peepmatic: Do not use paths in linear IR

Rather than using paths from the root instruction to the instruction we are
matching against or checking if it is constant or whatever, use temporary
variables. When we successfully match an instruction's opcode, we simultaneously
define these temporaries for the instruction's operands. This is similar to how
open-coding these matches in Rust would use `match` expressions with pattern
matching to bind the operands to variables at the same time.

This saves about 1.8% of instructions retired when Peepmatic is enabled.

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

@@ -5,7 +5,6 @@ use crate::instruction_set::InstructionSet;
 use crate::integer_interner::IntegerInterner;
 use crate::linear::{Action, MatchOp, MatchResult};
 use crate::optimizer::PeepholeOptimizer;
-use crate::paths::PathInterner;
 use peepmatic_automata::Automaton;
 use serde::{Deserialize, Serialize};
 use std::fmt::Debug;
@@ -25,9 +24,6 @@ pub struct PeepholeOptimizations<TOperator>
 where
     TOperator: 'static + Copy + Debug + Eq + Hash,
 {
-    /// The instruction paths referenced by the peephole optimizations.
-    pub paths: PathInterner,
-
     /// Not all integers we're matching on fit in the `u32` that we use as the
     /// result of match operations. So we intern them and refer to them by id.
     pub integers: IntegerInterner,
@@ -88,6 +84,7 @@ where
         PeepholeOptimizer {
             peep_opt: self,
             instr_set,
+            left_hand_sides: vec![],
             right_hand_sides: vec![],
             actions: vec![],
             backtracking_states: vec![],