Auto merge of #127546 - workingjubilee:5-level-paging-exists, r=<try>

Correct outdated object size limit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.
     ///
     /// 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 address space 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}"),
         }
     }

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
@@ -2718,7 +2717,6 @@ 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] = &[];

tests/ui/const-generics/issue-112505-overflow.rs

@@ -1,3 +1,8 @@
+// ignore-tidy-linelength
+//@ normalize-stderr-32bit: "values of the type `[^`]+` are too big" -> "values of the type $$REALLY_TOO_BIG are too big"
+//@ normalize-stderr-64bit: "values of the type `[^`]+` are too big" -> "values of the type $$REALLY_TOO_BIG are too big"
+
+
 #![feature(transmute_generic_consts)]
 #![feature(generic_const_exprs)]
 #![allow(incomplete_features)]
@@ -31,6 +36,11 @@ fn overflow(v: [[[u32; 8888888]; 9999999]; 777777777]) -> [[[u32; 9999999]; 7777
     }
 }
 
+fn overflow_more(v: [[[u32; 8888888]; 9999999]; 777777777]) -> [[[u32; 9999999]; 777777777]; 239] {
+    unsafe { std::mem::transmute(v) } //~ ERROR cannot transmute between types of different sizes
+}
+
+
 fn transpose<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [[u32; W]; H] {
     unsafe {
         std::mem::transmute(v)

tests/ui/const-generics/issue-112505-overflow.stderr

@@ -1,11 +1,11 @@
 error: the constant `W` is not of type `usize`
-  --> $DIR/transmute-fail.rs:12:42
+  --> $DIR/transmute-fail.rs:17:42
    |
 LL | fn bar<const W: bool, const H: usize>(v: [[u32; H]; W]) -> [[u32; W]; H] {
    |                                          ^^^^^^^^^^^^^ expected `usize`, found `bool`
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:7:9
+  --> $DIR/transmute-fail.rs:12:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
@@ -14,13 +14,13 @@ LL |         std::mem::transmute(v)
    = note: target type: `[[u32; W + 1]; H]` (size can vary because of [u32; W + 1])
 
 error: the constant `W` is not of type `usize`
-  --> $DIR/transmute-fail.rs:15:9
+  --> $DIR/transmute-fail.rs:20:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^ expected `usize`, found `bool`
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:22:9
+  --> $DIR/transmute-fail.rs:27:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
@@ -29,16 +29,25 @@ LL |         std::mem::transmute(v)
    = note: target type: `[u32; W * H * H]` (this type does not have a fixed size)
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:29:9
+  --> $DIR/transmute-fail.rs:34:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
    |
-   = note: source type: `[[[u32; 8888888]; 9999999]; 777777777]` (values of the type `[[u32; 8888888]; 9999999]` are too big for the current architecture)
-   = note: target type: `[[[u32; 9999999]; 777777777]; 8888888]` (values of the type `[[u32; 9999999]; 777777777]` are too big for the current architecture)
+   = note: source type: `[[[u32; 8888888]; 9999999]; 777777777]` (values of the type $REALLY_TOO_BIG are too big for the current architecture)
+   = note: target type: `[[[u32; 9999999]; 777777777]; 8888888]` (values of the type $REALLY_TOO_BIG are too big for the current architecture)
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:36:9
+  --> $DIR/transmute-fail.rs:40:14
+   |
+LL |     unsafe { std::mem::transmute(v) }
+   |              ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[[u32; 8888888]; 9999999]; 777777777]` (values of the type $REALLY_TOO_BIG are too big for the current architecture)
+   = note: target type: `[[[u32; 9999999]; 777777777]; 239]` (values of the type $REALLY_TOO_BIG are too big for the current architecture)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:46:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
@@ -47,7 +56,7 @@ LL |         std::mem::transmute(v)
    = note: target type: `[[u32; W]; H]` (size can vary because of [u32; W])
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:47:9
+  --> $DIR/transmute-fail.rs:57:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
@@ -56,7 +65,7 @@ LL |         std::mem::transmute(v)
    = note: target type: `[u32; W * H]` (this type does not have a fixed size)
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:54:9
+  --> $DIR/transmute-fail.rs:64:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
@@ -65,7 +74,7 @@ LL |         std::mem::transmute(v)
    = note: target type: `[[u32; W]; H]` (size can vary because of [u32; W])
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:63:9
+  --> $DIR/transmute-fail.rs:73:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
@@ -74,7 +83,7 @@ LL |         std::mem::transmute(v)
    = note: target type: `[u32; D * W * H]` (this type does not have a fixed size)
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:72:9
+  --> $DIR/transmute-fail.rs:82:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
@@ -83,7 +92,7 @@ LL |         std::mem::transmute(v)
    = note: target type: `[[u32; D * W]; H]` (size can vary because of [u32; D * W])
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:79:9
+  --> $DIR/transmute-fail.rs:89:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
@@ -92,7 +101,7 @@ LL |         std::mem::transmute(v)
    = note: target type: `[u8; L * 2]` (this type does not have a fixed size)
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:86:9
+  --> $DIR/transmute-fail.rs:96:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
@@ -101,7 +110,7 @@ LL |         std::mem::transmute(v)
    = note: target type: `[u16; L]` (this type does not have a fixed size)
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:93:9
+  --> $DIR/transmute-fail.rs:103:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
@@ -110,14 +119,14 @@ LL |         std::mem::transmute(v)
    = note: target type: `[[u8; 1]; L]` (this type does not have a fixed size)
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/transmute-fail.rs:102:9
+  --> $DIR/transmute-fail.rs:112:9
    |
 LL |         std::mem::transmute(v)
    |         ^^^^^^^^^^^^^^^^^^^
    |
    = note: source type: `[[u32; 2 * H]; W + W]` (size can vary because of [u32; 2 * H])
    = note: target type: `[[u32; W + W]; 2 * H]` (size can vary because of [u32; W + W])
 
-error: aborting due to 14 previous errors
+error: aborting due to 15 previous errors
 
 For more information about this error, try `rustc --explain E0512`.

tests/ui/const-generics/transmute-fail.rs

@@ -4,31 +4,13 @@ struct ReallyBig {
 }
 
 // The limit for "too big for the current architecture" is dependent on the target pointer size
-// however it's artificially limited on 64 bits
-// logic copied from rustc_target::abi::TargetDataLayout::obj_size_bound()
+// but is artificially limited due to LLVM's internal architecture
+// logic based on rustc_target::abi::TargetDataLayout::obj_size_bound()
 const fn max_size() -> usize {
-    #[cfg(target_pointer_width = "16")]
-    {
-        1 << 15
-    }
-
-    #[cfg(target_pointer_width = "32")]
-    {
-        1 << 31
-    }
-
-    #[cfg(target_pointer_width = "64")]
-    {
-        1 << 47
-    }
-
-    #[cfg(not(any(
-        target_pointer_width = "16",
-        target_pointer_width = "32",
-        target_pointer_width = "64"
-    )))]
-    {
-        isize::MAX as usize
+    if usize::BITS < 61 {
+        1 << (usize::BITS - 1)
+    } else {
+        1 << 61
     }
 }
 

tests/ui/const-generics/transmute-fail.stderr

@@ -1,17 +1,17 @@
 error: extern static is too large for the current architecture
-  --> $DIR/extern-static-size-overflow.rs:38:5
+  --> $DIR/extern-static-size-overflow.rs:20:5
    |
 LL |     static BAZ: [u8; max_size()];
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: extern static is too large for the current architecture
-  --> $DIR/extern-static-size-overflow.rs:39:5
+  --> $DIR/extern-static-size-overflow.rs:21:5
    |
 LL |     static UWU: [usize; usize::MAX];
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: extern static is too large for the current architecture
-  --> $DIR/extern-static-size-overflow.rs:40:5
+  --> $DIR/extern-static-size-overflow.rs:22:5
    |
 LL |     static A: ReallyBig;
    |     ^^^^^^^^^^^^^^^^^^^

tests/ui/extern/extern-static-size-overflow.rs

@@ -6,7 +6,7 @@
 type BIG = Option<[u32; (1<<29)-1]>;
 
 #[cfg(target_pointer_width = "64")]
-type BIG = Option<[u32; (1<<45)-1]>;
+type BIG = Option<[u32; (1<<59)-1]>;
 
 fn main() {
     let big: BIG = None;

tests/ui/extern/extern-static-size-overflow.stderr

@@ -1,6 +1,9 @@
-//@ only-x86_64
+//@ only-64bit
 
-const HUGE_SIZE: usize = !0usize / 8;
+// This test validates we gracefully fail computing a const or static of absurdly large size.
+// The oddly-specific number is because of LLVM measuring object sizes in bits.
+
+const HUGE_SIZE: usize = 1 << 61;
 
 
 pub struct TooBigArray {

tests/ui/limits/huge-enum.rs

@@ -1,14 +1,14 @@
 error[E0080]: could not evaluate static initializer
-  --> $DIR/issue-56762.rs:16:1
+  --> $DIR/huge-static.rs:19:1
    |
 LL | static MY_TOO_BIG_ARRAY_1: TooBigArray = TooBigArray::new();
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ values of the type `[u8; 2305843009213693951]` are too big for the current architecture
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ values of the type `[u8; 2305843009213693952]` are too big for the current architecture
 
 error[E0080]: could not evaluate static initializer
-  --> $DIR/issue-56762.rs:19:1
+  --> $DIR/huge-static.rs:22:1
    |
 LL | static MY_TOO_BIG_ARRAY_2: [u8; HUGE_SIZE] = [0x00; HUGE_SIZE];
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ values of the type `[u8; 2305843009213693951]` are too big for the current architecture
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ values of the type `[u8; 2305843009213693952]` are too big for the current architecture
 
 error: aborting due to 2 previous errors
 

tests/ui/limits/issue-56762.rs tests/ui/limits/huge-static.rs

@@ -1,7 +1,9 @@
+// ignore-tidy-linelength
 //@ build-fail
 //@ normalize-stderr-test: "S32" -> "SXX"
 //@ normalize-stderr-test: "S1M" -> "SXX"
-//@ error-pattern: too big for the current
+//@ normalize-stderr-32bit: "values of the type `[^`]+` are too big" -> "values of the type $$REALLY_TOO_BIG are too big"
+//@ normalize-stderr-64bit: "values of the type `[^`]+` are too big" -> "values of the type $$REALLY_TOO_BIG are too big"
 
 struct S32<T> {
     v0: T,

tests/ui/limits/issue-56762.stderr tests/ui/limits/huge-static.stderr

@@ -1,5 +1,5 @@
-error: values of the type `SXX<SXX<SXX<u32>>>` are too big for the current architecture
-  --> $DIR/huge-struct.rs:46:9
+error: values of the type $REALLY_TOO_BIG are too big for the current architecture
+  --> $DIR/huge-struct.rs:48:9
    |
 LL |     let fat: Option<SXX<SXX<SXX<u32>>>> = None;
    |         ^^^