[LLVMdev] Call to non-constant memset() being generated where libc is not available

[Jason Kim]

On Sun, Jan 30, 2011 at 11:20 PM, Nick Lewycky <nicholas at mxc.ca> wrote:
> David Meyer wrote:
>> I am compiling something without standard libraries, including no libc.
>>
>> Somehow, this bitcode is being generated by plain array manipulation code:
>>
>>    %12 = add i8 %11, -19
>>    %tmp35 = icmp sgt i32 %9, 1
>>    %smax36 = select i1 %tmp35, i32 %9, i32 1
>>    call void @llvm.memset.p0i8.i32(i8* getelementptr inbounds ([100 x
>> i8]* @global_array_char, i32 0, i32 0), i8 %12, i32 %smax36, i32 1, i1
>> false)
>>
>> (global_array_char is an array of length 100, which only partially gets
>> used.)
>
> That's not quite enough to go on. What's the original code, and what is
> this? Are we looking at an array initialization here?
>
>> This gets lowered by LLC to a library call to memset(), which cannot be
>> satisfied.
>>
>> Any advice?

Pdox, is this happening on ARM as well?

>
> As Duncan pointed out, memset may be generated as part of the ABI even
> in a freestanding (ie., no libc) environment. I think memcpy is in the
> same boat.

>
> If you have a different target with a different ABI that doesn't provide
> memset/memcpy, you could try writing your own generic lowering in
> Target/X86. Or you could always link against something native that
> provides memset/memcpy, which is what I strongly recommend.
>
>> Thanks,
>> David Meyer