c64x compiler not efficient with static inline function and structures

The compiler generates surprisingly slow code for the example below

Given this struct and function definition:

typedef struct _S32_FP
{
   S32 value;          
   S32 fractionBits;   
} S32_FP;

static inline S32_FP S32_FP_SCALE_UP(S32_FP a)
{
   S32_FP result;
   S32 shiftLeft = _norm(a.value);
   result.fractionBits = a.fractionBits + shiftLeft;
   result.value = a.value << shiftLeft;
   return result;
}

This code is much slower:

response.denominator = S32_FP_SCALE_UP(response.denominator);
response.numerator   = S32_FP_SCALE_UP(response.numerator);

...than this equivalent, manually inlined, version:

const S32 shiftLeftDenominator = _norm(response.denominator.value);
response.denominator.fractionBits += shiftLeftDenominator;
response.denominator.value <<= shiftLeftDenominator;
const S32 shiftLeftNumerator = _norm(response.numerator.value);
response.numerator.fractionBits += shiftLeftNumerator;
response.numerator.value <<= shiftLeftNumerator;

The compiler appears to get in trouble optimizing the struct assignments. 

The compiler option used are:

"C:\ti\ccsv5\tools\compiler\c6000/bin/cl6x" -fr <???> -c -mv64+ --diag_warning=225 --interrupt_threshold=70000 --abi=coffabi -O3 --auto_inline=10000