[swift-evolution] Optimization attributes

Jacob Bandes-Storch jtbandes at gmail.com
Thu Jan 7 16:10:03 CST 2016

Would these be more appropriate as scoped modifiers similar to

    func foo() {
        #unchecked {
            // stuff in here is unchecked

On Thu, Jan 7, 2016 at 1:55 PM, Charles Kissinger via swift-evolution <
swift-evolution at swift.org> wrote:

> I wanted to float the idea of adding new attributes for function and
> method declarations that would allow various safety checks to be turned off
> (or on) at the level of individual functions. Examples of such attributes
> would be:
> @uncheckedmath  // integer overflow
> @uncheckedbounds  // array bounds
> @unchecked      // no safety checks, equivalent to -Ounchecked
> @fastmath         // if the —fastmath compiler option becomes available in
> the future
> These attributes could have an argument with a value of true or false,
> allowing the global compiler option to be overridden for particular
> functions.
> This is primarily motivated by the fact that the -Ounchecked compiler
> option is a very blunt instrument. It globally disables several unrelated
> safety checks such as integer overflow and array bounds checking. And it
> operates only at the level of an entire compilation unit. It is hard to
> reason about all the effects of this option across a large module, and
> isolating specific code to be compiled separately with -Ounchecked is
> inconvenient.
> These new attributes would allow specific safety checks to be enabled or
> disabled on a per-function basis. I think the overall effect would be safer
> programs, because developers would be less likely to resort to the global
> -Ounchecked compiler option when searching for better performance.
> Are optimization attributes such as these feasible?
> -CK
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