coverage: Memoize and simplify counter expressions

compiler/rustc_middle/src/mir/coverage.rs

@@ -187,8 +187,8 @@ impl Debug for CodeRegion {
     }
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, TyEncodable, TyDecodable, Hash, HashStable)]
-#[derive(TypeFoldable, TypeVisitable)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
+#[derive(TyEncodable, TyDecodable, TypeFoldable, TypeVisitable)]
 pub enum Op {
     Subtract,
     Add,

compiler/rustc_mir_transform/src/coverage/counters.rs

@@ -11,7 +11,7 @@ use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph, TraverseCoverage
 
 /// The coverage counter or counter expression associated with a particular
 /// BCB node or BCB edge.
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
 pub(super) enum BcbCounter {
     Counter { id: CounterId },
     Expression { id: ExpressionId },
@@ -35,6 +35,13 @@ impl Debug for BcbCounter {
     }
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+struct BcbExpression {
+    lhs: BcbCounter,
+    op: Op,
+    rhs: BcbCounter,
+}
+
 #[derive(Debug)]
 pub(super) enum CounterIncrementSite {
     Node { bcb: BasicCoverageBlock },
@@ -56,9 +63,13 @@ 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>,
+
     /// Table of expression data, associating each expression ID with its
     /// corresponding operator (+ or -) and its LHS/RHS operands.
-    expressions: IndexVec<ExpressionId, Expression>,
+    expressions: IndexVec<ExpressionId, BcbExpression>,
+    /// Remember expressions that have already been created (or simplified),
+    /// so that we don't create unnecessary duplicates.
+    expressions_memo: FxHashMap<BcbExpression, BcbCounter>,
 }
 
 impl CoverageCounters {
@@ -76,6 +87,7 @@ impl CoverageCounters {
             bcb_counters: IndexVec::from_elem_n(None, num_bcbs),
             bcb_edge_counters: FxHashMap::default(),
             expressions: IndexVec::new(),
+            expressions_memo: FxHashMap::default(),
         };
 
         MakeBcbCounters::new(&mut this, basic_coverage_blocks)
@@ -90,8 +102,57 @@ impl CoverageCounters {
     }
 
     fn make_expression(&mut self, lhs: BcbCounter, op: Op, rhs: BcbCounter) -> BcbCounter {
-        let expression = Expression { lhs: lhs.as_term(), op, rhs: rhs.as_term() };
-        let id = self.expressions.push(expression);
+        let new_expr = BcbExpression { lhs, op, rhs };
+        *self
+            .expressions_memo
+            .entry(new_expr)
+            .or_insert_with(|| Self::make_expression_inner(&mut self.expressions, new_expr))
+    }
+
+    /// This is an associated function so that we can call it while borrowing
+    /// `&mut self.expressions_memo`.
+    fn make_expression_inner(
+        expressions: &mut IndexVec<ExpressionId, BcbExpression>,
+        new_expr: BcbExpression,
+    ) -> BcbCounter {
+        // Simplify expressions using basic algebra.
+        //
+        // Some of these cases might not actually occur in practice, depending
+        // on the details of how the instrumentor builds expressions.
+        let BcbExpression { lhs, op, rhs } = new_expr;
+
+        if let BcbCounter::Expression { id } = lhs {
+            let lhs_expr = &expressions[id];
+
+            // Simplify `(a - b) + b` to `a`.
+            if lhs_expr.op == Op::Subtract && op == Op::Add && lhs_expr.rhs == rhs {
+                return lhs_expr.lhs;
+            }
+            // Simplify `(a + b) - b` to `a`.
+            if lhs_expr.op == Op::Add && op == Op::Subtract && lhs_expr.rhs == rhs {
+                return lhs_expr.lhs;
+            }
+            // Simplify `(a + b) - a` to `b`.
+            if lhs_expr.op == Op::Add && op == Op::Subtract && lhs_expr.lhs == rhs {
+                return lhs_expr.rhs;
+            }
+        }
+
+        if let BcbCounter::Expression { id } = rhs {
+            let rhs_expr = &expressions[id];
+
+            // Simplify `a + (b - a)` to `b`.
+            if op == Op::Add && rhs_expr.op == Op::Subtract && lhs == rhs_expr.rhs {
+                return rhs_expr.lhs;
+            }
+            // Simplify `a - (a - b)` to `b`.
+            if op == Op::Subtract && rhs_expr.op == Op::Subtract && lhs == rhs_expr.lhs {
+                return rhs_expr.rhs;
+            }
+        }
+
+        // Simplification failed, so actually create the new expression.
+        let id = expressions.push(new_expr);
         BcbCounter::Expression { id }
     }
 
@@ -166,7 +227,21 @@ impl CoverageCounters {
     }
 
     pub(super) fn into_expressions(self) -> IndexVec<ExpressionId, Expression> {
-        self.expressions
+        let old_len = self.expressions.len();
+        let expressions = self
+            .expressions
+            .into_iter()
+            .map(|BcbExpression { lhs, op, rhs }| Expression {
+                lhs: lhs.as_term(),
+                op,
+                rhs: rhs.as_term(),
+            })
+            .collect::<IndexVec<ExpressionId, _>>();
+
+        // Expression IDs are indexes into this vector, so make sure we didn't
+        // accidentally invalidate them by changing its length.
+        assert_eq!(old_len, expressions.len());
+        expressions
     }
 }
 

tests/coverage/abort.cov-map

@@ -1,45 +1,37 @@
 Function name: abort::main
-Raw bytes (105): 0x[01, 01, 12, 01, 47, 05, 09, 03, 0d, 42, 11, 03, 0d, 11, 3e, 42, 11, 03, 0d, 3b, 15, 11, 3e, 42, 11, 03, 0d, 15, 36, 3b, 15, 11, 3e, 42, 11, 03, 0d, 05, 09, 0d, 01, 0e, 01, 01, 1b, 03, 02, 0b, 00, 18, 42, 01, 0c, 00, 19, 11, 00, 1a, 02, 0a, 3e, 02, 0a, 00, 0b, 3b, 02, 0c, 00, 19, 15, 00, 1a, 00, 31, 36, 00, 31, 00, 32, 33, 04, 0c, 00, 19, 05, 00, 1a, 00, 31, 09, 00, 31, 00, 32, 47, 01, 09, 00, 17, 0d, 02, 05, 01, 02]
+Raw bytes (89): 0x[01, 01, 0a, 01, 27, 05, 09, 03, 0d, 22, 11, 03, 0d, 03, 0d, 22, 15, 03, 0d, 03, 0d, 05, 09, 0d, 01, 0e, 01, 01, 1b, 03, 02, 0b, 00, 18, 22, 01, 0c, 00, 19, 11, 00, 1a, 02, 0a, 0e, 02, 0a, 00, 0b, 22, 02, 0c, 00, 19, 15, 00, 1a, 00, 31, 1a, 00, 31, 00, 32, 22, 04, 0c, 00, 19, 05, 00, 1a, 00, 31, 09, 00, 31, 00, 32, 27, 01, 09, 00, 17, 0d, 02, 05, 01, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 18
-- expression 0 operands: lhs = Counter(0), rhs = Expression(17, Add)
+Number of expressions: 10
+- expression 0 operands: lhs = Counter(0), rhs = Expression(9, Add)
 - expression 1 operands: lhs = Counter(1), rhs = Counter(2)
 - expression 2 operands: lhs = Expression(0, Add), rhs = Counter(3)
-- expression 3 operands: lhs = Expression(16, Sub), rhs = Counter(4)
+- expression 3 operands: lhs = Expression(8, Sub), rhs = Counter(4)
 - expression 4 operands: lhs = Expression(0, Add), rhs = Counter(3)
-- expression 5 operands: lhs = Counter(4), rhs = Expression(15, Sub)
-- expression 6 operands: lhs = Expression(16, Sub), rhs = Counter(4)
+- expression 5 operands: lhs = Expression(0, Add), rhs = Counter(3)
+- expression 6 operands: lhs = Expression(8, Sub), rhs = Counter(5)
 - expression 7 operands: lhs = Expression(0, Add), rhs = Counter(3)
-- expression 8 operands: lhs = Expression(14, Add), rhs = Counter(5)
-- expression 9 operands: lhs = Counter(4), rhs = Expression(15, Sub)
-- expression 10 operands: lhs = Expression(16, Sub), rhs = Counter(4)
-- expression 11 operands: lhs = Expression(0, Add), rhs = Counter(3)
-- expression 12 operands: lhs = Counter(5), rhs = Expression(13, Sub)
-- expression 13 operands: lhs = Expression(14, Add), rhs = Counter(5)
-- expression 14 operands: lhs = Counter(4), rhs = Expression(15, Sub)
-- expression 15 operands: lhs = Expression(16, Sub), rhs = Counter(4)
-- expression 16 operands: lhs = Expression(0, Add), rhs = Counter(3)
-- expression 17 operands: lhs = Counter(1), rhs = Counter(2)
+- expression 8 operands: lhs = Expression(0, Add), rhs = Counter(3)
+- expression 9 operands: lhs = Counter(1), rhs = Counter(2)
 Number of file 0 mappings: 13
 - Code(Counter(0)) at (prev + 14, 1) to (start + 1, 27)
 - Code(Expression(0, Add)) at (prev + 2, 11) to (start + 0, 24)
     = (c0 + (c1 + c2))
-- Code(Expression(16, Sub)) at (prev + 1, 12) to (start + 0, 25)
+- Code(Expression(8, Sub)) at (prev + 1, 12) to (start + 0, 25)
     = ((c0 + (c1 + c2)) - c3)
 - Code(Counter(4)) at (prev + 0, 26) to (start + 2, 10)
-- Code(Expression(15, Sub)) at (prev + 2, 10) to (start + 0, 11)
+- Code(Expression(3, Sub)) at (prev + 2, 10) to (start + 0, 11)
     = (((c0 + (c1 + c2)) - c3) - c4)
-- Code(Expression(14, Add)) at (prev + 2, 12) to (start + 0, 25)
-    = (c4 + (((c0 + (c1 + c2)) - c3) - c4))
+- Code(Expression(8, Sub)) at (prev + 2, 12) to (start + 0, 25)
+    = ((c0 + (c1 + c2)) - c3)
 - Code(Counter(5)) at (prev + 0, 26) to (start + 0, 49)
-- Code(Expression(13, Sub)) at (prev + 0, 49) to (start + 0, 50)
-    = ((c4 + (((c0 + (c1 + c2)) - c3) - c4)) - c5)
-- Code(Expression(12, Add)) at (prev + 4, 12) to (start + 0, 25)
-    = (c5 + ((c4 + (((c0 + (c1 + c2)) - c3) - c4)) - c5))
+- Code(Expression(6, Sub)) at (prev + 0, 49) to (start + 0, 50)
+    = (((c0 + (c1 + c2)) - c3) - c5)
+- Code(Expression(8, Sub)) at (prev + 4, 12) to (start + 0, 25)
+    = ((c0 + (c1 + c2)) - c3)
 - Code(Counter(1)) at (prev + 0, 26) to (start + 0, 49)
 - Code(Counter(2)) at (prev + 0, 49) to (start + 0, 50)
-- Code(Expression(17, Add)) at (prev + 1, 9) to (start + 0, 23)
+- Code(Expression(9, Add)) at (prev + 1, 9) to (start + 0, 23)
     = (c1 + c2)
 - Code(Counter(3)) at (prev + 2, 5) to (start + 1, 2)
 

tests/coverage/async.cov-map

@@ -7,19 +7,17 @@ Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 9, 1) to (start + 0, 25)
 
 Function name: async::c::{closure#0}
-Raw bytes (28): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 09, 19, 01, 0e, 05, 02, 09, 00, 0a, 02, 02, 09, 00, 0a, 07, 02, 01, 00, 02]
+Raw bytes (26): 0x[01, 01, 01, 01, 05, 04, 01, 09, 19, 01, 0e, 05, 02, 09, 00, 0a, 02, 02, 09, 00, 0a, 01, 02, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
+Number of expressions: 1
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(1), rhs = Expression(0, Sub)
 Number of file 0 mappings: 4
 - Code(Counter(0)) at (prev + 9, 25) to (start + 1, 14)
 - Code(Counter(1)) at (prev + 2, 9) to (start + 0, 10)
 - Code(Expression(0, Sub)) at (prev + 2, 9) to (start + 0, 10)
     = (c0 - c1)
-- Code(Expression(1, Add)) at (prev + 2, 1) to (start + 0, 2)
-    = (c1 + (c0 - c1))
+- Code(Counter(0)) at (prev + 2, 1) to (start + 0, 2)
 
 Function name: async::d
 Raw bytes (9): 0x[01, 01, 00, 01, 01, 11, 01, 00, 14]
@@ -188,19 +186,17 @@ Number of file 0 mappings: 9
     = ((c1 + c2) + c3)
 
 Function name: async::j::c
-Raw bytes (28): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 37, 05, 01, 12, 05, 02, 0d, 00, 0e, 02, 0a, 0d, 00, 0e, 07, 02, 05, 00, 06]
+Raw bytes (26): 0x[01, 01, 01, 01, 05, 04, 01, 37, 05, 01, 12, 05, 02, 0d, 00, 0e, 02, 0a, 0d, 00, 0e, 01, 02, 05, 00, 06]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
+Number of expressions: 1
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(1), rhs = Expression(0, Sub)
 Number of file 0 mappings: 4
 - Code(Counter(0)) at (prev + 55, 5) to (start + 1, 18)
 - Code(Counter(1)) at (prev + 2, 13) to (start + 0, 14)
 - Code(Expression(0, Sub)) at (prev + 10, 13) to (start + 0, 14)
     = (c0 - c1)
-- Code(Expression(1, Add)) at (prev + 2, 5) to (start + 0, 6)
-    = (c1 + (c0 - c1))
+- Code(Counter(0)) at (prev + 2, 5) to (start + 0, 6)
 
 Function name: async::j::d
 Raw bytes (9): 0x[01, 01, 00, 01, 01, 46, 05, 00, 17]

tests/coverage/async2.cov-map

@@ -7,17 +7,15 @@ Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 13, 1) to (start + 0, 23)
 
 Function name: async2::async_func::{closure#0}
-Raw bytes (26): 0x[01, 01, 01, 05, 00, 04, 01, 0d, 17, 03, 09, 05, 03, 0a, 02, 06, 00, 02, 06, 00, 07, 03, 01, 01, 00, 02]
+Raw bytes (24): 0x[01, 01, 00, 04, 01, 0d, 17, 03, 09, 05, 03, 0a, 02, 06, 00, 02, 06, 00, 07, 01, 01, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 1
-- expression 0 operands: lhs = Counter(1), rhs = Zero
+Number of expressions: 0
 Number of file 0 mappings: 4
 - Code(Counter(0)) at (prev + 13, 23) to (start + 3, 9)
 - Code(Counter(1)) at (prev + 3, 10) to (start + 2, 6)
 - Code(Zero) at (prev + 2, 6) to (start + 0, 7)
-- Code(Expression(0, Add)) at (prev + 1, 1) to (start + 0, 2)
-    = (c1 + Zero)
+- Code(Counter(0)) at (prev + 1, 1) to (start + 0, 2)
 
 Function name: async2::async_func_just_println
 Raw bytes (9): 0x[01, 01, 00, 01, 01, 15, 01, 00, 24]
@@ -44,15 +42,13 @@ Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 25, 1) to (start + 7, 2)
 
 Function name: async2::non_async_func
-Raw bytes (26): 0x[01, 01, 01, 05, 00, 04, 01, 05, 01, 03, 09, 05, 03, 0a, 02, 06, 00, 02, 06, 00, 07, 03, 01, 01, 00, 02]
+Raw bytes (24): 0x[01, 01, 00, 04, 01, 05, 01, 03, 09, 05, 03, 0a, 02, 06, 00, 02, 06, 00, 07, 01, 01, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 1
-- expression 0 operands: lhs = Counter(1), rhs = Zero
+Number of expressions: 0
 Number of file 0 mappings: 4
 - Code(Counter(0)) at (prev + 5, 1) to (start + 3, 9)
 - Code(Counter(1)) at (prev + 3, 10) to (start + 2, 6)
 - Code(Zero) at (prev + 2, 6) to (start + 0, 7)
-- Code(Expression(0, Add)) at (prev + 1, 1) to (start + 0, 2)
-    = (c1 + Zero)
+- Code(Counter(0)) at (prev + 1, 1) to (start + 0, 2)
 

tests/coverage/async_block.cov-map

@@ -1,32 +1,28 @@
 Function name: async_block::main
-Raw bytes (38): 0x[01, 01, 02, 01, 05, 03, 05, 06, 01, 05, 01, 00, 0b, 05, 01, 09, 00, 0a, 03, 00, 0e, 00, 13, 05, 00, 14, 01, 16, 05, 07, 0a, 02, 06, 06, 03, 01, 00, 02]
+Raw bytes (36): 0x[01, 01, 01, 01, 05, 06, 01, 05, 01, 00, 0b, 05, 01, 09, 00, 0a, 03, 00, 0e, 00, 13, 05, 00, 14, 01, 16, 05, 07, 0a, 02, 06, 01, 03, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
+Number of expressions: 1
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Expression(0, Add), rhs = Counter(1)
 Number of file 0 mappings: 6
 - Code(Counter(0)) at (prev + 5, 1) to (start + 0, 11)
 - Code(Counter(1)) at (prev + 1, 9) to (start + 0, 10)
 - Code(Expression(0, Add)) at (prev + 0, 14) to (start + 0, 19)
     = (c0 + c1)
 - Code(Counter(1)) at (prev + 0, 20) to (start + 1, 22)
 - Code(Counter(1)) at (prev + 7, 10) to (start + 2, 6)
-- Code(Expression(1, Sub)) at (prev + 3, 1) to (start + 0, 2)
-    = ((c0 + c1) - c1)
+- Code(Counter(0)) at (prev + 3, 1) to (start + 0, 2)
 
 Function name: async_block::main::{closure#0}
-Raw bytes (28): 0x[01, 01, 02, 01, 05, 05, 02, 04, 01, 07, 1c, 01, 17, 05, 01, 18, 02, 0e, 02, 02, 14, 02, 0e, 07, 03, 09, 00, 0a]
+Raw bytes (26): 0x[01, 01, 01, 01, 05, 04, 01, 07, 1c, 01, 17, 05, 01, 18, 02, 0e, 02, 02, 14, 02, 0e, 01, 03, 09, 00, 0a]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
+Number of expressions: 1
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(1), rhs = Expression(0, Sub)
 Number of file 0 mappings: 4
 - Code(Counter(0)) at (prev + 7, 28) to (start + 1, 23)
 - Code(Counter(1)) at (prev + 1, 24) to (start + 2, 14)
 - Code(Expression(0, Sub)) at (prev + 2, 20) to (start + 2, 14)
     = (c0 - c1)
-- Code(Expression(1, Add)) at (prev + 3, 9) to (start + 0, 10)
-    = (c1 + (c0 - c1))
+- Code(Counter(0)) at (prev + 3, 9) to (start + 0, 10)
 

tests/coverage/branch/generics.cov-map

@@ -1,10 +1,9 @@
 Function name: generics::print_size::<()>
-Raw bytes (35): 0x[01, 01, 02, 01, 05, 05, 02, 05, 01, 06, 01, 01, 24, 20, 05, 02, 01, 08, 00, 24, 05, 00, 25, 02, 06, 02, 02, 0c, 02, 06, 07, 03, 01, 00, 02]
+Raw bytes (33): 0x[01, 01, 01, 01, 05, 05, 01, 06, 01, 01, 24, 20, 05, 02, 01, 08, 00, 24, 05, 00, 25, 02, 06, 02, 02, 0c, 02, 06, 01, 03, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
+Number of expressions: 1
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(1), rhs = Expression(0, Sub)
 Number of file 0 mappings: 5
 - Code(Counter(0)) at (prev + 6, 1) to (start + 1, 36)
 - Branch { true: Counter(1), false: Expression(0, Sub) } at (prev + 1, 8) to (start + 0, 36)
@@ -13,16 +12,14 @@ Number of file 0 mappings: 5
 - Code(Counter(1)) at (prev + 0, 37) to (start + 2, 6)
 - Code(Expression(0, Sub)) at (prev + 2, 12) to (start + 2, 6)
     = (c0 - c1)
-- Code(Expression(1, Add)) at (prev + 3, 1) to (start + 0, 2)
-    = (c1 + (c0 - c1))
+- Code(Counter(0)) at (prev + 3, 1) to (start + 0, 2)
 
 Function name: generics::print_size::<u32>
-Raw bytes (35): 0x[01, 01, 02, 01, 05, 05, 02, 05, 01, 06, 01, 01, 24, 20, 05, 02, 01, 08, 00, 24, 05, 00, 25, 02, 06, 02, 02, 0c, 02, 06, 07, 03, 01, 00, 02]
+Raw bytes (33): 0x[01, 01, 01, 01, 05, 05, 01, 06, 01, 01, 24, 20, 05, 02, 01, 08, 00, 24, 05, 00, 25, 02, 06, 02, 02, 0c, 02, 06, 01, 03, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
+Number of expressions: 1
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(1), rhs = Expression(0, Sub)
 Number of file 0 mappings: 5
 - Code(Counter(0)) at (prev + 6, 1) to (start + 1, 36)
 - Branch { true: Counter(1), false: Expression(0, Sub) } at (prev + 1, 8) to (start + 0, 36)
@@ -31,16 +28,14 @@ Number of file 0 mappings: 5
 - Code(Counter(1)) at (prev + 0, 37) to (start + 2, 6)
 - Code(Expression(0, Sub)) at (prev + 2, 12) to (start + 2, 6)
     = (c0 - c1)
-- Code(Expression(1, Add)) at (prev + 3, 1) to (start + 0, 2)
-    = (c1 + (c0 - c1))
+- Code(Counter(0)) at (prev + 3, 1) to (start + 0, 2)
 
 Function name: generics::print_size::<u64>
-Raw bytes (35): 0x[01, 01, 02, 01, 05, 05, 02, 05, 01, 06, 01, 01, 24, 20, 05, 02, 01, 08, 00, 24, 05, 00, 25, 02, 06, 02, 02, 0c, 02, 06, 07, 03, 01, 00, 02]
+Raw bytes (33): 0x[01, 01, 01, 01, 05, 05, 01, 06, 01, 01, 24, 20, 05, 02, 01, 08, 00, 24, 05, 00, 25, 02, 06, 02, 02, 0c, 02, 06, 01, 03, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 2
+Number of expressions: 1
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(1), rhs = Expression(0, Sub)
 Number of file 0 mappings: 5
 - Code(Counter(0)) at (prev + 6, 1) to (start + 1, 36)
 - Branch { true: Counter(1), false: Expression(0, Sub) } at (prev + 1, 8) to (start + 0, 36)
@@ -49,6 +44,5 @@ Number of file 0 mappings: 5
 - Code(Counter(1)) at (prev + 0, 37) to (start + 2, 6)
 - Code(Expression(0, Sub)) at (prev + 2, 12) to (start + 2, 6)
     = (c0 - c1)
-- Code(Expression(1, Add)) at (prev + 3, 1) to (start + 0, 2)
-    = (c1 + (c0 - c1))
+- Code(Counter(0)) at (prev + 3, 1) to (start + 0, 2)