Auto merge of #82338 - RalfJung:interp-error-allocs, r=oli-obk

all InterpError allocate now, so adjust alloc-error-check

Cc https://github.com/rust-lang/rust/pull/82116#discussion_r578310770
r? `@oli-obk`

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -543,12 +543,12 @@ fn is_init(&self, ptr: Pointer<Tag>, size: Size) -> Result<(), Range<Size>> {
     /// error which will report the first range of bytes which is uninitialized.
     fn check_init(&self, ptr: Pointer<Tag>, size: Size) -> InterpResult<'tcx> {
         self.is_init(ptr, size).or_else(|idx_range| {
-            throw_ub!(InvalidUninitBytes(Some(Box::new(UninitBytesAccess {
+            throw_ub!(InvalidUninitBytes(Some(UninitBytesAccess {
                 access_ptr: ptr.erase_tag(),
                 access_size: size,
                 uninit_ptr: Pointer::new(ptr.alloc_id, idx_range.start),
                 uninit_size: idx_range.end - idx_range.start, // `Size` subtraction
-            }))))
+            })))
         })
     }
 

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -9,7 +9,7 @@
 use rustc_session::CtfeBacktrace;
 use rustc_span::def_id::DefId;
 use rustc_target::abi::{Align, Size};
-use std::{any::Any, backtrace::Backtrace, fmt, mem};
+use std::{any::Any, backtrace::Backtrace, fmt};
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, HashStable, TyEncodable, TyDecodable)]
 pub enum ErrorHandled {
@@ -263,7 +263,7 @@ pub enum UndefinedBehaviorInfo<'tcx> {
     /// Using a string that is not valid UTF-8,
     InvalidStr(std::str::Utf8Error),
     /// Using uninitialized data where it is not allowed.
-    InvalidUninitBytes(Option<Box<UninitBytesAccess>>),
+    InvalidUninitBytes(Option<UninitBytesAccess>),
     /// Working with a local that is not currently live.
     DeadLocal,
     /// Data size is not equal to target size.
@@ -445,7 +445,7 @@ pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
 }
 
 #[cfg(target_arch = "x86_64")]
-static_assert_size!(InterpError<'_>, 40);
+static_assert_size!(InterpError<'_>, 72);
 
 pub enum InterpError<'tcx> {
     /// The program caused undefined behavior.
@@ -486,19 +486,14 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 }
 
 impl InterpError<'_> {
-    /// Some errors allocate to be created as they contain free-form strings.
-    /// And sometimes we want to be sure that did not happen as it is a
-    /// waste of resources.
-    pub fn allocates(&self) -> bool {
+    /// Some errors to string formatting even if the error is never printed.
+    /// To avoid performance issues, there are places where we want to be sure to never raise these formatting errors,
+    /// so this method lets us detect them and `bug!` on unexpected errors.
+    pub fn formatted_string(&self) -> bool {
         match self {
-            // Zero-sized boxes do not allocate.
-            InterpError::MachineStop(b) => mem::size_of_val::<dyn MachineStopType>(&**b) > 0,
             InterpError::Unsupported(UnsupportedOpInfo::Unsupported(_))
             | InterpError::UndefinedBehavior(UndefinedBehaviorInfo::ValidationFailure(_))
-            | InterpError::UndefinedBehavior(UndefinedBehaviorInfo::Ub(_))
-            | InterpError::UndefinedBehavior(UndefinedBehaviorInfo::InvalidUninitBytes(Some(_))) => {
-                true
-            }
+            | InterpError::UndefinedBehavior(UndefinedBehaviorInfo::Ub(_)) => true,
             _ => false,
         }
     }

compiler/rustc_mir/src/interpret/intern.rs

@@ -352,14 +352,6 @@ pub fn intern_const_alloc_recursive<M: CompileTimeMachine<'mir, 'tcx, const_eval
                         error
                     ),
                 );
-                // Some errors shouldn't come up because creating them causes
-                // an allocation, which we should avoid. When that happens,
-                // dedicated error variants should be introduced instead.
-                assert!(
-                    !error.kind().allocates(),
-                    "interning encountered allocating error: {}",
-                    error
-                );
             }
         }
     }

compiler/rustc_mir/src/transform/const_prop.rs

@@ -466,8 +466,8 @@ fn use_ecx<F, T>(&mut self, f: F) -> Option<T>
                 // an allocation, which we should avoid. When that happens,
                 // dedicated error variants should be introduced instead.
                 assert!(
-                    !error.kind().allocates(),
-                    "const-prop encountered allocating error: {}",
+                    !error.kind().formatted_string(),
+                    "const-prop encountered formatting error: {}",
                     error
                 );
                 None