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