llvm dev - Jan 2011 - [LLVMdev] Call to non-constant memset() being generated where libc is not available

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.)

This gets lowered by LLC to a library call to memset(), which cannot be
satisfied.

Any advice?

Thanks,
David Meyer
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Hi David,
> I am compiling something without standard libraries, including no libc.
compile with -fno-builtin  That said, note that GCC for example requires memset
to be available even in a freestanding environment.

Ciao, Duncan.
>
> 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.)
>
> This gets lowered by LLC to a library call to memset(), which cannot be
satisfied.
>
> Any advice?
>
> Thanks,
> David Meyer
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

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?
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
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

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