Rollup merge of #109435 - oli-obk:🇨🇭🥚_copy_op, r=RalfJung

Detect uninhabited types early in const eval

r? `@RalfJung`

implements https://github.com/rust-lang/rust/pull/108442#discussion_r1143003840

this is a breaking change, as some UB during const eval is now detected instead of silently being ignored. Users can see this and other UB that may cause future breakage with `-Zextra-const-ub-checks` or just by running miri on their code, which sets that flag by default.

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -2,7 +2,7 @@ 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;
+use rustc_middle::ty::layout::{FnAbiOf, TyAndLayout};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_session::lint::builtin::INVALID_ALIGNMENT;
 use std::borrow::Borrow;
@@ -335,8 +335,8 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
     }
 
     #[inline(always)]
-    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
+    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>, layout: TyAndLayout<'tcx>) -> bool {
-        ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks
+        ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks || layout.abi.is_uninhabited()
     }
 
     fn alignment_check_failed(

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -8,6 +8,7 @@ use std::hash::Hash;
 
 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
 use rustc_middle::mir;
+use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::def_id::DefId;
 use rustc_target::abi::{Align, Size};
@@ -145,8 +146,8 @@ pub trait Machine<'mir, 'tcx>: Sized {
         check: CheckAlignment,
     ) -> InterpResult<'tcx, ()>;
 
-    /// Whether to enforce the validity invariant
+    /// Whether to enforce the validity invariant for a specific layout.
-    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
+    fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>, layout: TyAndLayout<'tcx>) -> bool;
 
     /// Whether function calls should be [ABI](CallAbi)-checked.
     fn enforce_abi(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {

compiler/rustc_const_eval/src/interpret/place.rs

@@ -461,7 +461,7 @@ where
     ) -> InterpResult<'tcx> {
         self.write_immediate_no_validate(src, dest)?;
 
-        if M::enforce_validity(self) {
+        if M::enforce_validity(self, dest.layout) {
             // Data got changed, better make sure it matches the type!
             self.validate_operand(&self.place_to_op(dest)?)?;
         }
@@ -616,7 +616,7 @@ where
     ) -> InterpResult<'tcx> {
         self.copy_op_no_validate(src, dest, allow_transmute)?;
 
-        if M::enforce_validity(self) {
+        if M::enforce_validity(self, dest.layout) {
             // Data got changed, better make sure it matches the type!
             self.validate_operand(&self.place_to_op(dest)?)?;
         }

compiler/rustc_mir_transform/src/const_prop.rs

@@ -180,7 +180,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for ConstPropMachine<'mir, 'tcx>
     }
 
     #[inline(always)]
-    fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
+    fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>, _layout: TyAndLayout<'tcx>) -> bool {
         false // for now, we don't enforce validity
     }
     fn alignment_check_failed(

compiler/rustc_mir_transform/src/dataflow_const_prop.rs

@@ -8,6 +8,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def::DefKind;
 use rustc_middle::mir::visit::{MutVisitor, Visitor};
 use rustc_middle::mir::*;
+use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_mir_dataflow::value_analysis::{Map, State, TrackElem, ValueAnalysis, ValueOrPlace};
 use rustc_mir_dataflow::{lattice::FlatSet, Analysis, ResultsVisitor, SwitchIntEdgeEffects};
@@ -548,7 +549,7 @@ impl<'mir, 'tcx> rustc_const_eval::interpret::Machine<'mir, 'tcx> for DummyMachi
         unimplemented!()
     }
 
-    fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
+    fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>, _layout: TyAndLayout<'tcx>) -> bool {
         unimplemented!()
     }
     fn alignment_check_failed(

src/tools/miri/src/machine.rs

@@ -812,7 +812,7 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
     }
 
     #[inline(always)]
-    fn enforce_validity(ecx: &MiriInterpCx<'mir, 'tcx>) -> bool {
+    fn enforce_validity(ecx: &MiriInterpCx<'mir, 'tcx>, _layout: TyAndLayout<'tcx>) -> bool {
         ecx.machine.validate
     }
 

tests/ui/consts/const-eval/ub-uninhabit.rs

@@ -14,12 +14,12 @@ union MaybeUninit<T: Copy> {
 }
 
 const BAD_BAD_BAD: Bar = unsafe { MaybeUninit { uninit: () }.init };
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
 
 const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
 //~^ ERROR it is undefined behavior to use this value
 
 const BAD_BAD_ARRAY: [Bar; 1] = unsafe { MaybeUninit { uninit: () }.init };
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
 
 fn main() {}

tests/ui/consts/const-eval/ub-uninhabit.stderr

@@ -1,11 +1,8 @@
-error[E0080]: it is undefined behavior to use this value
+error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-uninhabit.rs:16:1
+  --> $DIR/ub-uninhabit.rs:16:35
    |
 LL | const BAD_BAD_BAD: Bar = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a value of uninhabited type Bar
+   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a value of uninhabited type Bar
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: $SIZE, align: $ALIGN) {}
 
 error[E0080]: it is undefined behavior to use this value
   --> $DIR/ub-uninhabit.rs:19:1
@@ -18,14 +15,11 @@ LL | const BAD_BAD_REF: &Bar = unsafe { mem::transmute(1usize) };
                HEX_DUMP
            }
 
-error[E0080]: it is undefined behavior to use this value
+error[E0080]: evaluation of constant value failed
-  --> $DIR/ub-uninhabit.rs:22:1
+  --> $DIR/ub-uninhabit.rs:22:42
    |
 LL | const BAD_BAD_ARRAY: [Bar; 1] = unsafe { MaybeUninit { uninit: () }.init };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered a value of uninhabited type Bar
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered a value of uninhabited type Bar
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: $SIZE, align: $ALIGN) {}
 
 error: aborting due to 3 previous errors
 

tests/ui/consts/const-eval/validate_uninhabited_zsts.32bit.stderr

@@ -24,14 +24,11 @@ note: inside `FOO`
 LL | const FOO: [empty::Empty; 3] = [foo(); 3];
    |                                 ^^^^^
 
-error[E0080]: it is undefined behavior to use this value
+error[E0080]: evaluation of constant value failed
-  --> $DIR/validate_uninhabited_zsts.rs:21:1
+  --> $DIR/validate_uninhabited_zsts.rs:21:42
    |
 LL | const BAR: [empty::Empty; 3] = [unsafe { std::mem::transmute(()) }; 3];
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0].0: encountered a value of uninhabited type empty::Void
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered a value of uninhabited type empty::Void
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 0, align: 1) {}
 
 warning: the type `empty::Empty` does not permit zero-initialization
   --> $DIR/validate_uninhabited_zsts.rs:21:42

tests/ui/consts/const-eval/validate_uninhabited_zsts.64bit.stderr

@@ -24,14 +24,11 @@ note: inside `FOO`
 LL | const FOO: [empty::Empty; 3] = [foo(); 3];
    |                                 ^^^^^
 
-error[E0080]: it is undefined behavior to use this value
+error[E0080]: evaluation of constant value failed
-  --> $DIR/validate_uninhabited_zsts.rs:21:1
+  --> $DIR/validate_uninhabited_zsts.rs:21:42
    |
 LL | const BAR: [empty::Empty; 3] = [unsafe { std::mem::transmute(()) }; 3];
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0].0: encountered a value of uninhabited type empty::Void
+   |                                          ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .0: encountered a value of uninhabited type empty::Void
-   |
-   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
-   = note: the raw bytes of the constant (size: 0, align: 1) {}
 
 warning: the type `empty::Empty` does not permit zero-initialization
   --> $DIR/validate_uninhabited_zsts.rs:21:42

tests/ui/consts/const-eval/validate_uninhabited_zsts.rs

@@ -19,7 +19,7 @@ pub mod empty {
 const FOO: [empty::Empty; 3] = [foo(); 3];
 
 const BAR: [empty::Empty; 3] = [unsafe { std::mem::transmute(()) }; 3];
-//~^ ERROR it is undefined behavior to use this value
+//~^ ERROR evaluation of constant value failed
 //~| WARN the type `empty::Empty` does not permit zero-initialization
 
 fn main() {

tests/ui/consts/issue-64506.rs

@@ -1,4 +1,4 @@
-// check-pass
+// check-fail
 
 #[derive(Copy, Clone)]
 pub struct ChildStdin {
@@ -14,6 +14,7 @@ const FOO: () = {
         b: (),
     }
     let x = unsafe { Foo { b: () }.a };
+    //~^ ERROR: evaluation of constant value failed
     let x = &x.inner;
 };
 

tests/ui/consts/issue-64506.stderr

@@ -0,0 +1,9 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/issue-64506.rs:16:22
+   |
+LL |     let x = unsafe { Foo { b: () }.a };
+   |                      ^^^^^^^^^^^^^^^ constructing invalid value at .inner: encountered a value of uninhabited type AnonPipe
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.