simple_gvn: recognize commutative operators (#6135)

* simple_gvn: recognize commutative operators

Normalize instructions with commutative opcodes by sorting the arguments. This
means instructions like `iadd v0, v1` and `iadd v1, v0` will be considered
identical by GVN and deduplicated.

* Remove `UsubSat` and `SsubSat` from `is_commutative`

They are not actually commutative

* Remove `TODO`s

* Move InstructionData normalization into helper fn

* Add normalization of commutative instructions in the epgrah implementation

* Handle reflexive icmp/fcmps in GVN

* Change formatting of `normalize_in_place`

* suggestions from code review

cranelift/codegen/src/simple_gvn.rs

@@ -35,6 +35,14 @@ struct HashKey<'a, 'f: 'a> {
     ty: Type,
     pos: &'a RefCell<FuncCursor<'f>>,
 }
+
+impl<'a, 'f: 'a> HashKey<'a, 'f> {
+    fn new(mut inst: InstructionData, ty: Type, pos: &'a RefCell<FuncCursor<'f>>) -> Self {
+        inst.normalize_in_place();
+        Self { inst, ty, pos }
+    }
+}
+
 impl<'a, 'f: 'a> Hash for HashKey<'a, 'f> {
     fn hash<H: Hasher>(&self, state: &mut H) {
         let pool = &self.pos.borrow().func.dfg.value_lists;
@@ -113,11 +121,7 @@ pub fn do_simple_gvn(func: &mut Function, domtree: &mut DominatorTree) {
             }
 
             let ctrl_typevar = func.dfg.ctrl_typevar(inst);
-            let key = HashKey {
-                inst: func.dfg.insts[inst],
-                ty: ctrl_typevar,
-                pos: &pos,
-            };
+            let key = HashKey::new(func.dfg.insts[inst], ctrl_typevar, &pos);
             use crate::scoped_hash_map::Entry::*;
             match visible_values.entry(key) {
                 Occupied(entry) => {