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
getStackAdjustmentSize(const BinaryContext & BC,const MCInst & Inst,int64_t & Adjustment)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
isIndifferentToSP(const MCInst & Inst,const BinaryContext & BC)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
shouldProcess(const BinaryFunction & Function)53 bool shouldProcess(const BinaryFunction &Function) {
54 return Function.isSimple() && Function.hasCFG() && !Function.isIgnored();
55 }
56
runForAllWeCare(std::map<uint64_t,BinaryFunction> & BFs,std::function<void (BinaryFunction &)> Task)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
combineAdjustments(BinaryFunction & BF)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
runOnFunctions(BinaryContext & BC)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