On 20/06/14 02:02 PM, Josh Haberman wrote:
> Does Rust have any way of optimizing away repeated calls to the same
> function where possible? Like GCC's "pure" function attribute?
>
> To get a little more crazy, say you're working with a Map. Sometimes
> it's convenient to write code like this:
>
> if (map.contains_key(foo)) {
> let val = map.get(foo);
> // ...
> }
>
> This code, naively compiled, would perform two lookups. But only one is
> logically required, and caching the lookup would only require a single
> pointer.
>
> Is there any reasonable scenario under which the compiler could decide
> to allocate stack space to cache that lookup, so that the code above
> would be optimized to only perform one lookup?
>
> JoshRust has no way to mark effects. LLVM is able to infer the readonly, readnone and nounwind attributes in some cases, but not most.
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