1//===- StaticDataAnnotator - Annotate static data's section prefix --------===//
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// To reason about module-wide data hotness in a module granularity, this file
10// implements a module pass StaticDataAnnotator to work coordinately with the
11// StaticDataSplitter pass.
12//
13// The StaticDataSplitter pass is a machine function pass. It analyzes data
14// hotness based on code and adds counters in StaticDataProfileInfo via its
15// wrapper pass StaticDataProfileInfoWrapper.
16// The StaticDataProfileInfoWrapper sits in the middle between the
17// StaticDataSplitter and StaticDataAnnotator passes.
18// The StaticDataAnnotator pass is a module pass. It iterates global variables
19// in the module, looks up counters from StaticDataProfileInfo and sets the
20// section prefix based on profiles.
21//
22// The three-pass structure is implemented for practical reasons, to work around
23// the limitation that a module pass based on legacy pass manager cannot make
24// use of MachineBlockFrequencyInfo analysis. In the future, we can consider
25// porting the StaticDataSplitter pass to a module-pass using the new pass
26// manager framework. That way, analysis are lazily computed as opposed to
27// eagerly scheduled, and a module pass can use MachineBlockFrequencyInfo.
28//===----------------------------------------------------------------------===//
29
30#include "llvm/Analysis/ProfileSummaryInfo.h"
31#include "llvm/Analysis/StaticDataProfileInfo.h"
32#include "llvm/CodeGen/Passes.h"
33#include "llvm/IR/Analysis.h"
34#include "llvm/IR/Module.h"
35#include "llvm/IR/PassManager.h"
36#include "llvm/InitializePasses.h"
37#include "llvm/Pass.h"
38
39#define DEBUG_TYPE "static-data-annotator"
40
41using namespace llvm;
42
43/// A module pass which iterates global variables in the module and annotates
44/// their section prefixes based on profile-driven analysis.
45class StaticDataAnnotator : public ModulePass {
46public:
47 static char ID;
48
49 StaticDataProfileInfo *SDPI = nullptr;
50 const ProfileSummaryInfo *PSI = nullptr;
51
52 StaticDataAnnotator() : ModulePass(ID) {
53 initializeStaticDataAnnotatorPass(*PassRegistry::getPassRegistry());
54 }
55
56 void getAnalysisUsage(AnalysisUsage &AU) const override {
57 AU.addRequired<StaticDataProfileInfoWrapperPass>();
58 AU.addRequired<ProfileSummaryInfoWrapperPass>();
59 AU.setPreservesAll();
60 ModulePass::getAnalysisUsage(AU);
61 }
62
63 StringRef getPassName() const override { return "Static Data Annotator"; }
64
65 bool runOnModule(Module &M) override;
66};
67
68bool StaticDataAnnotator::runOnModule(Module &M) {
69 SDPI = &getAnalysis<StaticDataProfileInfoWrapperPass>()
70 .getStaticDataProfileInfo();
71 PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
72
73 if (!PSI->hasProfileSummary())
74 return false;
75
76 bool Changed = false;
77 for (auto &GV : M.globals()) {
78 if (GV.isDeclarationForLinker())
79 continue;
80
81 // The implementation below assumes prior passes don't set section prefixes,
82 // and specifically do 'assign' rather than 'update'. So report error if a
83 // section prefix is already set.
84 if (auto maybeSectionPrefix = GV.getSectionPrefix();
85 maybeSectionPrefix && !maybeSectionPrefix->empty())
86 llvm::report_fatal_error(reason: "Global variable " + GV.getName() +
87 " already has a section prefix " +
88 *maybeSectionPrefix);
89
90 StringRef SectionPrefix = SDPI->getConstantSectionPrefix(C: &GV, PSI);
91 if (SectionPrefix.empty())
92 continue;
93
94 GV.setSectionPrefix(SectionPrefix);
95 Changed = true;
96 }
97
98 return Changed;
99}
100
101char StaticDataAnnotator::ID = 0;
102
103INITIALIZE_PASS(StaticDataAnnotator, DEBUG_TYPE, "Static Data Annotator", false,
104 false)
105
106ModulePass *llvm::createStaticDataAnnotatorPass() {
107 return new StaticDataAnnotator();
108}
109