[LLVMdev] backend for intrinsic functions

Cameron McInally cameron.mcinally at nyu.edu
Fri May 17 13:08:42 PDT 2013

Hey Ali,

On Fri, May 17, 2013 at 3:46 PM, Ali Javadi <aj14889 at yahoo.com> wrote:

> Hi,
> I have some newly defined intrinsic functions in my llvm IR code, which I
> want to translate to X86 instruction set. As a first step, I want to be
> able to generate "nop" for these instructions, so the program at least
> compiles successfully.
> The call to my intrinsic function looks like this in the IR:
> call void @llvm.X(i16 %43)
> From what I understand it may be possible to pattern match this to the nop
> instructions in the backend.

I would first attempt this in LowerINTRINSIC_WO_CHAIN(...)
from lib/Target/X86/X86ISelLowering.cpp. That may or may not be the right
way to go... just a thought.

> I did not find an example of intrinsic function translation in the X86
> backend. Could you explain how this can be done, or point me to some places
> to look?

As for matching intrinsics, check out lib/Target/X86/X86InstrSSE.td. For
example, here is a pattern that matches a 256 bit unaligned store intrinsic
to the AVX vmovups instruction.

def : Pat<(int_x86_avx_storeu_ps_256 addr:$dst, VR256:$src),
          (VMOVUPSYmr addr:$dst, VR256:$src)>;

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