Question to movsi3.

["Yves Kurz" <yves.kurz@xxxxxxxxx>]

Hello

I am creating a GCC backend for our PLC interpreter. But now I have
run into a problem with the movsi3 instruction.

Our interpreter understands the following instructions:

XLA reg, const_int           reg <- const_int

COPY reg1, reg2            reg2 <- reg1
XST reg1, reg2               store value in reg1 to memory address in reg2
XLD reg1, reg2               load value at address in reg1 into register reg2


In my MD file I implemented it as follows:

(define_memory_constraint "R"
   "An address that can be used for XST/XLD"
   (and (match_code "mem")
      (match_test "GET_CODE (XEXP (op, 0)) == REG"))
)

;;  Move Instructions
(define_expand "movsi"
  [(set (match_operand:SI 0 "nonimmediate_operand" "r,r,R,r")
    (match_operand:SI 1 "general_operand" "r,iF,r,R"))]
  ""
  {
    if (GET_CODE (operands[0]) == MEM && GET_CODE (operands[1]) != REG)
      if (!no_new_pseudos)
        operands[1] = force_reg (SImode, operands[1]);
  }
)

(define_insn "movsi_regs"
  [(set (match_operand:SI 0 "register_operand" "=r, r")
    (match_operand:SI 1 "nonmemory_operand" "r, iF"))]
  ""
  "@
  COPY %1, %0
  XLA %0, %1"
  [(set_attr "length" "2,2")]
)

(define_insn "movsi_load"
  [(set (match_operand:SI 0 "register_operand" "=r")
    (match_operand:SI 1 "memory_operand" "R"))]
  ""
  "XLD %1, %0"
  [(set_attr "length" "2")]
)

(define_insn "movsi_store"
  [(set (match_operand:SI 0 "memory_operand" "=R")
    (match_operand:SI 1 "register_operand" "r"))]
  ""
  "XST %1, %0"
  [(set_attr "length" "2")]
)

This code works if I compile exactly one function in a c source file.
It will not work if i have something like:

extern int  a

void a2 () {
   a = a + a;
}
void aq () {
  a = a * a;
}

The output of function aq is not correct. It is missing the XLA
instruction. It seems to me that the compiler assumes that the
register %1 contains already the address of a. But the code does not
work if first function aq and then a2 is called.

SUB      a2
        XLA  %1, a             ; movsi_regs
        XLD  %1, %0          ; movsi_load
        ADD %0, %0, %0   ; addsi3/1
        XST  %0, %1          ; movsi_store
ENDSUB


SUB aq
        XLD %1, %0          ; movsi_load
        MUL %0, %0, %0  ; mulsi3/1
        XST   %0, %1        ; movsi_store
ENDSUB

Any ideas?

Thank you