On Tue, Aug 22, 2017 at 6:37 PM, Chandler Carruth via Phabricator < revi...@reviews.llvm.org> wrote:
> chandlerc added a comment. > > I'm really not a fan of the degree of complexity and subtlety that this > introduces into the frontend, all to allow particular backend optimizations. > > I feel like this is Clang working around a fundamental deficiency in LLVM > and we should instead find a way to fix this in LLVM itself. > > As has been pointed out before, user code can synthesize large integers > that small bit sequences are extracted from, and Clang and LLVM should > handle those just as well as actual bitfields. > > Can we see how far we can push the LLVM side before we add complexity to > Clang here? I understand that there remain challenges to LLVM's stuff, but > I don't think those challenges make *all* of the LLVM improvements off the > table, I don't think we've exhausted all ways of improving the LLVM changes > being proposed, and I think we should still land all of those and > re-evaluate how important these issues are when all of that is in place. > The main challenge of doing this in LLVM is that inter-procedural analysis (and possibly cross module) is needed (for store forwarding issues). Wei, perhaps you can provide concrete test case to illustrate the issue so that reviewers have a good understanding. David > > > Repository: > rL LLVM > > https://reviews.llvm.org/D36562 > > > >
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