[LLVMdev] static functions and optimization

[Reed Kotler]

Seems like -femit-all-decls partially works around this.

But I would still like to solve the real problem of creating a function 
which is local/static but which cannot be thrown away by the optimizer 
if not referenced.


On 07/24/2013 04:07 PM, Reed Kotler wrote:
> Maybe there is some attribute I can add this will not allow the function
> to be discarded.
>
> On 07/24/2013 03:45 PM, reed kotler wrote:
>> I have some stub functions that are essentially static, but they cannot
>> be removed.
>>
>> What linkage type should I use in that case. Internal linkage appears to
>> get the functions discarded if they are not referenced under certain
>> optimizations.
>>
>> This is part of the gcc mips16 hack for floating point.
>>
>> For example, a function like floor from the math library will be called
>> with an external reference to function floor.
>>
>> At that time, the compiler does not know whether floor was compiled as
>> mips16 or mips32.
>>
>> It generates the call to floor as if it is a mips16 compiled function.
>>
>> It also generates a stub that the linker can use if during link time it
>> is discovered that "floor" is a mips32 function.
>>
>> The stubs, which are mips32 code, will move the first argument register
>> into a floating point register, call floor, and upon return will move
>> the integer return value into a floating point register.
>>
>> If I designate this function as having internal linkage, then in some
>> cases, the optimizer will throw it away.
>>
>> In that case, at link time it will call floor, and if floor is compiled
>> as mips32, this will break a mips16 compiled program.
>>
>> The linker does not know there is an issue because only functions with
>> certain kinds of signatures need a helper function for the call.