1 //===---- ScopInliner.cpp - Polyhedral based inliner ----------------------===//
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 // Take a SCC and:
10 // 1. If it has more than one component, bail out (contains cycles)
11 // 2. If it has just one component, and if the function is entirely a scop,
12 //    inline it.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "polly/LinkAllPasses.h"
17 #include "polly/ScopDetection.h"
18 #include "llvm/Analysis/CallGraph.h"
19 #include "llvm/Analysis/CallGraphSCCPass.h"
20 #include "llvm/IR/PassManager.h"
21 #include "llvm/Passes/PassBuilder.h"
22 #include "llvm/Transforms/IPO/AlwaysInliner.h"
23 
24 #define DEBUG_TYPE "polly-scop-inliner"
25 
26 using namespace llvm;
27 using namespace polly;
28 
29 extern bool polly::PollyAllowFullFunction;
30 
31 namespace {
32 class ScopInliner : public CallGraphSCCPass {
33   using llvm::Pass::doInitialization;
34 
35 public:
36   static char ID;
37 
38   ScopInliner() : CallGraphSCCPass(ID) {}
39 
40   bool doInitialization(CallGraph &CG) override {
41     if (!polly::PollyAllowFullFunction) {
42       report_fatal_error(
43           "Aborting from ScopInliner because it only makes sense to run with "
44           "-polly-allow-full-function. "
45           "The heurtistic for ScopInliner checks that the full function is a "
46           "Scop, which happens if and only if polly-allow-full-function is "
47           " enabled. "
48           " If not, the entry block is not included in the Scop");
49     }
50     return true;
51   }
52 
53   bool runOnSCC(CallGraphSCC &SCC) override {
54     // We do not try to inline non-trivial SCCs because this would lead to
55     // "infinite" inlining if we are not careful.
56     if (SCC.size() > 1)
57       return false;
58     assert(SCC.size() == 1 && "found empty SCC");
59     Function *F = (*SCC.begin())->getFunction();
60 
61     // If the function is a nullptr, or the function is a declaration.
62     if (!F)
63       return false;
64     if (F->isDeclaration()) {
65       LLVM_DEBUG(dbgs() << "Skipping " << F->getName()
66                         << "because it is a declaration.\n");
67       return false;
68     }
69 
70     PassBuilder PB;
71     // Populate analysis managers and register Polly-specific analyses.
72     LoopAnalysisManager LAM;
73     FunctionAnalysisManager FAM;
74     CGSCCAnalysisManager CGAM;
75     ModuleAnalysisManager MAM;
76     FAM.registerPass([] { return ScopAnalysis(); });
77     PB.registerModuleAnalyses(MAM);
78     PB.registerCGSCCAnalyses(CGAM);
79     PB.registerFunctionAnalyses(FAM);
80     PB.registerLoopAnalyses(LAM);
81     PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
82 
83     RegionInfo &RI = FAM.getResult<RegionInfoAnalysis>(*F);
84     ScopDetection &SD = FAM.getResult<ScopAnalysis>(*F);
85 
86     const bool HasScopAsTopLevelRegion =
87         SD.ValidRegions.count(RI.getTopLevelRegion()) > 0;
88 
89     bool Changed = false;
90     if (HasScopAsTopLevelRegion) {
91       LLVM_DEBUG(dbgs() << "Skipping " << F->getName()
92                         << " has scop as top level region");
93       F->addFnAttr(llvm::Attribute::AlwaysInline);
94 
95       ModulePassManager MPM;
96       MPM.addPass(AlwaysInlinerPass());
97       Module *M = F->getParent();
98       assert(M && "Function has illegal module");
99       PreservedAnalyses PA = MPM.run(*M, MAM);
100       if (!PA.areAllPreserved())
101         Changed = true;
102     } else {
103       LLVM_DEBUG(dbgs() << F->getName()
104                         << " does NOT have scop as top level region\n");
105     }
106 
107     return Changed;
108   };
109 
110   void getAnalysisUsage(AnalysisUsage &AU) const override {
111     CallGraphSCCPass::getAnalysisUsage(AU);
112   }
113 };
114 } // namespace
115 char ScopInliner::ID;
116 
117 Pass *polly::createScopInlinerPass() {
118   ScopInliner *pass = new ScopInliner();
119   return pass;
120 }
121 
122 INITIALIZE_PASS_BEGIN(
123     ScopInliner, "polly-scop-inliner",
124     "inline functions based on how much of the function is a scop.", false,
125     false)
126 INITIALIZE_PASS_END(
127     ScopInliner, "polly-scop-inliner",
128     "inline functions based on how much of the function is a scop.", false,
129     false)
130