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//===- HexagonCFGOptimizer.cpp - CFG optimizations ------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "Hexagon.h"
#include "MCTargetDesc/HexagonMCTargetDesc.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/ErrorHandling.h"
#include <cassert>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "hexagon_cfg"
namespace llvm {
FunctionPass *createHexagonCFGOptimizer();
void initializeHexagonCFGOptimizerPass(PassRegistry&);
} // end namespace llvm
namespace {
class HexagonCFGOptimizer : public MachineFunctionPass {
private:
void InvertAndChangeJumpTarget(MachineInstr &, MachineBasicBlock *);
bool isOnFallThroughPath(MachineBasicBlock *MBB);
public:
static char ID;
HexagonCFGOptimizer() : MachineFunctionPass(ID) {
initializeHexagonCFGOptimizerPass(*PassRegistry::getPassRegistry());
}
StringRef getPassName() const override { return "Hexagon CFG Optimizer"; }
bool runOnMachineFunction(MachineFunction &Fn) override;
MachineFunctionProperties getRequiredProperties() const override {
return MachineFunctionProperties().set(
MachineFunctionProperties::Property::NoVRegs);
}
};
} // end anonymous namespace
char HexagonCFGOptimizer::ID = 0;
static bool IsConditionalBranch(int Opc) {
switch (Opc) {
case Hexagon::J2_jumpt:
case Hexagon::J2_jumptpt:
case Hexagon::J2_jumpf:
case Hexagon::J2_jumpfpt:
case Hexagon::J2_jumptnew:
case Hexagon::J2_jumpfnew:
case Hexagon::J2_jumptnewpt:
case Hexagon::J2_jumpfnewpt:
return true;
}
return false;
}
static bool IsUnconditionalJump(int Opc) {
return (Opc == Hexagon::J2_jump);
}
void HexagonCFGOptimizer::InvertAndChangeJumpTarget(
MachineInstr &MI, MachineBasicBlock *NewTarget) {
const TargetInstrInfo *TII =
MI.getParent()->getParent()->getSubtarget().getInstrInfo();
int NewOpcode = 0;
switch (MI.getOpcode()) {
case Hexagon::J2_jumpt:
NewOpcode = Hexagon::J2_jumpf;
break;
case Hexagon::J2_jumpf:
NewOpcode = Hexagon::J2_jumpt;
break;
case Hexagon::J2_jumptnewpt:
NewOpcode = Hexagon::J2_jumpfnewpt;
break;
case Hexagon::J2_jumpfnewpt:
NewOpcode = Hexagon::J2_jumptnewpt;
break;
default:
llvm_unreachable("Cannot handle this case");
}
MI.setDesc(TII->get(NewOpcode));
MI.getOperand(1).setMBB(NewTarget);
}
bool HexagonCFGOptimizer::isOnFallThroughPath(MachineBasicBlock *MBB) {
if (MBB->canFallThrough())
return true;
for (MachineBasicBlock *PB : MBB->predecessors())
if (PB->isLayoutSuccessor(MBB) && PB->canFallThrough())
return true;
return false;
}
bool HexagonCFGOptimizer::runOnMachineFunction(MachineFunction &Fn) {
if (skipFunction(Fn.getFunction()))
return false;
// Loop over all of the basic blocks.
for (MachineBasicBlock &MBB : Fn) {
// Traverse the basic block.
MachineBasicBlock::iterator MII = MBB.getFirstTerminator();
if (MII != MBB.end()) {
MachineInstr &MI = *MII;
int Opc = MI.getOpcode();
if (IsConditionalBranch(Opc)) {
// (Case 1) Transform the code if the following condition occurs:
// BB1: if (p0) jump BB3
// ...falls-through to BB2 ...
// BB2: jump BB4
// ...next block in layout is BB3...
// BB3: ...
//
// Transform this to:
// BB1: if (!p0) jump BB4
// Remove BB2
// BB3: ...
//
// (Case 2) A variation occurs when BB3 contains a JMP to BB4:
// BB1: if (p0) jump BB3
// ...falls-through to BB2 ...
// BB2: jump BB4
// ...other basic blocks ...
// BB4:
// ...not a fall-thru
// BB3: ...
// jump BB4
//
// Transform this to:
// BB1: if (!p0) jump BB4
// Remove BB2
// BB3: ...
// BB4: ...
unsigned NumSuccs = MBB.succ_size();
MachineBasicBlock::succ_iterator SI = MBB.succ_begin();
MachineBasicBlock* FirstSucc = *SI;
MachineBasicBlock* SecondSucc = *(++SI);
MachineBasicBlock* LayoutSucc = nullptr;
MachineBasicBlock* JumpAroundTarget = nullptr;
if (MBB.isLayoutSuccessor(FirstSucc)) {
LayoutSucc = FirstSucc;
JumpAroundTarget = SecondSucc;
} else if (MBB.isLayoutSuccessor(SecondSucc)) {
LayoutSucc = SecondSucc;
JumpAroundTarget = FirstSucc;
} else {
// Odd case...cannot handle.
}
// The target of the unconditional branch must be JumpAroundTarget.
// TODO: If not, we should not invert the unconditional branch.
MachineBasicBlock* CondBranchTarget = nullptr;
if (MI.getOpcode() == Hexagon::J2_jumpt ||
MI.getOpcode() == Hexagon::J2_jumpf) {
CondBranchTarget = MI.getOperand(1).getMBB();
}
if (!LayoutSucc || (CondBranchTarget != JumpAroundTarget)) {
continue;
}
if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) {
// Ensure that BB2 has one instruction -- an unconditional jump.
if ((LayoutSucc->size() == 1) &&
IsUnconditionalJump(LayoutSucc->front().getOpcode())) {
assert(JumpAroundTarget && "jump target is needed to process second basic block");
MachineBasicBlock* UncondTarget =
LayoutSucc->front().getOperand(0).getMBB();
// Check if the layout successor of BB2 is BB3.
bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget);
bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) &&
!JumpAroundTarget->empty() &&
IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) &&
JumpAroundTarget->pred_size() == 1 &&
JumpAroundTarget->succ_size() == 1;
if (case1 || case2) {
InvertAndChangeJumpTarget(MI, UncondTarget);
MBB.replaceSuccessor(JumpAroundTarget, UncondTarget);
// Remove the unconditional branch in LayoutSucc.
LayoutSucc->erase(LayoutSucc->begin());
LayoutSucc->replaceSuccessor(UncondTarget, JumpAroundTarget);
// This code performs the conversion for case 2, which moves
// the block to the fall-thru case (BB3 in the code above).
if (case2 && !case1) {
JumpAroundTarget->moveAfter(LayoutSucc);
// only move a block if it doesn't have a fall-thru. otherwise
// the CFG will be incorrect.
if (!isOnFallThroughPath(UncondTarget))
UncondTarget->moveAfter(JumpAroundTarget);
}
// Correct live-in information. Is used by post-RA scheduler
// The live-in to LayoutSucc is now all values live-in to
// JumpAroundTarget.
std::vector<MachineBasicBlock::RegisterMaskPair> OrigLiveIn(
LayoutSucc->livein_begin(), LayoutSucc->livein_end());
std::vector<MachineBasicBlock::RegisterMaskPair> NewLiveIn(
JumpAroundTarget->livein_begin(),
JumpAroundTarget->livein_end());
for (const auto &OrigLI : OrigLiveIn)
LayoutSucc->removeLiveIn(OrigLI.PhysReg);
for (const auto &NewLI : NewLiveIn)
LayoutSucc->addLiveIn(NewLI);
}
}
}
}
}
}
return true;
}
//===----------------------------------------------------------------------===//
// Public Constructor Functions
//===----------------------------------------------------------------------===//
INITIALIZE_PASS(HexagonCFGOptimizer, "hexagon-cfg", "Hexagon CFG Optimizer",
false, false)
FunctionPass *llvm::createHexagonCFGOptimizer() {
return new HexagonCFGOptimizer();
}