Auto merge of #54693 - RalfJung:ctfe-scalar-pair-undef, r=oli-obk

do not normalize all non-scalar constants to a ConstValue::ScalarPair

We still need `ConstValue::ScalarPair` for match handling (matching slices and strings), but that will never see anything `Undef`. For non-fat-ptr `ScalarPair`, just point to the allocation like larger data structures do.

Fixes #54387

r? @eddyb

Author: bors

src/librustc/ich/impls_ty.rs

@@ -391,11 +391,6 @@ for ::mir::interpret::ConstValue<'gcx> {
     }
 }
 
-impl_stable_hash_for!(enum mir::interpret::ScalarMaybeUndef {
-    Scalar(v),
-    Undef
-});
-
 impl_stable_hash_for!(struct mir::interpret::Pointer {
     alloc_id,
     offset

src/librustc/mir/interpret/mod.rs

@@ -23,7 +23,7 @@ pub use self::error::{
     FrameInfo, ConstEvalResult,
 };
 
-pub use self::value::{Scalar, ConstValue, ScalarMaybeUndef};
+pub use self::value::{Scalar, ConstValue};
 
 use std::fmt;
 use mir;

src/librustc/mir/interpret/value.rs

@@ -24,15 +24,18 @@ pub enum ConstValue<'tcx> {
     /// to allow HIR creation to happen for everything before needing to be able to run constant
     /// evaluation
     Unevaluated(DefId, &'tcx Substs<'tcx>),
+
     /// Used only for types with layout::abi::Scalar ABI and ZSTs
     ///
     /// Not using the enum `Value` to encode that this must not be `Undef`
     Scalar(Scalar),
-    /// Used only for types with layout::abi::ScalarPair
+
+    /// Used only for *fat pointers* with layout::abi::ScalarPair
     ///
-    /// The second field may be undef in case of `Option<usize>::None`
-    ScalarPair(Scalar, ScalarMaybeUndef),
-    /// Used only for the remaining cases. An allocation + offset into the allocation.
+    /// Needed for pattern matching code related to slices and strings.
+    ScalarPair(Scalar, Scalar),
+
+    /// An allocation + offset into the allocation.
     /// Invariant: The AllocId matches the allocation.
     ByRef(AllocId, &'tcx Allocation, Size),
 }
@@ -67,12 +70,12 @@ impl<'tcx> ConstValue<'tcx> {
         ConstValue::ScalarPair(val, Scalar::Bits {
             bits: len as u128,
             size: cx.data_layout().pointer_size.bytes() as u8,
-        }.into())
+        })
     }
 
     #[inline]
     pub fn new_dyn_trait(val: Scalar, vtable: Pointer) -> Self {
-        ConstValue::ScalarPair(val, Scalar::Ptr(vtable).into())
+        ConstValue::ScalarPair(val, Scalar::Ptr(vtable))
     }
 }
 
@@ -340,96 +343,3 @@ pub enum Scalar<Id=AllocId> {
     /// relocation and its associated offset together as a `Pointer` here.
     Ptr(Pointer<Id>),
 }
-
-#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, RustcEncodable, RustcDecodable, Hash)]
-pub enum ScalarMaybeUndef<Id=AllocId> {
-    Scalar(Scalar<Id>),
-    Undef,
-}
-
-impl From<Scalar> for ScalarMaybeUndef {
-    #[inline(always)]
-    fn from(s: Scalar) -> Self {
-        ScalarMaybeUndef::Scalar(s)
-    }
-}
-
-impl<'tcx> ScalarMaybeUndef {
-    #[inline]
-    pub fn not_undef(self) -> EvalResult<'static, Scalar> {
-        match self {
-            ScalarMaybeUndef::Scalar(scalar) => Ok(scalar),
-            ScalarMaybeUndef::Undef => err!(ReadUndefBytes(Size::from_bytes(0))),
-        }
-    }
-
-    #[inline(always)]
-    pub fn to_ptr(self) -> EvalResult<'tcx, Pointer> {
-        self.not_undef()?.to_ptr()
-    }
-
-    #[inline(always)]
-    pub fn to_bits(self, target_size: Size) -> EvalResult<'tcx, u128> {
-        self.not_undef()?.to_bits(target_size)
-    }
-
-    #[inline(always)]
-    pub fn to_bool(self) -> EvalResult<'tcx, bool> {
-        self.not_undef()?.to_bool()
-    }
-
-    #[inline(always)]
-    pub fn to_char(self) -> EvalResult<'tcx, char> {
-        self.not_undef()?.to_char()
-    }
-
-    #[inline(always)]
-    pub fn to_f32(self) -> EvalResult<'tcx, f32> {
-        self.not_undef()?.to_f32()
-    }
-
-    #[inline(always)]
-    pub fn to_f64(self) -> EvalResult<'tcx, f64> {
-        self.not_undef()?.to_f64()
-    }
-
-    #[inline(always)]
-    pub fn to_u8(self) -> EvalResult<'tcx, u8> {
-        self.not_undef()?.to_u8()
-    }
-
-    #[inline(always)]
-    pub fn to_u32(self) -> EvalResult<'tcx, u32> {
-        self.not_undef()?.to_u32()
-    }
-
-    #[inline(always)]
-    pub fn to_u64(self) -> EvalResult<'tcx, u64> {
-        self.not_undef()?.to_u64()
-    }
-
-    #[inline(always)]
-    pub fn to_usize(self, cx: impl HasDataLayout) -> EvalResult<'tcx, u64> {
-        self.not_undef()?.to_usize(cx)
-    }
-
-    #[inline(always)]
-    pub fn to_i8(self) -> EvalResult<'tcx, i8> {
-        self.not_undef()?.to_i8()
-    }
-
-    #[inline(always)]
-    pub fn to_i32(self) -> EvalResult<'tcx, i32> {
-        self.not_undef()?.to_i32()
-    }
-
-    #[inline(always)]
-    pub fn to_i64(self) -> EvalResult<'tcx, i64> {
-        self.not_undef()?.to_i64()
-    }
-
-    #[inline(always)]
-    pub fn to_isize(self, cx: impl HasDataLayout) -> EvalResult<'tcx, i64> {
-        self.not_undef()?.to_isize(cx)
-    }
-}

src/librustc/mir/mod.rs

@@ -17,7 +17,7 @@ use hir::def::CtorKind;
 use hir::def_id::DefId;
 use hir::{self, HirId, InlineAsm};
 use middle::region;
-use mir::interpret::{ConstValue, EvalErrorKind, Scalar, ScalarMaybeUndef};
+use mir::interpret::{ConstValue, EvalErrorKind, Scalar};
 use mir::visit::MirVisitable;
 use rustc_apfloat::ieee::{Double, Single};
 use rustc_apfloat::Float;
@@ -2397,7 +2397,7 @@ pub fn fmt_const_val(f: &mut impl Write, const_val: &ty::Const<'_>) -> fmt::Resu
     // print string literals
     if let ConstValue::ScalarPair(ptr, len) = value {
         if let Scalar::Ptr(ptr) = ptr {
-            if let ScalarMaybeUndef::Scalar(Scalar::Bits { bits: len, .. }) = len {
+            if let Scalar::Bits { bits: len, .. } = len {
                 if let Ref(_, &ty::TyS { sty: Str, .. }, _) = ty.sty {
                     return ty::tls::with(|tcx| {
                         let alloc = tcx.alloc_map.lock().get(ptr.alloc_id);

src/librustc_codegen_llvm/mir/operand.rs

@@ -8,9 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use rustc::mir::interpret::ConstEvalErr;
+use rustc::mir::interpret::{ConstValue, ConstEvalErr};
 use rustc::mir;
-use rustc::mir::interpret::{ConstValue, ScalarMaybeUndef};
 use rustc::ty;
 use rustc::ty::layout::{self, Align, LayoutOf, TyLayout};
 use rustc_data_structures::sync::Lrc;
@@ -114,15 +113,12 @@ impl OperandRef<'ll, 'tcx> {
                     layout.scalar_pair_element_llvm_type(bx.cx, 0, true),
                 );
                 let b_layout = layout.scalar_pair_element_llvm_type(bx.cx, 1, true);
-                let b_llval = match b {
-                    ScalarMaybeUndef::Scalar(b) => scalar_to_llvm(
-                        bx.cx,
-                        b,
-                        b_scalar,
-                        b_layout,
-                    ),
-                    ScalarMaybeUndef::Undef => C_undef(b_layout),
-                };
+                let b_llval = scalar_to_llvm(
+                    bx.cx,
+                    b,
+                    b_scalar,
+                    b_layout,
+                );
                 OperandValue::Pair(a_llval, b_llval)
             },
             ConstValue::ByRef(_, alloc, offset) => {

src/librustc_mir/const_eval.rs

@@ -17,7 +17,7 @@ use rustc::hir::{self, def_id::DefId};
 use rustc::mir::interpret::ConstEvalErr;
 use rustc::mir;
 use rustc::ty::{self, TyCtxt, Instance, query::TyCtxtAt};
-use rustc::ty::layout::{LayoutOf, TyLayout};
+use rustc::ty::layout::{self, LayoutOf, TyLayout};
 use rustc::ty::subst::Subst;
 use rustc_data_structures::indexed_vec::IndexVec;
 
@@ -97,8 +97,18 @@ pub(crate) fn eval_promoted<'a, 'mir, 'tcx>(
 pub fn op_to_const<'tcx>(
     ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
     op: OpTy<'tcx>,
-    normalize: bool,
+    may_normalize: bool,
 ) -> EvalResult<'tcx, &'tcx ty::Const<'tcx>> {
+    // We do not normalize just any data.  Only scalar layout and fat pointers.
+    let normalize = may_normalize
+        && match op.layout.abi {
+            layout::Abi::Scalar(..) => true,
+            layout::Abi::ScalarPair(..) => {
+                // Must be a fat pointer
+                op.layout.ty.builtin_deref(true).is_some()
+            },
+            _ => false,
+        };
     let normalized_op = if normalize {
         ecx.try_read_value(op)?
     } else {
@@ -125,7 +135,7 @@ pub fn op_to_const<'tcx>(
         Ok(Value::Scalar(x)) =>
             ConstValue::Scalar(x.not_undef()?),
         Ok(Value::ScalarPair(a, b)) =>
-            ConstValue::ScalarPair(a.not_undef()?, b),
+            ConstValue::ScalarPair(a.not_undef()?, b.not_undef()?),
     };
     Ok(ty::Const::from_const_value(ecx.tcx.tcx, val, op.layout.ty))
 }

src/librustc_mir/hair/pattern/mod.rs

@@ -1124,13 +1124,6 @@ pub fn compare_const_vals<'a, 'tcx>(
                         len_b,
                     ),
                 ) if ptr_a.offset.bytes() == 0 && ptr_b.offset.bytes() == 0 => {
-                    let len_a = len_a.not_undef().ok();
-                    let len_b = len_b.not_undef().ok();
-                    if len_a.is_none() || len_b.is_none() {
-                        tcx.sess.struct_err("str slice len is undef").delay_as_bug();
-                    }
-                    let len_a = len_a?;
-                    let len_b = len_b?;
                     if let Ok(len_a) = len_a.to_bits(tcx.data_layout.pointer_size) {
                         if let Ok(len_b) = len_b.to_bits(tcx.data_layout.pointer_size) {
                             if len_a == len_b {

src/librustc_mir/interpret/eval_context.rs

@@ -25,14 +25,13 @@ use rustc_data_structures::indexed_vec::IndexVec;
 use rustc::mir::interpret::{
     GlobalId, Scalar, FrameInfo, AllocId,
     EvalResult, EvalErrorKind,
-    ScalarMaybeUndef,
     truncate, sign_extend,
 };
 
 use syntax::source_map::{self, Span};
 
 use super::{
-    Value, Operand, MemPlace, MPlaceTy, Place,
+    Value, Operand, MemPlace, MPlaceTy, Place, ScalarMaybeUndef,
     Memory, Machine
 };
 

src/librustc_mir/interpret/memory.rs

@@ -21,15 +21,15 @@ use std::ptr;
 
 use rustc::ty::{self, Instance, query::TyCtxtAt};
 use rustc::ty::layout::{self, Align, TargetDataLayout, Size, HasDataLayout};
-use rustc::mir::interpret::{Pointer, AllocId, Allocation, ConstValue, ScalarMaybeUndef, GlobalId,
+use rustc::mir::interpret::{Pointer, AllocId, Allocation, ConstValue, GlobalId,
                             EvalResult, Scalar, EvalErrorKind, AllocType, PointerArithmetic,
                             truncate};
 pub use rustc::mir::interpret::{write_target_uint, read_target_uint};
 use rustc_data_structures::fx::{FxHashSet, FxHashMap};
 
 use syntax::ast::Mutability;
 
-use super::Machine;
+use super::{Machine, ScalarMaybeUndef};
 
 #[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
 pub enum MemoryKind<T> {

src/librustc_mir/interpret/mod.rs

@@ -34,4 +34,4 @@ pub use self::memory::{Memory, MemoryKind};
 
 pub use self::machine::Machine;
 
-pub use self::operand::{Value, ValTy, Operand, OpTy};
+pub use self::operand::{ScalarMaybeUndef, Value, ValTy, Operand, OpTy};