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/IR/Module.h"
19 #include "llvm/Pass.h"
20 #include "llvm/Support/CommandLine.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 public:
36   static char ID;
37 
38   AMDGPUAlwaysInline(bool GlobalOpt = false) :
39     ModulePass(ID), GlobalOpt(GlobalOpt) { }
40   bool runOnModule(Module &M) override;
41 
42   void getAnalysisUsage(AnalysisUsage &AU) const override {
43     AU.setPreservesAll();
44  }
45 };
46 
47 } // End anonymous namespace
48 
49 INITIALIZE_PASS(AMDGPUAlwaysInline, "amdgpu-always-inline",
50                 "AMDGPU Inline All Functions", false, false)
51 
52 char AMDGPUAlwaysInline::ID = 0;
53 
54 static void
55 recursivelyVisitUsers(GlobalValue &GV,
56                       SmallPtrSetImpl<Function *> &FuncsToAlwaysInline) {
57   SmallVector<User *, 16> Stack(GV.users());
58 
59   SmallPtrSet<const Value *, 8> Visited;
60 
61   while (!Stack.empty()) {
62     User *U = Stack.pop_back_val();
63     if (!Visited.insert(U).second)
64       continue;
65 
66     if (Instruction *I = dyn_cast<Instruction>(U)) {
67       Function *F = I->getParent()->getParent();
68       if (!AMDGPU::isEntryFunctionCC(F->getCallingConv())) {
69         // FIXME: This is a horrible hack. We should always respect noinline,
70         // and just let us hit the error when we can't handle this.
71         //
72         // Unfortunately, clang adds noinline to all functions at -O0. We have
73         // to override this here. until that's fixed.
74         F->removeFnAttr(Attribute::NoInline);
75 
76         FuncsToAlwaysInline.insert(F);
77         Stack.push_back(F);
78       }
79 
80       // No need to look at further users, but we do need to inline any callers.
81       continue;
82     }
83 
84     append_range(Stack, U->users());
85   }
86 }
87 
88 static bool alwaysInlineImpl(Module &M, bool GlobalOpt) {
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.getAddressSpace();
123     if ((AS == AMDGPUAS::REGION_ADDRESS) ||
124         (AS == AMDGPUAS::LOCAL_ADDRESS &&
125          !AMDGPUTargetMachine::EnableLowerModuleLDS))
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 bool AMDGPUAlwaysInline::runOnModule(Module &M) {
155   return alwaysInlineImpl(M, GlobalOpt);
156 }
157 
158 ModulePass *llvm::createAMDGPUAlwaysInlinePass(bool GlobalOpt) {
159   return new AMDGPUAlwaysInline(GlobalOpt);
160 }
161 
162 PreservedAnalyses AMDGPUAlwaysInlinePass::run(Module &M,
163                                               ModuleAnalysisManager &AM) {
164   alwaysInlineImpl(M, GlobalOpt);
165   return PreservedAnalyses::all();
166 }
167