MaxAtomicInlineWidth of SPIR64TargetInfo


We are developing the atomic built-in function for OpenCL 2.0. we use SPIR64 as the target and hope to lower the llvm built-in functions like ‘__c11_atomic_fetch_and_sub’ to instructions like ‘atomicrmw’, but the MaxAtomicInlineWidth of SPIR64TargetInfo is not set by default, so the EmitAtomicExpr goes to libcall path and got function ‘__atomic_fetch_sub_4’, which is unexpected.

After set the variable MaxAtomicInlineWidth, the EmitAtomicExpr take the non-libcall path and get instruction: ‘%1 = atomicrmw volatile sub i32* %arrayinit.begin, i32 1 acquire’

class SPIR64TargetInfo : public SPIRTargetInfo {


SPIR64TargetInfo(const llvm::Triple &Triple) : SPIRTargetInfo(Triple) {

PointerWidth = PointerAlign = 64;

SizeType = TargetInfo::UnsignedLong;

PtrDiffType = IntPtrType = TargetInfo::SignedLong;

DataLayoutString = “e-i64:64-v16:16-v24:32-v32:32-v48:64-”


+ MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 64;


void getTargetDefines(const LangOptions &Opts,

MacroBuilder &Builder) const override {

DefineStd(Builder, “SPIR64”, Opts);


So the question is why some other targets set the MaxAtomicInlineWidth when created but SPIR64TargetInfo did NOT? Shall we add it as above?


The mentioned OpenCL test kernel is as below, command is ‘./clang -cc1 -emit-llvm -triple spir64 -cl-std=CL2.0 -o atomic_functions.spir’:

__kernel void atomic_functions()


volatile atomic_uint ptest[2] = {0};

int test = __c11_atomic_fetch_sub(&ptest[0], 1, 1);


Luo Xionghu

Best Regards

When adding C11 atomics support to the Hexagon backend, I ended up adding almost exactly the same line. I suspect that the reason it wasn’t already there is that the people adding C11 and C++11 didn’t want to try and modify backends they were unfamiliar with.

Hi Anastasia,

Do you have any comment/suggestion on this?



Yes, I think it makes sense to set the max width in SPIR for atomics to 64 (at least looking at OpenCL and SPIR spec of atomics).

If you send this as a patch to me and cfe-commits, I will review.