Auto merge of #146575 - Zalathar:rollup-m6p4yrm, r=Zalathar

Rollup of 8 pull requests

Successful merges:

 - #146402 (interpret: fix overlapping aggregate initialization)
 - #146530 (rustc_codegen_llvm: Adjust RISC-V inline assembly's clobber list)
 - #146533 (Note some previous attempts to change the Default impl for `[T; 0]`)
 - #146539 (fix 404 MCP link)
 - #146546 (Switch `std::vec::PeekMut::pop` from self to this parameter.)
 - #146549 (On FreeBSD, use readdir instead of readdir_r)
 - #146559 (Fix typo in error message)
 - #146563 (bootstrap.py: disable incremental build for bootstrap in CI)

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

Author: bors

.mailmap

@@ -609,6 +609,7 @@ Shohei Wada <pc@wada314.jp>
 Shotaro Yamada <sinkuu@sinkuu.xyz>
 Shotaro Yamada <sinkuu@sinkuu.xyz> <sinkuu@users.noreply.github.com>
 Shyam Sundar B <shyambaskaran@outlook.com>
+Sidney Cammeresi <sac@cheesecake.org> <sac@readyset.io>
 Simon Barber-Dueck <sbarberdueck@gmail.com> Simon BD <simon@server>
 Simon Sapin <simon@exyr.org> <simon.sapin@exyr.org>
 Simonas Kazlauskas <git@kazlauskas.me> Simonas Kazlauskas <github@kazlauskas.me>

compiler/rustc_codegen_llvm/src/asm.rs

@@ -240,6 +240,7 @@ impl<'ll, 'tcx> AsmBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                 }
                 InlineAsmArch::RiscV32 | InlineAsmArch::RiscV64 => {
                     constraints.extend_from_slice(&[
+                        "~{fflags}".to_string(),
                         "~{vtype}".to_string(),
                         "~{vl}".to_string(),
                         "~{vxsat}".to_string(),

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -1,5 +1,5 @@
 use itertools::Itertools as _;
-use rustc_abi::{self as abi, FIRST_VARIANT};
+use rustc_abi::{self as abi, BackendRepr, FIRST_VARIANT};
 use rustc_middle::ty::adjustment::PointerCoercion;
 use rustc_middle::ty::layout::{HasTyCtxt, HasTypingEnv, LayoutOf, TyAndLayout};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
@@ -25,6 +25,15 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         match *rvalue {
             mir::Rvalue::Use(ref operand) => {
                 let cg_operand = self.codegen_operand(bx, operand);
+                // Crucially, we do *not* use `OperandValue::Ref` for types with
+                // `BackendRepr::Scalar | BackendRepr::ScalarPair`. This ensures we match the MIR
+                // semantics regarding when assignment operators allow overlap of LHS and RHS.
+                if matches!(
+                    cg_operand.layout.backend_repr,
+                    BackendRepr::Scalar(..) | BackendRepr::ScalarPair(..),
+                ) {
+                    debug_assert!(!matches!(cg_operand.val, OperandValue::Ref(..)));
+                }
                 // FIXME: consider not copying constants through stack. (Fixable by codegen'ing
                 // constants into `OperandValue::Ref`; why don’t we do that yet if we don’t?)
                 cg_operand.val.store(bx, dest);

compiler/rustc_const_eval/src/interpret/place.rs

@@ -858,7 +858,7 @@ where
     /// Also, if you use this you are responsible for validating that things get copied at the
     /// right type.
     #[instrument(skip(self), level = "trace")]
-    fn copy_op_no_validate(
+    pub(super) fn copy_op_no_validate(
         &mut self,
         src: &impl Projectable<'tcx, M::Provenance>,
         dest: &impl Writeable<'tcx, M::Provenance>,

compiler/rustc_const_eval/src/interpret/step.rs

@@ -310,7 +310,6 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         operands: &IndexSlice<FieldIdx, mir::Operand<'tcx>>,
         dest: &PlaceTy<'tcx, M::Provenance>,
     ) -> InterpResult<'tcx> {
-        self.write_uninit(dest)?; // make sure all the padding ends up as uninit
         let (variant_index, variant_dest, active_field_index) = match *kind {
             mir::AggregateKind::Adt(_, variant_index, _, _, active_field_index) => {
                 let variant_dest = self.project_downcast(dest, variant_index)?;
@@ -346,9 +345,20 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             let field_index = active_field_index.unwrap_or(field_index);
             let field_dest = self.project_field(&variant_dest, field_index)?;
             let op = self.eval_operand(operand, Some(field_dest.layout))?;
-            self.copy_op(&op, &field_dest)?;
+            // We validate manually below so we don't have to do it here.
+            self.copy_op_no_validate(&op, &field_dest, /*allow_transmute*/ false)?;
         }
-        self.write_discriminant(variant_index, dest)
+        self.write_discriminant(variant_index, dest)?;
+        // Validate that the entire thing is valid, and reset padding that might be in between the
+        // fields.
+        if M::enforce_validity(self, dest.layout()) {
+            self.validate_operand(
+                dest,
+                M::enforce_validity_recursively(self, dest.layout()),
+                /*reset_provenance_and_padding*/ true,
+            )?;
+        }
+        interp_ok(())
     }
 
     /// Repeats `operand` into the destination. `dest` must have array type, and that type

compiler/rustc_middle/messages.ftl

@@ -84,7 +84,7 @@ middle_failed_writing_file =
 # Note: We only mention patterns here since the error can only occur with references, and those
 # are forbidden in const generics.
 middle_invalid_const_in_valtree = constant {$global_const_id} cannot be used as pattern
-    .note = constants that reference mutable or external memory cannot be used as pattern
+    .note = constants that reference mutable or external memory cannot be used as patterns
 
 middle_layout_cycle =
     a cycle occurred during layout computation

compiler/rustc_middle/src/mir/syntax.rs

@@ -327,9 +327,11 @@ pub enum StatementKind<'tcx> {
     /// interesting for optimizations? Do we want to allow such optimizations?
     ///
     /// **Needs clarification**: We currently require that the LHS place not overlap with any place
-    /// read as part of computation of the RHS for some rvalues (generally those not producing
-    /// primitives). This requirement is under discussion in [#68364]. As a part of this discussion,
-    /// it is also unclear in what order the components are evaluated.
+    /// read as part of computation of the RHS for some rvalues. This requirement is under
+    /// discussion in [#68364]. Specifically, overlap is permitted only for assignments of a type
+    /// with `BackendRepr::Scalar | BackendRepr::ScalarPair` where all the scalar fields are
+    /// [`Scalar::Initialized`][rustc_abi::Scalar::Initialized]. As a part of this discussion, it is
+    /// also unclear in what order the components are evaluated.
     ///
     /// [#68364]: https://github.com/rust-lang/rust/issues/68364
     ///

library/alloc/src/vec/peek_mut.rs

@@ -29,9 +29,9 @@ impl<'a, T> PeekMut<'a, T> {
 
     /// Removes the peeked value from the vector and returns it.
     #[unstable(feature = "vec_peek_mut", issue = "122742")]
-    pub fn pop(self) -> T {
+    pub fn pop(this: Self) -> T {
         // SAFETY: PeekMut is only constructed if the vec is non-empty
-        unsafe { self.vec.pop().unwrap_unchecked() }
+        unsafe { this.vec.pop().unwrap_unchecked() }
     }
 }
 

library/alloctests/tests/vec.rs

@@ -15,7 +15,7 @@ use std::ops::Bound::*;
 use std::panic::{AssertUnwindSafe, catch_unwind};
 use std::rc::Rc;
 use std::sync::atomic::{AtomicU32, Ordering};
-use std::vec::{Drain, IntoIter};
+use std::vec::{Drain, IntoIter, PeekMut};
 
 use crate::testing::macros::struct_with_counted_drop;
 
@@ -2647,7 +2647,7 @@ fn test_peek_mut() {
         assert_eq!(*p, 2);
         *p = 0;
         assert_eq!(*p, 0);
-        p.pop();
+        PeekMut::pop(p);
         assert_eq!(vec.len(), 1);
     } else {
         unreachable!()

library/core/src/array/mod.rs

@@ -472,6 +472,11 @@ impl<T: Copy> SpecArrayClone for T {
 // The Default impls cannot be done with const generics because `[T; 0]` doesn't
 // require Default to be implemented, and having different impl blocks for
 // different numbers isn't supported yet.
+//
+// Trying to improve the `[T; 0]` situation has proven to be difficult.
+// Please see these issues for more context on past attempts and crater runs:
+// - https://github.com/rust-lang/rust/issues/61415
+// - https://github.com/rust-lang/rust/pull/145457
 
 macro_rules! array_impl_default {
     {$n:expr, $t:ident $($ts:ident)*} => {