Don't perform gvn on instructions with other_side_effects().

cranelift/filetests/simple_gvn/reject.cton

@@ -0,0 +1,11 @@
+test simple-gvn
+
+function %other_side_effects(i32) -> i32 {
+ebb0(v0: i32):
+   regmove v0, %10 -> %20
+   regmove v0, %10 -> %20
+   regmove v0, %20 -> %10
+; check: regmove v0, %10 -> %20
+; check: regmove v0, %10 -> %20
+    return v0
+}

lib/cretonne/src/simple_gvn.rs

@@ -8,7 +8,7 @@ use std::collections::HashMap;
 /// Test whether the given opcode is unsafe to even consider for GVN.
 fn trivially_unsafe_for_gvn(opcode: Opcode) -> bool {
     opcode.is_call() || opcode.is_branch() || opcode.is_terminator() || opcode.is_return() ||
-    opcode.can_trap()
+    opcode.can_trap() || opcode.other_side_effects()
 }
 
 /// Perform simple GVN on `func`.