RL78 problem with hardware multiplier/divider accumulator in G13 CPUs with GCC compiler V15.01

Question

I have some code in an INTERRUPT service routine that multiplies two 16 bit values into a 32 bit result 
 
 I also have some code in the main loop that multiplies two 16 bit values into a 32 bit result 
 
 Looking at the Interrupt function I see that it uses the Hardware multiplier/divider accumulator to do the grunt work 
 
 Looking at the main loop Code I see that it uses the Hardware multiplier/divider accumulator to do the grunt work

==>> The problem I have noticed is that the main loop sometimes gets wrong results

I am using the GCC Compiler V15.01

Solution 1 ) how to tell the GCC C Compiler to NOT use the Hardware multiplier/divider accumulator in INTERRUPT functions !!!! 
 
 Solution 2) Turn off and back on INTs in the main loop around the Hardware multiplier/divider accumulator code to prevent ISR getting in the middle 
 
 Solution 3) Use a software shift and Add method to do the multiply

My preference is to use Solution 1)

FrankL · Accepted Answer

A third possibility would be to disable interrupts while doing the multiplication. To do this you could pack the call for multiplication in a macro like this: 
 #define MULTIPLY(IN1, IN2, OUT) \ 
 __builtin_rl78_di (); \ 
 OUT = IN1 * IN2; \ 
 __builtin_rl78_ei ();