ZJIT: Add asm.sub_into helper

Author: st0012

zjit/src/backend/lir.rs

@@ -2233,6 +2233,11 @@ impl Assembler {
         out
     }
 
+    pub fn sub_into(&mut self, left: Opnd, right: Opnd) -> Opnd {
+        self.push_insn(Insn::Sub { left, right, out: left });
+        left
+    }
+
     #[must_use]
     pub fn mul(&mut self, left: Opnd, right: Opnd) -> Opnd {
         let out = self.new_vreg(Opnd::match_num_bits(&[left, right]));

zjit/src/codegen.rs

@@ -1474,8 +1474,7 @@ fn gen_string_concat(jit: &mut JITState, asm: &mut Assembler, strings: Vec<Opnd>
     let allocation_size = aligned_stack_bytes(n);
 
     asm_comment!(asm, "allocate {} bytes on C stack for {} strings", allocation_size, n);
-    let new_sp = asm.sub(NATIVE_STACK_PTR, allocation_size.into());
-    asm.mov(NATIVE_STACK_PTR, new_sp);
+    asm.sub_into(NATIVE_STACK_PTR, allocation_size.into());
 
     // Calculate the total offset from NATIVE_BASE_PTR to our buffer
     let total_offset_from_base = (frame_size + allocation_size) as i32;