Auto merge of rust-lang#74202 - oli-obk:mir_const, r=RalfJung

Reduce the amount of interning and `layout_of` calls in const eval.

r? @ghost

If we just want to get at some bits of a constant, we don't need to intern it before extracting those bits.
Also, if we want to read a `usize` or `bool`, we can fetch the size without invoking a query.

Author: bors

src/librustc_middle/mir/interpret/value.rs

@@ -60,6 +60,18 @@ impl<'tcx> ConstValue<'tcx> {
         self.try_to_scalar()?.to_bits(size).ok()
     }
 
+    pub fn try_to_bool(&self) -> Option<bool> {
+        match self.try_to_bits(Size::from_bytes(1))? {
+            0 => Some(false),
+            1 => Some(true),
+            _ => None,
+        }
+    }
+
+    pub fn try_to_machine_usize(&self, tcx: TyCtxt<'tcx>) -> Option<u64> {
+        Some(self.try_to_bits(tcx.data_layout.pointer_size)? as u64)
+    }
+
     pub fn try_to_bits_for_ty(
         &self,
         tcx: TyCtxt<'tcx>,

src/librustc_middle/ty/consts.rs

@@ -1,111 +1,203 @@
-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,
+use crate::mir::interpret::ConstValue;
+use crate::mir::interpret::{LitToConstInput, Scalar};
+use crate::ty::subst::InternalSubsts;
+use crate::ty::{self, Ty, TyCtxt};
+use crate::ty::{ParamEnv, ParamEnvAnd};
+use rustc_errors::ErrorReported;
+use rustc_hir as hir;
+use rustc_hir::def_id::LocalDefId;
+use rustc_macros::HashStable;
+
+mod int;
+mod kind;
+
+pub use int::*;
+pub use kind::*;
+
+/// Typed constant value.
+#[derive(Copy, Clone, Debug, Hash, RustcEncodable, RustcDecodable, Eq, PartialEq, Ord, PartialOrd)]
+#[derive(HashStable)]
+pub struct Const<'tcx> {
+    pub ty: Ty<'tcx>,
+
+    pub val: ConstKind<'tcx>,
 }
 
-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 }
+#[cfg(target_arch = "x86_64")]
+static_assert_size!(Const<'_>, 48);
+
+impl<'tcx> Const<'tcx> {
+    /// Literals and const generic parameters are eagerly converted to a constant, everything else
+    /// becomes `Unevaluated`.
+    pub fn from_anon_const(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx Self {
+        Self::from_opt_const_arg_anon_const(tcx, ty::WithOptConstParam::unknown(def_id))
     }
-}
 
-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),
+    pub fn from_opt_const_arg_anon_const(
+        tcx: TyCtxt<'tcx>,
+        def: ty::WithOptConstParam<LocalDefId>,
+    ) -> &'tcx Self {
+        debug!("Const::from_anon_const(def={:?})", def);
+
+        let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
+
+        let body_id = match tcx.hir().get(hir_id) {
+            hir::Node::AnonConst(ac) => ac.body,
+            _ => span_bug!(
+                tcx.def_span(def.did.to_def_id()),
+                "from_anon_const can only process anonymous constants"
+            ),
+        };
+
+        let expr = &tcx.hir().body(body_id).value;
+
+        let ty = tcx.type_of(def.def_id_for_type_of());
+
+        let lit_input = match expr.kind {
+            hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
+            hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => match expr.kind {
+                hir::ExprKind::Lit(ref lit) => {
+                    Some(LitToConstInput { lit: &lit.node, ty, neg: true })
                 }
+                _ => None,
+            },
+            _ => None,
+        };
+
+        if let Some(lit_input) = lit_input {
+            // If an error occurred, ignore that it's a literal and leave reporting the error up to
+            // mir.
+            if let Ok(c) = tcx.at(expr.span).lit_to_const(lit_input) {
+                return c;
             } 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(())
+                tcx.sess.delay_span_bug(expr.span, "Const::from_anon_const: couldn't lit_to_const");
             }
-        } 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(())
+        }
+
+        // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
+        // currently have to be wrapped in curly brackets, so it's necessary to special-case.
+        let expr = match &expr.kind {
+            hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
+                block.expr.as_ref().unwrap()
+            }
+            _ => expr,
+        };
+
+        use hir::{def::DefKind::ConstParam, def::Res, ExprKind, Path, QPath};
+        let val = match expr.kind {
+            ExprKind::Path(QPath::Resolved(_, &Path { res: Res::Def(ConstParam, def_id), .. })) => {
+                // Find the name and index of the const parameter by indexing the generics of
+                // the parent item and construct a `ParamConst`.
+                let hir_id = tcx.hir().as_local_hir_id(def_id.expect_local());
+                let item_id = tcx.hir().get_parent_node(hir_id);
+                let item_def_id = tcx.hir().local_def_id(item_id);
+                let generics = tcx.generics_of(item_def_id.to_def_id());
+                let index =
+                    generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id).to_def_id()];
+                let name = tcx.hir().name(hir_id);
+                ty::ConstKind::Param(ty::ParamConst::new(index, name))
             }
+            _ => ty::ConstKind::Unevaluated(
+                def.to_global(),
+                InternalSubsts::identity_for_item(tcx, def.did.to_def_id()),
+                None,
+            ),
+        };
+
+        tcx.mk_const(ty::Const { val, ty })
+    }
+
+    #[inline]
+    /// Interns the given value as a constant.
+    pub fn from_value(tcx: TyCtxt<'tcx>, val: ConstValue<'tcx>, ty: Ty<'tcx>) -> &'tcx Self {
+        tcx.mk_const(Self { val: ConstKind::Value(val), ty })
+    }
+
+    #[inline]
+    /// Interns the given scalar as a constant.
+    pub fn from_scalar(tcx: TyCtxt<'tcx>, val: Scalar, ty: Ty<'tcx>) -> &'tcx Self {
+        Self::from_value(tcx, ConstValue::Scalar(val), ty)
+    }
+
+    #[inline]
+    /// Creates a constant with the given integer value and interns it.
+    pub fn from_bits(tcx: TyCtxt<'tcx>, bits: u128, ty: ParamEnvAnd<'tcx, Ty<'tcx>>) -> &'tcx Self {
+        let size = tcx
+            .layout_of(ty)
+            .unwrap_or_else(|e| panic!("could not compute layout for {:?}: {:?}", ty, e))
+            .size;
+        Self::from_scalar(tcx, Scalar::from_uint(bits, size), ty.value)
+    }
+
+    #[inline]
+    /// Creates an interned zst constant.
+    pub fn zero_sized(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> &'tcx Self {
+        Self::from_scalar(tcx, Scalar::zst(), ty)
+    }
+
+    #[inline]
+    /// Creates an interned bool constant.
+    pub fn from_bool(tcx: TyCtxt<'tcx>, v: bool) -> &'tcx Self {
+        Self::from_bits(tcx, v as u128, ParamEnv::empty().and(tcx.types.bool))
+    }
+
+    #[inline]
+    /// Creates an interned usize constant.
+    pub fn from_usize(tcx: TyCtxt<'tcx>, n: u64) -> &'tcx Self {
+        Self::from_bits(tcx, n as u128, ParamEnv::empty().and(tcx.types.usize))
+    }
+
+    #[inline]
+    /// Attempts to evaluate the given constant to bits. Can fail to evaluate in the presence of
+    /// generics (or erroneous code) or if the value can't be represented as bits (e.g. because it
+    /// contains const generic parameters or pointers).
+    pub fn try_eval_bits(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        param_env: ParamEnv<'tcx>,
+        ty: Ty<'tcx>,
+    ) -> Option<u128> {
+        assert_eq!(self.ty, ty);
+        let size = tcx.layout_of(param_env.with_reveal_all().and(ty)).ok()?.size;
+        // if `ty` does not depend on generic parameters, use an empty param_env
+        self.val.eval(tcx, param_env).try_to_bits(size)
+    }
+
+    #[inline]
+    pub fn try_eval_bool(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<bool> {
+        self.val.eval(tcx, param_env).try_to_bool()
+    }
+
+    #[inline]
+    pub fn try_eval_usize(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Option<u64> {
+        self.val.eval(tcx, param_env).try_to_machine_usize(tcx)
+    }
+
+    #[inline]
+    /// Tries to evaluate the constant if it is `Unevaluated`. If that doesn't succeed, return the
+    /// unevaluated constant.
+    pub fn eval(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> &Const<'tcx> {
+        if let Some(val) = self.val.try_eval(tcx, param_env) {
+            match val {
+                Ok(val) => Const::from_value(tcx, val, self.ty),
+                Err(ErrorReported) => tcx.const_error(self.ty),
+            }
+        } else {
+            self
         }
     }
+
+    #[inline]
+    /// Panics if the value cannot be evaluated or doesn't contain a valid integer of the given type.
+    pub fn eval_bits(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: Ty<'tcx>) -> u128 {
+        self.try_eval_bits(tcx, param_env, ty)
+            .unwrap_or_else(|| bug!("expected bits of {:#?}, got {:#?}", ty, self))
+    }
+
+    #[inline]
+    /// Panics if the value cannot be evaluated or doesn't contain a valid `usize`.
+    pub fn eval_usize(&self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> u64 {
+        self.try_eval_usize(tcx, param_env)
+            .unwrap_or_else(|| bug!("expected usize, got {:#?}", self))
+    }
 }