Rename assert_uninit_valid intrinsic

It's not about "uninit" anymore but about "filling with 0x01 bytes" so
the name should at least try to reflect that.

compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs

@@ -713,7 +713,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
             let res = CValue::by_val(swap(&mut fx.bcx, val), arg.layout());
             ret.write_cvalue(fx, res);
         }
-        sym::assert_inhabited | sym::assert_zero_valid | sym::assert_uninit_valid => {
+        sym::assert_inhabited | sym::assert_zero_valid | sym::assert_mem_uninitialized_valid => {
             intrinsic_args!(fx, args => (); intrinsic);
 
             let layout = fx.layout_of(substs.type_at(0));
@@ -742,7 +742,9 @@ fn codegen_regular_intrinsic_call<'tcx>(
                 return;
             }
 
-            if intrinsic == sym::assert_uninit_valid && !fx.tcx.permits_uninit_init(layout) {
+            if intrinsic == sym::assert_mem_uninitialized_valid
+                && !fx.tcx.permits_uninit_init(layout)
+            {
                 with_no_trimmed_paths!({
                     crate::base::codegen_panic(
                         fx,

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -666,12 +666,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         enum AssertIntrinsic {
             Inhabited,
             ZeroValid,
-            UninitValid,
+            MemUninitializedValid,
         }
         let panic_intrinsic = intrinsic.and_then(|i| match i {
             sym::assert_inhabited => Some(AssertIntrinsic::Inhabited),
             sym::assert_zero_valid => Some(AssertIntrinsic::ZeroValid),
-            sym::assert_uninit_valid => Some(AssertIntrinsic::UninitValid),
+            sym::assert_mem_uninitialized_valid => Some(AssertIntrinsic::MemUninitializedValid),
             _ => None,
         });
         if let Some(intrinsic) = panic_intrinsic {
@@ -682,7 +682,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             let do_panic = match intrinsic {
                 Inhabited => layout.abi.is_uninhabited(),
                 ZeroValid => !bx.tcx().permits_zero_init(layout),
-                UninitValid => !bx.tcx().permits_uninit_init(layout),
+                MemUninitializedValid => !bx.tcx().permits_uninit_init(layout),
             };
             Some(if do_panic {
                 let msg_str = with_no_visible_paths!({

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -432,7 +432,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             sym::transmute => {
                 self.copy_op(&args[0], dest, /*allow_transmute*/ true)?;
             }
-            sym::assert_inhabited | sym::assert_zero_valid | sym::assert_uninit_valid => {
+            sym::assert_inhabited
+            | sym::assert_zero_valid
+            | sym::assert_mem_uninitialized_valid => {
                 let ty = instance.substs.type_at(0);
                 let layout = self.layout_of(ty)?;
 
@@ -464,7 +466,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     }
                 }
 
-                if intrinsic_name == sym::assert_uninit_valid {
+                if intrinsic_name == sym::assert_mem_uninitialized_valid {
                     let should_panic = !self.tcx.permits_uninit_init(layout);
 
                     if should_panic {

compiler/rustc_hir_analysis/src/check/intrinsic.rs

@@ -75,7 +75,7 @@ pub fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: DefId) -> hir
         sym::abort
         | sym::assert_inhabited
         | sym::assert_zero_valid
-        | sym::assert_uninit_valid
+        | sym::assert_mem_uninitialized_valid
         | sym::size_of
         | sym::min_align_of
         | sym::needs_drop
@@ -193,9 +193,9 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
             }
             sym::rustc_peek => (1, vec![param(0)], param(0)),
             sym::caller_location => (0, vec![], tcx.caller_location_ty()),
-            sym::assert_inhabited | sym::assert_zero_valid | sym::assert_uninit_valid => {
-                (1, Vec::new(), tcx.mk_unit())
-            }
+            sym::assert_inhabited
+            | sym::assert_zero_valid
+            | sym::assert_mem_uninitialized_valid => (1, Vec::new(), tcx.mk_unit()),
             sym::forget => (1, vec![param(0)], tcx.mk_unit()),
             sym::transmute => (2, vec![param(0)], param(1)),
             sym::prefetch_read_data

compiler/rustc_span/src/symbol.rs

@@ -377,9 +377,9 @@ symbols! {
         assert_eq_macro,
         assert_inhabited,
         assert_macro,
+        assert_mem_uninitialized_valid,
         assert_ne_macro,
         assert_receiver_is_total_eq,
-        assert_uninit_valid,
         assert_zero_valid,
         asserting,
         associated_const_equality,

library/core/src/intrinsics.rs

@@ -959,13 +959,14 @@ extern "rust-intrinsic" {
     #[rustc_safe_intrinsic]
     pub fn assert_zero_valid<T>();
 
-    /// A guard for unsafe functions that cannot ever be executed if `T` has invalid
-    /// bit patterns: This will statically either panic, or do nothing.
+    /// A guard for `std::mem::uninitialized`. Checks whether a repeated bit pattern `0x01`
+    /// is legal for `T`: This will statically either panic, or do nothing.
     ///
     /// This intrinsic does not have a stable counterpart.
     #[rustc_const_unstable(feature = "const_assert_type2", issue = "none")]
     #[rustc_safe_intrinsic]
-    pub fn assert_uninit_valid<T>();
+    #[cfg(not(bootstrap))]
+    pub fn assert_mem_uninitialized_valid<T>();
 
     /// Gets a reference to a static `Location` indicating where it was called.
     ///

library/core/src/mem/mod.rs

@@ -682,7 +682,8 @@ pub unsafe fn zeroed<T>() -> T {
 pub unsafe fn uninitialized<T>() -> T {
     // SAFETY: the caller must guarantee that an uninitialized value is valid for `T`.
     unsafe {
-        intrinsics::assert_uninit_valid::<T>();
+        #[cfg(not(bootstrap))] // If the compiler hits this itself then it deserves the UB.
+        intrinsics::assert_mem_uninitialized_valid::<T>();
         let mut val = MaybeUninit::<T>::uninit();
 
         // Fill memory with 0x01, as an imperfect mitigation for old code that uses this function on

src/test/ui/consts/assert-type-intrinsics.rs

@@ -13,7 +13,7 @@ fn main() {
         //~^ERROR: evaluation of constant value failed
     };
     const _BAD2: () = {
-        intrinsics::assert_uninit_valid::<&'static i32>();
+        intrinsics::assert_mem_uninitialized_valid::<&'static i32>();
         //~^ERROR: evaluation of constant value failed
     };
     const _BAD3: () = {

src/test/ui/consts/assert-type-intrinsics.stderr

@@ -7,8 +7,8 @@ LL |         MaybeUninit::<!>::uninit().assume_init();
 error[E0080]: evaluation of constant value failed
   --> $DIR/assert-type-intrinsics.rs:16:9
    |
-LL |         intrinsics::assert_uninit_valid::<&'static i32>();
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ aborted execution: attempted to leave type `&i32` uninitialized, which is invalid
+LL |         intrinsics::assert_mem_uninitialized_valid::<&'static i32>();
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ aborted execution: attempted to leave type `&i32` uninitialized, which is invalid
 
 error[E0080]: evaluation of constant value failed
   --> $DIR/assert-type-intrinsics.rs:20:9