Replace MachInst::gen_zero_len_nop with gen_nop(0)

cranelift/codegen/src/machinst/mod.rs

@@ -148,9 +148,6 @@ pub trait MachInst: Clone + Debug {
         alloc_tmp: F,
     ) -> SmallVec<[Self; 4]>;
 
-    /// Generate a zero-length no-op.
-    fn gen_zero_len_nop() -> Self;
-
     /// Possibly operate on a value directly in a spill-slot rather than a
     /// register. Useful if the machine has register-memory instruction forms
     /// (e.g., add directly from or directly to memory), like x86.

cranelift/codegen/src/machinst/vcode.rs

@@ -726,7 +726,7 @@ impl<I: VCodeInst> RegallocFunction for VCode<I> {
     }
 
     fn gen_zero_len_nop(&self) -> I {
-        I::gen_zero_len_nop()
+        I::gen_nop(0)
     }
 
     fn maybe_direct_reload(&self, insn: &I, reg: VirtualReg, slot: SpillSlot) -> Option<I> {