bolt/lib/Passes/AllocCombiner.cpp

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