fix spill code

Author: tenderlove

zjit/src/backend/arm64/mod.rs

@@ -699,12 +699,14 @@ impl Assembler {
         }
 
         /// split_stack_membase but without split_large_disp. This should be used only by lea.
-        fn split_only_stack_membase(asm: &mut Assembler, opnd: Opnd, scratch_opnd: Opnd, stack_state: &StackState) -> Opnd {
+        fn split_only_stack_membase(_asm: &mut Assembler, opnd: Opnd, _scratch_opnd: Opnd, stack_state: &StackState) -> Opnd {
             if let Opnd::Mem(Mem { base: stack_membase @ MemBase::Stack { .. }, disp: opnd_disp, num_bits: opnd_num_bits }) = opnd {
-                let base = Opnd::Mem(stack_state.stack_membase_to_mem(stack_membase));
-                let base = split_large_disp(asm, base, scratch_opnd);
-                asm.load_into(scratch_opnd, base);
-                Opnd::Mem(Mem { base: MemBase::Reg(scratch_opnd.unwrap_reg().reg_no), disp: opnd_disp, num_bits: opnd_num_bits })
+                // Convert MemBase::Stack to MemBase::Reg(NATIVE_BASE_PTR) with the
+                // correct stack displacement. The stack slot value lives directly at
+                // [NATIVE_BASE_PTR + stack_disp], so we just adjust the base and
+                // combine displacements — no indirection needed.
+                let Mem { base, disp: stack_disp, .. } = stack_state.stack_membase_to_mem(stack_membase);
+                Opnd::Mem(Mem { base, disp: stack_disp + opnd_disp, num_bits: opnd_num_bits })
             } else {
                 opnd
             }