From f5d6b3af6966470f7f3beac16ec2bd77b04d8905 Mon Sep 17 00:00:00 2001 From: gnzlbg Date: Thu, 21 Mar 2019 09:15:52 +0100 Subject: [PATCH 1/4] Moves test::black_box to core::hint This changes removes a cyclic dependency between the "test" and "libtest" crates, where "libtest" depends on "test" for "black_box", but "test" depends on "libtest" for everything else. I've chosen the "hint" module because there seems to be enough consensus in the discussion of RFC2360 that this module is where such an intrinsic would belong, but this PR does not implement that RFC! (note: if that RFC ever gets merged, the API, docs, etc. of this API will need to change). For backwards compatibility reasons I've chosen to also keep the "test" feature gate for these instead of adding a new feature gate. If we change the feature gate, we'll potentially all benchmarks, and while that's something that we could do, it seems unnecessary to do that now - if RFC2360 gets merged, we'll need to do that anyways. --- src/libcore/hint.rs | 19 +++++++++++++++++++ src/libtest/lib.rs | 18 +----------------- 2 files changed, 20 insertions(+), 17 deletions(-) diff --git a/src/libcore/hint.rs b/src/libcore/hint.rs index b2f82ef0d175c..d6ddab0d8f5fb 100644 --- a/src/libcore/hint.rs +++ b/src/libcore/hint.rs @@ -91,3 +91,22 @@ pub fn spin_loop() { } } } + +/// A function that is opaque to the optimizer, to allow benchmarks to +/// pretend to use outputs to assist in avoiding dead-code +/// elimination. +/// +/// This function is a no-op, and does not even read from `dummy`. +#[cfg_attr(any(target_arch = "asmjs", target_arch = "wasm32"), inline(never))] +#[unstable(feature = "test", issue = "27812")] +pub fn black_box(dummy: T) -> T { + #[cfg(not(any(target_arch = "asmjs", target_arch = "wasm32")))] { + // we need to "use" the argument in some way LLVM can't + // introspect. + unsafe { asm!("" : : "r"(&dummy)) } + dummy + } + #[cfg(any(target_arch = "asmjs", target_arch = "wasm32"))] { + dummy + } +} diff --git a/src/libtest/lib.rs b/src/libtest/lib.rs index cb0ce480e4273..5c91c0ec43b19 100644 --- a/src/libtest/lib.rs +++ b/src/libtest/lib.rs @@ -27,23 +27,7 @@ pub use libtest::{ TestResult, TrFailed, TrFailedMsg, TrIgnored, TrOk, stats::Summary }; -/// A function that is opaque to the optimizer, to allow benchmarks to -/// pretend to use outputs to assist in avoiding dead-code -/// elimination. -/// -/// This function is a no-op, and does not even read from `dummy`. -#[cfg(not(any(target_arch = "asmjs", target_arch = "wasm32")))] -pub fn black_box(dummy: T) -> T { - // we need to "use" the argument in some way LLVM can't - // introspect. - unsafe { asm!("" : : "r"(&dummy)) } - dummy -} -#[cfg(any(target_arch = "asmjs", target_arch = "wasm32"))] -#[inline(never)] -pub fn black_box(dummy: T) -> T { - dummy -} +pub use std::hint::black_box; #[cfg(test)] mod tests { From f2443831e97279d94902997d2c012d2e92d5d996 Mon Sep 17 00:00:00 2001 From: gnzlbg Date: Mon, 25 Mar 2019 11:42:21 +0100 Subject: [PATCH 2/4] Remove dupplicated config --- src/libcore/hint.rs | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/src/libcore/hint.rs b/src/libcore/hint.rs index d6ddab0d8f5fb..75d64bbe0fb08 100644 --- a/src/libcore/hint.rs +++ b/src/libcore/hint.rs @@ -97,7 +97,6 @@ pub fn spin_loop() { /// elimination. /// /// This function is a no-op, and does not even read from `dummy`. -#[cfg_attr(any(target_arch = "asmjs", target_arch = "wasm32"), inline(never))] #[unstable(feature = "test", issue = "27812")] pub fn black_box(dummy: T) -> T { #[cfg(not(any(target_arch = "asmjs", target_arch = "wasm32")))] { @@ -107,6 +106,7 @@ pub fn black_box(dummy: T) -> T { dummy } #[cfg(any(target_arch = "asmjs", target_arch = "wasm32"))] { - dummy + #[inline(never)] fn black_box_(x: T) -> T { x } + black_box_(dummy) } } From cfa76c438a907bf223e4487ab4da2500277474cc Mon Sep 17 00:00:00 2001 From: gnzlbg Date: Mon, 25 Mar 2019 11:49:08 +0100 Subject: [PATCH 3/4] black_box should inhibit optimizations on platforms without inline assembly --- src/libcore/hint.rs | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/src/libcore/hint.rs b/src/libcore/hint.rs index 75d64bbe0fb08..abaf0b31b468f 100644 --- a/src/libcore/hint.rs +++ b/src/libcore/hint.rs @@ -106,7 +106,10 @@ pub fn black_box(dummy: T) -> T { dummy } #[cfg(any(target_arch = "asmjs", target_arch = "wasm32"))] { - #[inline(never)] fn black_box_(x: T) -> T { x } - black_box_(dummy) - } + unsafe { + let ret = crate::ptr::read_volatile(&dummy); + crate::mem::forget(dummy); + ret + } + } } From 24db5174191c915bb7a61809837aaa5cb98cfa11 Mon Sep 17 00:00:00 2001 From: gnzlbg Date: Mon, 25 Mar 2019 18:11:42 +0100 Subject: [PATCH 4/4] black_box should use inline assembly on wasm32 --- src/libcore/hint.rs | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/src/libcore/hint.rs b/src/libcore/hint.rs index abaf0b31b468f..e73a1a2879347 100644 --- a/src/libcore/hint.rs +++ b/src/libcore/hint.rs @@ -99,17 +99,17 @@ pub fn spin_loop() { /// This function is a no-op, and does not even read from `dummy`. #[unstable(feature = "test", issue = "27812")] pub fn black_box(dummy: T) -> T { - #[cfg(not(any(target_arch = "asmjs", target_arch = "wasm32")))] { + #[cfg(not(target_arch = "asmjs"))] { // we need to "use" the argument in some way LLVM can't // introspect. unsafe { asm!("" : : "r"(&dummy)) } dummy } - #[cfg(any(target_arch = "asmjs", target_arch = "wasm32"))] { + #[cfg(target_arch = "asmjs")] { unsafe { let ret = crate::ptr::read_volatile(&dummy); crate::mem::forget(dummy); ret } - } + } }