peepmatic: Simplify linear IR

This commit splits "increments" in two; they previously contained both the
linearized left- and right-hand sides. But only the first increment ever had any
actions, so it was confusing (and space wasting) that all increments had an
"actions" vector. No more!

This commit separates the linearized left-hand side ("matches") from the
linearized right-hand side ("actions").

cranelift/peepmatic/crates/runtime/src/linear.rs

@@ -37,8 +37,13 @@ pub struct Optimization<TOperator>
 where
     TOperator: 'static + Copy + Debug + Eq + Hash,
 {
-    /// The chain of increments for this optimization.
-    pub increments: Vec<Increment<TOperator>>,
+    /// The chain of match operations and expected results for this
+    /// optimization.
+    pub matches: Vec<Match>,
+
+    /// Actions to perform, given that the operation resulted in the expected
+    /// value.
+    pub actions: Vec<Action<TOperator>>,
 }
 
 /// Match any value.
@@ -61,31 +66,20 @@ pub fn bool_to_match_result(b: bool) -> MatchResult {
     unsafe { Ok(NonZeroU32::new_unchecked(b + 1)) }
 }
 
-/// A partial match of an optimization's LHS and partial construction of its
-/// RHS.
+/// A partial match of an optimization's LHS.
 ///
-/// An increment is a matching operation, the expected result from that
-/// operation to continue to the next increment, and the actions to take to
-/// build up the LHS scope and RHS instructions given that we got the expected
-/// result from this increment's matching operation. Each increment will
-/// basically become a state and a transition edge out of that state in the
-/// final automata.
+/// An match is composed of a matching operation and the expected result of that
+/// operation. Each match will basically become a state and a transition edge
+/// out of that state in the final automata.
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub struct Increment<TOperator>
-where
-    TOperator: 'static + Copy + Debug + Eq + Hash,
-{
+pub struct Match {
     /// The matching operation to perform.
     pub operation: MatchOp,
 
     /// The expected result of our matching operation, that enables us to
-    /// continue to the next increment, or `Else` for "don't care"
-    /// wildcard-style matching.
+    /// continue to the next match, or `Else` for "don't care" wildcard-style
+    /// matching.
     pub expected: MatchResult,
-
-    /// Actions to perform, given that the operation resulted in the expected
-    /// value.
-    pub actions: Vec<Action<TOperator>>,
 }
 
 /// A matching operation to be performed on some Cranelift instruction as part