Enable const evaluation for f16 and f128

This excludes casting, which needs more tests.

Author: tgross35

compiler/rustc_const_eval/src/interpret/operator.rs

@@ -362,14 +362,18 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 let left = left.to_scalar();
                 let right = right.to_scalar();
                 Ok(match fty {
-                    FloatTy::F16 => unimplemented!("f16_f128"),
+                    FloatTy::F16 => {
+                        self.binary_float_op(bin_op, layout, left.to_f16()?, right.to_f16()?)
+                    }
                     FloatTy::F32 => {
                         self.binary_float_op(bin_op, layout, left.to_f32()?, right.to_f32()?)
                     }
                     FloatTy::F64 => {
                         self.binary_float_op(bin_op, layout, left.to_f64()?, right.to_f64()?)
                     }
-                    FloatTy::F128 => unimplemented!("f16_f128"),
+                    FloatTy::F128 => {
+                        self.binary_float_op(bin_op, layout, left.to_f128()?, right.to_f128()?)
+                    }
                 })
             }
             _ if left.layout.ty.is_integral() => {
@@ -431,8 +435,10 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 let val = val.to_scalar();
                 // No NaN adjustment here, `-` is a bitwise operation!
                 let res = match (un_op, fty) {
+                    (Neg, FloatTy::F16) => Scalar::from_f16(-val.to_f16()?),
                     (Neg, FloatTy::F32) => Scalar::from_f32(-val.to_f32()?),
                     (Neg, FloatTy::F64) => Scalar::from_f64(-val.to_f64()?),
+                    (Neg, FloatTy::F128) => Scalar::from_f128(-val.to_f128()?),
                     _ => span_bug!(self.cur_span(), "Invalid float op {:?}", un_op),
                 };
                 Ok(ImmTy::from_scalar(res, layout))

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

@@ -69,6 +69,13 @@ impl<Prov: Provenance> fmt::LowerHex for Scalar<Prov> {
     }
 }
 
+impl<Prov> From<Half> for Scalar<Prov> {
+    #[inline(always)]
+    fn from(f: Half) -> Self {
+        Scalar::from_f16(f)
+    }
+}
+
 impl<Prov> From<Single> for Scalar<Prov> {
     #[inline(always)]
     fn from(f: Single) -> Self {
@@ -83,6 +90,13 @@ impl<Prov> From<Double> for Scalar<Prov> {
     }
 }
 
+impl<Prov> From<Quad> for Scalar<Prov> {
+    #[inline(always)]
+    fn from(f: Quad) -> Self {
+        Scalar::from_f128(f)
+    }
+}
+
 impl<Prov> From<ScalarInt> for Scalar<Prov> {
     #[inline(always)]
     fn from(ptr: ScalarInt) -> Self {