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//===- AMDGPUOpenCLEnqueuedBlockLowering.cpp - Lower enqueued block -------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// \file
// This post-linking pass replaces the function pointer of enqueued
// block kernel with a global variable (runtime handle) and adds
// "runtime-handle" attribute to the enqueued block kernel.
// In LLVM CodeGen the runtime-handle metadata will be translated to
// RuntimeHandle metadata in code object. Runtime allocates a global buffer
// for each kernel with RuntimeHandle metadata and saves the kernel address
// required for the AQL packet into the buffer. __enqueue_kernel function
// in device library knows that the invoke function pointer in the block
// literal is actually runtime handle and loads the kernel address from it
// and put it into AQL packet for dispatching.
// This cannot be done in FE since FE cannot create a unique global variable
// with external linkage across LLVM modules. The global variable with internal
// linkage does not work since optimization passes will try to replace loads
// of the global variable with its initialization value.
// It also identifies the kernels directly or indirectly enqueues kernels
// and adds "calls-enqueue-kernel" function attribute to them, which will
// be used to determine whether to emit runtime metadata for the kernel
// enqueue related hidden kernel arguments.
#include "AMDGPU.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Mangler.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#define DEBUG_TYPE "amdgpu-lower-enqueued-block"
using namespace llvm;
namespace {
/// Lower enqueued blocks.
class AMDGPUOpenCLEnqueuedBlockLowering : public ModulePass {
static char ID;
explicit AMDGPUOpenCLEnqueuedBlockLowering() : ModulePass(ID) {}
bool runOnModule(Module &M) override;
} // end anonymous namespace
char AMDGPUOpenCLEnqueuedBlockLowering::ID = 0;
char &llvm::AMDGPUOpenCLEnqueuedBlockLoweringID =
"Lower OpenCL enqueued blocks", false, false)
ModulePass* llvm::createAMDGPUOpenCLEnqueuedBlockLoweringPass() {
return new AMDGPUOpenCLEnqueuedBlockLowering();
/// Collect direct or indrect callers of \p F and save them
/// to \p Callers.
static void collectCallers(Function *F, DenseSet<Function *> &Callers) {
for (auto U : F->users()) {
if (auto *CI = dyn_cast<CallInst>(&*U)) {
auto *Caller = CI->getParent()->getParent();
if (Callers.insert(Caller).second)
collectCallers(Caller, Callers);
/// If \p U is instruction or constant, collect functions which directly or
/// indirectly use it.
static void collectFunctionUsers(User *U, DenseSet<Function *> &Funcs) {
if (auto *I = dyn_cast<Instruction>(U)) {
auto *F = I->getParent()->getParent();
if (Funcs.insert(F).second)
collectCallers(F, Funcs);
if (!isa<Constant>(U))
for (auto UU : U->users())
collectFunctionUsers(&*UU, Funcs);
bool AMDGPUOpenCLEnqueuedBlockLowering::runOnModule(Module &M) {
DenseSet<Function *> Callers;
auto &C = M.getContext();
bool Changed = false;
for (auto &F : M.functions()) {
if (F.hasFnAttribute("enqueued-block")) {
if (!F.hasName()) {
SmallString<64> Name;
Mangler::getNameWithPrefix(Name, "__amdgpu_enqueued_kernel",
LLVM_DEBUG(dbgs() << "found enqueued kernel: " << F.getName() << '\n');
auto RuntimeHandle = (F.getName() + ".runtime_handle").str();
auto T = ArrayType::get(Type::getInt64Ty(C), 2);
auto *GV = new GlobalVariable(
M, T,
/*isConstant=*/false, GlobalValue::ExternalLinkage,
/*Initializer=*/Constant::getNullValue(T), RuntimeHandle,
/*InsertBefore=*/nullptr, GlobalValue::NotThreadLocal,
LLVM_DEBUG(dbgs() << "runtime handle created: " << *GV << '\n');
for (auto U : F.users()) {
auto *UU = &*U;
if (!isa<ConstantExpr>(UU))
collectFunctionUsers(UU, Callers);
auto *BitCast = cast<ConstantExpr>(UU);
auto *NewPtr = ConstantExpr::getPointerCast(GV, BitCast->getType());
F.addFnAttr("runtime-handle", RuntimeHandle);
Changed = true;
for (auto F : Callers) {
if (F->getCallingConv() != CallingConv::AMDGPU_KERNEL)
LLVM_DEBUG(dbgs() << "mark enqueue_kernel caller:" << F->getName() << '\n');
return Changed;