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//===-- FuncletLayout.cpp - Contiguously lay out funclets -----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements basic block placement transformations which result in
// funclets being contiguous.
//
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetSubtargetInfo.h"
using namespace llvm;
#define DEBUG_TYPE "funclet-layout"
namespace {
class FuncletLayout : public MachineFunctionPass {
public:
static char ID; // Pass identification, replacement for typeid
FuncletLayout() : MachineFunctionPass(ID) {
initializeFuncletLayoutPass(*PassRegistry::getPassRegistry());
}
bool runOnMachineFunction(MachineFunction &F) override;
};
}
static void
collectFuncletMembers(DenseMap<MachineBasicBlock *, int> &FuncletMembership,
int Funclet, MachineBasicBlock *MBB) {
// Don't revisit blocks.
if (FuncletMembership.count(MBB) > 0) {
// FIXME: This is a hack, we need to assert this unconditionally.
bool IsProbablyUnreachableBlock =
MBB->empty() ||
(MBB->succ_empty() && !MBB->getFirstTerminator()->isReturn() &&
MBB->size() == 1);
if (!IsProbablyUnreachableBlock) {
if (FuncletMembership[MBB] != Funclet) {
assert(false && "MBB is part of two funclets!");
report_fatal_error("MBB is part of two funclets!");
}
}
return;
}
// Add this MBB to our funclet.
FuncletMembership[MBB] = Funclet;
bool IsReturn = false;
int NumTerminators = 0;
for (MachineInstr &MI : MBB->terminators()) {
IsReturn |= MI.isReturn();
++NumTerminators;
}
assert((!IsReturn || NumTerminators == 1) &&
"Expected only one terminator when a return is present!");
// Returns are boundaries where funclet transfer can occur, don't follow
// successors.
if (IsReturn)
return;
for (MachineBasicBlock *SMBB : MBB->successors())
if (!SMBB->isEHPad())
collectFuncletMembers(FuncletMembership, Funclet, SMBB);
}
char FuncletLayout::ID = 0;
char &llvm::FuncletLayoutID = FuncletLayout::ID;
INITIALIZE_PASS(FuncletLayout, "funclet-layout",
"Contiguously Lay Out Funclets", false, false)
bool FuncletLayout::runOnMachineFunction(MachineFunction &F) {
// We don't have anything to do if there aren't any EH pads.
if (!F.getMMI().hasEHFunclets())
return false;
const TargetInstrInfo *TII = F.getSubtarget().getInstrInfo();
SmallVector<MachineBasicBlock *, 16> FuncletBlocks;
SmallVector<std::pair<MachineBasicBlock *, int>, 16> CatchRetSuccessors;
for (MachineBasicBlock &MBB : F) {
if (MBB.isEHFuncletEntry())
FuncletBlocks.push_back(&MBB);
MachineBasicBlock::iterator MBBI = MBB.getFirstTerminator();
if (MBBI->getOpcode() != TII->getCatchReturnOpcode())
continue;
MachineBasicBlock *Successor = MBBI->getOperand(0).getMBB();
MachineBasicBlock *SuccessorColor = MBBI->getOperand(1).getMBB();
CatchRetSuccessors.push_back({Successor, SuccessorColor->getNumber()});
}
// We don't have anything to do if there aren't any EH pads.
if (FuncletBlocks.empty())
return false;
DenseMap<MachineBasicBlock *, int> FuncletMembership;
// Identify all the basic blocks reachable from the function entry.
collectFuncletMembers(FuncletMembership, F.front().getNumber(), F.begin());
// Next, identify all the blocks inside the funclets.
for (MachineBasicBlock *MBB : FuncletBlocks)
collectFuncletMembers(FuncletMembership, MBB->getNumber(), MBB);
// Finally, identify all the targets of a catchret.
for (std::pair<MachineBasicBlock *, int> CatchRetPair : CatchRetSuccessors)
collectFuncletMembers(FuncletMembership, CatchRetPair.second,
CatchRetPair.first);
F.sort([&](MachineBasicBlock &x, MachineBasicBlock &y) {
return FuncletMembership[&x] < FuncletMembership[&y];
});
// Conservatively assume we changed something.
return true;
}
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