[PATCH] D76096: [clang] allow const structs/unions/arrays to be constant expressions for C

[Eli Friedman via Phabricator via cfe-commits]

efriedma added a comment.

> But prior to D151587 <https://reviews.llvm.org/D151587>, we did that for C++. Why is C special here?  And prior to this patch, we did that for C++ 11+. Why is C++ 03 special here?

I'm trying to avoid regressions.

C++11 made constant evaluation a lot more complicated, so in C++11 we evaluate() every global to determine const-ness.  But it's always worked that way, so there's no regression.  I'm not exactly happy C++11 made everything more expensive, but fixing that is a lot harder, and not a regression.

> So I feel like your feedback is pulling me in opposite directions. You want to avoid the fast path falling back to the slow path, but improvements to the fast path directly result in "complete parallel infrastructure" which you also don't want. Those seem mutually exclusive to me. Is there a third option? Am I attacking a strawman? (Regardless, I don't want to seem unappreciative of the reviews, advice, or discussion).

The primary thing that makes Evaluate/APValue slow is the fact that it has a very inefficient representation of structs and arrays.  Using it to evaluate simple integer expressions is largely comparable to non-Evaluate() methods.  The idea is to maintain the parallel infrastructure for structs and arrays, but not for other things.


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  https://reviews.llvm.org/D76096/new/

https://reviews.llvm.org/D76096