[swift-users] Why are Swift Loops slow?

Andrew Trick atrick at apple.com
Wed Oct 12 17:24:35 CDT 2016

> On Oct 12, 2016, at 9:05 AM, Joe Groff via swift-users <swift-users at swift.org> wrote:
> It looks like LLVM does not recognize the overflow traps Swift emits on arithmetic operations as dead code, so that prevents it from completely eliminating the Swift loop.  That's a bug worth fixing in Swift, but unlikely to make a major difference in real, non-dead code. 

The traps aren’t dead if they are reachable. Eventually we will teach LLVM about less-strict trap semantics so they can be speculated and reordered. But for now we can do that sort of thing in SIL in the most important cases.

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