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//===-- LVLGen.cpp - LVL instruction generator ----------------------------===//
//
// 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 "VE.h"
#include "VESubtarget.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
using namespace llvm;
#define DEBUG_TYPE "lvl-gen"
namespace {
struct LVLGen : public MachineFunctionPass {
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
static char ID;
LVLGen() : MachineFunctionPass(ID) {}
bool runOnMachineBasicBlock(MachineBasicBlock &MBB);
bool runOnMachineFunction(MachineFunction &F) override;
unsigned getVL(const MachineInstr &MI);
int getVLIndex(unsigned Opcode);
};
char LVLGen::ID = 0;
} // end of anonymous namespace
FunctionPass *llvm::createLVLGenPass() { return new LVLGen; }
int LVLGen::getVLIndex(unsigned Opcode) {
const MCInstrDesc &MCID = TII->get(Opcode);
// If an instruction has VLIndex information, return it.
if (HAS_VLINDEX(MCID.TSFlags))
return GET_VLINDEX(MCID.TSFlags);
return -1;
}
// returns a register holding a vector length. NoRegister is returned when
// this MI does not have a vector length.
unsigned LVLGen::getVL(const MachineInstr &MI) {
int Index = getVLIndex(MI.getOpcode());
if (Index >= 0)
return MI.getOperand(Index).getReg();
return VE::NoRegister;
}
bool LVLGen::runOnMachineBasicBlock(MachineBasicBlock &MBB) {
#define RegName(no) \
(MBB.getParent()->getSubtarget<VESubtarget>().getRegisterInfo()->getName(no))
bool Changed = false;
bool HasRegForVL = false;
unsigned RegForVL;
for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end();) {
MachineBasicBlock::iterator MI = I;
// Check whether MI uses a vector length operand. If so, we prepare for VL
// register. We would like to reuse VL register as much as possible. We
// also would like to keep the number of LEA instructions as fewer as
// possible. Therefore, we use a regular scalar register to hold immediate
// values to load VL register. And try to reuse identical scalar registers
// to avoid new LVLr instructions as much as possible.
unsigned Reg = getVL(*MI);
if (Reg != VE::NoRegister) {
LLVM_DEBUG(dbgs() << "Vector instruction found: ");
LLVM_DEBUG(MI->dump());
LLVM_DEBUG(dbgs() << "Vector length is " << RegName(Reg) << ". ");
LLVM_DEBUG(dbgs() << "Current VL is "
<< (HasRegForVL ? RegName(RegForVL) : "unknown")
<< ". ");
if (!HasRegForVL || RegForVL != Reg) {
// Use VL, but a different value in a different scalar register.
// So, generate new LVL instruction just before the current instruction.
LLVM_DEBUG(dbgs() << "Generate a LVL instruction to load "
<< RegName(Reg) << ".\n");
BuildMI(MBB, I, MI->getDebugLoc(), TII->get(VE::LVLr)).addReg(Reg);
HasRegForVL = true;
RegForVL = Reg;
Changed = true;
} else {
LLVM_DEBUG(dbgs() << "Reuse current VL.\n");
}
}
// Check the update of a given scalar register holding an immediate value
// for VL register. Also, a call doesn't preserve VL register.
if (HasRegForVL) {
if (MI->definesRegister(RegForVL, TRI) ||
MI->modifiesRegister(RegForVL, TRI) ||
MI->killsRegister(RegForVL, TRI) || MI->isCall()) {
// The latest VL is needed to be updated, so disable HasRegForVL.
LLVM_DEBUG(dbgs() << RegName(RegForVL) << " is needed to be updated: ");
LLVM_DEBUG(MI->dump());
HasRegForVL = false;
}
}
++I;
}
return Changed;
}
bool LVLGen::runOnMachineFunction(MachineFunction &F) {
LLVM_DEBUG(dbgs() << "********** Begin LVLGen **********\n");
LLVM_DEBUG(dbgs() << "********** Function: " << F.getName() << '\n');
LLVM_DEBUG(F.dump());
bool Changed = false;
const VESubtarget &Subtarget = F.getSubtarget<VESubtarget>();
TII = Subtarget.getInstrInfo();
TRI = Subtarget.getRegisterInfo();
for (MachineBasicBlock &MBB : F)
Changed |= runOnMachineBasicBlock(MBB);
if (Changed) {
LLVM_DEBUG(dbgs() << "\n");
LLVM_DEBUG(F.dump());
}
LLVM_DEBUG(dbgs() << "********** End LVLGen **********\n");
return Changed;
}
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