1 //===- bolt/Passes/AllocCombiner.cpp --------------------------------------===//
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 // This file implements the AllocCombinerPass class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "bolt/Passes/AllocCombiner.h"
14 
15 #define DEBUG_TYPE "alloccombiner"
16 
17 using namespace llvm;
18 
19 namespace opts {
20 
21 extern cl::opt<bolt::FrameOptimizationType> FrameOptimization;
22 
23 } // end namespace opts
24 
25 namespace llvm {
26 namespace bolt {
27 
28 namespace {
29 
30 bool getStackAdjustmentSize(const BinaryContext &BC, const MCInst &Inst,
31                             int64_t &Adjustment) {
32   return BC.MIB->evaluateStackOffsetExpr(
33       Inst, Adjustment, std::make_pair(BC.MIB->getStackPointer(), 0LL),
34       std::make_pair(0, 0LL));
35 }
36 
37 bool isIndifferentToSP(const MCInst &Inst, const BinaryContext &BC) {
38   if (BC.MIB->isCFI(Inst))
39     return true;
40 
41   const MCInstrDesc II = BC.MII->get(Inst.getOpcode());
42   if (BC.MIB->isTerminator(Inst) ||
43       II.hasImplicitDefOfPhysReg(BC.MIB->getStackPointer(), BC.MRI.get()) ||
44       II.hasImplicitUseOfPhysReg(BC.MIB->getStackPointer()))
45     return false;
46 
47   for (const MCOperand &Operand : MCPlus::primeOperands(Inst))
48     if (Operand.isReg() && Operand.getReg() == BC.MIB->getStackPointer())
49       return false;
50   return true;
51 }
52 
53 bool shouldProcess(const BinaryFunction &Function) {
54   return Function.isSimple() && Function.hasCFG() && !Function.isIgnored();
55 }
56 
57 void runForAllWeCare(std::map<uint64_t, BinaryFunction> &BFs,
58                      std::function<void(BinaryFunction &)> Task) {
59   for (auto &It : BFs) {
60     BinaryFunction &Function = It.second;
61     if (shouldProcess(Function))
62       Task(Function);
63   }
64 }
65 
66 } // end anonymous namespace
67 
68 void AllocCombinerPass::combineAdjustments(BinaryFunction &BF) {
69   BinaryContext &BC = BF.getBinaryContext();
70   for (BinaryBasicBlock &BB : BF) {
71     MCInst *Prev = nullptr;
72     for (auto I = BB.rbegin(), E = BB.rend(); I != E; ++I) {
73       MCInst &Inst = *I;
74       if (isIndifferentToSP(Inst, BC))
75         continue; // Skip updating Prev
76 
77       int64_t Adjustment = 0LL;
78       if (!Prev || !BC.MIB->isStackAdjustment(Inst) ||
79           !BC.MIB->isStackAdjustment(*Prev) ||
80           !getStackAdjustmentSize(BC, *Prev, Adjustment)) {
81         Prev = &Inst;
82         continue;
83       }
84 
85       LLVM_DEBUG({
86         dbgs() << "At \"" << BF.getPrintName() << "\", combining: \n";
87         Inst.dump();
88         Prev->dump();
89         dbgs() << "Adjustment: " << Adjustment << "\n";
90       });
91 
92       if (BC.MIB->isSUB(Inst))
93         Adjustment = -Adjustment;
94 
95       BC.MIB->addToImm(Inst, Adjustment, BC.Ctx.get());
96 
97       LLVM_DEBUG({
98         dbgs() << "After adjustment:\n";
99         Inst.dump();
100       });
101 
102       BB.eraseInstruction(BB.findInstruction(Prev));
103       ++NumCombined;
104       DynamicCountCombined += BB.getKnownExecutionCount();
105       FuncsChanged.insert(&BF);
106       Prev = &Inst;
107     }
108   }
109 }
110 
111 void AllocCombinerPass::runOnFunctions(BinaryContext &BC) {
112   if (opts::FrameOptimization == FOP_NONE)
113     return;
114 
115   runForAllWeCare(BC.getBinaryFunctions(), [&](BinaryFunction &Function) {
116     combineAdjustments(Function);
117   });
118 
119   outs() << "BOLT-INFO: Allocation combiner: " << NumCombined
120          << " empty spaces coalesced (dyn count: " << DynamicCountCombined
121          << ").\n";
122 }
123 
124 } // end namespace bolt
125 } // end namespace llvm
126