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 
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 
71 ModulePass* llvm::createAMDGPUOpenCLEnqueuedBlockLoweringPass() {
72   return new AMDGPUOpenCLEnqueuedBlockLowering();
73 }
74 
75 bool AMDGPUOpenCLEnqueuedBlockLowering::runOnModule(Module &M) {
76   DenseSet<Function *> Callers;
77   auto &C = M.getContext();
78   bool Changed = false;
79 
80   // ptr kernel_object, i32 private_segment_size, i32 group_segment_size
81   StructType *HandleTy = nullptr;
82 
83   for (auto &F : M.functions()) {
84     if (F.hasFnAttribute("enqueued-block")) {
85       if (!F.hasName()) {
86         SmallString<64> Name;
87         Mangler::getNameWithPrefix(Name, "__amdgpu_enqueued_kernel",
88                                    M.getDataLayout());
89         F.setName(Name);
90       }
91       LLVM_DEBUG(dbgs() << "found enqueued kernel: " << F.getName() << '\n');
92       auto RuntimeHandle = (F.getName() + ".runtime_handle").str();
93       if (!HandleTy) {
94         Type *Int32 = Type::getInt32Ty(C);
95         HandleTy =
96             StructType::create(C, {PointerType::getUnqual(C), Int32, Int32},
97                                "block.runtime.handle.t");
98       }
99 
100       auto *GV = new GlobalVariable(
101           M, HandleTy,
102           /*isConstant=*/true, GlobalValue::ExternalLinkage,
103           /*Initializer=*/Constant::getNullValue(HandleTy), RuntimeHandle,
104           /*InsertBefore=*/nullptr, GlobalValue::NotThreadLocal,
105           AMDGPUAS::GLOBAL_ADDRESS,
106           /*isExternallyInitialized=*/true);
107       LLVM_DEBUG(dbgs() << "runtime handle created: " << *GV << '\n');
108 
109       F.replaceAllUsesWith(ConstantExpr::getAddrSpaceCast(GV, F.getType()));
110       F.addFnAttr("runtime-handle", RuntimeHandle);
111       F.setLinkage(GlobalValue::ExternalLinkage);
112       Changed = true;
113     }
114   }
115 
116   return Changed;
117 }
118