Use it in the library, and InstSimplify it away in the easy places

Author: scottmcm

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -9,7 +9,7 @@ use crate::MemFlags;
 
 use rustc_hir as hir;
 use rustc_middle::mir;
-use rustc_middle::mir::Operand;
+use rustc_middle::mir::{AggregateKind, Operand};
 use rustc_middle::ty::cast::{CastTy, IntTy};
 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, TyAndLayout};
 use rustc_middle::ty::{self, adjustment::PointerCoercion, Instance, Ty, TyCtxt};
@@ -717,6 +717,24 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 OperandRef { val: OperandValue::Immediate(static_), layout }
             }
             mir::Rvalue::Use(ref operand) => self.codegen_operand(bx, operand),
+            mir::Rvalue::Aggregate(box mir::AggregateKind::RawPtr(..), ref fields) => {
+                let ty = rvalue.ty(self.mir, self.cx.tcx());
+                let layout = self.cx.layout_of(self.monomorphize(ty));
+                let [data, meta] = &*fields.raw else {
+                    bug!("RawPtr fields: {fields:?}");
+                };
+                let data = self.codegen_operand(bx, data);
+                let meta = self.codegen_operand(bx, meta);
+                match (data.val, meta.val) {
+                    (p @ OperandValue::Immediate(_), OperandValue::ZeroSized) => {
+                        OperandRef { val: p, layout }
+                    }
+                    (OperandValue::Immediate(p), OperandValue::Immediate(m)) => {
+                        OperandRef { val: OperandValue::Pair(p, m), layout }
+                    }
+                    _ => bug!("RawPtr operands {data:?} {meta:?}"),
+                }
+            }
             mir::Rvalue::Repeat(..) | mir::Rvalue::Aggregate(..) => {
                 // According to `rvalue_creates_operand`, only ZST
                 // aggregate rvalues are allowed to be operands.
@@ -1029,6 +1047,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             mir::Rvalue::ThreadLocalRef(_) |
             mir::Rvalue::Use(..) => // (*)
                 true,
+            // This always produces a `ty::RawPtr`, so will be Immediate or Pair
+            mir::Rvalue::Aggregate(box AggregateKind::RawPtr(..), ..) => true,
             mir::Rvalue::Repeat(..) |
             mir::Rvalue::Aggregate(..) => {
                 let ty = rvalue.ty(self.mir, self.cx.tcx());

compiler/rustc_const_eval/src/interpret/operand.rs

@@ -583,6 +583,17 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         Ok(self.read_immediate(op)?.to_scalar())
     }
 
+    pub fn read_mem_place_meta(
+        &self,
+        op: &impl Readable<'tcx, M::Provenance>,
+    ) -> InterpResult<'tcx, MemPlaceMeta<M::Provenance>> {
+        Ok(if op.layout().is_zst() {
+            MemPlaceMeta::None
+        } else {
+            MemPlaceMeta::Meta(self.read_scalar(op)?)
+        })
+    }
+
     // Pointer-sized reads are fairly common and need target layout access, so we wrap them in
     // convenience functions.
 

compiler/rustc_const_eval/src/interpret/step.rs

@@ -9,7 +9,7 @@ use rustc_middle::mir;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_target::abi::{FieldIdx, FIRST_VARIANT};
 
-use super::{ImmTy, InterpCx, InterpResult, Machine, PlaceTy, Projectable, Scalar};
+use super::{ImmTy, Immediate, InterpCx, InterpResult, Machine, PlaceTy, Projectable, Scalar};
 use crate::util;
 
 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
@@ -303,6 +303,21 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let variant_dest = self.project_downcast(dest, variant_index)?;
                 (variant_index, variant_dest, active_field_index)
             }
+            mir::AggregateKind::RawPtr(..) => {
+                // Trying to `project_field` into pointers tends not to work,
+                // so build the `Immediate` from the parts directly.
+                let [data, meta] = &operands.raw else {
+                    bug!("{kind:?} should have 2 operands, had {operands:?}");
+                };
+                let data = self.eval_operand(data, None)?;
+                let data = self.read_pointer(&data)?;
+                let meta = self.eval_operand(meta, None)?;
+                let meta = self.read_mem_place_meta(&meta)?;
+                let ptr_imm = Immediate::new_pointer_with_meta(data, meta, self);
+                let ptr = ImmTy::from_immediate(ptr_imm, dest.layout);
+                self.copy_op(&ptr, dest)?;
+                return Ok(());
+            }
             _ => (FIRST_VARIANT, dest.clone(), None),
         };
         if active_field_index.is_some() {

compiler/rustc_mir_transform/src/instsimplify.rs

@@ -36,6 +36,7 @@ impl<'tcx> MirPass<'tcx> for InstSimplify {
                         ctx.simplify_bool_cmp(&statement.source_info, rvalue);
                         ctx.simplify_ref_deref(&statement.source_info, rvalue);
                         ctx.simplify_len(&statement.source_info, rvalue);
+                        ctx.simplify_ptr_aggregate(&statement.source_info, rvalue);
                         ctx.simplify_cast(rvalue);
                     }
                     _ => {}
@@ -58,8 +59,17 @@ struct InstSimplifyContext<'tcx, 'a> {
 
 impl<'tcx> InstSimplifyContext<'tcx, '_> {
     fn should_simplify(&self, source_info: &SourceInfo, rvalue: &Rvalue<'tcx>) -> bool {
+        self.should_simplify_custom(source_info, "Rvalue", rvalue)
+    }
+
+    fn should_simplify_custom(
+        &self,
+        source_info: &SourceInfo,
+        label: &str,
+        value: impl std::fmt::Debug,
+    ) -> bool {
         self.tcx.consider_optimizing(|| {
-            format!("InstSimplify - Rvalue: {rvalue:?} SourceInfo: {source_info:?}")
+            format!("InstSimplify - {label}: {value:?} SourceInfo: {source_info:?}")
         })
     }
 
@@ -147,6 +157,30 @@ impl<'tcx> InstSimplifyContext<'tcx, '_> {
         }
     }
 
+    /// Transform "Aggregate(RawPtr, \[p, ()\])" ==> "Cast(PtrToPtr, p)".
+    fn simplify_ptr_aggregate(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
+        if let Rvalue::Aggregate(box AggregateKind::RawPtr(pointee_ty, mutability), fields) = rvalue
+        {
+            let meta_ty = fields.raw[1].ty(self.local_decls, self.tcx);
+            if meta_ty.is_unit() {
+                // The mutable borrows we're holding prevent printing `rvalue` here
+                if !self.should_simplify_custom(
+                    source_info,
+                    "Aggregate::RawPtr",
+                    (&pointee_ty, *mutability, &fields),
+                ) {
+                    return;
+                }
+
+                let mut fields = std::mem::take(fields);
+                let _meta = fields.pop().unwrap();
+                let data = fields.pop().unwrap();
+                let ptr_ty = Ty::new_ptr(self.tcx, *pointee_ty, *mutability);
+                *rvalue = Rvalue::Cast(CastKind::PtrToPtr, data, ptr_ty);
+            }
+        }
+    }
+
     fn simplify_ub_check(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
         if let Rvalue::NullaryOp(NullOp::UbChecks, _) = *rvalue {
             let const_ = Const::from_bool(self.tcx, self.tcx.sess.ub_checks());

library/core/src/intrinsics.rs

@@ -2786,6 +2786,7 @@ pub unsafe fn vtable_align(_ptr: *const ()) -> usize {
 /// change the possible layouts of pointers.
 #[rustc_nounwind]
 #[unstable(feature = "core_intrinsics", issue = "none")]
+#[rustc_const_unstable(feature = "ptr_metadata", issue = "81513")]
 #[rustc_intrinsic]
 #[rustc_intrinsic_must_be_overridden]
 #[cfg(not(bootstrap))]

library/core/src/ptr/metadata.rs

@@ -2,6 +2,8 @@
 
 use crate::fmt;
 use crate::hash::{Hash, Hasher};
+#[cfg(not(bootstrap))]
+use crate::intrinsics::aggregate_raw_ptr;
 use crate::marker::Freeze;
 
 /// Provides the pointer metadata type of any pointed-to type.
@@ -113,10 +115,17 @@ pub const fn from_raw_parts<T: ?Sized>(
     data_pointer: *const (),
     metadata: <T as Pointee>::Metadata,
 ) -> *const T {
-    // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
-    // and PtrComponents<T> have the same memory layouts. Only std can make this
-    // guarantee.
-    unsafe { PtrRepr { components: PtrComponents { data_pointer, metadata } }.const_ptr }
+    #[cfg(bootstrap)]
+    {
+        // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
+        // and PtrComponents<T> have the same memory layouts. Only std can make this
+        // guarantee.
+        unsafe { PtrRepr { components: PtrComponents { data_pointer, metadata } }.const_ptr }
+    }
+    #[cfg(not(bootstrap))]
+    {
+        aggregate_raw_ptr(data_pointer, metadata)
+    }
 }
 
 /// Performs the same functionality as [`from_raw_parts`], except that a
@@ -130,10 +139,17 @@ pub const fn from_raw_parts_mut<T: ?Sized>(
     data_pointer: *mut (),
     metadata: <T as Pointee>::Metadata,
 ) -> *mut T {
-    // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
-    // and PtrComponents<T> have the same memory layouts. Only std can make this
-    // guarantee.
-    unsafe { PtrRepr { components: PtrComponents { data_pointer, metadata } }.mut_ptr }
+    #[cfg(bootstrap)]
+    {
+        // SAFETY: Accessing the value from the `PtrRepr` union is safe since *const T
+        // and PtrComponents<T> have the same memory layouts. Only std can make this
+        // guarantee.
+        unsafe { PtrRepr { components: PtrComponents { data_pointer, metadata } }.mut_ptr }
+    }
+    #[cfg(not(bootstrap))]
+    {
+        aggregate_raw_ptr(data_pointer, metadata)
+    }
 }
 
 #[repr(C)]

library/core/tests/ptr.rs

@@ -1163,3 +1163,11 @@ fn test_null_array_as_slice() {
     assert!(ptr.is_null());
     assert_eq!(ptr.len(), 4);
 }
+
+#[test]
+fn test_ptr_from_raw_parts_in_const() {
+    const EMPTY_SLICE_PTR: *const [i32] =
+        std::ptr::slice_from_raw_parts(std::ptr::without_provenance(123), 456);
+    assert_eq!(EMPTY_SLICE_PTR.addr(), 123);
+    assert_eq!(EMPTY_SLICE_PTR.len(), 456);
+}

library/core/tests/slice.rs

@@ -2678,3 +2678,16 @@ fn test_get_many_mut_duplicate() {
     let mut v = vec![1, 2, 3, 4, 5];
     assert!(v.get_many_mut([1, 3, 3, 4]).is_err());
 }
+
+#[test]
+fn test_slice_from_raw_parts_in_const() {
+    static FANCY: i32 = 4;
+    static FANCY_SLICE: &[i32] = unsafe { std::slice::from_raw_parts(&FANCY, 1) };
+    assert_eq!(FANCY_SLICE.as_ptr(), std::ptr::addr_of!(FANCY));
+    assert_eq!(FANCY_SLICE.len(), 1);
+
+    const EMPTY_SLICE: &[i32] =
+        unsafe { std::slice::from_raw_parts(std::ptr::without_provenance(123456), 0) };
+    assert_eq!(EMPTY_SLICE.as_ptr().addr(), 123456);
+    assert_eq!(EMPTY_SLICE.len(), 0);
+}

tests/mir-opt/instsimplify/casts.rs

@@ -1,6 +1,7 @@
 //@ unit-test: InstSimplify
 //@ compile-flags: -Zinline-mir
 #![crate_type = "lib"]
+#![feature(core_intrinsics)]
 
 #[inline(always)]
 fn generic_cast<T, U>(x: *const T) -> *const U {
@@ -23,3 +24,11 @@ pub fn roundtrip(x: *const u8) -> *const u8 {
     // CHECK: _2 = move _3 as *const u8 (PointerCoercion(MutToConstPointer));
     x as *mut u8 as *const u8
 }
+
+// EMIT_MIR casts.roundtrip.InstSimplify.diff
+pub fn cast_thin_via_aggregate(x: *const u8) -> *const () {
+    // CHECK-LABEL: fn cast_thin_via_aggregate(
+    // CHECK: _2 = _1;
+    // CHECK: _0 = move _2 as *const () (PtrToPtr);
+    std::intrinsics::aggregate_raw_ptr(x, ())
+}

tests/mir-opt/pre-codegen/slice_index.slice_ptr_get_unchecked_range.PreCodegen.after.panic-abort.mir

@@ -4,16 +4,66 @@ fn slice_ptr_get_unchecked_range(_1: *const [u32], _2: std::ops::Range<usize>) -
     debug slice => _1;
     debug index => _2;
     let mut _0: *const [u32];
+    let mut _3: usize;
+    let mut _4: usize;
     scope 1 (inlined std::ptr::const_ptr::<impl *const [u32]>::get_unchecked::<std::ops::Range<usize>>) {
         debug self => _1;
-        debug index => _2;
+        debug ((index: std::ops::Range<usize>).0: usize) => _3;
+        debug ((index: std::ops::Range<usize>).1: usize) => _4;
+        scope 2 (inlined <std::ops::Range<usize> as SliceIndex<[u32]>>::get_unchecked) {
+            debug ((self: std::ops::Range<usize>).0: usize) => _3;
+            debug ((self: std::ops::Range<usize>).1: usize) => _4;
+            debug slice => _1;
+            let _5: usize;
+            let mut _6: *const u32;
+            let mut _7: *const u32;
+            scope 3 {
+                debug new_len => _5;
+                scope 6 (inlined std::ptr::const_ptr::<impl *const [u32]>::as_ptr) {
+                    debug self => _1;
+                }
+                scope 7 (inlined std::ptr::const_ptr::<impl *const u32>::add) {
+                    debug self => _6;
+                    debug count => _3;
+                }
+                scope 8 (inlined slice_from_raw_parts::<u32>) {
+                    debug data => _7;
+                    debug len => _5;
+                    let mut _8: *const ();
+                    scope 9 (inlined std::ptr::const_ptr::<impl *const u32>::cast::<()>) {
+                        debug self => _7;
+                    }
+                    scope 10 (inlined std::ptr::from_raw_parts::<[u32]>) {
+                        debug data_pointer => _8;
+                        debug metadata => _5;
+                    }
+                }
+            }
+            scope 4 (inlined std::ptr::const_ptr::<impl *const [u32]>::len) {
+                debug self => _1;
+                scope 5 (inlined std::ptr::metadata::<[u32]>) {
+                    debug ptr => _1;
+                }
+            }
+        }
     }
 
     bb0: {
-        _0 = <std::ops::Range<usize> as SliceIndex<[u32]>>::get_unchecked(move _2, move _1) -> [return: bb1, unwind unreachable];
-    }
-
-    bb1: {
+        _3 = move (_2.0: usize);
+        _4 = move (_2.1: usize);
+        StorageLive(_5);
+        _5 = SubUnchecked(_4, _3);
+        StorageLive(_7);
+        StorageLive(_6);
+        _6 = _1 as *const u32 (PtrToPtr);
+        _7 = Offset(_6, _3);
+        StorageDead(_6);
+        StorageLive(_8);
+        _8 = _7 as *const () (PtrToPtr);
+        _0 = *const [u32] from (_8, _5);
+        StorageDead(_8);
+        StorageDead(_7);
+        StorageDead(_5);
         return;
     }
 }