Conditional expression compiler bug?

[hrvojeerjavec]

Hello,

I am using S32 design studio for power architecture with MPC5744P and I have been using the conditional statements.

The shortened code looks like this:

// variable declaration for the sake of type insight

float dutyCycle;

vuint16_t a, b, c;

uint16_t inv = FALSE;

//assign a value to variable a

a = (pSub->VAL1.R * dutyCycle);

//assign a value to variable b
b = (-((int16_t)(pSub->VAL1.R * dutyCycle)));

//assign a value to variable c using a and b -> correct value
c = (inv) ? a : b;

//assign a value to variable c using statements used for assigning a and b

//-> incorrectly returns 0
c = (inv) ? (pSub->VAL1.R * dutyCycle) : (-((int16_t)(pSub->VAL1.R * dutyCycle)));

The c variable will be assigned correctly when using a and b variables, but will be 0 if the values are entered directly in the conditional expression.

Do you know what this could be about?

[martin_kovar]

Hi,

could you please create some simple working example, which demonstrates your issue and post it here? From the source code you shared, it is difficult to reproduce you issue, because I have to check assembly code in debugger.

Could you please also write me, which version of S32 Design Studio you use (1.0 or 1.1)?

Regards,

Martin

[hrvojeerjavec]

I have been using the S32 Design Studio 1.1. This is a working example that is showing the misbehavior:

typedef                   short   int16_t;
typedef          unsigned short  uint16_t;
typedef volatile unsigned short vuint16_t;
int main(void) {
    float dutyCycle = 0.2f;
    vuint16_t val1 = 8000;
    vuint16_t a, b, c;
    uint16_t inv = 0;
    for(;;) {
        //assign a value to variable a
        a = (val1 * dutyCycle);
        //assign a value to variable b
        b = (-((int16_t)(val1 * dutyCycle)));
        //assign a value to variable c using a and b -> correct value
        c = (inv) ? a : b;
        //assign a value to variable c using statements used for assigning a and b
        //-> incorrectly returns 0
        c = (inv) ? (val1 * dutyCycle) : (-((int16_t)(val1 * dutyCycle)));
        /* Loop forever */
    }
}‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

[stanish]

Hello,

I'd recommend not to rely on implicit integer conversion here.

Could you try to cast the operands explicitly:

(vuint16_t)(-((int16_t)(val1 * dutyCycle)));

I have seen different results on different compilers (GHS vs. IAR vs. GCC,...).

hope it helps 

Stan

[hrvojeerjavec]

Thank you, this does give the correct result, although I would like to be able to rely on implicit integer conversion.

Seems it wasn't a problem in all other cases.

[martin_kovar]

Hi,

I consulted your use case with my colleague, who is compiler expert and it seems it is really compiler bug. So I reported it and I hope it will be fixed soon.

Regards,

Martin