//===--------------- PPCVSXFMAMutate.cpp - VSX FMA Mutation ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass mutates the form of VSX FMA instructions to avoid unnecessary
// copies.
//
//===----------------------------------------------------------------------===//
#include "PPCInstrInfo.h"
#include "MCTargetDesc/PPCPredicates.h"
#include "PPC.h"
#include "PPCInstrBuilder.h"
#include "PPCMachineFunctionInfo.h"
#include "PPCTargetMachine.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/PseudoSourceValue.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
static cl::opt<bool> DisableVSXFMAMutate("disable-ppc-vsx-fma-mutation",
cl::desc("Disable VSX FMA instruction mutation"), cl::Hidden);
#define DEBUG_TYPE "ppc-vsx-fma-mutate"
namespace llvm { namespace PPC {
int getAltVSXFMAOpcode(uint16_t Opcode);
} }
namespace {
// PPCVSXFMAMutate pass - For copies between VSX registers and non-VSX registers
// (Altivec and scalar floating-point registers), we need to transform the
// copies into subregister copies with other restrictions.
struct PPCVSXFMAMutate : public MachineFunctionPass {
static char ID;
PPCVSXFMAMutate() : MachineFunctionPass(ID) {
initializePPCVSXFMAMutatePass(*PassRegistry::getPassRegistry());
}
LiveIntervals *LIS;
const PPCInstrInfo *TII;
protected:
bool processBlock(MachineBasicBlock &MBB) {
bool Changed = false;
MachineRegisterInfo &MRI = MBB.getParent()->getRegInfo();
const TargetRegisterInfo *TRI = &TII->getRegisterInfo();
for (MachineBasicBlock::iterator I = MBB.begin(), IE = MBB.end();
I != IE; ++I) {
MachineInstr *MI = I;
// The default (A-type) VSX FMA form kills the addend (it is taken from
// the target register, which is then updated to reflect the result of
// the FMA). If the instruction, however, kills one of the registers
// used for the product, then we can use the M-form instruction (which
// will take that value from the to-be-defined register).
int AltOpc = PPC::getAltVSXFMAOpcode(MI->getOpcode());
if (AltOpc == -1)
continue;
// This pass is run after register coalescing, and so we're looking for
// a situation like this:
// ...
// %vreg5<def> = COPY %vreg9; VSLRC:%vreg5,%vreg9
// %vreg5<def,tied1> = XSMADDADP %vreg5<tied0>, %vreg17, %vreg16,
// %RM<imp-use>; VSLRC:%vreg5,%vreg17,%vreg16
// ...
// %vreg9<def,tied1> = XSMADDADP %vreg9<tied0>, %vreg17, %vreg19,
// %RM<imp-use>; VSLRC:%vreg9,%vreg17,%vreg19
// ...
// Where we can eliminate the copy by changing from the A-type to the
// M-type instruction. Specifically, for this example, this means:
// %vreg5<def,tied1> = XSMADDADP %vreg5<tied0>, %vreg17, %vreg16,
// %RM<imp-use>; VSLRC:%vreg5,%vreg17,%vreg16
// is replaced by:
// %vreg16<def,tied1> = XSMADDMDP %vreg16<tied0>, %vreg18, %vreg9,
// %RM<imp-use>; VSLRC:%vreg16,%vreg18,%vreg9
// and we remove: %vreg5<def> = COPY %vreg9; VSLRC:%vreg5,%vreg9
SlotIndex FMAIdx = LIS->getInstructionIndex(MI);
VNInfo *AddendValNo =
LIS->getInterval(MI->getOperand(1).getReg()).Query(FMAIdx).valueIn();
// This can be null if the register is undef.
if (!AddendValNo)
continue;
MachineInstr *AddendMI = LIS->getInstructionFromIndex(AddendValNo->def);
// The addend and this instruction must be in the same block.
if (!AddendMI || AddendMI->getParent() != MI->getParent())
continue;
// The addend must be a full copy within the same register class.
if (!AddendMI->isFullCopy())
continue;
unsigned AddendSrcReg = AddendMI->getOperand(1).getReg();
if (TargetRegisterInfo::isVirtualRegister(AddendSrcReg)) {
if (MRI.getRegClass(AddendMI->getOperand(0).getReg()) !=
MRI.getRegClass(AddendSrcReg))
continue;
} else {
// If AddendSrcReg is a physical register, make sure the destination
// register class contains it.
if (!MRI.getRegClass(AddendMI->getOperand(0).getReg())
->contains(AddendSrcReg))
continue;
}
// In theory, there could be other uses of the addend copy before this
// fma. We could deal with this, but that would require additional
// logic below and I suspect it will not occur in any relevant
// situations. Additionally, check whether the copy source is killed
// prior to the fma. In order to replace the addend here with the
// source of the copy, it must still be live here. We can't use
// interval testing for a physical register, so as long as we're
// walking the MIs we may as well test liveness here.
//
// FIXME: There is a case that occurs in practice, like this:
// %vreg9<def> = COPY %F1; VSSRC:%vreg9
// ...
// %vreg6<def> = COPY %vreg9; VSSRC:%vreg6,%vreg9
// %vreg7<def> = COPY %vreg9; VSSRC:%vreg7,%vreg9
// %vreg9<def,tied1> = XSMADDASP %vreg9<tied0>, %vreg1, %vreg4; VSSRC:
// %vreg6<def,tied1> = XSMADDASP %vreg6<tied0>, %vreg1, %vreg2; VSSRC:
// %vreg7<def,tied1> = XSMADDASP %vreg7<tied0>, %vreg1, %vreg3; VSSRC:
// which prevents an otherwise-profitable transformation.
bool OtherUsers = false, KillsAddendSrc = false;
for (auto J = std::prev(I), JE = MachineBasicBlock::iterator(AddendMI);
J != JE; --J) {
if (J->readsVirtualRegister(AddendMI->getOperand(0).getReg())) {
OtherUsers = true;
break;
}
if (J->modifiesRegister(AddendSrcReg, TRI) ||
J->killsRegister(AddendSrcReg, TRI)) {
KillsAddendSrc = true;
break;
}
}
if (OtherUsers || KillsAddendSrc)
continue;
// Find one of the product operands that is killed by this instruction.
unsigned KilledProdOp = 0, OtherProdOp = 0;
if (LIS->getInterval(MI->getOperand(2).getReg())
.Query(FMAIdx).isKill()) {
KilledProdOp = 2;
OtherProdOp = 3;
} else if (LIS->getInterval(MI->getOperand(3).getReg())
.Query(FMAIdx).isKill()) {
KilledProdOp = 3;
OtherProdOp = 2;
}
// If there are no killed product operands, then this transformation is
// likely not profitable.
if (!KilledProdOp)
continue;
// If the addend copy is used only by this MI, then the addend source
// register is likely not live here. This could be fixed (based on the
// legality checks above, the live range for the addend source register
// could be extended), but it seems likely that such a trivial copy can
// be coalesced away later, and thus is not worth the effort.
if (TargetRegisterInfo::isVirtualRegister(AddendSrcReg) &&
!LIS->getInterval(AddendSrcReg).liveAt(FMAIdx))
continue;
// Transform: (O2 * O3) + O1 -> (O2 * O1) + O3.
unsigned KilledProdReg = MI->getOperand(KilledProdOp).getReg();
unsigned OtherProdReg = MI->getOperand(OtherProdOp).getReg();
unsigned AddSubReg = AddendMI->getOperand(1).getSubReg();
unsigned KilledProdSubReg = MI->getOperand(KilledProdOp).getSubReg();
unsigned OtherProdSubReg = MI->getOperand(OtherProdOp).getSubReg();
bool AddRegKill = AddendMI->getOperand(1).isKill();
bool KilledProdRegKill = MI->getOperand(KilledProdOp).isKill();
bool OtherProdRegKill = MI->getOperand(OtherProdOp).isKill();
bool AddRegUndef = AddendMI->getOperand(1).isUndef();
bool KilledProdRegUndef = MI->getOperand(KilledProdOp).isUndef();
bool OtherProdRegUndef = MI->getOperand(OtherProdOp).isUndef();
unsigned OldFMAReg = MI->getOperand(0).getReg();
// The transformation doesn't work well with things like:
// %vreg5 = A-form-op %vreg5, %vreg11, %vreg5;
// so leave such things alone.
if (OldFMAReg == KilledProdReg)
continue;
// If there isn't a class that fits, we can't perform the transform.
// This is needed for correctness with a mixture of VSX and Altivec
// instructions to make sure that a low VSX register is not assigned to
// the Altivec instruction.
if (!MRI.constrainRegClass(KilledProdReg,
MRI.getRegClass(OldFMAReg)))
continue;
assert(OldFMAReg == AddendMI->getOperand(0).getReg() &&
"Addend copy not tied to old FMA output!");
DEBUG(dbgs() << "VSX FMA Mutation:\n " << *MI;);
MI->getOperand(0).setReg(KilledProdReg);
MI->getOperand(1).setReg(KilledProdReg);
MI->getOperand(3).setReg(AddendSrcReg);
MI->getOperand(2).setReg(OtherProdReg);
MI->getOperand(0).setSubReg(KilledProdSubReg);
MI->getOperand(1).setSubReg(KilledProdSubReg);
MI->getOperand(3).setSubReg(AddSubReg);
MI->getOperand(2).setSubReg(OtherProdSubReg);
MI->getOperand(1).setIsKill(KilledProdRegKill);
MI->getOperand(3).setIsKill(AddRegKill);
MI->getOperand(2).setIsKill(OtherProdRegKill);
MI->getOperand(1).setIsUndef(KilledProdRegUndef);
MI->getOperand(3).setIsUndef(AddRegUndef);
MI->getOperand(2).setIsUndef(OtherProdRegUndef);
MI->setDesc(TII->get(AltOpc));
DEBUG(dbgs() << " -> " << *MI);
// The killed product operand was killed here, so we can reuse it now
// for the result of the fma.
LiveInterval &FMAInt = LIS->getInterval(OldFMAReg);
VNInfo *FMAValNo = FMAInt.getVNInfoAt(FMAIdx.getRegSlot());
for (auto UI = MRI.reg_nodbg_begin(OldFMAReg), UE = MRI.reg_nodbg_end();
UI != UE;) {
MachineOperand &UseMO = *UI;
MachineInstr *UseMI = UseMO.getParent();
++UI;
// Don't replace the result register of the copy we're about to erase.
if (UseMI == AddendMI)
continue;
UseMO.substVirtReg(KilledProdReg, KilledProdSubReg, *TRI);
}
// Extend the live intervals of the killed product operand to hold the
// fma result.
LiveInterval &NewFMAInt = LIS->getInterval(KilledProdReg);
for (LiveInterval::iterator AI = FMAInt.begin(), AE = FMAInt.end();
AI != AE; ++AI) {
// Don't add the segment that corresponds to the original copy.
if (AI->valno == AddendValNo)
continue;
VNInfo *NewFMAValNo =
NewFMAInt.getNextValue(AI->start,
LIS->getVNInfoAllocator());
NewFMAInt.addSegment(LiveInterval::Segment(AI->start, AI->end,
NewFMAValNo));
}
DEBUG(dbgs() << " extended: " << NewFMAInt << '\n');
// Extend the live interval of the addend source (it might end at the
// copy to be removed, or somewhere in between there and here). This
// is necessary only if it is a physical register.
if (!TargetRegisterInfo::isVirtualRegister(AddendSrcReg))
for (MCRegUnitIterator Units(AddendSrcReg, TRI); Units.isValid();
++Units) {
unsigned Unit = *Units;
LiveRange &AddendSrcRange = LIS->getRegUnit(Unit);
AddendSrcRange.extendInBlock(LIS->getMBBStartIdx(&MBB),
FMAIdx.getRegSlot());
DEBUG(dbgs() << " extended: " << AddendSrcRange << '\n');
}
FMAInt.removeValNo(FMAValNo);
DEBUG(dbgs() << " trimmed: " << FMAInt << '\n');
// Remove the (now unused) copy.
DEBUG(dbgs() << " removing: " << *AddendMI << '\n');
LIS->RemoveMachineInstrFromMaps(AddendMI);
AddendMI->eraseFromParent();
Changed = true;
}
return Changed;
}
public:
bool runOnMachineFunction(MachineFunction &MF) override {
// If we don't have VSX then go ahead and return without doing
// anything.
const PPCSubtarget &STI = MF.getSubtarget<PPCSubtarget>();
if (!STI.hasVSX())
return false;
LIS = &getAnalysis<LiveIntervals>();
TII = STI.getInstrInfo();
bool Changed = false;
if (DisableVSXFMAMutate)
return Changed;
for (MachineFunction::iterator I = MF.begin(); I != MF.end();) {
MachineBasicBlock &B = *I++;
if (processBlock(B))
Changed = true;
}
return Changed;
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<LiveIntervals>();
AU.addPreserved<LiveIntervals>();
AU.addRequired<SlotIndexes>();
AU.addPreserved<SlotIndexes>();
MachineFunctionPass::getAnalysisUsage(AU);
}
};
}
INITIALIZE_PASS_BEGIN(PPCVSXFMAMutate, DEBUG_TYPE,
"PowerPC VSX FMA Mutation", false, false)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_DEPENDENCY(SlotIndexes)
INITIALIZE_PASS_END(PPCVSXFMAMutate, DEBUG_TYPE,
"PowerPC VSX FMA Mutation", false, false)
char &llvm::PPCVSXFMAMutateID = PPCVSXFMAMutate::ID;
char PPCVSXFMAMutate::ID = 0;
FunctionPass *llvm::createPPCVSXFMAMutatePass() {
return new PPCVSXFMAMutate();
}