enable const-float-classify test again, and explain the const float tests better

Author: RalfJung

tests/ui/consts/const-float-bits-conv.rs

@@ -1,32 +1,35 @@
 //@ compile-flags: -Zmir-opt-level=0
 //@ run-pass
 
+// This tests conversion between floats and bits, not just for const evaluation
+// but also for regular runtime code.
+
 #![feature(const_float_bits_conv)]
 #![feature(const_float_classify)]
 #![feature(f16)]
 #![feature(f128)]
 #![allow(unused_macro_rules)]
-// Don't promote
-const fn nop<T>(x: T) -> T { x }
+
+use std::hint::black_box;
 
 macro_rules! const_assert {
     ($a:expr) => {
         {
             const _: () = assert!($a);
-            assert!(nop($a));
+            assert!(black_box($a));
         }
     };
     ($a:expr, $b:expr) => {
         {
             const _: () = assert!($a == $b);
-            assert_eq!(nop($a), nop($b));
+            assert_eq!(black_box($a), black_box($b));
         }
     };
 }
 
 fn has_broken_floats() -> bool {
     // i586 targets are broken due to <https://github.com/rust-lang/rust/issues/114479>.
-    std::env::var("TARGET").is_ok_and(|v| v.contains("i586"))
+    cfg!(all(target_arch = "x86", not(target_feature = "sse2")))
 }
 
 #[cfg(target_arch = "x86_64")]

tests/ui/consts/const-float-classify.rs

@@ -1,26 +1,25 @@
 //@ compile-flags: -Zmir-opt-level=0 -Znext-solver
-//@ known-bug: #110395
-// FIXME(effects) run-pass
+//@ run-pass
+
+// This tests the float classification functions, not just for const evaluation
+// but also for regular runtime code.
 
 #![feature(const_float_bits_conv)]
 #![feature(const_float_classify)]
-#![feature(const_trait_impl, effects)]
-#![allow(incomplete_features)]
-
-// Don't promote
-const fn nop<T>(x: T) -> T { x }
 
-impl const PartialEq<NonDet> for bool {
-    fn eq(&self, _: &NonDet) -> bool {
-        true
-    }
-}
+use std::hint::black_box;
 
 macro_rules! const_assert {
+    ($a:expr, NonDet) => {
+        {
+            const _: () = { let _val = $a; };
+            let _val = black_box($a);
+        }
+    };
     ($a:expr, $b:expr) => {
         {
             const _: () = assert!($a == $b);
-            assert!(nop($a) == nop($b));
+            assert!(black_box($a) == black_box($b));
         }
     };
 }
@@ -52,12 +51,9 @@ macro_rules! suite_inner {
     ( $ty:ident [$( $fn:ident ),*]) => {};
 }
 
-#[derive(Debug)]
-struct NonDet;
-
-// The result of the `is_sign` methods are not checked for correctness, since LLVM does not
+// The result of the `is_sign` methods are not checked for correctness, since we do not
 // guarantee anything about the signedness of NaNs. See
-// https://github.com/rust-lang/rust/issues/55131.
+// https://rust-lang.github.io/rfcs/3514-float-semantics.html.
 
 suite! {
                    [is_nan, is_infinite, is_finite, is_normal, is_sign_positive, is_sign_negative]
@@ -74,4 +70,5 @@ suite! {
 fn main() {
     f32();
     f64();
+    // FIXME(f16_f128): also test f16 and f128
 }