[cfe-dev] [PATCH] [OpenCL] Conversions for ternary operations between scalar and vector

[Sahasrabuddhe, Sameer]

On 12/17/2014 6:33 PM, Colin Riddell wrote:
>
> I have went through the examples you provided and marked which rules I 
> disagree/am unsure about
>> Some notable examples:
>>
>>    exp1     exp2    exp3     result   eval     reason
>>   --------+-------+--------+--------+--------+--------
>>    char2    int     int      error    -        7.1
> Can you remind me where the wording about number of bits matching 
> is....  I am not sure about this one because  220 also states that " 
> The second and third expressions can be any type, as long their types 
> match". Which to me, suggests that the char2 ?  int : int example is 
> allowed. Also in table 6.14, for select() in  c ? b : a     a and b 
> need to have matching types, but  c can be different as long as its 
> integer

Page 220 also states that if the condition is a vector, then the 
operator is equivalent to calling the select builtin. The select builtin 
in table 6.14 says that c must have the same number of elements and 
*bits* as the other two.

>> char2    int2    int2     error    -        4.1
> Same logic applies for this.
>> int2     char    char     error    -        7.1
> And this.
>>    int2     int2    float2   error    -        5
> Agree it should error, but because no implicit conversion is allowed 
> between int2 and float2

Yup. The "5" here refers to point 5, which in turn specifies that "usual 
arithmetic conversions" (Section 6.2.6) are used. The same section says 
that no implicit conversion is allowed. So we are both saying the same 
thing.

>> int2     int2    float    error    -        5
> Not sure about this one, my understanding here is that an attempt will 
> be made at converting the float to  a vec2. Maybe I misunderstand this 
> rule?

Section 6.2.6 states that the scalar cannot be of higher rank than the 
vector when converting. Looking at it another way, if we managed to 
convert the float to a float2, it cannot be implicitly converted to int2 
or vice versa.

>> int2     char2   char2    error    -        4.1
> Same as my first point

And same explanation applies. The difference between 4.1 and 7.1 is that 
in 4.1, the result type is already a vector type and the rules of the 
select builtin apply right away. But in 7.1, the result type is a scalar 
type, and this is probably undefined behaviour. We are choosing to 
define it as if the scalar was turned into a vector without changing its 
element type, which is not covered by any conversion rule.

Sameer.

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