//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "systemz-elim-compare"
-
#include "SystemZTargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
using namespace llvm;
+#define DEBUG_TYPE "systemz-elim-compare"
+
+STATISTIC(BranchOnCounts, "Number of branch-on-count instructions");
STATISTIC(EliminatedComparisons, "Number of eliminated comparisons");
STATISTIC(FusedComparisons, "Number of fused compare-and-branch instructions");
namespace {
- class SystemZElimCompare : public MachineFunctionPass {
- public:
- static char ID;
- SystemZElimCompare(const SystemZTargetMachine &tm)
- : MachineFunctionPass(ID), TII(0), TRI(0) {}
-
- virtual const char *getPassName() const {
- return "SystemZ Comparison Elimination";
- }
+// Represents the references to a particular register in one or more
+// instructions.
+struct Reference {
+ Reference()
+ : Def(false), Use(false), IndirectDef(false), IndirectUse(false) {}
+
+ Reference &operator|=(const Reference &Other) {
+ Def |= Other.Def;
+ IndirectDef |= Other.IndirectDef;
+ Use |= Other.Use;
+ IndirectUse |= Other.IndirectUse;
+ return *this;
+ }
+
+ LLVM_EXPLICIT operator bool() const { return Def || Use; }
+
+ // True if the register is defined or used in some form, either directly or
+ // via a sub- or super-register.
+ bool Def;
+ bool Use;
- bool processBlock(MachineBasicBlock *MBB);
- bool runOnMachineFunction(MachineFunction &F);
+ // True if the register is defined or used indirectly, by a sub- or
+ // super-register.
+ bool IndirectDef;
+ bool IndirectUse;
+};
- private:
- bool adjustCCMasksForInstr(MachineInstr *MI, MachineInstr *Compare,
- SmallVectorImpl<MachineInstr *> &CCUsers);
- bool optimizeCompareZero(MachineInstr *Compare,
+class SystemZElimCompare : public MachineFunctionPass {
+public:
+ static char ID;
+ SystemZElimCompare(const SystemZTargetMachine &tm)
+ : MachineFunctionPass(ID), TII(nullptr), TRI(nullptr) {}
+
+ const char *getPassName() const override {
+ return "SystemZ Comparison Elimination";
+ }
+
+ bool processBlock(MachineBasicBlock &MBB);
+ bool runOnMachineFunction(MachineFunction &F) override;
+
+private:
+ Reference getRegReferences(MachineInstr *MI, unsigned Reg);
+ bool convertToBRCT(MachineInstr *MI, MachineInstr *Compare,
+ SmallVectorImpl<MachineInstr *> &CCUsers);
+ bool convertToLoadAndTest(MachineInstr *MI);
+ bool adjustCCMasksForInstr(MachineInstr *MI, MachineInstr *Compare,
SmallVectorImpl<MachineInstr *> &CCUsers);
- bool fuseCompareAndBranch(MachineInstr *Compare,
- SmallVectorImpl<MachineInstr *> &CCUsers);
+ bool optimizeCompareZero(MachineInstr *Compare,
+ SmallVectorImpl<MachineInstr *> &CCUsers);
+ bool fuseCompareAndBranch(MachineInstr *Compare,
+ SmallVectorImpl<MachineInstr *> &CCUsers);
- const SystemZInstrInfo *TII;
- const TargetRegisterInfo *TRI;
- };
+ const SystemZInstrInfo *TII;
+ const TargetRegisterInfo *TRI;
+};
- char SystemZElimCompare::ID = 0;
-} // end of anonymous namespace
+char SystemZElimCompare::ID = 0;
+} // end anonymous namespace
FunctionPass *llvm::createSystemZElimComparePass(SystemZTargetMachine &TM) {
return new SystemZElimCompare(TM);
}
// Return true if CC is live out of MBB.
-static bool isCCLiveOut(MachineBasicBlock *MBB) {
- for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
- SE = MBB->succ_end(); SI != SE; ++SI)
+static bool isCCLiveOut(MachineBasicBlock &MBB) {
+ for (auto SI = MBB.succ_begin(), SE = MBB.succ_end(); SI != SE; ++SI)
if ((*SI)->isLiveIn(SystemZ::CC))
return true;
return false;
MI->getOperand(0).getSubReg() == SubReg)
return true;
+ switch (MI->getOpcode()) {
+ case SystemZ::LR:
+ case SystemZ::LGR:
+ case SystemZ::LGFR:
+ case SystemZ::LTR:
+ case SystemZ::LTGR:
+ case SystemZ::LTGFR:
+ case SystemZ::LER:
+ case SystemZ::LDR:
+ case SystemZ::LXR:
+ case SystemZ::LTEBR:
+ case SystemZ::LTDBR:
+ case SystemZ::LTXBR:
+ if (MI->getOperand(1).getReg() == Reg &&
+ MI->getOperand(1).getSubReg() == SubReg)
+ return true;
+ }
+
return false;
}
+// Describe the references to Reg in MI, including sub- and super-registers.
+Reference SystemZElimCompare::getRegReferences(MachineInstr *MI, unsigned Reg) {
+ Reference Ref;
+ for (unsigned I = 0, E = MI->getNumOperands(); I != E; ++I) {
+ const MachineOperand &MO = MI->getOperand(I);
+ if (MO.isReg()) {
+ if (unsigned MOReg = MO.getReg()) {
+ if (MOReg == Reg || TRI->regsOverlap(MOReg, Reg)) {
+ if (MO.isUse()) {
+ Ref.Use = true;
+ Ref.IndirectUse |= (MOReg != Reg);
+ }
+ if (MO.isDef()) {
+ Ref.Def = true;
+ Ref.IndirectDef |= (MOReg != Reg);
+ }
+ }
+ }
+ }
+ }
+ return Ref;
+}
+
+// Compare compares the result of MI against zero. If MI is an addition
+// of -1 and if CCUsers is a single branch on nonzero, eliminate the addition
+// and convert the branch to a BRCT(G). Return true on success.
+bool
+SystemZElimCompare::convertToBRCT(MachineInstr *MI, MachineInstr *Compare,
+ SmallVectorImpl<MachineInstr *> &CCUsers) {
+ // Check whether we have an addition of -1.
+ unsigned Opcode = MI->getOpcode();
+ unsigned BRCT;
+ if (Opcode == SystemZ::AHI)
+ BRCT = SystemZ::BRCT;
+ else if (Opcode == SystemZ::AGHI)
+ BRCT = SystemZ::BRCTG;
+ else
+ return false;
+ if (MI->getOperand(2).getImm() != -1)
+ return false;
+
+ // Check whether we have a single JLH.
+ if (CCUsers.size() != 1)
+ return false;
+ MachineInstr *Branch = CCUsers[0];
+ if (Branch->getOpcode() != SystemZ::BRC ||
+ Branch->getOperand(0).getImm() != SystemZ::CCMASK_ICMP ||
+ Branch->getOperand(1).getImm() != SystemZ::CCMASK_CMP_NE)
+ return false;
+
+ // We already know that there are no references to the register between
+ // MI and Compare. Make sure that there are also no references between
+ // Compare and Branch.
+ unsigned SrcReg = Compare->getOperand(0).getReg();
+ MachineBasicBlock::iterator MBBI = Compare, MBBE = Branch;
+ for (++MBBI; MBBI != MBBE; ++MBBI)
+ if (getRegReferences(MBBI, SrcReg))
+ return false;
+
+ // The transformation is OK. Rebuild Branch as a BRCT(G).
+ MachineOperand Target(Branch->getOperand(2));
+ Branch->RemoveOperand(2);
+ Branch->RemoveOperand(1);
+ Branch->RemoveOperand(0);
+ Branch->setDesc(TII->get(BRCT));
+ MachineInstrBuilder(*Branch->getParent()->getParent(), Branch)
+ .addOperand(MI->getOperand(0))
+ .addOperand(MI->getOperand(1))
+ .addOperand(Target)
+ .addReg(SystemZ::CC, RegState::ImplicitDefine);
+ MI->removeFromParent();
+ return true;
+}
+
+// If MI is a load instruction, try to convert it into a LOAD AND TEST.
+// Return true on success.
+bool SystemZElimCompare::convertToLoadAndTest(MachineInstr *MI) {
+ unsigned Opcode = TII->getLoadAndTest(MI->getOpcode());
+ if (!Opcode)
+ return false;
+
+ MI->setDesc(TII->get(Opcode));
+ MachineInstrBuilder(*MI->getParent()->getParent(), MI)
+ .addReg(SystemZ::CC, RegState::ImplicitDefine);
+ return true;
+}
+
// The CC users in CCUsers are testing the result of a comparison of some
// value X against zero and we know that any CC value produced by MI
// would also reflect the value of X. Try to adjust CCUsers so that
unsigned MIFlags = Desc.TSFlags;
// See which compare-style condition codes are available.
- unsigned ReusableCCMask = 0;
- if (MIFlags & SystemZII::CCHasZero)
- ReusableCCMask |= SystemZ::CCMASK_CMP_EQ;
+ unsigned ReusableCCMask = SystemZII::getCompareZeroCCMask(MIFlags);
// For unsigned comparisons with zero, only equality makes sense.
unsigned CompareFlags = Compare->getDesc().TSFlags;
- if (!(CompareFlags & SystemZII::IsLogical) &&
- (MIFlags & SystemZII::CCHasOrder))
- ReusableCCMask |= SystemZ::CCMASK_CMP_LT | SystemZ::CCMASK_CMP_GT;
+ if (CompareFlags & SystemZII::IsLogical)
+ ReusableCCMask &= SystemZ::CCMASK_CMP_EQ;
if (ReusableCCMask == 0)
return false;
return true;
}
+// Return true if Compare is a comparison against zero.
+static bool isCompareZero(MachineInstr *Compare) {
+ switch (Compare->getOpcode()) {
+ case SystemZ::LTEBRCompare:
+ case SystemZ::LTDBRCompare:
+ case SystemZ::LTXBRCompare:
+ return true;
+
+ default:
+ return (Compare->getNumExplicitOperands() == 2 &&
+ Compare->getOperand(1).isImm() &&
+ Compare->getOperand(1).getImm() == 0);
+ }
+}
+
// Try to optimize cases where comparison instruction Compare is testing
// a value against zero. Return true on success and if Compare should be
// deleted as dead. CCUsers is the list of instructions that use the CC
bool SystemZElimCompare::
optimizeCompareZero(MachineInstr *Compare,
SmallVectorImpl<MachineInstr *> &CCUsers) {
- // Check whether this is a comparison against zero.
- if (Compare->getNumExplicitOperands() != 2 ||
- !Compare->getOperand(1).isImm() ||
- Compare->getOperand(1).getImm() != 0)
+ if (!isCompareZero(Compare))
return false;
// Search back for CC results that are based on the first operand.
unsigned SrcReg = Compare->getOperand(0).getReg();
unsigned SrcSubReg = Compare->getOperand(0).getSubReg();
- MachineBasicBlock *MBB = Compare->getParent();
- MachineBasicBlock::iterator MBBI = Compare, MBBE = MBB->begin();
+ MachineBasicBlock &MBB = *Compare->getParent();
+ MachineBasicBlock::iterator MBBI = Compare, MBBE = MBB.begin();
+ Reference CCRefs;
+ Reference SrcRefs;
while (MBBI != MBBE) {
--MBBI;
MachineInstr *MI = MBBI;
- if (resultTests(MI, SrcReg, SrcSubReg) &&
- adjustCCMasksForInstr(MI, Compare, CCUsers)) {
- EliminatedComparisons += 1;
- return true;
+ if (resultTests(MI, SrcReg, SrcSubReg)) {
+ // Try to remove both MI and Compare by converting a branch to BRCT(G).
+ // We don't care in this case whether CC is modified between MI and
+ // Compare.
+ if (!CCRefs.Use && !SrcRefs && convertToBRCT(MI, Compare, CCUsers)) {
+ BranchOnCounts += 1;
+ return true;
+ }
+ // Try to eliminate Compare by reusing a CC result from MI.
+ if ((!CCRefs && convertToLoadAndTest(MI)) ||
+ (!CCRefs.Def && adjustCCMasksForInstr(MI, Compare, CCUsers))) {
+ EliminatedComparisons += 1;
+ return true;
+ }
}
- if (MI->modifiesRegister(SrcReg, TRI) ||
- MI->modifiesRegister(SystemZ::CC, TRI))
+ SrcRefs |= getRegReferences(MI, SrcReg);
+ if (SrcRefs.Def)
+ return false;
+ CCRefs |= getRegReferences(MI, SystemZ::CC);
+ if (CCRefs.Use && CCRefs.Def)
return false;
}
return false;
// Process all comparison instructions in MBB. Return true if something
// changed.
-bool SystemZElimCompare::processBlock(MachineBasicBlock *MBB) {
+bool SystemZElimCompare::processBlock(MachineBasicBlock &MBB) {
bool Changed = false;
// Walk backwards through the block looking for comparisons, recording
// instructions before it.
bool CompleteCCUsers = !isCCLiveOut(MBB);
SmallVector<MachineInstr *, 4> CCUsers;
- MachineBasicBlock::iterator MBBI = MBB->end();
- while (MBBI != MBB->begin()) {
+ MachineBasicBlock::iterator MBBI = MBB.end();
+ while (MBBI != MBB.begin()) {
MachineInstr *MI = --MBBI;
if (CompleteCCUsers &&
MI->isCompare() &&
continue;
}
- if (MI->definesRegister(SystemZ::CC, TRI)) {
+ Reference CCRefs(getRegReferences(MI, SystemZ::CC));
+ if (CCRefs.Def) {
CCUsers.clear();
- CompleteCCUsers = true;
- } else if (MI->modifiesRegister(SystemZ::CC, TRI))
- CompleteCCUsers = false;
-
- if (CompleteCCUsers && MI->readsRegister(SystemZ::CC, TRI))
+ CompleteCCUsers = !CCRefs.IndirectDef;
+ }
+ if (CompleteCCUsers && CCRefs.Use)
CCUsers.push_back(MI);
}
return Changed;
}
bool SystemZElimCompare::runOnMachineFunction(MachineFunction &F) {
- TII = static_cast<const SystemZInstrInfo *>(F.getTarget().getInstrInfo());
+ TII = static_cast<const SystemZInstrInfo *>(F.getSubtarget().getInstrInfo());
TRI = &TII->getRegisterInfo();
bool Changed = false;
- for (MachineFunction::iterator MFI = F.begin(), MFE = F.end();
- MFI != MFE; ++MFI)
- Changed |= processBlock(MFI);
+ for (auto &MBB : F)
+ Changed |= processBlock(MBB);
return Changed;
}
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