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Return passed value from black_box

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By returning the passed value black_box can be used on data being
passed to a function being benchmarked. This ensures the compiler
does not optimize the function for the input which could result in
the entire function being optimized away.
This commit is contained in:
Travis Watkins 2015-01-03 02:49:42 -06:00
parent 3d5fbae338
commit 2cc81ac531
1 changed files with 2 additions and 1 deletions
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src/libtest/lib.rs
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@ -1332,10 +1332,11 @@ impl MetricMap {
/// elimination. /// elimination.
/// ///
/// This function is a no-op, and does not even read from `dummy`. /// This function is a no-op, and does not even read from `dummy`.
pub fn black_box<T>(dummy: T) { pub fn black_box<T>(dummy: T) -> T {
// we need to "use" the argument in some way LLVM can't // we need to "use" the argument in some way LLVM can't
// introspect. // introspect.
unsafe {asm!("" : : "r"(&dummy))} unsafe {asm!("" : : "r"(&dummy))}
dummy
} }