add memset const and dynamic support for f16

Author: 39ali

crates/rustc_codegen_spirv/src/builder/builder_methods.rs

@@ -407,6 +407,11 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 )),
             },
             SpirvType::Float(width) => match width {
+                16 => {
+                    let ty = SpirvType::Float(16).def(self.span(), self);
+                    self.def_constant(ty, SpirvConst::Scalar(memset_fill_u16(fill_byte) as u128))
+                        .def(self)
+                }
                 32 => self
                     .constant_f32(self.span(), f32::from_bits(memset_fill_u32(fill_byte)))
                     .def(self),
@@ -461,6 +466,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 )),
             },
             SpirvType::Float(width) => match width {
+                16 => memset_dynamic_scalar(self, fill_var, 2, true),
                 32 => memset_dynamic_scalar(self, fill_var, 4, true),
                 64 => memset_dynamic_scalar(self, fill_var, 8, true),
                 _ => self.fatal(format!("memset on float width {width} not implemented yet")),
@@ -2425,6 +2431,22 @@ impl<'a, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'tcx> {
         };
         let dest_pointee_size = self.lookup_type(dest_pointee).sizeof(self);
 
+        // Casting to a pointer-to-ZST (e.g. `*f16 -> *()`) is a no-op from a
+        // memory standpoint: ZSTs have no fields and can never be loaded or
+        // stored. The only real use is address-level queries (null / alignment
+        // checks inside `ub_checks::assert_unsafe_precondition!`) which cannot
+        // be expressed in SPIR-V logical addressing anyway. Emit the bitcast
+        // directly without a `LogicalPtrCast` zombie so that UB-check
+        // boilerplate in the standard library doesn't produce spurious errors.
+        if dest_pointee_size == Some(Size::ZERO) {
+            let original_ptr = ptr.def(self);
+            return self
+                .emit()
+                .bitcast(dest_ty, None, original_ptr)
+                .unwrap()
+                .with_type(dest_ty);
+        }
+
         if let Some((indices, _)) = self.recover_access_chain_from_offset(
             ptr_pointee,
             Size::ZERO,