machinst: make get_output_reg target independent;

cranelift/codegen/src/machinst/helpers.rs

@@ -1,6 +1,8 @@
 //! Miscellaneous helpers for machine backends.
 
+use super::{InsnOutput, LowerCtx, VCodeInst};
 use crate::ir::Type;
+use regalloc::{Reg, Writable};
 
 /// Returns the size (in bits) of a given type.
 pub fn ty_bits(ty: Type) -> usize {
@@ -16,3 +18,11 @@ pub(crate) fn ty_has_int_representation(ty: Type) -> bool {
 pub(crate) fn ty_has_float_or_vec_representation(ty: Type) -> bool {
     ty.is_vector() || ty.is_float()
 }
+
+/// Allocate a register for an instruction output and return it.
+pub(crate) fn get_output_reg<I: VCodeInst, C: LowerCtx<I = I>>(
+    ctx: &mut C,
+    spec: InsnOutput,
+) -> Writable<Reg> {
+    ctx.get_output(spec.insn, spec.output)
+}