mirror of
https://github.com/llvm/llvm-project.git
synced 2025-05-03 08:16:06 +00:00
61785ffcfc
This PR replaces `isMachineBlockAddressTaken` by `hasAddressTaken` to include blocks which have their IR address taken as well. These blocks are also not removable since their predecessors' terminators do not directly point to the block.
101 lines
3.6 KiB
C++
101 lines
3.6 KiB
C++
//===-- GCEmptyBasicBlocks.cpp ----------------------------------*- C++ -*-===//
|
|
//
|
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
|
|
// See https://llvm.org/LICENSE.txt for license information.
|
|
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
///
|
|
/// \file
|
|
/// This file contains the implementation of empty blocks garbage collection
|
|
/// pass.
|
|
///
|
|
//===----------------------------------------------------------------------===//
|
|
#include "llvm/ADT/SmallVector.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/CodeGen/MachineBasicBlock.h"
|
|
#include "llvm/CodeGen/MachineFunction.h"
|
|
#include "llvm/CodeGen/MachineFunctionPass.h"
|
|
#include "llvm/CodeGen/MachineJumpTableInfo.h"
|
|
#include "llvm/CodeGen/Passes.h"
|
|
#include "llvm/CodeGen/TargetInstrInfo.h"
|
|
#include "llvm/InitializePasses.h"
|
|
|
|
using namespace llvm;
|
|
|
|
#define DEBUG_TYPE "gc-empty-basic-blocks"
|
|
|
|
STATISTIC(NumEmptyBlocksRemoved, "Number of empty blocks removed");
|
|
|
|
class GCEmptyBasicBlocks : public MachineFunctionPass {
|
|
public:
|
|
static char ID;
|
|
|
|
GCEmptyBasicBlocks() : MachineFunctionPass(ID) {
|
|
initializeGCEmptyBasicBlocksPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
StringRef getPassName() const override {
|
|
return "Remove Empty Basic Blocks.";
|
|
}
|
|
|
|
bool runOnMachineFunction(MachineFunction &MF) override;
|
|
};
|
|
|
|
bool GCEmptyBasicBlocks::runOnMachineFunction(MachineFunction &MF) {
|
|
if (MF.size() < 2)
|
|
return false;
|
|
MachineJumpTableInfo *JTI = MF.getJumpTableInfo();
|
|
int NumRemoved = 0;
|
|
|
|
// Iterate over all blocks except the last one. We can't remove the last block
|
|
// since it has no fallthrough block to rewire its predecessors to.
|
|
for (MachineFunction::iterator MBB = MF.begin(),
|
|
LastMBB = MachineFunction::iterator(MF.back()),
|
|
NextMBB;
|
|
MBB != LastMBB; MBB = NextMBB) {
|
|
NextMBB = std::next(MBB);
|
|
// TODO If a block is an eh pad, or it has address taken, we don't remove
|
|
// it. Removing such blocks is possible, but it probably requires a more
|
|
// complex logic.
|
|
if (MBB->isEHPad() || MBB->hasAddressTaken())
|
|
continue;
|
|
// Skip blocks with real code.
|
|
bool HasAnyRealCode = llvm::any_of(*MBB, [](const MachineInstr &MI) {
|
|
return !MI.isPosition() && !MI.isImplicitDef() && !MI.isKill() &&
|
|
!MI.isDebugInstr();
|
|
});
|
|
if (HasAnyRealCode)
|
|
continue;
|
|
|
|
LLVM_DEBUG(dbgs() << "Removing basic block " << MBB->getName()
|
|
<< " in function " << MF.getName() << ":\n"
|
|
<< *MBB << "\n");
|
|
SmallVector<MachineBasicBlock *, 8> Preds(MBB->predecessors());
|
|
// Rewire the predecessors of this block to use the next block.
|
|
for (auto &Pred : Preds)
|
|
Pred->ReplaceUsesOfBlockWith(&*MBB, &*NextMBB);
|
|
// Update the jump tables.
|
|
if (JTI)
|
|
JTI->ReplaceMBBInJumpTables(&*MBB, &*NextMBB);
|
|
// Remove this block from predecessors of all its successors.
|
|
while (!MBB->succ_empty())
|
|
MBB->removeSuccessor(MBB->succ_end() - 1);
|
|
// Finally, remove the block from the function.
|
|
MBB->eraseFromParent();
|
|
++NumRemoved;
|
|
}
|
|
NumEmptyBlocksRemoved += NumRemoved;
|
|
return NumRemoved != 0;
|
|
}
|
|
|
|
char GCEmptyBasicBlocks::ID = 0;
|
|
INITIALIZE_PASS(GCEmptyBasicBlocks, "gc-empty-basic-blocks",
|
|
"Removes empty basic blocks and redirects their uses to their "
|
|
"fallthrough blocks.",
|
|
false, false)
|
|
|
|
MachineFunctionPass *llvm::createGCEmptyBasicBlocksPass() {
|
|
return new GCEmptyBasicBlocks();
|
|
}
|