std function call destroys the stack

[shhyou]

In computation, intermediate results are kept on the stack, yet standard function calls assume space for arguments be reserved on the stack.

puts(printf("OK"))
; => OK2

However,

puts(1 +  printf("OK"))
; => ?

[jserv]

At present, rubi lacks of appropriate calling convention. @suhorng, would you like to revise the existing design? I assume the compatibility of Ruby.

[shhyou]

Actually, that Rubi pushes its argument from left to right is fine and consistent. It's the intermix of standard library function calls (back into C) that mess up the stack. I'm not sure to what degree are we to refine Rubi prototype? The simplest way would be excluding standard function calls from expressions and regarding them as statements in Rubi syntax. Otherwise, we could change std function calls to

+ | sub esp, sizeof(int32_t)*5
  do {
    relExpr();
    | mov [esp + a], eax
    a += 4;
  } while (skip(','));
  | call dword [esi + offset]
+ | add esp, sizeof(int32_t)*5

Adapting Rubi functions to C calling conventions would have similar effect. Their argument counts are known anyway.

I can't think of a simple way to support variadic functions though. Either swaping arguments on the stack after all of them have been evaluated or counting argument number prior to code gen would be a little mess.

[jserv]

@suhorng :
For former Ruby, there is a package named after ffi to perform C calling convention over existing libraries. However, we don't really need similar mechanisms for rubi since only essential function calls should be supported at the moment. I would defer to your proposed prototype changes for further compatibility.