Revert "Auto merge of #113166 - moulins:ref-niches-initial, r=oli-obk"

This reverts commit 557359f92512ca88b62a602ebda291f17a953002, reversing
changes made to 1e6c09a803fd543a98bfbe1624d697a55300a786.

7 files changed, 74 insertions, 71 deletions

diff --git a/compiler/rustc_const_eval/messages.ftl b/compiler/rustc_const_eval/messages.ftl
index 8833f55831c..d8eade5bd2a 100644
--- a/compiler/rustc_const_eval/messages.ftl
+++ b/compiler/rustc_const_eval/messages.ftl
@@ -244,6 +244,7 @@ const_eval_not_enough_caller_args =
 const_eval_null_box = {$front_matter}: encountered a null box
 const_eval_null_fn_ptr = {$front_matter}: encountered a null function pointer
 const_eval_null_ref = {$front_matter}: encountered a null reference
+const_eval_nullable_ptr_out_of_range = {$front_matter}: encountered a potentially null pointer, but expected something that cannot possibly fail to be {$in_range}
 const_eval_nullary_intrinsic_fail =
     could not evaluate nullary intrinsic
 
diff --git a/compiler/rustc_const_eval/src/const_eval/machine.rs b/compiler/rustc_const_eval/src/const_eval/machine.rs
index 0a9a47b2837..267795a6cb4 100644
--- a/compiler/rustc_const_eval/src/const_eval/machine.rs
+++ b/compiler/rustc_const_eval/src/const_eval/machine.rs
@@ -1,6 +1,7 @@
 use rustc_hir::def::DefKind;
 use rustc_hir::{LangItem, CRATE_HIR_ID};
 use rustc_middle::mir;
+use rustc_middle::mir::interpret::PointerArithmetic;
 use rustc_middle::ty::layout::{FnAbiOf, TyAndLayout};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_session::lint::builtin::INVALID_ALIGNMENT;
@@ -16,7 +17,7 @@ use rustc_ast::Mutability;
 use rustc_hir::def_id::DefId;
 use rustc_middle::mir::AssertMessage;
 use rustc_span::symbol::{sym, Symbol};
-use rustc_target::abi::{Align, HasDataLayout as _, Size};
+use rustc_target::abi::{Align, Size};
 use rustc_target::spec::abi::Abi as CallAbi;
 
 use crate::errors::{LongRunning, LongRunningWarn};
@@ -303,8 +304,8 @@ impl<'mir, 'tcx: 'mir> CompileTimeEvalContext<'mir, 'tcx> {
                     Ok(ControlFlow::Break(()))
                 } else {
                     // Not alignable in const, return `usize::MAX`.
-                    let usize_max = self.data_layout().target_usize_max();
-                    self.write_scalar(Scalar::from_target_usize(usize_max, self), dest)?;
+                    let usize_max = Scalar::from_target_usize(self.target_usize_max(), self);
+                    self.write_scalar(usize_max, dest)?;
                     self.return_to_block(ret)?;
                     Ok(ControlFlow::Break(()))
                 }
@@ -332,7 +333,7 @@ impl<'mir, 'tcx: 'mir> CompileTimeEvalContext<'mir, 'tcx> {
             // Inequality with integers other than null can never be known for sure.
             (Scalar::Int(int), ptr @ Scalar::Ptr(..))
             | (ptr @ Scalar::Ptr(..), Scalar::Int(int))
-                if int.is_null() && !self.ptr_scalar_range(ptr)?.contains(&0) =>
+                if int.is_null() && !self.scalar_may_be_null(ptr)? =>
             {
                 0
             }
diff --git a/compiler/rustc_const_eval/src/errors.rs b/compiler/rustc_const_eval/src/errors.rs
index 61ce695ccd2..ca38cce710e 100644
--- a/compiler/rustc_const_eval/src/errors.rs
+++ b/compiler/rustc_const_eval/src/errors.rs
@@ -617,6 +617,7 @@ impl<'tcx> ReportErrorExt for ValidationErrorInfo<'tcx> {
             MutableRefInConst => const_eval_mutable_ref_in_const,
             NullFnPtr => const_eval_null_fn_ptr,
             NeverVal => const_eval_never_val,
+            NullablePtrOutOfRange { .. } => const_eval_nullable_ptr_out_of_range,
             PtrOutOfRange { .. } => const_eval_ptr_out_of_range,
             OutOfRange { .. } => const_eval_out_of_range,
             UnsafeCell => const_eval_unsafe_cell,
@@ -731,7 +732,9 @@ impl<'tcx> ReportErrorExt for ValidationErrorInfo<'tcx> {
             | InvalidFnPtr { value } => {
                 err.set_arg("value", value);
             }
-            PtrOutOfRange { range, max_value } => add_range_arg(range, max_value, handler, err),
+            NullablePtrOutOfRange { range, max_value } | PtrOutOfRange { range, max_value } => {
+                add_range_arg(range, max_value, handler, err)
+            }
             OutOfRange { range, max_value, value } => {
                 err.set_arg("value", value);
                 add_range_arg(range, max_value, handler, err);
diff --git a/compiler/rustc_const_eval/src/interpret/discriminant.rs b/compiler/rustc_const_eval/src/interpret/discriminant.rs
index 99ea0ab18bc..f23a455c2ca 100644
--- a/compiler/rustc_const_eval/src/interpret/discriminant.rs
+++ b/compiler/rustc_const_eval/src/interpret/discriminant.rs
@@ -2,7 +2,8 @@
 
 use rustc_middle::ty::layout::{LayoutOf, PrimitiveExt};
 use rustc_middle::{mir, ty};
-use rustc_target::abi::{self, TagEncoding, VariantIdx, Variants, WrappingRange};
+use rustc_target::abi::{self, TagEncoding};
+use rustc_target::abi::{VariantIdx, Variants};
 
 use super::{ImmTy, InterpCx, InterpResult, Machine, OpTy, PlaceTy, Scalar};
 
@@ -179,24 +180,19 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 // discriminant (encoded in niche/tag) and variant index are the same.
                 let variants_start = niche_variants.start().as_u32();
                 let variants_end = niche_variants.end().as_u32();
-                let variants_len = u128::from(variants_end - variants_start);
                 let variant = match tag_val.try_to_int() {
                     Err(dbg_val) => {
                         // So this is a pointer then, and casting to an int failed.
                         // Can only happen during CTFE.
-                        // The pointer and niches ranges must be disjoint, then we know
-                        // this is the untagged variant (as the value is not in the niche).
-                        // Everything else, we conservatively reject.
-                        let range = self.ptr_scalar_range(tag_val)?;
-                        let niches = WrappingRange {
-                            start: niche_start,
-                            end: niche_start.wrapping_add(variants_len),
-                        };
-                        if niches.overlaps_range(range) {
+                        // The niche must be just 0, and the ptr not null, then we know this is
+                        // okay. Everything else, we conservatively reject.
+                        let ptr_valid = niche_start == 0
+                            && variants_start == variants_end
+                            && !self.scalar_may_be_null(tag_val)?;
+                        if !ptr_valid {
                             throw_ub!(InvalidTag(dbg_val))
-                        } else {
-                            untagged_variant
                         }
+                        untagged_variant
                     }
                     Ok(tag_bits) => {
                         let tag_bits = tag_bits.assert_bits(tag_layout.size);
@@ -209,7 +205,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         let variant_index_relative =
                             variant_index_relative_val.to_scalar().assert_bits(tag_val.layout.size);
                         // Check if this is in the range that indicates an actual discriminant.
-                        if variant_index_relative <= variants_len {
+                        if variant_index_relative <= u128::from(variants_end - variants_start) {
                             let variant_index_relative = u32::try_from(variant_index_relative)
                                 .expect("we checked that this fits into a u32");
                             // Then computing the absolute variant idx should not overflow any more.
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index 8ec9a71bf3a..04cae23f852 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -5,7 +5,9 @@
 use rustc_hir::def_id::DefId;
 use rustc_middle::mir::{
     self,
-    interpret::{Allocation, ConstAllocation, ConstValue, GlobalId, InterpResult, Scalar},
+    interpret::{
+        Allocation, ConstAllocation, ConstValue, GlobalId, InterpResult, PointerArithmetic, Scalar,
+    },
     BinOp, NonDivergingIntrinsic,
 };
 use rustc_middle::ty;
@@ -13,7 +15,7 @@ use rustc_middle::ty::layout::{LayoutOf as _, ValidityRequirement};
 use rustc_middle::ty::GenericArgsRef;
 use rustc_middle::ty::{Ty, TyCtxt};
 use rustc_span::symbol::{sym, Symbol};
-use rustc_target::abi::{Abi, Align, HasDataLayout as _, Primitive, Size};
+use rustc_target::abi::{Abi, Align, Primitive, Size};
 
 use super::{
     util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, Machine, OpTy, PlaceTy,
@@ -359,12 +361,11 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 )?;
 
                 // Perform division by size to compute return value.
-                let dl = self.data_layout();
                 let ret_layout = if intrinsic_name == sym::ptr_offset_from_unsigned {
-                    assert!(0 <= dist && dist <= dl.target_isize_max());
+                    assert!(0 <= dist && dist <= self.target_isize_max());
                     usize_layout
                 } else {
-                    assert!(dl.target_isize_min() <= dist && dist <= dl.target_isize_max());
+                    assert!(self.target_isize_min() <= dist && dist <= self.target_isize_max());
                     isize_layout
                 };
                 let pointee_layout = self.layout_of(instance_args.type_at(0))?;
diff --git a/compiler/rustc_const_eval/src/interpret/memory.rs b/compiler/rustc_const_eval/src/interpret/memory.rs
index 29fc5ffcfe7..7b44a20ef03 100644
--- a/compiler/rustc_const_eval/src/interpret/memory.rs
+++ b/compiler/rustc_const_eval/src/interpret/memory.rs
@@ -10,7 +10,6 @@ use std::assert_matches::assert_matches;
 use std::borrow::Cow;
 use std::collections::VecDeque;
 use std::fmt;
-use std::ops::RangeInclusive;
 use std::ptr;
 
 use rustc_ast::Mutability;
@@ -1223,34 +1222,24 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
 /// Machine pointer introspection.
 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
-    /// Turn a pointer-sized scalar into a (non-empty) range of possible values.
+    /// Test if this value might be null.
     /// If the machine does not support ptr-to-int casts, this is conservative.
-    pub fn ptr_scalar_range(
-        &self,
-        scalar: Scalar<M::Provenance>,
-    ) -> InterpResult<'tcx, RangeInclusive<u64>> {
-        if let Ok(int) = scalar.to_target_usize(self) {
-            return Ok(int..=int);
-        }
-
-        let ptr = scalar.to_pointer(self)?;
-
-        // Can only happen during CTFE.
-        Ok(match self.ptr_try_get_alloc_id(ptr) {
-            Ok((alloc_id, offset, _)) => {
-                let offset = offset.bytes();
-                let (size, align, _) = self.get_alloc_info(alloc_id);
-                let dl = self.data_layout();
-                if offset > size.bytes() {
-                    // If the pointer is out-of-bounds, we do not have a
-                    // meaningful range to return.
-                    0..=dl.target_usize_max()
-                } else {
-                    let (min, max) = dl.address_range_for(size, align);
-                    (min + offset)..=(max + offset)
+    pub fn scalar_may_be_null(&self, scalar: Scalar<M::Provenance>) -> InterpResult<'tcx, bool> {
+        Ok(match scalar.try_to_int() {
+            Ok(int) => int.is_null(),
+            Err(_) => {
+                // Can only happen during CTFE.
+                let ptr = scalar.to_pointer(self)?;
+                match self.ptr_try_get_alloc_id(ptr) {
+                    Ok((alloc_id, offset, _)) => {
+                        let (size, _align, _kind) = self.get_alloc_info(alloc_id);
+                        // If the pointer is out-of-bounds, it may be null.
+                        // Note that one-past-the-end (offset == size) is still inbounds, and never null.
+                        offset > size
+                    }
+                    Err(_offset) => bug!("a non-int scalar is always a pointer"),
                 }
             }
-            Err(_offset) => bug!("a non-int scalar is always a pointer"),
         })
     }
 
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
index 108394d224b..21c655988a0 100644
--- a/compiler/rustc_const_eval/src/interpret/validity.rs
+++ b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -19,7 +19,9 @@ use rustc_middle::mir::interpret::{
 use rustc_middle::ty;
 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
 use rustc_span::symbol::{sym, Symbol};
-use rustc_target::abi::{Abi, FieldIdx, Scalar as ScalarAbi, Size, VariantIdx, Variants};
+use rustc_target::abi::{
+    Abi, FieldIdx, Scalar as ScalarAbi, Size, VariantIdx, Variants, WrappingRange,
+};
 
 use std::hash::Hash;
 
@@ -552,7 +554,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                     // FIXME: Check if the signature matches
                 } else {
                     // Otherwise (for standalone Miri), we have to still check it to be non-null.
-                    if self.ecx.ptr_scalar_range(value)?.contains(&0) {
+                    if self.ecx.scalar_may_be_null(value)? {
                         throw_validation_failure!(self.path, NullFnPtr);
                     }
                 }
@@ -593,36 +595,46 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
     ) -> InterpResult<'tcx> {
         let size = scalar_layout.size(self.ecx);
         let valid_range = scalar_layout.valid_range(self.ecx);
+        let WrappingRange { start, end } = valid_range;
         let max_value = size.unsigned_int_max();
-        assert!(valid_range.end <= max_value);
-        match scalar.try_to_int() {
-            Ok(int) => {
-                // We have an explicit int: check it against the valid range.
-                let bits = int.assert_bits(size);
-                if valid_range.contains(bits) {
-                    Ok(())
-                } else {
-                    throw_validation_failure!(
-                        self.path,
-                        OutOfRange { value: format!("{bits}"), range: valid_range, max_value }
-                    )
-                }
-            }
+        assert!(end <= max_value);
+        let bits = match scalar.try_to_int() {
+            Ok(int) => int.assert_bits(size),
             Err(_) => {
                 // So this is a pointer then, and casting to an int failed.
                 // Can only happen during CTFE.
-                // We check if the possible addresses are compatible with the valid range.
-                let range = self.ecx.ptr_scalar_range(scalar)?;
-                if valid_range.contains_range(range) {
-                    Ok(())
+                // We support 2 kinds of ranges here: full range, and excluding zero.
+                if start == 1 && end == max_value {
+                    // Only null is the niche. So make sure the ptr is NOT null.
+                    if self.ecx.scalar_may_be_null(scalar)? {
+                        throw_validation_failure!(
+                            self.path,
+                            NullablePtrOutOfRange { range: valid_range, max_value }
+                        )
+                    } else {
+                        return Ok(());
+                    }
+                } else if scalar_layout.is_always_valid(self.ecx) {
+                    // Easy. (This is reachable if `enforce_number_validity` is set.)
+                    return Ok(());
                 } else {
-                    // Reject conservatively, because the pointer *could* have a bad value.
+                    // Conservatively, we reject, because the pointer *could* have a bad
+                    // value.
                     throw_validation_failure!(
                         self.path,
                         PtrOutOfRange { range: valid_range, max_value }
                     )
                 }
             }
+        };
+        // Now compare.
+        if valid_range.contains(bits) {
+            Ok(())
+        } else {
+            throw_validation_failure!(
+                self.path,
+                OutOfRange { value: format!("{bits}"), range: valid_range, max_value }
+            )
         }
     }
 }