Give some intrinsics fallback bodies

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -407,9 +407,9 @@ pub fn check_intrinsic_type(
             }
             sym::float_to_int_unchecked => (2, 0, vec![param(0)], param(1)),
 
-            sym::assume => (0, 0, vec![tcx.types.bool], Ty::new_unit(tcx)),
-            sym::likely => (0, 0, vec![tcx.types.bool], tcx.types.bool),
-            sym::unlikely => (0, 0, vec![tcx.types.bool], tcx.types.bool),
+            sym::assume => (0, 1, vec![tcx.types.bool], Ty::new_unit(tcx)),
+            sym::likely => (0, 1, vec![tcx.types.bool], tcx.types.bool),
+            sym::unlikely => (0, 1, vec![tcx.types.bool], tcx.types.bool),
 
             sym::read_via_copy => (1, 0, vec![Ty::new_imm_ptr(tcx, param(0))], param(0)),
             sym::write_via_move => {

library/core/src/intrinsics.rs

@@ -937,52 +937,68 @@ extern "rust-intrinsic" {
     #[rustc_nounwind]
     pub fn unreachable() -> !;
 
-    /// Informs the optimizer that a condition is always true.
-    /// If the condition is false, the behavior is undefined.
-    ///
-    /// No code is generated for this intrinsic, but the optimizer will try
-    /// to preserve it (and its condition) between passes, which may interfere
-    /// with optimization of surrounding code and reduce performance. It should
-    /// not be used if the invariant can be discovered by the optimizer on its
-    /// own, or if it does not enable any significant optimizations.
-    ///
-    /// This intrinsic does not have a stable counterpart.
-    #[rustc_const_stable(feature = "const_assume", since = "1.77.0")]
-    #[rustc_nounwind]
-    pub fn assume(b: bool);
+}
 
-    /// Hints to the compiler that branch condition is likely to be true.
-    /// Returns the value passed to it.
-    ///
-    /// Any use other than with `if` statements will probably not have an effect.
-    ///
-    /// Note that, unlike most intrinsics, this is safe to call;
-    /// it does not require an `unsafe` block.
-    /// Therefore, implementations must not require the user to uphold
-    /// any safety invariants.
-    ///
-    /// This intrinsic does not have a stable counterpart.
-    #[rustc_const_unstable(feature = "const_likely", issue = "none")]
-    #[rustc_safe_intrinsic]
-    #[rustc_nounwind]
-    pub fn likely(b: bool) -> bool;
+/// Informs the optimizer that a condition is always true.
+/// If the condition is false, the behavior is undefined.
+///
+/// No code is generated for this intrinsic, but the optimizer will try
+/// to preserve it (and its condition) between passes, which may interfere
+/// with optimization of surrounding code and reduce performance. It should
+/// not be used if the invariant can be discovered by the optimizer on its
+/// own, or if it does not enable any significant optimizations.
+///
+/// This intrinsic does not have a stable counterpart.
+#[rustc_const_stable(feature = "const_assume", since = "1.77.0")]
+#[rustc_nounwind]
+#[unstable(feature = "core_intrinsics", issue = "none")]
+#[cfg_attr(not(bootstrap), rustc_intrinsic)]
+pub const unsafe fn assume(b: bool) {
+    if !b {
+        // SAFETY: the caller must guarantee the argument is never `false`
+        unsafe { unreachable() }
+    }
+}
 
-    /// Hints to the compiler that branch condition is likely to be false.
-    /// Returns the value passed to it.
-    ///
-    /// Any use other than with `if` statements will probably not have an effect.
-    ///
-    /// Note that, unlike most intrinsics, this is safe to call;
-    /// it does not require an `unsafe` block.
-    /// Therefore, implementations must not require the user to uphold
-    /// any safety invariants.
-    ///
-    /// This intrinsic does not have a stable counterpart.
-    #[rustc_const_unstable(feature = "const_likely", issue = "none")]
-    #[rustc_safe_intrinsic]
-    #[rustc_nounwind]
-    pub fn unlikely(b: bool) -> bool;
+/// Hints to the compiler that branch condition is likely to be true.
+/// Returns the value passed to it.
+///
+/// Any use other than with `if` statements will probably not have an effect.
+///
+/// Note that, unlike most intrinsics, this is safe to call;
+/// it does not require an `unsafe` block.
+/// Therefore, implementations must not require the user to uphold
+/// any safety invariants.
+///
+/// This intrinsic does not have a stable counterpart.
+#[rustc_const_unstable(feature = "const_likely", issue = "none")]
+#[unstable(feature = "core_intrinsics", issue = "none")]
+#[cfg_attr(not(bootstrap), rustc_intrinsic)]
+#[rustc_nounwind]
+pub const fn likely(b: bool) -> bool {
+    b
+}
+
+/// Hints to the compiler that branch condition is likely to be false.
+/// Returns the value passed to it.
+///
+/// Any use other than with `if` statements will probably not have an effect.
+///
+/// Note that, unlike most intrinsics, this is safe to call;
+/// it does not require an `unsafe` block.
+/// Therefore, implementations must not require the user to uphold
+/// any safety invariants.
+///
+/// This intrinsic does not have a stable counterpart.
+#[rustc_const_unstable(feature = "const_likely", issue = "none")]
+#[unstable(feature = "core_intrinsics", issue = "none")]
+#[cfg_attr(not(bootstrap), rustc_intrinsic)]
+#[rustc_nounwind]
+pub const fn unlikely(b: bool) -> bool {
+    b
+}
 
+extern "rust-intrinsic" {
     /// Executes a breakpoint trap, for inspection by a debugger.
     ///
     /// This intrinsic does not have a stable counterpart.

tests/ui/intrinsics/safe-intrinsic-mismatch.rs

@@ -5,12 +5,12 @@
 extern "rust-intrinsic" {
     fn size_of<T>() -> usize; //~ ERROR intrinsic safety mismatch
     //~^ ERROR intrinsic safety mismatch
-
-    #[rustc_safe_intrinsic]
-    fn assume(b: bool); //~ ERROR intrinsic safety mismatch
-    //~^ ERROR intrinsic safety mismatch
 }
 
+#[rustc_intrinsic]
+const fn assume(_b: bool) {} //~ ERROR intrinsic safety mismatch
+//~| ERROR intrinsic has wrong type
+
 #[rustc_intrinsic]
 const fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {}
 //~^ ERROR intrinsic safety mismatch

tests/ui/intrinsics/safe-intrinsic-mismatch.stderr

@@ -4,12 +4,6 @@ error: intrinsic safety mismatch between list of intrinsics within the compiler
 LL |     fn size_of<T>() -> usize;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `assume`
-  --> $DIR/safe-intrinsic-mismatch.rs:10:5
-   |
-LL |     fn assume(b: bool);
-   |     ^^^^^^^^^^^^^^^^^^
-
 error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `size_of`
   --> $DIR/safe-intrinsic-mismatch.rs:6:5
    |
@@ -19,12 +13,19 @@ LL |     fn size_of<T>() -> usize;
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `assume`
-  --> $DIR/safe-intrinsic-mismatch.rs:10:5
+  --> $DIR/safe-intrinsic-mismatch.rs:11:1
    |
-LL |     fn assume(b: bool);
-   |     ^^^^^^^^^^^^^^^^^^
+LL | const fn assume(_b: bool) {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0308]: intrinsic has wrong type
+  --> $DIR/safe-intrinsic-mismatch.rs:11:16
    |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+LL | const fn assume(_b: bool) {}
+   |                ^ expected unsafe fn, found normal fn
+   |
+   = note: expected signature `unsafe fn(_)`
+              found signature `fn(_)`
 
 error: intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `const_deallocate`
   --> $DIR/safe-intrinsic-mismatch.rs:15:1

tests/ui/reify-intrinsic.rs

@@ -13,10 +13,9 @@ fn b() {
 }
 
 fn c() {
-    let _ = [
-        std::intrinsics::likely,
+    let _: [unsafe extern "rust-intrinsic" fn(bool) -> bool; 2] = [
+        std::intrinsics::likely, //~ ERROR cannot coerce
         std::intrinsics::unlikely,
-        //~^ ERROR cannot coerce
     ];
 }
 

tests/ui/reify-intrinsic.stderr

@@ -16,14 +16,13 @@ LL |     let _ = std::mem::transmute as unsafe extern "rust-intrinsic" fn(isize)
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0308]: cannot coerce intrinsics to function pointers
-  --> $DIR/reify-intrinsic.rs:18:9
+  --> $DIR/reify-intrinsic.rs:17:9
    |
-LL |         std::intrinsics::unlikely,
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^ cannot coerce intrinsics to function pointers
+LL |         std::intrinsics::likely,
+   |         ^^^^^^^^^^^^^^^^^^^^^^^ cannot coerce intrinsics to function pointers
    |
-   = note: expected fn item `extern "rust-intrinsic" fn(_) -> _ {likely}`
-              found fn item `extern "rust-intrinsic" fn(_) -> _ {unlikely}`
-   = note: different fn items have unique types, even if their signatures are the same
+   = note: expected fn pointer `unsafe extern "rust-intrinsic" fn(_) -> _`
+                 found fn item `fn(_) -> _ {likely}`
 
 error: aborting due to 3 previous errors