Re: [PATCH V2 0/4] Unify C and C++ handling of loops and switches

[Sandra Loosemore <sandra@codesourcery.com>]

On 9/17/20 8:32 AM, Jason Merrill wrote:

> We discussed this in a team meeting the other day, and agreed that it's 
> probably simpler to switch back to gotos for C++ than fix up all the 
> optimizers.  And that there probably isn't much benefit to the 
> middle-end to retain the higher level representation longer.

When I looked into the history of the C++ change to use LOOP_EXPR, it 
seemed the primary motivation was to allow the constexpr evaluator to 
recognize loops and the optimization benefits were only lightly tested. 
But now the constexpr evaluator doesn't need LOOP_EXPR, and meanwhile I 
think the loop infrastructure and loop optimization test cases have been 
tuned for the C-style output.

> Though the patch needed to the Fortran compiler sounds like a regression 
> from this change.  Has someone looked at where that's coming from?

I tried, but wasn't able to come up with a self-contained test case 
small enough that I could actually analyze what it was doing, but that 
still triggered the warning.  In fact I am still unsure whether it is a 
bug that we weren't diagnosing that warning before, rather than that it 
showed up now.  :-S  As a programmer looking at that code, I thought the 
warning was justifiable, at least.

> Have you done any benchmark comparison for C++ tests with this change? 
> If not, please plan to monitor the lnt.opensuse.org benchmark results 
> for impact after the change is committed.

I haven't done any benchmarking myself, but yes, I will keep an eye on 
those benchmark results.

> The C++ changes are OK.  A C maintainer will need to sign off on the 
> changes there.

Thanks for the review!

-Sandra