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llvm-mirror/lib/Target/Hexagon/HexagonNewValueJump.cpp
Duncan Sands 18d2eeeba4 Silence a gcc-4.6 warning: GCC fails to understand that secondReg and cmpOp2 are 
correlated, and thinks that cmpOp2 may be used uninitialized.

llvm-svn: 158263
2012-06-09 10:04:03 +00:00

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//===----- HexagonNewValueJump.cpp - Hexagon Backend New Value Jump -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This implements NewValueJump pass in Hexagon.
// Ideally, we should merge this as a Peephole pass prior to register
// allocation, but because we have a spill in between the feeder and new value
// jump instructions, we are forced to write after register allocation.
// Having said that, we should re-attempt to pull this earlier at some point
// in future.
// The basic approach looks for sequence of predicated jump, compare instruciton
// that genereates the predicate and, the feeder to the predicate. Once it finds
// all, it collapses compare and jump instruction into a new valu jump
// intstructions.
//
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "hexagon-nvj"
#include "llvm/PassSupport.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/ScheduleDAGInstrs.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/MachineFunctionAnalysis.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetRegisterInfo.h"
#include "Hexagon.h"
#include "HexagonTargetMachine.h"
#include "HexagonRegisterInfo.h"
#include "HexagonSubtarget.h"
#include "HexagonInstrInfo.h"
#include "HexagonMachineFunctionInfo.h"
#include <map>
#include "llvm/Support/CommandLine.h"
using namespace llvm;
STATISTIC(NumNVJGenerated, "Number of New Value Jump Instructions created");
static cl::opt<int>
DbgNVJCount("nvj-count", cl::init(-1), cl::Hidden, cl::desc(
"Maximum number of predicated jumps to be converted to New Value Jump"));
static cl::opt<bool> DisableNewValueJumps("disable-nvjump", cl::Hidden,
cl::ZeroOrMore, cl::init(false),
cl::desc("Disable New Value Jumps"));
namespace {
struct HexagonNewValueJump : public MachineFunctionPass {
const HexagonInstrInfo *QII;
const HexagonRegisterInfo *QRI;
public:
static char ID;
HexagonNewValueJump() : MachineFunctionPass(ID) { }
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
MachineFunctionPass::getAnalysisUsage(AU);
}
const char *getPassName() const {
return "Hexagon NewValueJump";
}
virtual bool runOnMachineFunction(MachineFunction &Fn);
private:
};
} // end of anonymous namespace
char HexagonNewValueJump::ID = 0;
// We have identified this II could be feeder to NVJ,
// verify that it can be.
static bool canBeFeederToNewValueJump(const HexagonInstrInfo *QII,
const TargetRegisterInfo *TRI,
MachineBasicBlock::iterator II,
MachineBasicBlock::iterator end,
MachineBasicBlock::iterator skip,
MachineFunction &MF) {
// Predicated instruction can not be feeder to NVJ.
if (QII->isPredicated(II))
return false;
// Bail out if feederReg is a paired register (double regs in
// our case). One would think that we can check to see if a given
// register cmpReg1 or cmpReg2 is a sub register of feederReg
// using -- if (QRI->isSubRegister(feederReg, cmpReg1) logic
// before the callsite of this function
// But we can not as it comes in the following fashion.
// %D0<def> = Hexagon_S2_lsr_r_p %D0<kill>, %R2<kill>
// %R0<def> = KILL %R0, %D0<imp-use,kill>
// %P0<def> = CMPEQri %R0<kill>, 0
// Hence, we need to check if it's a KILL instruction.
if (II->getOpcode() == TargetOpcode::KILL)
return false;
// Make sure there there is no 'def' or 'use' of any of the uses of
// feeder insn between it's definition, this MI and jump, jmpInst
// skipping compare, cmpInst.
// Here's the example.
// r21=memub(r22+r24<<#0)
// p0 = cmp.eq(r21, #0)
// r4=memub(r3+r21<<#0)
// if (p0.new) jump:t .LBB29_45
// Without this check, it will be converted into
// r4=memub(r3+r21<<#0)
// r21=memub(r22+r24<<#0)
// p0 = cmp.eq(r21, #0)
// if (p0.new) jump:t .LBB29_45
// and result WAR hazards if converted to New Value Jump.
for (unsigned i = 0; i < II->getNumOperands(); ++i) {
if (II->getOperand(i).isReg() &&
(II->getOperand(i).isUse() || II->getOperand(i).isDef())) {
MachineBasicBlock::iterator localII = II;
++localII;
unsigned Reg = II->getOperand(i).getReg();
for (MachineBasicBlock::iterator localBegin = localII;
localBegin != end; ++localBegin) {
if (localBegin == skip ) continue;
// Check for Subregisters too.
if (localBegin->modifiesRegister(Reg, TRI) ||
localBegin->readsRegister(Reg, TRI))
return false;
}
}
}
return true;
}
// These are the common checks that need to performed
// to determine if
// 1. compare instruction can be moved before jump.
// 2. feeder to the compare instruction can be moved before jump.
static bool commonChecksToProhibitNewValueJump(bool afterRA,
MachineBasicBlock::iterator MII) {
// If store in path, bail out.
if (MII->getDesc().mayStore())
return false;
// if call in path, bail out.
if (MII->getOpcode() == Hexagon::CALLv3)
return false;
// if NVJ is running prior to RA, do the following checks.
if (!afterRA) {
// The following Target Opcode instructions are spurious
// to new value jump. If they are in the path, bail out.
// KILL sets kill flag on the opcode. It also sets up a
// single register, out of pair.
// %D0<def> = Hexagon_S2_lsr_r_p %D0<kill>, %R2<kill>
// %R0<def> = KILL %R0, %D0<imp-use,kill>
// %P0<def> = CMPEQri %R0<kill>, 0
// PHI can be anything after RA.
// COPY can remateriaze things in between feeder, compare and nvj.
if (MII->getOpcode() == TargetOpcode::KILL ||
MII->getOpcode() == TargetOpcode::PHI ||
MII->getOpcode() == TargetOpcode::COPY)
return false;
// The following pseudo Hexagon instructions sets "use" and "def"
// of registers by individual passes in the backend. At this time,
// we don't know the scope of usage and definitions of these
// instructions.
if (MII->getOpcode() == Hexagon::TFR_condset_rr ||
MII->getOpcode() == Hexagon::TFR_condset_ii ||
MII->getOpcode() == Hexagon::TFR_condset_ri ||
MII->getOpcode() == Hexagon::TFR_condset_ir ||
MII->getOpcode() == Hexagon::LDriw_pred ||
MII->getOpcode() == Hexagon::STriw_pred)
return false;
}
return true;
}
static bool canCompareBeNewValueJump(const HexagonInstrInfo *QII,
const TargetRegisterInfo *TRI,
MachineBasicBlock::iterator II,
unsigned pReg,
bool secondReg,
bool optLocation,
MachineBasicBlock::iterator end,
MachineFunction &MF) {
MachineInstr *MI = II;
// If the second operand of the compare is an imm, make sure it's in the
// range specified by the arch.
if (!secondReg) {
int64_t v = MI->getOperand(2).getImm();
if (MI->getOpcode() == Hexagon::CMPGEri ||
(MI->getOpcode() == Hexagon::CMPGEUri && v > 0))
--v;
if (!(isUInt<5>(v) ||
((MI->getOpcode() == Hexagon::CMPEQri ||
MI->getOpcode() == Hexagon::CMPGTri ||
MI->getOpcode() == Hexagon::CMPGEri) &&
(v == -1))))
return false;
}
unsigned cmpReg1, cmpOp2 = 0; // cmpOp2 assignment silences compiler warning.
cmpReg1 = MI->getOperand(1).getReg();
if (secondReg) {
cmpOp2 = MI->getOperand(2).getReg();
// Make sure that that second register is not from COPY
// At machine code level, we don't need this, but if we decide
// to move new value jump prior to RA, we would be needing this.
MachineRegisterInfo &MRI = MF.getRegInfo();
if (secondReg && !TargetRegisterInfo::isPhysicalRegister(cmpOp2)) {
MachineInstr *def = MRI.getVRegDef(cmpOp2);
if (def->getOpcode() == TargetOpcode::COPY)
return false;
}
}
// Walk the instructions after the compare (predicate def) to the jump,
// and satisfy the following conditions.
++II ;
for (MachineBasicBlock::iterator localII = II; localII != end;
++localII) {
// Check 1.
// If "common" checks fail, bail out.
if (!commonChecksToProhibitNewValueJump(optLocation, localII))
return false;
// Check 2.
// If there is a def or use of predicate (result of compare), bail out.
if (localII->modifiesRegister(pReg, TRI) ||
localII->readsRegister(pReg, TRI))
return false;
// Check 3.
// If there is a def of any of the use of the compare (operands of compare),
// bail out.
// Eg.
// p0 = cmp.eq(r2, r0)
// r2 = r4
// if (p0.new) jump:t .LBB28_3
if (localII->modifiesRegister(cmpReg1, TRI) ||
(secondReg && localII->modifiesRegister(cmpOp2, TRI)))
return false;
}
return true;
}
// Given a compare operator, return a matching New Value Jump
// compare operator. Make sure that MI here is included in
// HexagonInstrInfo.cpp::isNewValueJumpCandidate
static unsigned getNewValueJumpOpcode(const MachineInstr *MI, int reg,
bool secondRegNewified) {
switch (MI->getOpcode()) {
case Hexagon::CMPEQrr:
return Hexagon::JMP_EQrrPt_nv_V4;
case Hexagon::CMPEQri: {
if (reg >= 0)
return Hexagon::JMP_EQriPt_nv_V4;
else
return Hexagon::JMP_EQriPtneg_nv_V4;
}
case Hexagon::CMPLTrr:
case Hexagon::CMPGTrr: {
if (secondRegNewified)
return Hexagon::JMP_GTrrdnPt_nv_V4;
else
return Hexagon::JMP_GTrrPt_nv_V4;
}
case Hexagon::CMPGEri: {
if (reg >= 1)
return Hexagon::JMP_GTriPt_nv_V4;
else
return Hexagon::JMP_GTriPtneg_nv_V4;
}
case Hexagon::CMPGTri: {
if (reg >= 0)
return Hexagon::JMP_GTriPt_nv_V4;
else
return Hexagon::JMP_GTriPtneg_nv_V4;
}
case Hexagon::CMPLTUrr:
case Hexagon::CMPGTUrr: {
if (secondRegNewified)
return Hexagon::JMP_GTUrrdnPt_nv_V4;
else
return Hexagon::JMP_GTUrrPt_nv_V4;
}
case Hexagon::CMPGTUri:
return Hexagon::JMP_GTUriPt_nv_V4;
case Hexagon::CMPGEUri: {
if (reg == 0)
return Hexagon::JMP_EQrrPt_nv_V4;
else
return Hexagon::JMP_GTUriPt_nv_V4;
}
default:
llvm_unreachable("Could not find matching New Value Jump instruction.");
}
// return *some value* to avoid compiler warning
return 0;
}
bool HexagonNewValueJump::runOnMachineFunction(MachineFunction &MF) {
DEBUG(dbgs() << "********** Hexagon New Value Jump **********\n"
<< "********** Function: "
<< MF.getFunction()->getName() << "\n");
#if 0
// for now disable this, if we move NewValueJump before register
// allocation we need this information.
LiveVariables &LVs = getAnalysis<LiveVariables>();
#endif
QII = static_cast<const HexagonInstrInfo *>(MF.getTarget().getInstrInfo());
QRI =
static_cast<const HexagonRegisterInfo *>(MF.getTarget().getRegisterInfo());
if (!QRI->Subtarget.hasV4TOps() ||
DisableNewValueJumps) {
return false;
}
int nvjCount = DbgNVJCount;
int nvjGenerated = 0;
// Loop through all the bb's of the function
for (MachineFunction::iterator MBBb = MF.begin(), MBBe = MF.end();
MBBb != MBBe; ++MBBb) {
MachineBasicBlock* MBB = MBBb;
DEBUG(dbgs() << "** dumping bb ** "
<< MBB->getNumber() << "\n");
DEBUG(MBB->dump());
DEBUG(dbgs() << "\n" << "********** dumping instr bottom up **********\n");
bool foundJump = false;
bool foundCompare = false;
bool invertPredicate = false;
unsigned predReg = 0; // predicate reg of the jump.
unsigned cmpReg1 = 0;
int cmpOp2 = 0;
bool MO1IsKill = false;
bool MO2IsKill = false;
MachineBasicBlock::iterator jmpPos;
MachineBasicBlock::iterator cmpPos;
MachineInstr *cmpInstr = NULL, *jmpInstr = NULL;
MachineBasicBlock *jmpTarget = NULL;
bool afterRA = false;
bool isSecondOpReg = false;
bool isSecondOpNewified = false;
// Traverse the basic block - bottom up
for (MachineBasicBlock::iterator MII = MBB->end(), E = MBB->begin();
MII != E;) {
MachineInstr *MI = --MII;
if (MI->isDebugValue()) {
continue;
}
if ((nvjCount == 0) || (nvjCount > -1 && nvjCount <= nvjGenerated))
break;
DEBUG(dbgs() << "Instr: "; MI->dump(); dbgs() << "\n");
if (!foundJump &&
(MI->getOpcode() == Hexagon::JMP_c ||
MI->getOpcode() == Hexagon::JMP_cNot ||
MI->getOpcode() == Hexagon::JMP_cdnPt ||
MI->getOpcode() == Hexagon::JMP_cdnPnt ||
MI->getOpcode() == Hexagon::JMP_cdnNotPt ||
MI->getOpcode() == Hexagon::JMP_cdnNotPnt)) {
// This is where you would insert your compare and
// instr that feeds compare
jmpPos = MII;
jmpInstr = MI;
predReg = MI->getOperand(0).getReg();
afterRA = TargetRegisterInfo::isPhysicalRegister(predReg);
// If ifconverter had not messed up with the kill flags of the
// operands, the following check on the kill flag would suffice.
// if(!jmpInstr->getOperand(0).isKill()) break;
// This predicate register is live out out of BB
// this would only work if we can actually use Live
// variable analysis on phy regs - but LLVM does not
// provide LV analysis on phys regs.
//if(LVs.isLiveOut(predReg, *MBB)) break;
// Get all the successors of this block - which will always
// be 2. Check if the predicate register is live in in those
// successor. If yes, we can not delete the predicate -
// I am doing this only because LLVM does not provide LiveOut
// at the BB level.
bool predLive = false;
for (MachineBasicBlock::const_succ_iterator SI = MBB->succ_begin(),
SIE = MBB->succ_end(); SI != SIE; ++SI) {
MachineBasicBlock* succMBB = *SI;
if (succMBB->isLiveIn(predReg)) {
predLive = true;
}
}
if (predLive)
break;
jmpTarget = MI->getOperand(1).getMBB();
foundJump = true;
if (MI->getOpcode() == Hexagon::JMP_cNot ||
MI->getOpcode() == Hexagon::JMP_cdnNotPt ||
MI->getOpcode() == Hexagon::JMP_cdnNotPnt) {
invertPredicate = true;
}
continue;
}
// No new value jump if there is a barrier. A barrier has to be in its
// own packet. A barrier has zero operands. We conservatively bail out
// here if we see any instruction with zero operands.
if (foundJump && MI->getNumOperands() == 0)
break;
if (foundJump &&
!foundCompare &&
MI->getOperand(0).isReg() &&
MI->getOperand(0).getReg() == predReg) {
// Not all compares can be new value compare. Arch Spec: 7.6.1.1
if (QII->isNewValueJumpCandidate(MI)) {
assert((MI->getDesc().isCompare()) &&
"Only compare instruction can be collapsed into New Value Jump");
isSecondOpReg = MI->getOperand(2).isReg();
if (!canCompareBeNewValueJump(QII, QRI, MII, predReg, isSecondOpReg,
afterRA, jmpPos, MF))
break;
cmpInstr = MI;
cmpPos = MII;
foundCompare = true;
// We need cmpReg1 and cmpOp2(imm or reg) while building
// new value jump instruction.
cmpReg1 = MI->getOperand(1).getReg();
if (MI->getOperand(1).isKill())
MO1IsKill = true;
if (isSecondOpReg) {
cmpOp2 = MI->getOperand(2).getReg();
if (MI->getOperand(2).isKill())
MO2IsKill = true;
} else
cmpOp2 = MI->getOperand(2).getImm();
continue;
}
}
if (foundCompare && foundJump) {
// If "common" checks fail, bail out on this BB.
if (!commonChecksToProhibitNewValueJump(afterRA, MII))
break;
bool foundFeeder = false;
MachineBasicBlock::iterator feederPos = MII;
if (MI->getOperand(0).isReg() &&
MI->getOperand(0).isDef() &&
(MI->getOperand(0).getReg() == cmpReg1 ||
(isSecondOpReg &&
MI->getOperand(0).getReg() == (unsigned) cmpOp2))) {
unsigned feederReg = MI->getOperand(0).getReg();
// First try to see if we can get the feeder from the first operand
// of the compare. If we can not, and if secondOpReg is true
// (second operand of the compare is also register), try that one.
// TODO: Try to come up with some heuristic to figure out which
// feeder would benefit.
if (feederReg == cmpReg1) {
if (!canBeFeederToNewValueJump(QII, QRI, MII, jmpPos, cmpPos, MF)) {
if (!isSecondOpReg)
break;
else
continue;
} else
foundFeeder = true;
}
if (!foundFeeder &&
isSecondOpReg &&
feederReg == (unsigned) cmpOp2)
if (!canBeFeederToNewValueJump(QII, QRI, MII, jmpPos, cmpPos, MF))
break;
if (isSecondOpReg) {
// In case of CMPLT, or CMPLTU, or EQ with the second register
// to newify, swap the operands.
if (cmpInstr->getOpcode() == Hexagon::CMPLTrr ||
cmpInstr->getOpcode() == Hexagon::CMPLTUrr ||
(cmpInstr->getOpcode() == Hexagon::CMPEQrr &&
feederReg == (unsigned) cmpOp2)) {
unsigned tmp = cmpReg1;
bool tmpIsKill = MO1IsKill;
cmpReg1 = cmpOp2;
MO1IsKill = MO2IsKill;
cmpOp2 = tmp;
MO2IsKill = tmpIsKill;
}
// Now we have swapped the operands, all we need to check is,
// if the second operand (after swap) is the feeder.
// And if it is, make a note.
if (feederReg == (unsigned)cmpOp2)
isSecondOpNewified = true;
}
// Now that we are moving feeder close the jump,
// make sure we are respecting the kill values of
// the operands of the feeder.
bool updatedIsKill = false;
for (unsigned i = 0; i < MI->getNumOperands(); i++) {
MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isUse()) {
unsigned feederReg = MO.getReg();
for (MachineBasicBlock::iterator localII = feederPos,
end = jmpPos; localII != end; localII++) {
MachineInstr *localMI = localII;
for (unsigned j = 0; j < localMI->getNumOperands(); j++) {
MachineOperand &localMO = localMI->getOperand(j);
if (localMO.isReg() && localMO.isUse() &&
localMO.isKill() && feederReg == localMO.getReg()) {
// We found that there is kill of a use register
// Set up a kill flag on the register
localMO.setIsKill(false);
MO.setIsKill();
updatedIsKill = true;
break;
}
}
if (updatedIsKill) break;
}
}
if (updatedIsKill) break;
}
MBB->splice(jmpPos, MI->getParent(), MI);
MBB->splice(jmpPos, MI->getParent(), cmpInstr);
DebugLoc dl = MI->getDebugLoc();
MachineInstr *NewMI;
assert((QII->isNewValueJumpCandidate(cmpInstr)) &&
"This compare is not a New Value Jump candidate.");
unsigned opc = getNewValueJumpOpcode(cmpInstr, cmpOp2,
isSecondOpNewified);
if (invertPredicate)
opc = QII->getInvertedPredicatedOpcode(opc);
// Manage the conversions from CMPGEUri to either CMPEQrr
// or CMPGTUri properly. See Arch spec for CMPGEUri instructions.
// This has to be after the getNewValueJumpOpcode function call as
// second operand of the compare could be modified in this logic.
if (cmpInstr->getOpcode() == Hexagon::CMPGEUri) {
if (cmpOp2 == 0) {
cmpOp2 = cmpReg1;
MO2IsKill = MO1IsKill;
isSecondOpReg = true;
} else
--cmpOp2;
}
// Manage the conversions from CMPGEri to CMPGTUri properly.
// See Arch spec for CMPGEri instructions.
if (cmpInstr->getOpcode() == Hexagon::CMPGEri)
--cmpOp2;
if (isSecondOpReg) {
NewMI = BuildMI(*MBB, jmpPos, dl,
QII->get(opc))
.addReg(cmpReg1, getKillRegState(MO1IsKill))
.addReg(cmpOp2, getKillRegState(MO2IsKill))
.addMBB(jmpTarget);
}
else {
NewMI = BuildMI(*MBB, jmpPos, dl,
QII->get(opc))
.addReg(cmpReg1, getKillRegState(MO1IsKill))
.addImm(cmpOp2)
.addMBB(jmpTarget);
}
assert(NewMI && "New Value Jump Instruction Not created!");
if (cmpInstr->getOperand(0).isReg() &&
cmpInstr->getOperand(0).isKill())
cmpInstr->getOperand(0).setIsKill(false);
if (cmpInstr->getOperand(1).isReg() &&
cmpInstr->getOperand(1).isKill())
cmpInstr->getOperand(1).setIsKill(false);
cmpInstr->eraseFromParent();
jmpInstr->eraseFromParent();
++nvjGenerated;
++NumNVJGenerated;
break;
}
}
}
}
return true;
}
FunctionPass *llvm::createHexagonNewValueJump() {
return new HexagonNewValueJump();
}
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