Enable f16 in assembly on aarch64 platforms that support it

Signed-off-by: rongfu.leng <[email protected]>

Author: lengrongfu

Diff for: compiler/rustc_target/src/asm/aarch64.rs

@@ -59,9 +59,9 @@ impl AArch64InlineAsmRegClass {
         match self {
             Self::reg => types! { _: I8, I16, I32, I64, F32, F64; },
             Self::vreg | Self::vreg_low16 => types! {
-                neon: I8, I16, I32, I64, F32, F64,
+                neon: I8, I16, I32, I64, F16, F32, F64,
                     VecI8(8), VecI16(4), VecI32(2), VecI64(1), VecF32(2), VecF64(1),
-                    VecI8(16), VecI16(8), VecI32(4), VecI64(2), VecF32(4), VecF64(2);
+                    VecI8(16), VecI16(8), VecI32(4), VecI64(2), VecF16(4),VecF16(8),VecF32(4), VecF64(2);
             },
             Self::preg => &[],
         }

Diff for: library/backtrace

@@ -111,7 +111,7 @@ error: type `Simd256bit` cannot be used with this register class
 LL |         asm!("{}", in(vreg) f64x4);
    |                             ^^^^^
    |
-   = note: register class `vreg` supports these types: i8, i16, i32, i64, f32, f64, i8x8, i16x4, i32x2, i64x1, f32x2, f64x1, i8x16, i16x8, i32x4, i64x2, f32x4, f64x2
+   = note: register class `vreg` supports these types: i8, i16, i32, i64, f16, f32, f64, i8x8, i16x4, i32x2, i64x1, f32x2, f64x1, i8x16, i16x8, i32x4, i64x2, f16x4, f16x8, f32x4, f64x2
 
 error: incompatible types for asm inout argument
   --> $DIR/type-check-3.rs:88:33

Diff for: src/doc/book

@@ -0,0 +1,21 @@
+//@ only-aarch64
+//@ run-pass
+
+#![feature(f16, f128)]
+use std::arch::asm;
+#[inline(never)]
+pub fn f32_to_f16_asm(a: f32) -> f16 {
+    let ret: f16;
+    unsafe {
+        asm!(
+        "fcvt    {ret:h}, {a:s}",
+        a = in(vreg) a,
+        ret = lateout(vreg) ret,
+        options(nomem, nostack),
+        );
+    }
+    ret
+}
+fn main() {
+    assert_eq!(f32_to_f16_asm(1.0 as f32), 1.0);
+}