machinst x64: generate copies of constants during lowering;

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

@@ -185,12 +185,12 @@ pub(crate) fn put_input_in_reg<C: LowerCtx<I = Inst>>(
     let from_bits = ty_bits(ty) as u8;
     let inputs = ctx.get_input(input.insn, input.input);
     let in_reg = if let Some(c) = inputs.constant {
+        // Generate constants fresh at each use to minimize long-range register pressure.
         let masked = if from_bits < 64 {
             c & ((1u64 << from_bits) - 1)
         } else {
             c
         };
-        // 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, |reg_class, ty| {
             ctx.alloc_tmp(reg_class, ty)