[llvm-dev] [RFC] A new intrinsic, `llvm.blackbox`, to explicitly prevent constprop, die, etc optimizations

[Richard Diamond via llvm-dev]

On Mon, Nov 2, 2015 at 7:19 PM, Sanjoy Das <sanjoy at playingwithpointers.com>
wrote:

> Why does this need to be an intrinsic (as opposed to generic "unknown
> function" to llvm)?
>
> Secondly, have you looked into a volatile store / load to an alloca? That
> should work with PNaCl and WebAssembly.
>
> E.g.
>
> define i32 @blackbox(i32 %arg) {
>  entry:
>   %p = alloca i32
>   store volatile i32 10, i32* %p  ;; or store %arg
>   %v = load volatile i32, i32* %p
>   ret i32 %v
> }


That volatility would have a negative performance impact.

Richard Diamond
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