Add mutations to remove local usage (#1402)

* Add rewrite rule to `wasm-mutate` to remove `local.set`

* Add rules for `wasm-mutate` to remove `local.tee`

* Add tests locals can be removed

Author: alexcrichton

crates/wasm-mutate/src/mutators/peephole.rs

@@ -1586,6 +1586,24 @@ mod tests {
         );
     }
 
+    #[test]
+    fn remove_local_set() {
+        test_default_peephole_mutator(
+            "(module (func (local i32) (local.set 0 (i32.const 0))))",
+            "(module (func (local i32) nop))",
+            4,
+        );
+    }
+
+    #[test]
+    fn remove_local_tee() {
+        test_default_peephole_mutator(
+            "(module (func (local i32) (local.tee 0 (i32.const 0)) drop))",
+            "(module (func (local i32) (i32.const 0) drop))",
+            4,
+        );
+    }
+
     fn test_peephole_mutator(
         original: &str,
         rules: &[Rewrite<super::Lang, PeepholeMutationAnalysis>],
@@ -1599,4 +1617,17 @@ mod tests {
         let mutator = PeepholeMutator::new_with_rules(3, rules.to_vec());
         config.match_mutation(original, mutator, expected);
     }
+
+    fn test_default_peephole_mutator(original: &str, expected: &str, seed: u64) {
+        let original_wasm = wat::parse_str(original).unwrap();
+        let mut config = WasmMutate::default();
+        config.fuel(10000);
+        config.seed(seed);
+        config.info = Some(ModuleInfo::new(&original_wasm).unwrap());
+
+        let mut mutator = PeepholeMutator::new(3);
+        let rules = mutator.get_rules(&config);
+        mutator.rules = Some(rules);
+        config.match_mutation(original, mutator, expected);
+    }
 }

crates/wasm-mutate/src/mutators/peephole/rules.rs

@@ -594,6 +594,16 @@ impl PeepholeMutator {
                         if self.is_type("?x", PrimitiveTypeInfo::I64)
                 );
             }
+
+            for i in 0..20 {
+                let name = format!("remove-local.set{i}");
+                let lhs = format!("(local.set.{i} ?x)");
+                self.add_rewrite(&mut rules, &name, &lhs, "nop", &[]);
+
+                let name = format!("remove-local.tee{i}");
+                let lhs = format!("(local.tee.{i} ?x)");
+                self.add_rewrite(&mut rules, &name, &lhs, "?x", &[]);
+            }
         }
 
         rules