
                 }
@@ -364,15 +364,15 @@ impl<'a> MakeBcbCounters<'a> {
         Ok(())
     }
 
-    fn get_or_make_counter_operand(&mut self, bcb: BasicCoverageBlock) -> Result<Operand, Error> {
+    fn get_or_make_counter_operand(&mut self, bcb: BasicCoverageBlock) -> Result<CovTerm, Error> {
         self.recursive_get_or_make_counter_operand(bcb, 1)
     }
 
     fn recursive_get_or_make_counter_operand(
         &mut self,
         bcb: BasicCoverageBlock,
         debug_indent_level: usize,
-    ) -> Result<Operand, Error> {
+    ) -> Result<CovTerm, Error> {
         // If the BCB already has a counter, return it.
         if let Some(counter_kind) = &self.coverage_counters.bcb_counters[bcb] {
             debug!(
@@ -381,7 +381,7 @@ impl<'a> MakeBcbCounters<'a> {
                 bcb,
                 counter_kind,
             );
-            return Ok(counter_kind.as_operand());
+            return Ok(counter_kind.as_term());
         }
 
         // A BCB with only one incoming edge gets a simple `Counter` (via `make_counter()`).
@@ -445,7 +445,7 @@ impl<'a> MakeBcbCounters<'a> {
                     NESTED_INDENT.repeat(debug_indent_level),
                     intermediate_expression
                 );
-                let intermediate_expression_operand = intermediate_expression.as_operand();
+                let intermediate_expression_operand = intermediate_expression.as_term();
                 self.coverage_counters.intermediate_expressions.push(intermediate_expression);
                 some_sumup_edge_counter_operand.replace(intermediate_expression_operand);
             }
@@ -468,7 +468,7 @@ impl<'a> MakeBcbCounters<'a> {
         &mut self,
         from_bcb: BasicCoverageBlock,
         to_bcb: BasicCoverageBlock,
-    ) -> Result<Operand, Error> {
+    ) -> Result<CovTerm, Error> {
         self.recursive_get_or_make_edge_counter_operand(from_bcb, to_bcb, 1)
     }
 
@@ -477,7 +477,7 @@ impl<'a> MakeBcbCounters<'a> {
         from_bcb: BasicCoverageBlock,
         to_bcb: BasicCoverageBlock,
         debug_indent_level: usize,
-    ) -> Result<Operand, Error> {
+    ) -> Result<CovTerm, Error> {
         // If the source BCB has only one successor (assumed to be the given target), an edge
         // counter is unnecessary. Just get or make a counter for the source BCB.
         let successors = self.bcb_successors(from_bcb).iter();
@@ -496,7 +496,7 @@ impl<'a> MakeBcbCounters<'a> {
                 to_bcb,
                 counter_kind
             );
-            return Ok(counter_kind.as_operand());
+            return Ok(counter_kind.as_term());
         }
 
         // Make a new counter to count this edge.