Rollup merge of #76434 - RalfJung:black-box, r=Mark-Simulacrum
do not inline black_box when building for Miri We cannot do the assembly trick in Miri, but let's at least make sure MIR inlining does not circumvent the black_box. Also use black_box instead of local optimization barriers in a few const tests.
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1720fd94e8
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@ -108,7 +108,8 @@ pub fn spin_loop() {
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/// Note however, that `black_box` is only (and can only be) provided on a "best-effort" basis. The
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/// extent to which it can block optimisations may vary depending upon the platform and code-gen
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/// backend used. Programs cannot rely on `black_box` for *correctness* in any way.
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#[inline]
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#[cfg_attr(not(miri), inline)]
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#[cfg_attr(miri, inline(never))]
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#[unstable(feature = "test", issue = "50297")]
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#[allow(unreachable_code)] // this makes #[cfg] a bit easier below.
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pub fn black_box<T>(mut dummy: T) -> T {
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@ -1,5 +1,7 @@
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// run-pass
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// Test a ZST enum whose dicriminant is ~0i128. This caused an ICE when casting to a i32.
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#![feature(test)]
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use std::hint::black_box;
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#[derive(Copy, Clone)]
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enum Nums {
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@ -12,9 +14,6 @@ const NEG_ONE_I32: i32 = Nums::NegOne as i32;
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const NEG_ONE_I64: i64 = Nums::NegOne as i64;
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const NEG_ONE_I128: i128 = Nums::NegOne as i128;
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#[inline(never)]
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fn identity<T>(t: T) -> T { t }
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fn test_as_arg(n: Nums) {
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assert_eq!(-1i8, n as i8);
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assert_eq!(-1i16, n as i16);
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@ -31,11 +30,11 @@ fn main() {
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assert_eq!(-1i64, kind as i64);
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assert_eq!(-1i128, kind as i128);
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assert_eq!(-1i8, identity(kind) as i8);
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assert_eq!(-1i16, identity(kind) as i16);
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assert_eq!(-1i32, identity(kind) as i32);
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assert_eq!(-1i64, identity(kind) as i64);
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assert_eq!(-1i128, identity(kind) as i128);
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assert_eq!(-1i8, black_box(kind) as i8);
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assert_eq!(-1i16, black_box(kind) as i16);
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assert_eq!(-1i32, black_box(kind) as i32);
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assert_eq!(-1i64, black_box(kind) as i64);
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assert_eq!(-1i128, black_box(kind) as i128);
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test_as_arg(Nums::NegOne);
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@ -1,14 +1,10 @@
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// run-pass
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#![feature(const_discriminant)]
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#![feature(test)]
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#![allow(dead_code)]
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use std::mem::{discriminant, Discriminant};
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// `discriminant(const_expr)` may get const-propagated.
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// As we want to check that const-eval is equal to ordinary exection,
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// we wrap `const_expr` with a function which is not const to prevent this.
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#[inline(never)]
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fn identity<T>(x: T) -> T { x }
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use std::hint::black_box;
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enum Test {
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A(u8),
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@ -31,10 +27,10 @@ const TEST_V: Discriminant<SingleVariant> = discriminant(&SingleVariant::V);
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fn main() {
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assert_eq!(TEST_A, TEST_A_OTHER);
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assert_eq!(TEST_A, discriminant(identity(&Test::A(17))));
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assert_eq!(TEST_B, discriminant(identity(&Test::B)));
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assert_eq!(TEST_A, discriminant(black_box(&Test::A(17))));
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assert_eq!(TEST_B, discriminant(black_box(&Test::B)));
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assert_ne!(TEST_A, TEST_B);
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assert_ne!(TEST_B, discriminant(identity(&Test::C { a: 42, b: 7 })));
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assert_ne!(TEST_B, discriminant(black_box(&Test::C { a: 42, b: 7 })));
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assert_eq!(TEST_V, discriminant(identity(&SingleVariant::V)));
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assert_eq!(TEST_V, discriminant(black_box(&SingleVariant::V)));
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}
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