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 RuntimeHandle 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/Constants.h"
38 #include "llvm/IR/Instructions.h"
39 #include "llvm/IR/Mangler.h"
40 #include "llvm/IR/Module.h"
41 #include "llvm/Pass.h"
42 #include "llvm/Support/Debug.h"
43
44 #define DEBUG_TYPE "amdgpu-lower-enqueued-block"
45
46 using namespace llvm;
47
48 namespace {
49
50 /// Lower enqueued blocks.
51 class AMDGPUOpenCLEnqueuedBlockLowering : public ModulePass {
52 public:
53 static char ID;
54
AMDGPUOpenCLEnqueuedBlockLowering()55 explicit AMDGPUOpenCLEnqueuedBlockLowering() : ModulePass(ID) {}
56
57 private:
58 bool runOnModule(Module &M) override;
59 };
60
61 } // end anonymous namespace
62
63 char AMDGPUOpenCLEnqueuedBlockLowering::ID = 0;
64
65 char &llvm::AMDGPUOpenCLEnqueuedBlockLoweringID =
66 AMDGPUOpenCLEnqueuedBlockLowering::ID;
67
68 INITIALIZE_PASS(AMDGPUOpenCLEnqueuedBlockLowering, DEBUG_TYPE,
69 "Lower OpenCL enqueued blocks", false, false)
70
createAMDGPUOpenCLEnqueuedBlockLoweringPass()71 ModulePass* llvm::createAMDGPUOpenCLEnqueuedBlockLoweringPass() {
72 return new AMDGPUOpenCLEnqueuedBlockLowering();
73 }
74
75 /// Collect direct or indirect callers of \p F and save them
76 /// to \p Callers.
collectCallers(Function * F,DenseSet<Function * > & Callers)77 static void collectCallers(Function *F, DenseSet<Function *> &Callers) {
78 for (auto U : F->users()) {
79 if (auto *CI = dyn_cast<CallInst>(&*U)) {
80 auto *Caller = CI->getParent()->getParent();
81 if (Callers.insert(Caller).second)
82 collectCallers(Caller, Callers);
83 }
84 }
85 }
86
87 /// If \p U is instruction or constant, collect functions which directly or
88 /// indirectly use it.
collectFunctionUsers(User * U,DenseSet<Function * > & Funcs)89 static void collectFunctionUsers(User *U, DenseSet<Function *> &Funcs) {
90 if (auto *I = dyn_cast<Instruction>(U)) {
91 auto *F = I->getParent()->getParent();
92 if (Funcs.insert(F).second)
93 collectCallers(F, Funcs);
94 return;
95 }
96 if (!isa<Constant>(U))
97 return;
98 for (auto UU : U->users())
99 collectFunctionUsers(&*UU, Funcs);
100 }
101
runOnModule(Module & M)102 bool AMDGPUOpenCLEnqueuedBlockLowering::runOnModule(Module &M) {
103 DenseSet<Function *> Callers;
104 auto &C = M.getContext();
105 bool Changed = false;
106 for (auto &F : M.functions()) {
107 if (F.hasFnAttribute("enqueued-block")) {
108 if (!F.hasName()) {
109 SmallString<64> Name;
110 Mangler::getNameWithPrefix(Name, "__amdgpu_enqueued_kernel",
111 M.getDataLayout());
112 F.setName(Name);
113 }
114 LLVM_DEBUG(dbgs() << "found enqueued kernel: " << F.getName() << '\n');
115 auto RuntimeHandle = (F.getName() + ".runtime_handle").str();
116 auto T = ArrayType::get(Type::getInt64Ty(C), 2);
117 auto *GV = new GlobalVariable(
118 M, T,
119 /*isConstant=*/false, GlobalValue::ExternalLinkage,
120 /*Initializer=*/Constant::getNullValue(T), RuntimeHandle,
121 /*InsertBefore=*/nullptr, GlobalValue::NotThreadLocal,
122 AMDGPUAS::GLOBAL_ADDRESS,
123 /*isExternallyInitialized=*/false);
124 LLVM_DEBUG(dbgs() << "runtime handle created: " << *GV << '\n');
125
126 for (auto U : F.users()) {
127 auto *UU = &*U;
128 if (!isa<ConstantExpr>(UU))
129 continue;
130 collectFunctionUsers(UU, Callers);
131 auto *BitCast = cast<ConstantExpr>(UU);
132 auto *NewPtr = ConstantExpr::getPointerCast(GV, BitCast->getType());
133 BitCast->replaceAllUsesWith(NewPtr);
134 F.addFnAttr("runtime-handle", RuntimeHandle);
135 F.setLinkage(GlobalValue::ExternalLinkage);
136 Changed = true;
137 }
138 }
139 }
140
141 for (auto F : Callers) {
142 if (F->getCallingConv() != CallingConv::AMDGPU_KERNEL)
143 continue;
144 F->addFnAttr("calls-enqueue-kernel");
145 LLVM_DEBUG(dbgs() << "mark enqueue_kernel caller:" << F->getName() << '\n');
146 }
147 return Changed;
148 }
149