Auto merge of #124703 - matthiaskrgr:rollup-2lljptd, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #123356 (Reduce code size of `thread::set_current`)
 - #124159 (Move thread parking to `sys::sync`)
 - #124293 (Let miri and const eval execute intrinsics' fallback bodies)
 - #124677 (Set non-leaf frame pointers on Fuchsia targets)
 - #124692 (We do not coerce `&mut &mut T -> *mut mut T`)
 - #124698 (Rewrite `rustdoc-determinism` test in Rust)
 - #124700 (Remove an unnecessary cast)
 - #124701 (Docs: suggest `uN::checked_sub` instead of check-then-unchecked)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_const_eval/src/const_eval/dummy_machine.rs

@@ -105,7 +105,7 @@ impl<'mir, 'tcx: 'mir> interpret::Machine<'mir, 'tcx> for DummyMachine {
         _destination: &interpret::MPlaceTy<'tcx, Self::Provenance>,
         _target: Option<BasicBlock>,
         _unwind: UnwindAction,
-    ) -> interpret::InterpResult<'tcx> {
+    ) -> interpret::InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
         unimplemented!()
     }
 

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -459,16 +459,26 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         dest: &MPlaceTy<'tcx, Self::Provenance>,
         target: Option<mir::BasicBlock>,
         _unwind: mir::UnwindAction,
-    ) -> InterpResult<'tcx> {
+    ) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
         // Shared intrinsics.
         if ecx.emulate_intrinsic(instance, args, dest, target)? {
-            return Ok(());
+            return Ok(None);
         }
         let intrinsic_name = ecx.tcx.item_name(instance.def_id());
 
         // CTFE-specific intrinsics.
         let Some(ret) = target else {
-            throw_unsup_format!("intrinsic `{intrinsic_name}` is not supported at compile-time");
+            // Handle diverging intrinsics. We can't handle any of them (that are not already
+            // handled above), but check if there is a fallback body.
+            if ecx.tcx.intrinsic(instance.def_id()).unwrap().must_be_overridden {
+                throw_unsup_format!(
+                    "intrinsic `{intrinsic_name}` is not supported at compile-time"
+                );
+            }
+            return Ok(Some(ty::Instance {
+                def: ty::InstanceDef::Item(instance.def_id()),
+                args: instance.args,
+            }));
         };
         match intrinsic_name {
             sym::ptr_guaranteed_cmp => {
@@ -536,14 +546,21 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
             // not the optimization stage.)
             sym::is_val_statically_known => ecx.write_scalar(Scalar::from_bool(false), dest)?,
             _ => {
-                throw_unsup_format!(
-                    "intrinsic `{intrinsic_name}` is not supported at compile-time"
-                );
+                // We haven't handled the intrinsic, let's see if we can use a fallback body.
+                if ecx.tcx.intrinsic(instance.def_id()).unwrap().must_be_overridden {
+                    throw_unsup_format!(
+                        "intrinsic `{intrinsic_name}` is not supported at compile-time"
+                    );
+                }
+                return Ok(Some(ty::Instance {
+                    def: ty::InstanceDef::Item(instance.def_id()),
+                    args: instance.args,
+                }));
             }
         }
 
         ecx.go_to_block(ret);
-        Ok(())
+        Ok(None)
     }
 
     fn assert_panic(

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -414,7 +414,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 }
                 self.copy_op(&self.project_index(&input, index)?, dest)?;
             }
-            sym::likely | sym::unlikely | sym::black_box => {
+            sym::black_box => {
                 // These just return their argument
                 self.copy_op(&args[0], dest)?;
             }

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -216,14 +216,17 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
 
     /// Directly process an intrinsic without pushing a stack frame. It is the hook's
     /// responsibility to advance the instruction pointer as appropriate.
+    ///
+    /// Returns `None` if the intrinsic was fully handled.
+    /// Otherwise, returns an `Instance` of the function that implements the intrinsic.
     fn call_intrinsic(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx, Self::Provenance>],
         destination: &MPlaceTy<'tcx, Self::Provenance>,
         target: Option<mir::BasicBlock>,
         unwind: mir::UnwindAction,
-    ) -> InterpResult<'tcx>;
+    ) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>>;
 
     /// Called to evaluate `Assert` MIR terminators that trigger a panic.
     fn assert_panic(

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -539,14 +539,28 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             ty::InstanceDef::Intrinsic(def_id) => {
                 assert!(self.tcx.intrinsic(def_id).is_some());
                 // FIXME: Should `InPlace` arguments be reset to uninit?
-                M::call_intrinsic(
+                if let Some(fallback) = M::call_intrinsic(
                     self,
                     instance,
                     &self.copy_fn_args(args),
                     destination,
                     target,
                     unwind,
-                )
+                )? {
+                    assert!(!self.tcx.intrinsic(fallback.def_id()).unwrap().must_be_overridden);
+                    assert!(matches!(fallback.def, ty::InstanceDef::Item(_)));
+                    return self.eval_fn_call(
+                        FnVal::Instance(fallback),
+                        (caller_abi, caller_fn_abi),
+                        args,
+                        with_caller_location,
+                        destination,
+                        target,
+                        unwind,
+                    );
+                } else {
+                    Ok(())
+                }
             }
             ty::InstanceDef::VTableShim(..)
             | ty::InstanceDef::ReifyShim(..)

compiler/rustc_resolve/src/macros.rs

@@ -141,7 +141,7 @@ pub(crate) fn registered_tools(tcx: TyCtxt<'_>, (): ()) -> RegisteredTools {
     }
     // We implicitly add `rustfmt`, `clippy`, `diagnostic` to known tools,
     // but it's not an error to register them explicitly.
-    let predefined_tools = [sym::clippy, sym::rustfmt, sym::diagnostic];
+    let predefined_tools = [sym::clippy, sym::rustfmt, sym::diagnostic, sym::miri];
     registered_tools.extend(predefined_tools.iter().cloned().map(Ident::with_dummy_span));
     registered_tools
 }

compiler/rustc_target/src/spec/base/fuchsia.rs

@@ -1,4 +1,6 @@
-use crate::spec::{crt_objects, cvs, Cc, LinkOutputKind, LinkerFlavor, Lld, TargetOptions};
+use crate::spec::{
+    crt_objects, cvs, Cc, FramePointer, LinkOutputKind, LinkerFlavor, Lld, TargetOptions,
+};
 
 pub fn opts() -> TargetOptions {
     // This mirrors the linker options provided by clang. We presume lld for
@@ -38,6 +40,7 @@ pub fn opts() -> TargetOptions {
         ]),
         position_independent_executables: true,
         has_thread_local: true,
+        frame_pointer: FramePointer::NonLeaf,
         ..Default::default()
     }
 }

library/core/src/intrinsics.rs

@@ -987,6 +987,7 @@ pub const unsafe fn assume(b: bool) {
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_intrinsic]
 #[rustc_nounwind]
+#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
 pub const fn likely(b: bool) -> bool {
     b
 }
@@ -1006,6 +1007,7 @@ pub const fn likely(b: bool) -> bool {
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_intrinsic]
 #[rustc_nounwind]
+#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
 pub const fn unlikely(b: bool) -> bool {
     b
 }
@@ -2469,6 +2471,7 @@ extern "rust-intrinsic" {
 #[rustc_nounwind]
 #[rustc_do_not_const_check]
 #[inline]
+#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
 pub const fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8 {
     (ptr == other) as u8
 }
@@ -2733,8 +2736,10 @@ pub const fn ub_checks() -> bool {
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_nounwind]
 #[rustc_intrinsic]
+#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
 pub const unsafe fn const_allocate(_size: usize, _align: usize) -> *mut u8 {
-    // const eval overrides this function, but runtime code should always just return null pointers.
+    // const eval overrides this function, but runtime code for now just returns null pointers.
+    // See <https://github.com/rust-lang/rust/issues/93935>.
     crate::ptr::null_mut()
 }
 
@@ -2752,7 +2757,10 @@ pub const unsafe fn const_allocate(_size: usize, _align: usize) -> *mut u8 {
 #[unstable(feature = "core_intrinsics", issue = "none")]
 #[rustc_nounwind]
 #[rustc_intrinsic]
-pub const unsafe fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {}
+#[cfg_attr(not(bootstrap), miri::intrinsic_fallback_checks_ub)]
+pub const unsafe fn const_deallocate(_ptr: *mut u8, _size: usize, _align: usize) {
+    // Runtime NOP
+}
 
 /// `ptr` must point to a vtable.
 /// The intrinsic will return the size stored in that vtable.

library/core/src/num/uint_macros.rs

@@ -77,7 +77,7 @@ macro_rules! uint_impl {
                       without modifying the original"]
         #[inline(always)]
         pub const fn count_ones(self) -> u32 {
-            return intrinsics::ctpop(self as $ActualT);
+            return intrinsics::ctpop(self);
         }
 
         /// Returns the number of zeros in the binary representation of `self`.
@@ -636,6 +636,31 @@ macro_rules! uint_impl {
         /// If you're just trying to avoid the panic in debug mode, then **do not**
         /// use this.  Instead, you're looking for [`wrapping_sub`].
         ///
+        /// If you find yourself writing code like this:
+        ///
+        /// ```
+        /// # let foo = 30_u32;
+        /// # let bar = 20;
+        /// if foo >= bar {
+        ///     // SAFETY: just checked it will not overflow
+        ///     let diff = unsafe { foo.unchecked_sub(bar) };
+        ///     // ... use diff ...
+        /// }
+        /// ```
+        ///
+        /// Consider changing it to
+        ///
+        /// ```
+        /// # let foo = 30_u32;
+        /// # let bar = 20;
+        /// if let Some(diff) = foo.checked_sub(bar) {
+        ///     // ... use diff ...
+        /// }
+        /// ```
+        ///
+        /// As that does exactly the same thing -- including telling the optimizer
+        /// that the subtraction cannot overflow -- but avoids needing `unsafe`.
+        ///
         /// # Safety
         ///
         /// This results in undefined behavior when

library/std/src/sys/pal/sgx/thread.rs

@@ -67,7 +67,7 @@ mod task_queue {
 pub mod wait_notify {
     use crate::pin::Pin;
     use crate::sync::Arc;
-    use crate::sys_common::thread_parking::Parker;
+    use crate::sys::sync::Parker;
 
     pub struct Notifier(Arc<Parker>);