On Fri, Sep 16, 2016 at 03:51:11PM -0400, Jason Merrill wrote: > On Mon, Sep 5, 2016 at 1:11 PM, Jakub Jelinek <ja...@redhat.com> wrote: > > + /* If body is a statement other than STATEMENT_LIST or BIND_EXPR, > > + it should be skipped. E.g. switch (a) b = a; */ > > + if (TREE_CODE (body) == STATEMENT_LIST > > + || TREE_CODE (body) == BIND_EXPR) > > I'm nervous about this optimization for useless code breaking other > things that might (one day) wrap a case label; I think I'd prefer to > drop the condition.
By droping the condition you mean unconditionally call cxx_eval_constant_expression (ctx, body, false, non_constant_p, overflow_p, jump_target); ? That is known not to work, that breaks the +constexpr int +bar (int x) +{ + int a = x; + switch (x) + a = x + 1; + return a; +} handling in the testcase, where body is the MODIFY_EXPR which doesn't have the label and thus needs to be skipped. The problem is that all the logic for skipping statements until the label is found is in cxx_eval_statement_list only. For STATEMENT_LIST that is called by cxx_eval_constant_expression, for BIND_EXPR if we are lucky enough that BIND_EXPR_BODY is a STATEMENT_LIST too (otherwise I assume even my patch doesn't fix it, it would need to verify that). If body is some other statement, then it really should be skipped, but it isn't, because cxx_eval_constant_expression ignores it. I wonder if we e.g. cxx_eval_constant_expression couldn't early in the function for if (*jump_target) return immediately unless code is something like STATEMENT_LIST or BIND_EXPR with BIND_EXPR_BODY being STATEMENT_LIST, or perhaps in the future other construct containing other stmts. I've beeing thinking about TRY block, but at least on the testcases I've tried it has been rejected in constexpr functions, I think one can't branch into statement expressions, so that should be fine, OpenMP/OpenACC constructs are hopefully also rejected in constexpr, what else? Jakub