Auto merge of #66927 - RalfJung:engines-dont-panic, r=oli-obk

Miri core engine: use throw_ub instead of throw_panic

See #66902 for context: panicking is not really an "interpreter error", but just part of a normal Rust execution. This is a first step towards removing the `InterpError::Panic` variant: the core Miri engine does not use it any more.

ConstProp and ConstEval still use it, though. This will be addressed in future PRs.

From what I can tell, all the error messages this removes are actually duplicates.

r? @oli-obk @wesleywiser

Author: bors

src/librustc/mir/interpret/error.rs

@@ -370,6 +370,14 @@ pub enum UndefinedBehaviorInfo {
     Unreachable,
     /// An enum discriminant was set to a value which was outside the range of valid values.
     InvalidDiscriminant(ScalarMaybeUndef),
+    /// A slice/array index projection went out-of-bounds.
+    BoundsCheckFailed { len: u64, index: u64 },
+    /// Something was divided by 0 (x / 0).
+    DivisionByZero,
+    /// Something was "remainded" by 0 (x % 0).
+    RemainderByZero,
+    /// Overflowing inbounds pointer arithmetic.
+    PointerArithOverflow,
 }
 
 impl fmt::Debug for UndefinedBehaviorInfo {
@@ -379,9 +387,18 @@ impl fmt::Debug for UndefinedBehaviorInfo {
             Ub(msg) | UbExperimental(msg) =>
                 write!(f, "{}", msg),
             Unreachable =>
-                write!(f, "entered unreachable code"),
+                write!(f, "entering unreachable code"),
             InvalidDiscriminant(val) =>
-                write!(f, "encountered invalid enum discriminant {}", val),
+                write!(f, "encountering invalid enum discriminant {}", val),
+            BoundsCheckFailed { ref len, ref index } =>
+                write!(f, "indexing out of bounds: the len is {:?} but the index is {:?}",
+                    len, index),
+            DivisionByZero =>
+                write!(f, "dividing by zero"),
+            RemainderByZero =>
+                write!(f, "calculating the remainder with a divisor of zero"),
+            PointerArithOverflow =>
+                write!(f, "overflowing in-bounds pointer arithmetic"),
         }
     }
 }

src/librustc/mir/interpret/pointer.rs

@@ -1,6 +1,5 @@
 use super::{AllocId, InterpResult};
 
-use crate::mir;
 use crate::ty::layout::{self, HasDataLayout, Size};
 
 use rustc_macros::HashStable;
@@ -88,13 +87,13 @@ pub trait PointerArithmetic: layout::HasDataLayout {
     #[inline]
     fn offset<'tcx>(&self, val: u64, i: u64) -> InterpResult<'tcx, u64> {
         let (res, over) = self.overflowing_offset(val, i);
-        if over { throw_panic!(Overflow(mir::BinOp::Add)) } else { Ok(res) }
+        if over { throw_ub!(PointerArithOverflow) } else { Ok(res) }
     }
 
     #[inline]
     fn signed_offset<'tcx>(&self, val: u64, i: i64) -> InterpResult<'tcx, u64> {
         let (res, over) = self.overflowing_signed_offset(val, i128::from(i));
-        if over { throw_panic!(Overflow(mir::BinOp::Add)) } else { Ok(res) }
+        if over { throw_ub!(PointerArithOverflow) } else { Ok(res) }
     }
 }
 

src/librustc_mir/interpret/operator.rs

@@ -177,8 +177,8 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 return Ok((Scalar::from_bool(op(&l, &r)), false, self.tcx.types.bool));
             }
             let op: Option<fn(i128, i128) -> (i128, bool)> = match bin_op {
-                Div if r == 0 => throw_panic!(DivisionByZero),
-                Rem if r == 0 => throw_panic!(RemainderByZero),
+                Div if r == 0 => throw_ub!(DivisionByZero),
+                Rem if r == 0 => throw_ub!(RemainderByZero),
                 Div => Some(i128::overflowing_div),
                 Rem => Some(i128::overflowing_rem),
                 Add => Some(i128::overflowing_add),
@@ -234,8 +234,8 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     Add => u128::overflowing_add,
                     Sub => u128::overflowing_sub,
                     Mul => u128::overflowing_mul,
-                    Div if r == 0 => throw_panic!(DivisionByZero),
-                    Rem if r == 0 => throw_panic!(RemainderByZero),
+                    Div if r == 0 => throw_ub!(DivisionByZero),
+                    Rem if r == 0 => throw_ub!(RemainderByZero),
                     Div => u128::overflowing_div,
                     Rem => u128::overflowing_rem,
                     _ => bug!(),

src/librustc_mir/interpret/place.rs

@@ -384,10 +384,8 @@ where
             layout::FieldPlacement::Array { stride, .. } => {
                 let len = base.len(self)?;
                 if field >= len {
-                    // This can be violated because the index (field) can be a runtime value
-                    // provided by the user.
-                    debug!("tried to access element {} of array/slice with length {}", field, len);
-                    throw_panic!(BoundsCheck { len, index: field });
+                    // This can only be reached in ConstProp and non-rustc-MIR.
+                    throw_ub!(BoundsCheckFailed { len, index: field });
                 }
                 stride * field
             }

src/test/compile-fail/consts/const-err3.rs

@@ -14,7 +14,6 @@ fn main() {
     //~^ ERROR const_err
     let _e = [5u8][1];
     //~^ ERROR const_err
-    //~| ERROR this expression will panic at runtime
     black_box(b);
     black_box(c);
     black_box(d);

src/test/ui/consts/array-literal-index-oob.stderr

@@ -12,7 +12,7 @@ error: reaching this expression at runtime will panic or abort
 LL |     &{[1, 2, 3][4]};
    |     --^^^^^^^^^^^^-
    |       |
-   |       index out of bounds: the len is 3 but the index is 4
+   |       indexing out of bounds: the len is 3 but the index is 4
 
 error: aborting due to 2 previous errors
 

src/test/ui/consts/const-err2.rs

@@ -23,7 +23,6 @@ fn main() {
     //~^ ERROR const_err
     let _e = [5u8][1];
     //~^ ERROR index out of bounds
-    //~| ERROR this expression will panic at runtime
     black_box(a);
     black_box(b);
     black_box(c);

src/test/ui/consts/const-err2.stderr

@@ -34,11 +34,5 @@ error: index out of bounds: the len is 1 but the index is 1
 LL |     let _e = [5u8][1];
    |              ^^^^^^^^
 
-error: this expression will panic at runtime
-  --> $DIR/const-err2.rs:24:14
-   |
-LL |     let _e = [5u8][1];
-   |              ^^^^^^^^ index out of bounds: the len is 1 but the index is 1
-
-error: aborting due to 6 previous errors
+error: aborting due to 5 previous errors
 

src/test/ui/consts/const-err3.rs

@@ -23,7 +23,6 @@ fn main() {
     //~^ ERROR const_err
     let _e = [5u8][1];
     //~^ ERROR const_err
-    //~| ERROR this expression will panic at runtime
     black_box(a);
     black_box(b);
     black_box(c);

src/test/ui/consts/const-err3.stderr

@@ -34,11 +34,5 @@ error: index out of bounds: the len is 1 but the index is 1
 LL |     let _e = [5u8][1];
    |              ^^^^^^^^
 
-error: this expression will panic at runtime
-  --> $DIR/const-err3.rs:24:14
-   |
-LL |     let _e = [5u8][1];
-   |              ^^^^^^^^ index out of bounds: the len is 1 but the index is 1
-
-error: aborting due to 6 previous errors
+error: aborting due to 5 previous errors