[cfe-dev] disabling loop idiom recognizer in clang

[jahanian]

On Apr 28, 2011, at 3:49 PM, Damjan Marion wrote:

> 
> 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 :)

Can you write it in a way that memset  conversion logic does not recognize it; such as i =0; for (; i <17; i++) c [i] = 0;

- fariborz

> 
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