introduce EH_ELSE tree and gimplifier

[Alexandre Oliva]

On Jun 27, 2019, Richard Biener <richard.guenther@gmail.com> wrote:

> On Thu, Jun 27, 2019 at 10:18 AM Alexandre Oliva <oliva@adacore.com> wrote:

>> @@ -909,6 +909,13 @@ DEFTREECODE (TRY_CATCH_EXPR, "try_catch_expr", tcc_statement, 2)
>> The second operand is a cleanup expression which is evaluated
>> on any exit (normal, exception, or jump out) from this expression.  */
>> DEFTREECODE (TRY_FINALLY_EXPR, "try_finally", tcc_statement, 2)
>> +
>> +/* Evaluate either the normal or the exceptional cleanup.  This must
>> +   only be present as the cleanup expression in a TRY_FINALLY_EXPR.
>> +   If the TRY_FINALLY_EXPR completes normally, the first operand of
>> +   EH_ELSE is used as a cleanup, otherwise the second operand is
>> +   used.  */
>> +DEFTREECODE (EH_ELSE, "eh_else", tcc_statement, 2)

> It's a bit weird that this is a tcc_statement as opposed to tcc_expression,

Erhm...  What's weird about it?  It is not something that belongs in an
arbitrary expr, it's a lot more like a top-level statement, like
try_finally, having side effects but no useful value.

> also I'd have called it EH_ELSE_EXPR for clarity.

Now *that* would be weird IMHO.  No offense intended, but I'd have
dropped the _EXPR from TRY_FINALLY_EXPR to make it match the
"try_finally" string.

What reasons are there for them to deserve the _EXPR suffix?

If I rename it to EH_ELSE_EXPR, should GIMPLE_EH_ELSE also get a _EXPR
suffix?


> I also wonder why TRY_FINALLY_EXPR didn't just get a third optional
> operand?

I considered that possibility, but I didn't expect EH_ELSE to be used
often enough to bloat every TRY_FINALLY_EXPR with another operand, plus
a flag or some other means to remove ambiguity between same-cleanup and
no-else-cleanup.

-- 
Alexandre Oliva, freedom fighter  he/him   https://FSFLA.org/blogs/lxo
Be the change, be Free!                 FSF Latin America board member
GNU Toolchain Engineer                        Free Software Evangelist
Hay que enGNUrecerse, pero sin perder la terGNUra jamás - Che GNUevara