1 //===- AMDGPUOpenCLEnqueuedBlockLowering.cpp - Lower enqueued block -------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // \file
10 // This post-linking pass replaces the function pointer of enqueued
11 // block kernel with a global variable (runtime handle) and adds
12 // "runtime-handle" attribute to the enqueued block kernel.
13 //
14 // In LLVM CodeGen the runtime-handle metadata will be translated to
15 // RuntimeHandle metadata in code object. Runtime allocates a global buffer
16 // for each kernel with RuntimeHandel metadata and saves the kernel address
17 // required for the AQL packet into the buffer. __enqueue_kernel function
18 // in device library knows that the invoke function pointer in the block
19 // literal is actually runtime handle and loads the kernel address from it
20 // and put it into AQL packet for dispatching.
21 //
22 // This cannot be done in FE since FE cannot create a unique global variable
23 // with external linkage across LLVM modules. The global variable with internal
24 // linkage does not work since optimization passes will try to replace loads
25 // of the global variable with its initialization value.
26 //
27 // It also identifies the kernels directly or indirectly enqueues kernels
28 // and adds "calls-enqueue-kernel" function attribute to them, which will
29 // be used to determine whether to emit runtime metadata for the kernel
30 // enqueue related hidden kernel arguments.
31 //
32 //===----------------------------------------------------------------------===//
33
34 #include "AMDGPU.h"
35 #include "llvm/ADT/DenseSet.h"
36 #include "llvm/ADT/SmallString.h"
37 #include "llvm/IR/Instructions.h"
38 #include "llvm/IR/Mangler.h"
39 #include "llvm/IR/Module.h"
40 #include "llvm/Pass.h"
41 #include "llvm/Support/Debug.h"
42
43 #define DEBUG_TYPE "amdgpu-lower-enqueued-block"
44
45 using namespace llvm;
46
47 namespace {
48
49 /// Lower enqueued blocks.
50 class AMDGPUOpenCLEnqueuedBlockLowering : public ModulePass {
51 public:
52 static char ID;
53
AMDGPUOpenCLEnqueuedBlockLowering()54 explicit AMDGPUOpenCLEnqueuedBlockLowering() : ModulePass(ID) {}
55
56 private:
57 bool runOnModule(Module &M) override;
58 };
59
60 } // end anonymous namespace
61
62 char AMDGPUOpenCLEnqueuedBlockLowering::ID = 0;
63
64 char &llvm::AMDGPUOpenCLEnqueuedBlockLoweringID =
65 AMDGPUOpenCLEnqueuedBlockLowering::ID;
66
67 INITIALIZE_PASS(AMDGPUOpenCLEnqueuedBlockLowering, DEBUG_TYPE,
68 "Lower OpenCL enqueued blocks", false, false)
69
createAMDGPUOpenCLEnqueuedBlockLoweringPass()70 ModulePass* llvm::createAMDGPUOpenCLEnqueuedBlockLoweringPass() {
71 return new AMDGPUOpenCLEnqueuedBlockLowering();
72 }
73
74 /// Collect direct or indrect callers of \p F and save them
75 /// to \p Callers.
collectCallers(Function * F,DenseSet<Function * > & Callers)76 static void collectCallers(Function *F, DenseSet<Function *> &Callers) {
77 for (auto U : F->users()) {
78 if (auto *CI = dyn_cast<CallInst>(&*U)) {
79 auto *Caller = CI->getParent()->getParent();
80 if (Callers.insert(Caller).second)
81 collectCallers(Caller, Callers);
82 }
83 }
84 }
85
86 /// If \p U is instruction or constant, collect functions which directly or
87 /// indirectly use it.
collectFunctionUsers(User * U,DenseSet<Function * > & Funcs)88 static void collectFunctionUsers(User *U, DenseSet<Function *> &Funcs) {
89 if (auto *I = dyn_cast<Instruction>(U)) {
90 auto *F = I->getParent()->getParent();
91 if (Funcs.insert(F).second)
92 collectCallers(F, Funcs);
93 return;
94 }
95 if (!isa<Constant>(U))
96 return;
97 for (auto UU : U->users())
98 collectFunctionUsers(&*UU, Funcs);
99 }
100
runOnModule(Module & M)101 bool AMDGPUOpenCLEnqueuedBlockLowering::runOnModule(Module &M) {
102 DenseSet<Function *> Callers;
103 auto &C = M.getContext();
104 bool Changed = false;
105 for (auto &F : M.functions()) {
106 if (F.hasFnAttribute("enqueued-block")) {
107 if (!F.hasName()) {
108 SmallString<64> Name;
109 Mangler::getNameWithPrefix(Name, "__amdgpu_enqueued_kernel",
110 M.getDataLayout());
111 F.setName(Name);
112 }
113 LLVM_DEBUG(dbgs() << "found enqueued kernel: " << F.getName() << '\n');
114 auto RuntimeHandle = (F.getName() + ".runtime_handle").str();
115 auto T = ArrayType::get(Type::getInt64Ty(C), 2);
116 auto *GV = new GlobalVariable(
117 M, T,
118 /*isConstant=*/false, GlobalValue::ExternalLinkage,
119 /*Initializer=*/Constant::getNullValue(T), RuntimeHandle,
120 /*InsertBefore=*/nullptr, GlobalValue::NotThreadLocal,
121 AMDGPUAS::GLOBAL_ADDRESS,
122 /*isExternallyInitialized=*/false);
123 LLVM_DEBUG(dbgs() << "runtime handle created: " << *GV << '\n');
124
125 for (auto U : F.users()) {
126 auto *UU = &*U;
127 if (!isa<ConstantExpr>(UU))
128 continue;
129 collectFunctionUsers(UU, Callers);
130 auto *BitCast = cast<ConstantExpr>(UU);
131 auto *NewPtr = ConstantExpr::getPointerCast(GV, BitCast->getType());
132 BitCast->replaceAllUsesWith(NewPtr);
133 F.addFnAttr("runtime-handle", RuntimeHandle);
134 F.setLinkage(GlobalValue::ExternalLinkage);
135 Changed = true;
136 }
137 }
138 }
139
140 for (auto F : Callers) {
141 if (F->getCallingConv() != CallingConv::AMDGPU_KERNEL)
142 continue;
143 F->addFnAttr("calls-enqueue-kernel");
144 LLVM_DEBUG(dbgs() << "mark enqueue_kernel caller:" << F->getName() << '\n');
145 }
146 return Changed;
147 }
148