Treat f16 as a u16 in ABI

Author: cijiugechu

src/abi.rs

@@ -86,6 +86,7 @@ impl GccType for Reg {
         match self.kind {
             RegKind::Integer => cx.type_ix(self.size.bits()),
             RegKind::Float => match self.size.bits() {
+                16 => cx.type_f16_for_abi(),
                 32 => cx.type_f32(),
                 64 => cx.type_f64(),
                 _ => bug!("unsupported float: {:?}", self),

src/type_.rs

@@ -97,6 +97,14 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
         }
     }
 
+    pub fn type_f16_for_abi(&self) -> Type<'gcc> {
+        #[cfg(feature = "master")]
+        if self.supports_f16_type {
+            return self.type_f16();
+        }
+        self.type_u16()
+    }
+
     pub fn type_i1(&self) -> Type<'gcc> {
         self.bool_type
     }

src/type_of.rs

@@ -285,6 +285,7 @@ impl<'tcx> LayoutGccExt<'tcx> for TyAndLayout<'tcx> {
         match scalar.primitive() {
             Int(i, true) => cx.type_from_integer(i),
             Int(i, false) => cx.type_from_unsigned_integer(i),
+            Float(abi::Float::F16) => cx.type_f16_for_abi(),
             Float(f) => cx.type_from_float(f),
             Pointer(address_space) => {
                 // If we know the alignment, pick something better than i8.

tests/compile/f16-abi.rs

@@ -0,0 +1,9 @@
+// Compiler:
+
+#![crate_type = "lib"]
+#![feature(f16)]
+
+#[unsafe(no_mangle)]
+pub extern "C" fn f16_identity(a: f16) -> f16 {
+    a
+}