1 //===- AMDGPUOpenCLEnqueuedBlockLowering.cpp - Lower enqueued block -------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // \file
11 // \brief This post-linking pass replaces the function pointer of enqueued
12 // block kernel with a global variable (runtime handle) and adds
13 // "runtime-handle" attribute to the enqueued block kernel.
14 //
15 // In LLVM CodeGen the runtime-handle metadata will be translated to
16 // RuntimeHandle metadata in code object. Runtime allocates a global buffer
17 // for each kernel with RuntimeHandel metadata and saves the kernel address
18 // required for the AQL packet into the buffer. __enqueue_kernel function
19 // in device library knows that the invoke function pointer in the block
20 // literal is actually runtime handle and loads the kernel address from it
21 // and put it into AQL packet for dispatching.
22 //
23 // This cannot be done in FE since FE cannot create a unique global variable
24 // with external linkage across LLVM modules. The global variable with internal
25 // linkage does not work since optimization passes will try to replace loads
26 // of the global variable with its initialization value.
27 //
28 //===----------------------------------------------------------------------===//
29 
30 #include "AMDGPU.h"
31 #include "llvm/ADT/StringRef.h"
32 #include "llvm/IR/Constants.h"
33 #include "llvm/IR/Module.h"
34 #include "llvm/Pass.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/raw_ostream.h"
37 
38 #define DEBUG_TYPE "amdgpu-lower-enqueued-block"
39 
40 using namespace llvm;
41 
42 namespace {
43 
44 /// \brief Lower enqueued blocks.
45 class AMDGPUOpenCLEnqueuedBlockLowering : public ModulePass {
46 public:
47   static char ID;
48 
49   explicit AMDGPUOpenCLEnqueuedBlockLowering() : ModulePass(ID) {}
50 
51 private:
52   bool runOnModule(Module &M) override;
53 };
54 
55 } // end anonymous namespace
56 
57 char AMDGPUOpenCLEnqueuedBlockLowering::ID = 0;
58 
59 char &llvm::AMDGPUOpenCLEnqueuedBlockLoweringID =
60     AMDGPUOpenCLEnqueuedBlockLowering::ID;
61 
62 INITIALIZE_PASS(AMDGPUOpenCLEnqueuedBlockLowering, DEBUG_TYPE,
63                 "Lower OpenCL enqueued blocks", false, false)
64 
65 ModulePass* llvm::createAMDGPUOpenCLEnqueuedBlockLoweringPass() {
66   return new AMDGPUOpenCLEnqueuedBlockLowering();
67 }
68 
69 bool AMDGPUOpenCLEnqueuedBlockLowering::runOnModule(Module &M) {
70   auto &C = M.getContext();
71   auto AS = AMDGPU::getAMDGPUAS(M);
72   bool Changed = false;
73   for (auto &F : M.functions()) {
74     if (F.hasFnAttribute("enqueued-block")) {
75       if (!F.hasOneUse() || !F.user_begin()->hasOneUse() ||
76           !isa<ConstantExpr>(*F.user_begin()) ||
77           !isa<ConstantExpr>(*F.user_begin()->user_begin())) {
78         continue;
79       }
80       auto *BitCast = cast<ConstantExpr>(*F.user_begin());
81       auto *AddrCast = cast<ConstantExpr>(*BitCast->user_begin());
82       auto RuntimeHandle = (F.getName() + "_runtime_handle").str();
83       auto *GV = new GlobalVariable(
84           M, Type::getInt8Ty(C)->getPointerTo(AS.GLOBAL_ADDRESS),
85           /*IsConstant=*/true, GlobalValue::ExternalLinkage,
86           /*Initializer=*/nullptr, RuntimeHandle, /*InsertBefore=*/nullptr,
87           GlobalValue::NotThreadLocal, AS.GLOBAL_ADDRESS,
88           /*IsExternallyInitialized=*/true);
89       DEBUG(dbgs() << "runtime handle created: " << *GV << '\n');
90       auto *NewPtr = ConstantExpr::getPointerCast(GV, AddrCast->getType());
91       AddrCast->replaceAllUsesWith(NewPtr);
92       F.addFnAttr("runtime-handle", RuntimeHandle);
93       F.setLinkage(GlobalValue::ExternalLinkage);
94       Changed = true;
95     }
96   }
97   return Changed;
98 }
99