Hacker News Reader

Comment by cleeus | Hacker News Reader

At this point we must ask which Update of VS 2015 as MS just replaced the Optimizer with an SSA based one. https://blogs.msdn.microsoft.com/vcblog/2016/05/04/new-code-...

View on HN

I'm the main developer of the new optimizer. It's a bit too much to say it replaces the old one, it's more of an addition. I was aware of this issue with initializing local arrays, it was on the TODO list - hopefully for the next VS.

Are you allowed to respond directly to the author in this case?

There's not much preventing any engineer at Microsoft from talking to developers. No lawyers need to be involved :-)

Why isn't the ssa optimizer mentioned in the Update 3 release notes? Is it enabled by default in Update 3?

I look forward to a fix, especially if the (I think) larger issue of large aggregates not being initialized efficiently is addressed. It feels like it is another instance of the same issue.

I hope the Python script is helpful for finding some of the odd variants that currently exist.

A good point, but already answered in the article:

> I recently noticed that it’s still an issue in VC++ 2015 Update 3

There's also the Clang/C2 toolchain, an option in the installer.

Clang/C2 doesn't use LLVM, it will use Microsoft's C2 backend.

That may be the case, but whatever the Clang frontend sends to C2 does produce better code than the Microsoft frontend. It probably already folds the stores at the frontend level, instead of leaving it to the backend to figure out.

Reply on news.ycombinator.com