[cfe-dev] disabling loop idiom recognizer in clang

[Damjan Marion]

On Apr 29, 2011, at 12:40 AM, Andrew Fish wrote:

> On Apr 28, 2011, at 3:17 PM, Damjan Marion wrote:
> 
>> 
>> On Apr 29, 2011, at 12:15 AM, Chris Lattner wrote:
>> 
>>> 
>>> On Apr 28, 2011, at 3:09 PM, Damjan Marion wrote:
>>> 
>>>> 
>>>> Hi,
>>>> 
>>>> is there a way to disable loop idiom recognizer in clang?
>>>> 
>>>> I have a problem with compiling early stage code for ARM architecture which should not be linked to external libraries but clang replaces loop with memset call in the code.
> 
> If it is just the loop you care about make the pointer volatile. 
> 
>>> 
>>> Yep, build with -fno-builtin or -ffreestanding.
>> 
>> It doesn't work. According to gcc docs (which clang probably follows): 
>> "GCC requires the freestanding environment provide memcpy, memmove, memset and memcmp."
> 
> 
> It works great, you just need your own copies of the functions.  That is what we did for ARM EFI firmware, for gcc, clang, and RVCT.  https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2/ArmPkg/Library/CompilerIntrinsicsLib/Arm/. Sorry no makefiles as they get auto-generated from ../ CompilerIntrinsicsLib.inf. No floating point, but no external libraries means well no external libraries! 

In my case writing my own functions is slightly overkill for just avoiding clang to convert "for (i = 0; i <17; i++) c [i] = 0;" to memset. Must be a way to tell him not to mess with my loop :)