Show the values and computation that would overflow a const evaluation or propagation

src/librustc_codegen_ssa/mir/block.rs

@@ -380,7 +380,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         // checked operation, just a comparison with the minimum
         // value, so we have to check for the assert message.
         if !bx.check_overflow() {
-            if let AssertKind::OverflowNeg = *msg {
+            if let AssertKind::OverflowNeg(_) = *msg {
                 const_cond = Some(expected);
             }
         }

src/librustc_middle/mir/mod.rs

@@ -2,6 +2,8 @@
 //!
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/mir/index.html
 
+// ignore-tidy-filelength
+
 use crate::mir::interpret::{GlobalAlloc, Scalar};
 use crate::mir::visit::MirVisitable;
 use crate::ty::adjustment::PointerCast;
@@ -1246,10 +1248,10 @@ pub enum TerminatorKind<'tcx> {
 #[derive(Clone, RustcEncodable, RustcDecodable, HashStable, PartialEq)]
 pub enum AssertKind<O> {
     BoundsCheck { len: O, index: O },
-    Overflow(BinOp),
-    OverflowNeg,
-    DivisionByZero,
-    RemainderByZero,
+    Overflow(BinOp, O, O),
+    OverflowNeg(O),
+    DivisionByZero(O),
+    RemainderByZero(O),
     ResumedAfterReturn(GeneratorKind),
     ResumedAfterPanic(GeneratorKind),
 }
@@ -1522,17 +1524,17 @@ impl<O> AssertKind<O> {
     pub fn description(&self) -> &'static str {
         use AssertKind::*;
         match self {
-            Overflow(BinOp::Add) => "attempt to add with overflow",
-            Overflow(BinOp::Sub) => "attempt to subtract with overflow",
-            Overflow(BinOp::Mul) => "attempt to multiply with overflow",
-            Overflow(BinOp::Div) => "attempt to divide with overflow",
-            Overflow(BinOp::Rem) => "attempt to calculate the remainder with overflow",
-            OverflowNeg => "attempt to negate with overflow",
-            Overflow(BinOp::Shr) => "attempt to shift right with overflow",
-            Overflow(BinOp::Shl) => "attempt to shift left with overflow",
-            Overflow(op) => bug!("{:?} cannot overflow", op),
-            DivisionByZero => "attempt to divide by zero",
-            RemainderByZero => "attempt to calculate the remainder with a divisor of zero",
+            Overflow(BinOp::Add, _, _) => "attempt to add with overflow",
+            Overflow(BinOp::Sub, _, _) => "attempt to subtract with overflow",
+            Overflow(BinOp::Mul, _, _) => "attempt to multiply with overflow",
+            Overflow(BinOp::Div, _, _) => "attempt to divide with overflow",
+            Overflow(BinOp::Rem, _, _) => "attempt to calculate the remainder with overflow",
+            OverflowNeg(_) => "attempt to negate with overflow",
+            Overflow(BinOp::Shr, _, _) => "attempt to shift right with overflow",
+            Overflow(BinOp::Shl, _, _) => "attempt to shift left with overflow",
+            Overflow(op, _, _) => bug!("{:?} cannot overflow", op),
+            DivisionByZero(_) => "attempt to divide by zero",
+            RemainderByZero(_) => "attempt to calculate the remainder with a divisor of zero",
             ResumedAfterReturn(GeneratorKind::Gen) => "generator resumed after completion",
             ResumedAfterReturn(GeneratorKind::Async(_)) => "`async fn` resumed after completion",
             ResumedAfterPanic(GeneratorKind::Gen) => "generator resumed after panicking",
@@ -1546,12 +1548,54 @@ impl<O> AssertKind<O> {
     where
         O: Debug,
     {
+        use AssertKind::*;
         match self {
-            AssertKind::BoundsCheck { ref len, ref index } => write!(
+            BoundsCheck { ref len, ref index } => write!(
                 f,
                 "\"index out of bounds: the len is {{}} but the index is {{}}\", {:?}, {:?}",
                 len, index
             ),
+
+            OverflowNeg(op) => {
+                write!(f, "\"attempt to negate {{}} which would overflow\", {:?}", op)
+            }
+            DivisionByZero(op) => write!(f, "\"attempt to divide {{}} by zero\", {:?}", op),
+            RemainderByZero(op) => write!(
+                f,
+                "\"attempt to calculate the remainder of {{}} with a divisor of zero\", {:?}",
+                op
+            ),
+            Overflow(BinOp::Add, l, r) => write!(
+                f,
+                "\"attempt to compute `{{}} + {{}}` which would overflow\", {:?}, {:?}",
+                l, r
+            ),
+            Overflow(BinOp::Sub, l, r) => write!(
+                f,
+                "\"attempt to compute `{{}} - {{}}` which would overflow\", {:?}, {:?}",
+                l, r
+            ),
+            Overflow(BinOp::Mul, l, r) => write!(
+                f,
+                "\"attempt to compute `{{}} * {{}}` which would overflow\", {:?}, {:?}",
+                l, r
+            ),
+            Overflow(BinOp::Div, l, r) => write!(
+                f,
+                "\"attempt to compute `{{}} / {{}}` which would overflow\", {:?}, {:?}",
+                l, r
+            ),
+            Overflow(BinOp::Rem, l, r) => write!(
+                f,
+                "\"attempt to compute the remainder of `{{}} % {{}}` which would overflow\", {:?}, {:?}",
+                l, r
+            ),
+            Overflow(BinOp::Shr, _, r) => {
+                write!(f, "\"attempt to shift right by {{}} which would overflow\", {:?}", r)
+            }
+            Overflow(BinOp::Shl, _, r) => {
+                write!(f, "\"attempt to shift left by {{}} which would overflow\", {:?}", r)
+            }
             _ => write!(f, "\"{}\"", self.description()),
         }
     }
@@ -1564,6 +1608,34 @@ impl<O: fmt::Debug> fmt::Debug for AssertKind<O> {
             BoundsCheck { ref len, ref index } => {
                 write!(f, "index out of bounds: the len is {:?} but the index is {:?}", len, index)
             }
+            OverflowNeg(op) => write!(f, "attempt to negate {:#?} which would overflow", op),
+            DivisionByZero(op) => write!(f, "attempt to divide {:#?} by zero", op),
+            RemainderByZero(op) => {
+                write!(f, "attempt to calculate the remainder of {:#?} with a divisor of zero", op)
+            }
+            Overflow(BinOp::Add, l, r) => {
+                write!(f, "attempt to compute `{:#?} + {:#?}` which would overflow", l, r)
+            }
+            Overflow(BinOp::Sub, l, r) => {
+                write!(f, "attempt to compute `{:#?} - {:#?}` which would overflow", l, r)
+            }
+            Overflow(BinOp::Mul, l, r) => {
+                write!(f, "attempt to compute `{:#?} * {:#?}` which would overflow", l, r)
+            }
+            Overflow(BinOp::Div, l, r) => {
+                write!(f, "attempt to compute `{:#?} / {:#?}` which would overflow", l, r)
+            }
+            Overflow(BinOp::Rem, l, r) => write!(
+                f,
+                "attempt to compute the remainder of `{:#?} % {:#?}` which would overflow",
+                l, r
+            ),
+            Overflow(BinOp::Shr, _, r) => {
+                write!(f, "attempt to shift right by {:#?} which would overflow", r)
+            }
+            Overflow(BinOp::Shl, _, r) => {
+                write!(f, "attempt to shift left by {:#?} which would overflow", r)
+            }
             _ => write!(f, "{}", self.description()),
         }
     }

src/librustc_middle/mir/type_foldable.rs

@@ -58,15 +58,14 @@ impl<'tcx> TypeFoldable<'tcx> for Terminator<'tcx> {
             Assert { ref cond, expected, ref msg, target, cleanup } => {
                 use AssertKind::*;
                 let msg = match msg {
-                    BoundsCheck { ref len, ref index } => {
+                    BoundsCheck { len, index } => {
                         BoundsCheck { len: len.fold_with(folder), index: index.fold_with(folder) }
                     }
-                    Overflow(_)
-                    | OverflowNeg
-                    | DivisionByZero
-                    | RemainderByZero
-                    | ResumedAfterReturn(_)
-                    | ResumedAfterPanic(_) => msg.clone(),
+                    Overflow(op, l, r) => Overflow(*op, l.fold_with(folder), r.fold_with(folder)),
+                    OverflowNeg(op) => OverflowNeg(op.fold_with(folder)),
+                    DivisionByZero(op) => DivisionByZero(op.fold_with(folder)),
+                    RemainderByZero(op) => RemainderByZero(op.fold_with(folder)),
+                    ResumedAfterReturn(_) | ResumedAfterPanic(_) => msg.clone(),
                 };
                 Assert { cond: cond.fold_with(folder), expected, msg, target, cleanup }
             }
@@ -117,12 +116,11 @@ impl<'tcx> TypeFoldable<'tcx> for Terminator<'tcx> {
                         BoundsCheck { ref len, ref index } => {
                             len.visit_with(visitor) || index.visit_with(visitor)
                         }
-                        Overflow(_)
-                        | OverflowNeg
-                        | DivisionByZero
-                        | RemainderByZero
-                        | ResumedAfterReturn(_)
-                        | ResumedAfterPanic(_) => false,
+                        Overflow(_, l, r) => l.visit_with(visitor) || r.visit_with(visitor),
+                        OverflowNeg(op) | DivisionByZero(op) | RemainderByZero(op) => {
+                            op.visit_with(visitor)
+                        }
+                        ResumedAfterReturn(_) | ResumedAfterPanic(_) => false,
                     }
                 } else {
                     false

src/librustc_middle/mir/visit.rs

@@ -571,7 +571,13 @@ macro_rules! make_mir_visitor {
                         self.visit_operand(len, location);
                         self.visit_operand(index, location);
                     }
-                    Overflow(_) | OverflowNeg | DivisionByZero | RemainderByZero |
+                    Overflow(_, l, r) => {
+                        self.visit_operand(l, location);
+                        self.visit_operand(r, location);
+                    }
+                    OverflowNeg(op) | DivisionByZero(op) | RemainderByZero(op) => {
+                        self.visit_operand(op, location);
+                    }
                     ResumedAfterReturn(_) | ResumedAfterPanic(_) => {
                         // Nothing to visit
                     }

src/librustc_middle/ty/consts.rs

@@ -0,0 +1,111 @@
+use crate::mir::interpret::truncate;
+use rustc_target::abi::Size;
+
+#[derive(Copy, Clone)]
+/// A type for representing any integer. Only used for printing.
+// FIXME: Use this for the integer-tree representation needed for type level ints and
+// const generics?
+pub struct ConstInt {
+    /// Number of bytes of the integer. Only 1, 2, 4, 8, 16 are legal values.
+    size: u8,
+    /// Whether the value is of a signed integer type.
+    signed: bool,
+    /// Whether the value is a `usize` or `isize` type.
+    is_ptr_sized_integral: bool,
+    /// Raw memory of the integer. All bytes beyond the `size` are unused and must be zero.
+    raw: u128,
+}
+
+impl ConstInt {
+    pub fn new(raw: u128, size: Size, signed: bool, is_ptr_sized_integral: bool) -> Self {
+        assert!(raw <= truncate(u128::MAX, size));
+        Self { raw, size: size.bytes() as u8, signed, is_ptr_sized_integral }
+    }
+}
+
+impl std::fmt::Debug for ConstInt {
+    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let Self { size, signed, raw, is_ptr_sized_integral } = *self;
+        if signed {
+            let bit_size = size * 8;
+            let min = 1u128 << (bit_size - 1);
+            let max = min - 1;
+            if raw == min {
+                match (size, is_ptr_sized_integral) {
+                    (_, true) => write!(fmt, "isize::MIN"),
+                    (1, _) => write!(fmt, "i8::MIN"),
+                    (2, _) => write!(fmt, "i16::MIN"),
+                    (4, _) => write!(fmt, "i32::MIN"),
+                    (8, _) => write!(fmt, "i64::MIN"),
+                    (16, _) => write!(fmt, "i128::MIN"),
+                    _ => bug!("ConstInt 0x{:x} with size = {} and signed = {}", raw, size, signed),
+                }
+            } else if raw == max {
+                match (size, is_ptr_sized_integral) {
+                    (_, true) => write!(fmt, "isize::MAX"),
+                    (1, _) => write!(fmt, "i8::MAX"),
+                    (2, _) => write!(fmt, "i16::MAX"),
+                    (4, _) => write!(fmt, "i32::MAX"),
+                    (8, _) => write!(fmt, "i64::MAX"),
+                    (16, _) => write!(fmt, "i128::MAX"),
+                    _ => bug!("ConstInt 0x{:x} with size = {} and signed = {}", raw, size, signed),
+                }
+            } else {
+                match size {
+                    1 => write!(fmt, "{}", raw as i8)?,
+                    2 => write!(fmt, "{}", raw as i16)?,
+                    4 => write!(fmt, "{}", raw as i32)?,
+                    8 => write!(fmt, "{}", raw as i64)?,
+                    16 => write!(fmt, "{}", raw as i128)?,
+                    _ => bug!("ConstInt 0x{:x} with size = {} and signed = {}", raw, size, signed),
+                }
+                if fmt.alternate() {
+                    match (size, is_ptr_sized_integral) {
+                        (_, true) => write!(fmt, "_isize")?,
+                        (1, _) => write!(fmt, "_i8")?,
+                        (2, _) => write!(fmt, "_i16")?,
+                        (4, _) => write!(fmt, "_i32")?,
+                        (8, _) => write!(fmt, "_i64")?,
+                        (16, _) => write!(fmt, "_i128")?,
+                        _ => bug!(),
+                    }
+                }
+                Ok(())
+            }
+        } else {
+            let max = truncate(u128::MAX, Size::from_bytes(size));
+            if raw == max {
+                match (size, is_ptr_sized_integral) {
+                    (_, true) => write!(fmt, "usize::MAX"),
+                    (1, _) => write!(fmt, "u8::MAX"),
+                    (2, _) => write!(fmt, "u16::MAX"),
+                    (4, _) => write!(fmt, "u32::MAX"),
+                    (8, _) => write!(fmt, "u64::MAX"),
+                    (16, _) => write!(fmt, "u128::MAX"),
+                    _ => bug!("ConstInt 0x{:x} with size = {} and signed = {}", raw, size, signed),
+                }
+            } else {
+                match size {
+                    1 => write!(fmt, "{}", raw as u8)?,
+                    2 => write!(fmt, "{}", raw as u16)?,
+                    4 => write!(fmt, "{}", raw as u32)?,
+                    8 => write!(fmt, "{}", raw as u64)?,
+                    16 => write!(fmt, "{}", raw as u128)?,
+                    _ => bug!("ConstInt 0x{:x} with size = {} and signed = {}", raw, size, signed),
+                }
+                if fmt.alternate() {
+                    match (size, is_ptr_sized_integral) {
+                        (_, true) => write!(fmt, "_usize")?,
+                        (1, _) => write!(fmt, "_u8")?,
+                        (2, _) => write!(fmt, "_u16")?,
+                        (4, _) => write!(fmt, "_u32")?,
+                        (8, _) => write!(fmt, "_u64")?,
+                        (16, _) => write!(fmt, "_u128")?,
+                        _ => bug!(),
+                    }
+                }
+                Ok(())
+            }
+        }
+    }
+}

src/librustc_middle/ty/mod.rs

@@ -84,6 +84,8 @@ pub use self::trait_def::TraitDef;
 
 pub use self::query::queries;
 
+pub use self::consts::ConstInt;
+
 pub mod adjustment;
 pub mod binding;
 pub mod cast;
@@ -108,6 +110,7 @@ pub mod trait_def;
 pub mod util;
 pub mod walk;
 
+mod consts;
 mod context;
 mod diagnostics;
 mod instance;

src/librustc_middle/ty/print/pretty.rs

@@ -1,10 +1,8 @@
 use crate::middle::cstore::{ExternCrate, ExternCrateSource};
-use crate::mir::interpret::{
-    sign_extend, truncate, AllocId, ConstValue, GlobalAlloc, Pointer, Scalar,
-};
+use crate::mir::interpret::{AllocId, ConstValue, GlobalAlloc, Pointer, Scalar};
 use crate::ty::layout::IntegerExt;
 use crate::ty::subst::{GenericArg, GenericArgKind, Subst};
-use crate::ty::{self, DefIdTree, ParamConst, Ty, TyCtxt, TypeFoldable};
+use crate::ty::{self, ConstInt, DefIdTree, ParamConst, Ty, TyCtxt, TypeFoldable};
 use rustc_apfloat::ieee::{Double, Single};
 use rustc_apfloat::Float;
 use rustc_ast::ast;
@@ -981,35 +979,14 @@ pub trait PrettyPrinter<'tcx>:
             }
             // Int
             (Scalar::Raw { data, .. }, ty::Uint(ui)) => {
-                let bit_size = Integer::from_attr(&self.tcx(), UnsignedInt(*ui)).size();
-                let max = truncate(u128::MAX, bit_size);
-
-                let ui_str = ui.name_str();
-                if data == max {
-                    p!(write("{}::MAX", ui_str))
-                } else {
-                    if print_ty { p!(write("{}{}", data, ui_str)) } else { p!(write("{}", data)) }
-                };
+                let size = Integer::from_attr(&self.tcx(), UnsignedInt(*ui)).size();
+                let int = ConstInt::new(data, size, false, ty.is_ptr_sized_integral());
+                if print_ty { p!(write("{:#?}", int)) } else { p!(write("{:?}", int)) }
             }
             (Scalar::Raw { data, .. }, ty::Int(i)) => {
                 let size = Integer::from_attr(&self.tcx(), SignedInt(*i)).size();
-                let bit_size = size.bits() as u128;
-                let min = 1u128 << (bit_size - 1);
-                let max = min - 1;
-
-                let i_str = i.name_str();
-                match data {
-                    d if d == min => p!(write("{}::MIN", i_str)),
-                    d if d == max => p!(write("{}::MAX", i_str)),
-                    _ => {
-                        let data = sign_extend(data, size) as i128;
-                        if print_ty {
-                            p!(write("{}{}", data, i_str))
-                        } else {
-                            p!(write("{}", data))
-                        }
-                    }
-                }
+                let int = ConstInt::new(data, size, true, ty.is_ptr_sized_integral());
+                if print_ty { p!(write("{:#?}", int)) } else { p!(write("{:?}", int)) }
             }
             // Char
             (Scalar::Raw { data, .. }, ty::Char) if char::from_u32(data as u32).is_some() => {