[llvm-dev] Writing simple intrinsic in clang
Friedman, Eli via llvm-dev
llvm-dev at lists.llvm.org
Tue Sep 25 11:12:01 PDT 2018
On 9/24/2018 6:47 AM, Павел Безбородов via llvm-dev wrote:
> I want to write a simple backend-specific instrinsic that will just
> call an instruction. How should I do that?
Is this really not documented anywhere...?
Anyway, the basic steps:
1. Add the builtin to the list of intrinsics for your target:
include/llvm/IR/IntrinsicsYourTarget.td. Use a GCCBuiltin for the
corresponding C intrinisc name.
2. Teach your target to lower the intrinsic to an instruction; you can
usually just use the name of the intrinsic in a pattern in
3. Add the builtin to include/clang/Basic/BuiltinsYourTarget.def
An example of an intrinsic implemented this way is int_arm_qadd8 in the
ARM backend (corresponding to the C builtin __builtin_arm_qadd8); it
should be straightforward to follow that example.
This approach assumes your intrinsic is simple: it returns at most one
value, and all the parameter and return types are legal. If that isn't
true, you might need to write some C++ code to handle it in clang or in
Maybe we should add this as a section to
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