machinst x64: add more FP support

cranelift/codegen/src/isa/aarch64/inst/mod.rs

@@ -2065,7 +2065,12 @@ impl MachInst for Inst {
         Inst::mov(to_reg, from_reg)
     }
 
-    fn gen_constant(to_reg: Writable<Reg>, value: u64, ty: Type) -> SmallVec<[Inst; 4]> {
+    fn gen_constant<F: FnMut(RegClass, Type) -> Writable<Reg>>(
+        to_reg: Writable<Reg>,
+        value: u64,
+        ty: Type,
+        _alloc_tmp: F,
+    ) -> SmallVec<[Inst; 4]> {
         if ty == F64 {
             let mut ret = SmallVec::new();
             ret.push(Inst::load_fp_constant64(to_reg, f64::from_bits(value)));

cranelift/codegen/src/isa/aarch64/lower.rs

@@ -219,7 +219,11 @@ pub(crate) fn put_input_in_reg<C: LowerCtx<I = Inst>>(
         };
         // Generate constants fresh at each use to minimize long-range register pressure.
         let to_reg = ctx.alloc_tmp(Inst::rc_for_type(ty).unwrap(), ty);
-        for inst in Inst::gen_constant(to_reg, masked, ty).into_iter() {
+        for inst in Inst::gen_constant(to_reg, masked, ty, |reg_class, ty| {
+            ctx.alloc_tmp(reg_class, ty)
+        })
+        .into_iter()
+        {
             ctx.emit(inst);
         }
         to_reg.to_reg()