Auto merge of rust-lang#121926 - tgross35:f16-f128-step3-feature-gate, r=compiler-errors,petrochenkov

`f16` and `f128` step 3: compiler support & feature gate

Continuation of rust-lang#121841, another portion of rust-lang#114607

This PR exposes the new types to the world and adds a feature gate. Marking this as a draft because I need some feedback on where I did the feature gate check. It also does not yet catch type via suffixed literals (so the feature gate test will fail, probably some others too because I haven't belssed).

If there is a better place to check all types after resolution, I can do that. If not, I figure maybe I can add a second gate location in AST when it checks numeric suffixes.

Unfortunately I still don't think there is much testing to be done for correctness (codegen tests or parsed value checks) until we have basic library support. I think that will be the next step.

Tracking issue: rust-lang#116909

r? `@compiler-errors`
cc `@Nilstrieb`
`@rustbot` label +F-f16_and_f128

Author: bors

compiler/rustc_ast/src/util/literal.rs

@@ -276,8 +276,10 @@ fn filtered_float_lit(
         Some(suffix) => LitKind::Float(
             symbol,
             ast::LitFloatType::Suffixed(match suffix {
+                sym::f16 => ast::FloatTy::F16,
                 sym::f32 => ast::FloatTy::F32,
                 sym::f64 => ast::FloatTy::F64,
+                sym::f128 => ast::FloatTy::F128,
                 _ => return Err(LitError::InvalidFloatSuffix(suffix)),
             }),
         ),

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -1,7 +1,7 @@
 use rustc_ast as ast;
 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
 use rustc_ast::{attr, AssocConstraint, AssocConstraintKind, NodeId};
-use rustc_ast::{PatKind, RangeEnd};
+use rustc_ast::{token, PatKind, RangeEnd};
 use rustc_feature::{AttributeGate, BuiltinAttribute, Features, GateIssue, BUILTIN_ATTRIBUTE_MAP};
 use rustc_session::parse::{feature_err, feature_err_issue, feature_warn};
 use rustc_session::Session;
@@ -378,6 +378,17 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             ast::ExprKind::TryBlock(_) => {
                 gate!(&self, try_blocks, e.span, "`try` expression is experimental");
             }
+            ast::ExprKind::Lit(token::Lit { kind: token::LitKind::Float, suffix, .. }) => {
+                match suffix {
+                    Some(sym::f16) => {
+                        gate!(&self, f16, e.span, "the type `f16` is unstable")
+                    }
+                    Some(sym::f128) => {
+                        gate!(&self, f128, e.span, "the type `f128` is unstable")
+                    }
+                    _ => (),
+                }
+            }
             _ => {}
         }
         visit::walk_expr(self, e)

compiler/rustc_feature/src/unstable.rs

@@ -463,6 +463,10 @@ declare_features! (
     (unstable, extended_varargs_abi_support, "1.65.0", Some(100189)),
     /// Allows defining `extern type`s.
     (unstable, extern_types, "1.23.0", Some(43467)),
+    /// Allow using 128-bit (quad precision) floating point numbers.
+    (unstable, f128, "CURRENT_RUSTC_VERSION", Some(116909)),
+    /// Allow using 16-bit (half precision) floating point numbers.
+    (unstable, f16, "CURRENT_RUSTC_VERSION", Some(116909)),
     /// Allows the use of `#[ffi_const]` on foreign functions.
     (unstable, ffi_const, "1.45.0", Some(58328)),
     /// Allows the use of `#[ffi_pure]` on foreign functions.

compiler/rustc_hir/src/hir.rs

@@ -2444,7 +2444,7 @@ pub enum PrimTy {
 
 impl PrimTy {
     /// All of the primitive types
-    pub const ALL: [Self; 17] = [
+    pub const ALL: [Self; 19] = [
         // any changes here should also be reflected in `PrimTy::from_name`
         Self::Int(IntTy::I8),
         Self::Int(IntTy::I16),
@@ -2458,9 +2458,10 @@ impl PrimTy {
         Self::Uint(UintTy::U64),
         Self::Uint(UintTy::U128),
         Self::Uint(UintTy::Usize),
+        Self::Float(FloatTy::F16),
         Self::Float(FloatTy::F32),
         Self::Float(FloatTy::F64),
-        // FIXME(f16_f128): add these when enabled below
+        Self::Float(FloatTy::F128),
         Self::Bool,
         Self::Char,
         Self::Str,
@@ -2508,12 +2509,10 @@ impl PrimTy {
             sym::u64 => Self::Uint(UintTy::U64),
             sym::u128 => Self::Uint(UintTy::U128),
             sym::usize => Self::Uint(UintTy::Usize),
+            sym::f16 => Self::Float(FloatTy::F16),
             sym::f32 => Self::Float(FloatTy::F32),
             sym::f64 => Self::Float(FloatTy::F64),
-            // FIXME(f16_f128): enabling these will open the gates of f16 and f128 being
-            // understood by rustc.
-            // sym::f16 => Self::Float(FloatTy::F16),
-            // sym::f128 => Self::Float(FloatTy::F128),
+            sym::f128 => Self::Float(FloatTy::F128),
             sym::bool => Self::Bool,
             sym::char => Self::Char,
             sym::str => Self::Str,

compiler/rustc_lint/src/types.rs

@@ -561,10 +561,11 @@ fn lint_literal<'tcx>(
         ty::Float(t) => {
             let is_infinite = match lit.node {
                 ast::LitKind::Float(v, _) => match t {
-                    ty::FloatTy::F16 => unimplemented!("f16_f128"),
+                    // FIXME(f16_f128): add this check once we have library support
+                    ty::FloatTy::F16 => Ok(false),
                     ty::FloatTy::F32 => v.as_str().parse().map(f32::is_infinite),
                     ty::FloatTy::F64 => v.as_str().parse().map(f64::is_infinite),
-                    ty::FloatTy::F128 => unimplemented!("f16_f128"),
+                    ty::FloatTy::F128 => Ok(false),
                 },
                 _ => bug!(),
             };

compiler/rustc_middle/src/mir/interpret/value.rs

@@ -3,7 +3,7 @@ use std::fmt;
 use either::{Either, Left, Right};
 
 use rustc_apfloat::{
-    ieee::{Double, Single},
+    ieee::{Double, Half, Quad, Single},
     Float,
 };
 use rustc_macros::HashStable;
@@ -201,6 +201,11 @@ impl<Prov> Scalar<Prov> {
         Self::from_int(i, cx.data_layout().pointer_size)
     }
 
+    #[inline]
+    pub fn from_f16(f: Half) -> Self {
+        Scalar::Int(f.into())
+    }
+
     #[inline]
     pub fn from_f32(f: Single) -> Self {
         Scalar::Int(f.into())
@@ -211,6 +216,11 @@ impl<Prov> Scalar<Prov> {
         Scalar::Int(f.into())
     }
 
+    #[inline]
+    pub fn from_f128(f: Quad) -> Self {
+        Scalar::Int(f.into())
+    }
+
     /// This is almost certainly not the method you want!  You should dispatch on the type
     /// and use `to_{u8,u16,...}`/`scalar_to_ptr` to perform ptr-to-int / int-to-ptr casts as needed.
     ///
@@ -422,6 +432,11 @@ impl<'tcx, Prov: Provenance> Scalar<Prov> {
         Ok(F::from_bits(self.to_bits(Size::from_bits(F::BITS))?))
     }
 
+    #[inline]
+    pub fn to_f16(self) -> InterpResult<'tcx, Half> {
+        self.to_float()
+    }
+
     #[inline]
     pub fn to_f32(self) -> InterpResult<'tcx, Single> {
         self.to_float()
@@ -431,4 +446,9 @@ impl<'tcx, Prov: Provenance> Scalar<Prov> {
     pub fn to_f64(self) -> InterpResult<'tcx, Double> {
         self.to_float()
     }
+
+    #[inline]
+    pub fn to_f128(self) -> InterpResult<'tcx, Quad> {
+        self.to_float()
+    }
 }

compiler/rustc_middle/src/ty/consts/int.rs

@@ -1,4 +1,4 @@
-use rustc_apfloat::ieee::{Double, Single};
+use rustc_apfloat::ieee::{Double, Half, Quad, Single};
 use rustc_apfloat::Float;
 use rustc_errors::{DiagArgValue, IntoDiagArg};
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
@@ -369,6 +369,11 @@ impl ScalarInt {
         Ok(F::from_bits(self.to_bits(Size::from_bits(F::BITS))?))
     }
 
+    #[inline]
+    pub fn try_to_f16(self) -> Result<Half, Size> {
+        self.try_to_float()
+    }
+
     #[inline]
     pub fn try_to_f32(self) -> Result<Single, Size> {
         self.try_to_float()
@@ -378,6 +383,11 @@ impl ScalarInt {
     pub fn try_to_f64(self) -> Result<Double, Size> {
         self.try_to_float()
     }
+
+    #[inline]
+    pub fn try_to_f128(self) -> Result<Quad, Size> {
+        self.try_to_float()
+    }
 }
 
 macro_rules! from {
@@ -450,6 +460,22 @@ impl TryFrom<ScalarInt> for char {
     }
 }
 
+impl From<Half> for ScalarInt {
+    #[inline]
+    fn from(f: Half) -> Self {
+        // We trust apfloat to give us properly truncated data.
+        Self { data: f.to_bits(), size: NonZero::new((Half::BITS / 8) as u8).unwrap() }
+    }
+}
+
+impl TryFrom<ScalarInt> for Half {
+    type Error = Size;
+    #[inline]
+    fn try_from(int: ScalarInt) -> Result<Self, Size> {
+        int.to_bits(Size::from_bytes(2)).map(Self::from_bits)
+    }
+}
+
 impl From<Single> for ScalarInt {
     #[inline]
     fn from(f: Single) -> Self {
@@ -482,6 +508,22 @@ impl TryFrom<ScalarInt> for Double {
     }
 }
 
+impl From<Quad> for ScalarInt {
+    #[inline]
+    fn from(f: Quad) -> Self {
+        // We trust apfloat to give us properly truncated data.
+        Self { data: f.to_bits(), size: NonZero::new((Quad::BITS / 8) as u8).unwrap() }
+    }
+}
+
+impl TryFrom<ScalarInt> for Quad {
+    type Error = Size;
+    #[inline]
+    fn try_from(int: ScalarInt) -> Result<Self, Size> {
+        int.to_bits(Size::from_bytes(16)).map(Self::from_bits)
+    }
+}
+
 impl fmt::Debug for ScalarInt {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         // Dispatch to LowerHex below.

compiler/rustc_mir_build/src/build/mod.rs

@@ -1,7 +1,7 @@
 use crate::build::expr::as_place::PlaceBuilder;
 use crate::build::scope::DropKind;
 use itertools::Itertools;
-use rustc_apfloat::ieee::{Double, Single};
+use rustc_apfloat::ieee::{Double, Half, Quad, Single};
 use rustc_apfloat::Float;
 use rustc_ast::attr;
 use rustc_data_structures::fx::FxHashMap;
@@ -1060,7 +1060,8 @@ pub(crate) fn parse_float_into_scalar(
 ) -> Option<Scalar> {
     let num = num.as_str();
     match float_ty {
-        ty::FloatTy::F16 => unimplemented!("f16_f128"),
+        // FIXME(f16_f128): When available, compare to the library parser as with `f32` and `f64`
+        ty::FloatTy::F16 => num.parse::<Half>().ok().map(Scalar::from_f16),
         ty::FloatTy::F32 => {
             let Ok(rust_f) = num.parse::<f32>() else { return None };
             let mut f = num
@@ -1107,7 +1108,8 @@ pub(crate) fn parse_float_into_scalar(
 
             Some(Scalar::from_f64(f))
         }
-        ty::FloatTy::F128 => unimplemented!("f16_f128"),
+        // FIXME(f16_f128): When available, compare to the library parser as with `f32` and `f64`
+        ty::FloatTy::F128 => num.parse::<Quad>().ok().map(Scalar::from_f128),
     }
 }
 

compiler/rustc_resolve/src/ident.rs

@@ -5,8 +5,10 @@ use rustc_middle::bug;
 use rustc_middle::ty;
 use rustc_session::lint::builtin::PROC_MACRO_DERIVE_RESOLUTION_FALLBACK;
 use rustc_session::lint::BuiltinLintDiag;
+use rustc_session::parse::feature_err;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::hygiene::{ExpnId, ExpnKind, LocalExpnId, MacroKind, SyntaxContext};
+use rustc_span::sym;
 use rustc_span::symbol::{kw, Ident};
 use rustc_span::Span;
 
@@ -598,7 +600,35 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                         result
                     }
                     Scope::BuiltinTypes => match this.builtin_types_bindings.get(&ident.name) {
-                        Some(binding) => Ok((*binding, Flags::empty())),
+                        Some(binding) => {
+                            if matches!(ident.name, sym::f16)
+                                && !this.tcx.features().f16
+                                && !ident.span.allows_unstable(sym::f16)
+                                && finalize.is_some()
+                            {
+                                feature_err(
+                                    this.tcx.sess,
+                                    sym::f16,
+                                    ident.span,
+                                    "the type `f16` is unstable",
+                                )
+                                .emit();
+                            }
+                            if matches!(ident.name, sym::f128)
+                                && !this.tcx.features().f128
+                                && !ident.span.allows_unstable(sym::f128)
+                                && finalize.is_some()
+                            {
+                                feature_err(
+                                    this.tcx.sess,
+                                    sym::f128,
+                                    ident.span,
+                                    "the type `f128` is unstable",
+                                )
+                                .emit();
+                            }
+                            Ok((*binding, Flags::empty()))
+                        }
                         None => Err(Determinacy::Determined),
                     },
                 };

compiler/rustc_resolve/src/late.rs

@@ -27,6 +27,7 @@ use rustc_middle::middle::resolve_bound_vars::Set1;
 use rustc_middle::{bug, span_bug};
 use rustc_session::config::{CrateType, ResolveDocLinks};
 use rustc_session::lint;
+use rustc_session::parse::feature_err;
 use rustc_span::source_map::{respan, Spanned};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{BytePos, Span, SyntaxContext};
@@ -4138,6 +4139,25 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
                     && PrimTy::from_name(path[0].ident.name).is_some() =>
             {
                 let prim = PrimTy::from_name(path[0].ident.name).unwrap();
+                let tcx = self.r.tcx();
+
+                let gate_err_sym_msg = match prim {
+                    PrimTy::Float(FloatTy::F16) if !tcx.features().f16 => {
+                        Some((sym::f16, "the type `f16` is unstable"))
+                    }
+                    PrimTy::Float(FloatTy::F128) if !tcx.features().f128 => {
+                        Some((sym::f128, "the type `f128` is unstable"))
+                    }
+                    _ => None,
+                };
+
+                if let Some((sym, msg)) = gate_err_sym_msg {
+                    let span = path[0].ident.span;
+                    if !span.allows_unstable(sym) {
+                        feature_err(tcx.sess, sym, span, msg).emit();
+                    }
+                };
+
                 PartialRes::with_unresolved_segments(Res::PrimTy(prim), path.len() - 1)
             }
             PathResult::Module(ModuleOrUniformRoot::Module(module)) => {