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 polly;
27 extern bool polly::PollyAllowFullFunction;
28 
29 namespace {
30 class ScopInliner : public CallGraphSCCPass {
31   using llvm::Pass::doInitialization;
32 
33 public:
34   static char ID;
35 
36   ScopInliner() : CallGraphSCCPass(ID) {}
37 
38   bool doInitialization(CallGraph &CG) override {
39     if (!polly::PollyAllowFullFunction) {
40       report_fatal_error(
41           "Aborting from ScopInliner because it only makes sense to run with "
42           "-polly-allow-full-function. "
43           "The heurtistic for ScopInliner checks that the full function is a "
44           "Scop, which happens if and only if polly-allow-full-function is "
45           " enabled. "
46           " If not, the entry block is not included in the Scop");
47     }
48     return true;
49   }
50 
51   bool runOnSCC(CallGraphSCC &SCC) override {
52     // We do not try to inline non-trivial SCCs because this would lead to
53     // "infinite" inlining if we are not careful.
54     if (SCC.size() > 1)
55       return false;
56     assert(SCC.size() == 1 && "found empty SCC");
57     Function *F = (*SCC.begin())->getFunction();
58 
59     // If the function is a nullptr, or the function is a declaration.
60     if (!F)
61       return false;
62     if (F->isDeclaration()) {
63       LLVM_DEBUG(dbgs() << "Skipping " << F->getName()
64                         << "because it is a declaration.\n");
65       return false;
66     }
67 
68     PassBuilder PB;
69     FunctionAnalysisManager FAM;
70     FAM.registerPass([] { return ScopAnalysis(); });
71     PB.registerFunctionAnalyses(FAM);
72 
73     RegionInfo &RI = FAM.getResult<RegionInfoAnalysis>(*F);
74     ScopDetection &SD = FAM.getResult<ScopAnalysis>(*F);
75 
76     const bool HasScopAsTopLevelRegion =
77         SD.ValidRegions.count(RI.getTopLevelRegion()) > 0;
78 
79     if (HasScopAsTopLevelRegion) {
80       LLVM_DEBUG(dbgs() << "Skipping " << F->getName()
81                         << " has scop as top level region");
82       F->addFnAttr(llvm::Attribute::AlwaysInline);
83 
84       ModuleAnalysisManager MAM;
85       PB.registerModuleAnalyses(MAM);
86       MAM.registerPass([&] { return FunctionAnalysisManagerModuleProxy(FAM); });
87       ModulePassManager MPM;
88       MPM.addPass(AlwaysInlinerPass());
89       Module *M = F->getParent();
90       assert(M && "Function has illegal module");
91       MPM.run(*M, MAM);
92     } else {
93       LLVM_DEBUG(dbgs() << F->getName()
94                         << " does NOT have scop as top level region\n");
95     }
96 
97     return false;
98   };
99 
100   void getAnalysisUsage(AnalysisUsage &AU) const override {
101     CallGraphSCCPass::getAnalysisUsage(AU);
102   }
103 };
104 } // namespace
105 char ScopInliner::ID;
106 
107 Pass *polly::createScopInlinerPass() {
108   ScopInliner *pass = new ScopInliner();
109   return pass;
110 }
111 
112 INITIALIZE_PASS_BEGIN(
113     ScopInliner, "polly-scop-inliner",
114     "inline functions based on how much of the function is a scop.", false,
115     false)
116 INITIALIZE_PASS_END(
117     ScopInliner, "polly-scop-inliner",
118     "inline functions based on how much of the function is a scop.", false,
119     false)
120