[llvm-dev] How to remove memcpy (original) (raw)

Wolfgang McSneed via llvm-dev llvm-dev at lists.llvm.org
Sat Oct 15 16:10:05 PDT 2016

Hi Mehdi and Joerg,

Thanks for your fast response! attached is the matrix_float.c file.

Also - I should point out that I am using MIPS ISS.

Thanks,

Wolf

Kind Regards,

Wolf

On Sat, Oct 15, 2016 at 6:07 PM, Joerg Sonnenberger via llvm-dev < llvm-dev at lists.llvm.org> wrote:

On Sat, Oct 15, 2016 at 04:01:36PM -0700, Mehdi Amini via llvm-dev wrote: > > > On Oct 15, 2016, at 3:56 PM, Wolfgang McSneed via llvm-dev <_ _llvm-dev at lists.llvm.org> wrote: > > > > Hi, > > > > I am hoping that someone can help me figure out how to prevent the insertion of "memcpy" from the assembly source. > > > > My target is an instruction set simulator that doesn't support this. > > > > Thank you for your valuable time. > > > > Wolf > > > > Here are my compile commands: > > $ clang -emit-llvm -fno-builtin -o3 --target=mips -S matrixfloat.c -o vlmatrixfloat.ll > > Technically -fno-bultin prevents the compiler from understand the > memset in the original code. The right option to prevent the compiler > from insert libc calls “out-of-the-blue” is -ffreestanding.

Huh? The -fno-builtin is not the problem. The compiler is expected to call certain functions even for -ffreestanding. memcpy and memset are two of those. It is certainly perfectly valid target lowering for llvm.memcpy to be turned back into a libcall. Joerg

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