[llvm] r176292 - Brag about function call vectorization in the docs.

[Duncan Sands]

Hi Hal,

>>> On that thought, we might want some kind of analysis that can
>>> determine if errno from some math function is unused so that we
>>> can optimize regardless of the conformance mode when possible.
>>
>> That's tricky though, errno is always a global variable but the way
>> it's accessed varies from operating system to operating system.
>
> I know, this is why I've not yet done this myself ;) -- We'd probably need some kind of errno-recognition framework. Thinking about it, it might make more sense for clang to recognize errno access and tag it somehow.

one traditional method that LLVM front-ends use to indicate that a math function
does not set errno, is to plunk the readonly or readnone attribute on its
declaration.  This is a bit naughty but works pretty well in practice IIRC, and
is independent of fast-math.

Ciao, Duncan.