1 //===-- AMDGPUAlwaysInlinePass.cpp - Promote Allocas ----------------------===//
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 /// This pass marks all internal functions as always_inline and creates
12 /// duplicates of all other functions and marks the duplicates as always_inline.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "AMDGPU.h"
17 #include "AMDGPUTargetMachine.h"
18 #include "Utils/AMDGPUBaseInfo.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/IR/Module.h"
21 #include "llvm/Transforms/Utils/Cloning.h"
22 
23 using namespace llvm;
24 
25 namespace {
26 
27 static cl::opt<bool> StressCalls(
28   "amdgpu-stress-function-calls",
29   cl::Hidden,
30   cl::desc("Force all functions to be noinline"),
31   cl::init(false));
32 
33 class AMDGPUAlwaysInline : public ModulePass {
34   bool GlobalOpt;
35 
36   void recursivelyVisitUsers(GlobalValue &GV,
37                              SmallPtrSetImpl<Function *> &FuncsToAlwaysInline);
38 public:
39   static char ID;
40 
41   AMDGPUAlwaysInline(bool GlobalOpt = false) :
42     ModulePass(ID), GlobalOpt(GlobalOpt) { }
43   bool runOnModule(Module &M) override;
44 
45   void getAnalysisUsage(AnalysisUsage &AU) const override {
46     AU.setPreservesAll();
47  }
48 };
49 
50 } // End anonymous namespace
51 
52 INITIALIZE_PASS(AMDGPUAlwaysInline, "amdgpu-always-inline",
53                 "AMDGPU Inline All Functions", false, false)
54 
55 char AMDGPUAlwaysInline::ID = 0;
56 
57 void AMDGPUAlwaysInline::recursivelyVisitUsers(
58   GlobalValue &GV,
59   SmallPtrSetImpl<Function *> &FuncsToAlwaysInline) {
60   SmallVector<User *, 16> Stack;
61 
62   SmallPtrSet<const Value *, 8> Visited;
63 
64   for (User *U : GV.users())
65     Stack.push_back(U);
66 
67   while (!Stack.empty()) {
68     User *U = Stack.pop_back_val();
69     if (!Visited.insert(U).second)
70       continue;
71 
72     if (Instruction *I = dyn_cast<Instruction>(U)) {
73       Function *F = I->getParent()->getParent();
74       if (!AMDGPU::isEntryFunctionCC(F->getCallingConv())) {
75         FuncsToAlwaysInline.insert(F);
76         Stack.push_back(F);
77       }
78 
79       // No need to look at further users, but we do need to inline any callers.
80       continue;
81     }
82 
83     for (User *UU : U->users())
84       Stack.push_back(UU);
85   }
86 }
87 
88 bool AMDGPUAlwaysInline::runOnModule(Module &M) {
89   std::vector<GlobalAlias*> AliasesToRemove;
90 
91   SmallPtrSet<Function *, 8> FuncsToAlwaysInline;
92   SmallPtrSet<Function *, 8> FuncsToNoInline;
93 
94   for (GlobalAlias &A : M.aliases()) {
95     if (Function* F = dyn_cast<Function>(A.getAliasee())) {
96       A.replaceAllUsesWith(F);
97       AliasesToRemove.push_back(&A);
98     }
99 
100     // FIXME: If the aliasee isn't a function, it's some kind of constant expr
101     // cast that won't be inlined through.
102   }
103 
104   if (GlobalOpt) {
105     for (GlobalAlias* A : AliasesToRemove) {
106       A->eraseFromParent();
107     }
108   }
109 
110   // Always force inlining of any function that uses an LDS global address. This
111   // is something of a workaround because we don't have a way of supporting LDS
112   // objects defined in functions. LDS is always allocated by a kernel, and it
113   // is difficult to manage LDS usage if a function may be used by multiple
114   // kernels.
115   //
116   // OpenCL doesn't allow declaring LDS in non-kernels, so in practice this
117   // should only appear when IPO passes manages to move LDs defined in a kernel
118   // into a single user function.
119 
120   for (GlobalVariable &GV : M.globals()) {
121     // TODO: Region address
122     unsigned AS = GV.getType()->getAddressSpace();
123     if (AS != AMDGPUAS::LOCAL_ADDRESS && AS != AMDGPUAS::REGION_ADDRESS)
124       continue;
125 
126     recursivelyVisitUsers(GV, FuncsToAlwaysInline);
127   }
128 
129   if (!AMDGPUTargetMachine::EnableFunctionCalls || StressCalls) {
130     auto IncompatAttr
131       = StressCalls ? Attribute::AlwaysInline : Attribute::NoInline;
132 
133     for (Function &F : M) {
134       if (!F.isDeclaration() && !F.use_empty() &&
135           !F.hasFnAttribute(IncompatAttr)) {
136         if (StressCalls) {
137           if (!FuncsToAlwaysInline.count(&F))
138             FuncsToNoInline.insert(&F);
139         } else
140           FuncsToAlwaysInline.insert(&F);
141       }
142     }
143   }
144 
145   for (Function *F : FuncsToAlwaysInline)
146     F->addFnAttr(Attribute::AlwaysInline);
147 
148   for (Function *F : FuncsToNoInline)
149     F->addFnAttr(Attribute::NoInline);
150 
151   return !FuncsToAlwaysInline.empty() || !FuncsToNoInline.empty();
152 }
153 
154 ModulePass *llvm::createAMDGPUAlwaysInlinePass(bool GlobalOpt) {
155   return new AMDGPUAlwaysInline(GlobalOpt);
156 }
157 
158