Do not propagate mem2reg attribute through to result

frontends/ast/simplify.cc

@@ -151,7 +151,8 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 					reg->is_reg = true;
 					reg->is_signed = node->is_signed;
 					for (auto &it : node->attributes)
-						reg->attributes.emplace(it.first, it.second->clone());
+						if (it.first != ID(mem2reg))
+							reg->attributes.emplace(it.first, it.second->clone());
 					reg->filename = node->filename;
 					reg->linenum = node->linenum;
 					children.push_back(reg);

tests/various/mem2reg.ys

@@ -11,3 +11,4 @@ proc
 cd top
 select -assert-count 1 m:data1 a:src=<<EOT:4 %i
 select -assert-count 2 w:data2[*] a:src=<<EOT:5 %i
+select -assert-none a:mem2reg