Auto merge of rust-lang#127546 - workingjubilee:5-level-paging-exists, r=saethlin

Correct outdated object size limit

The comment here about 48 bit addresses being enough was written in 2016 but was made incorrect in 2019 by 5-level paging, and then persisted for another 5 years before being noticed and corrected.

The bolding of the "exclusive" part is merely to call attention to something I missed when reading it and doublechecking the math.

try-job: i686-msvc
try-job: test-various

Author: bors

compiler/rustc_abi/src/lib.rs

@@ -337,23 +337,21 @@ impl TargetDataLayout {
         Ok(dl)
     }
 
-    /// Returns exclusive upper bound on object size.
+    /// Returns **exclusive** upper bound on object size in bytes.
     ///
     /// The theoretical maximum object size is defined as the maximum positive `isize` value.
     /// This ensures that the `offset` semantics remain well-defined by allowing it to correctly
     /// index every address within an object along with one byte past the end, along with allowing
     /// `isize` to store the difference between any two pointers into an object.
     ///
-    /// The upper bound on 64-bit currently needs to be lower because LLVM uses a 64-bit integer
-    /// to represent object size in bits. It would need to be 1 << 61 to account for this, but is
-    /// currently conservatively bounded to 1 << 47 as that is enough to cover the current usable
-    /// address space on 64-bit ARMv8 and x86_64.
+    /// LLVM uses a 64-bit integer to represent object size in *bits*, but we care only for bytes,
+    /// so we adopt such a more-constrained size bound due to its technical limitations.
     #[inline]
     pub fn obj_size_bound(&self) -> u64 {
         match self.pointer_size.bits() {
             16 => 1 << 15,
             32 => 1 << 31,
-            64 => 1 << 47,
+            64 => 1 << 61,
             bits => panic!("obj_size_bound: unknown pointer bit size {bits}"),
         }
     }

compiler/rustc_hir_analysis/messages.ftl

@@ -478,7 +478,7 @@ hir_analysis_tait_forward_compat2 = item does not constrain `{$opaque_type}`, bu
 
 hir_analysis_target_feature_on_main = `main` function is not allowed to have `#[target_feature]`
 
-hir_analysis_too_large_static = extern static is too large for the current architecture
+hir_analysis_too_large_static = extern static is too large for the target architecture
 
 hir_analysis_track_caller_on_main = `main` function is not allowed to be `#[track_caller]`
     .suggestion = remove this annotation

compiler/rustc_hir_typeck/src/intrinsicck.rs

@@ -95,7 +95,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     format!("{v} bits")
                 } else {
                     // `u128` should definitely be able to hold the size of different architectures
-                    // larger sizes should be reported as error `are too big for the current architecture`
+                    // larger sizes should be reported as error `are too big for the target architecture`
                     // otherwise we have a bug somewhere
                     bug!("{:?} overflow for u128", size)
                 }

compiler/rustc_middle/messages.ftl

@@ -103,5 +103,5 @@ middle_unknown_layout =
     the type `{$ty}` has an unknown layout
 
 middle_values_too_big =
-    values of the type `{$ty}` are too big for the current architecture
+    values of the type `{$ty}` are too big for the target architecture
 middle_written_to_path = the full type name has been written to '{$path}'

compiler/rustc_middle/src/ty/layout.rs

@@ -264,7 +264,7 @@ impl<'tcx> fmt::Display for LayoutError<'tcx> {
         match *self {
             LayoutError::Unknown(ty) => write!(f, "the type `{ty}` has an unknown layout"),
             LayoutError::SizeOverflow(ty) => {
-                write!(f, "values of the type `{ty}` are too big for the current architecture")
+                write!(f, "values of the type `{ty}` are too big for the target architecture")
             }
             LayoutError::NormalizationFailure(t, e) => write!(
                 f,

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

@@ -2269,12 +2269,12 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     }
                     rustc_transmute::Reason::SrcSizeOverflow => {
                         format!(
-                            "values of the type `{src}` are too big for the current architecture"
+                            "values of the type `{src}` are too big for the target architecture"
                         )
                     }
                     rustc_transmute::Reason::DstSizeOverflow => {
                         format!(
-                            "values of the type `{dst}` are too big for the current architecture"
+                            "values of the type `{dst}` are too big for the target architecture"
                         )
                     }
                     rustc_transmute::Reason::DstHasStricterAlignment {

src/tools/miri/tests/fail/type-too-large.stderr

@@ -1,8 +1,8 @@
-error: post-monomorphization error: values of the type `[u8; 2305843011361177600]` are too big for the current architecture
+error: post-monomorphization error: values of the type `[u8; 2305843011361177600]` are too big for the target architecture
   --> tests/fail/type-too-large.rs:LL:CC
    |
 LL |     _fat = [0; (1u64 << 61) as usize + (1u64 << 31) as usize];
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ values of the type `[u8; 2305843011361177600]` are too big for the current architecture
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ values of the type `[u8; 2305843011361177600]` are too big for the target architecture
    |
    = note: BACKTRACE:
    = note: inside `main` at tests/fail/type-too-large.rs:LL:CC

src/tools/tidy/src/issues.txt

@@ -552,7 +552,6 @@ ui/const-generics/infer/issue-77092.rs
 ui/const-generics/issue-102124.rs
 ui/const-generics/issue-105689.rs
 ui/const-generics/issue-106419-struct-with-multiple-const-params.rs
-ui/const-generics/issue-112505-overflow.rs
 ui/const-generics/issue-46511.rs
 ui/const-generics/issue-66451.rs
 ui/const-generics/issue-70408.rs
@@ -2717,7 +2716,6 @@ ui/limits/issue-15919-32.rs
 ui/limits/issue-15919-64.rs
 ui/limits/issue-17913.rs
 ui/limits/issue-55878.rs
-ui/limits/issue-56762.rs
 ui/limits/issue-69485-var-size-diffs-too-large.rs
 ui/limits/issue-75158-64.rs
 ui/linkage-attr/auxiliary/issue-12133-dylib.rs

tests/crashes/125476.rs

@@ -1,4 +1,4 @@
 //@ known-bug: rust-lang/rust#125476
 //@ only-x86_64
-pub struct Data([u8; usize::MAX >> 16]);
+pub struct Data([u8; usize::MAX >> 2]);
 const _: &'static [Data] = &[];