aaron.ballman added a comment. In D86559#2243575 <https://reviews.llvm.org/D86559#2243575>, @staffantj wrote:
> As one of the SG14 industry members driving this, I'm firmly in the camp that > this is what we're expecting. In the first case the 1/2 case are "neutral". > This is a very explicit, and local, marker. Anything else makes it so vague > as to be unusable for fine tuned code. Thank you for chiming in! > I should also make the point that we are not talking about a feature that is > expected, or indeed should be, used by anyone other than someone with an > exceedingly good understanding of what is going on. That doesn't mean we should design something that's really hard to use for average folks too. > This is not a "teach everyone about it, it's safe" feature. It's there to > produce a very fine-grained control in those cases where it really matters, > and where profiling-guided optimizations would produce exactly the wrong > result. Using this feature should be an automatic "is this needed" question > in a code review. It is needed sometimes, just rarely. +1 but I would point out that when PGO is enabled, this attribute is ignored, so it's an either/or feature. Either you get tuned optimizations, or you get to guess at them, but the current design doesn't let you mix and match. Do see that as being a major issue with the design? In D86559#2246127 <https://reviews.llvm.org/D86559#2246127>, @Mordante wrote: > In the example above if `x == 0` there will be a jump to `case 0` which then > falls through to `case 1` and `case 2` so `case 0` doesn't jump to `case 2` > and thus doesn't "execute" the label. My point was that the standard doesn't say the jump has to be executed, just that it has to exist. I think we both agree with how we'd like to interpret this bit, but if we're going to write a paper trying to improve the wording in the standard, I think this is a minor thing we could perhaps clean up. > I had thought about RAII before and I think there it's also not a real issue. > Your example does the same as: > > if (a) > [[likely]] SomeRAIIObj{*a}; > > > Here's no declaration and the attribute is allowed. If the RAII object is > used in a declaration I expect it usually will be inside a compound statement > to create a scope where the object is alive. In that case the attribute is > placed on the compound statement. I don't expect people to really write code > like this, but it may happen when using macros. This is a good point. I also agree that more RAII uses are going to use a compound statement than not. I think we're in agreement that this isn't a case we need to do anything special for. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D86559/new/ https://reviews.llvm.org/D86559 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
