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-rw-r--r--lib/CodeGen/MachineLICM.cpp339
1 files changed, 303 insertions, 36 deletions
diff --git a/lib/CodeGen/MachineLICM.cpp b/lib/CodeGen/MachineLICM.cpp
index 0361694d6636..b2e757d8d65d 100644
--- a/lib/CodeGen/MachineLICM.cpp
+++ b/lib/CodeGen/MachineLICM.cpp
@@ -22,8 +22,8 @@
#define DEBUG_TYPE "machine-licm"
#include "llvm/CodeGen/Passes.h"
-#include "llvm/CodeGen/MachineConstantPool.h"
#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
@@ -33,6 +33,7 @@
#include "llvm/Target/TargetMachine.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
@@ -41,32 +42,41 @@ using namespace llvm;
STATISTIC(NumHoisted, "Number of machine instructions hoisted out of loops");
STATISTIC(NumCSEed, "Number of hoisted machine instructions CSEed");
+STATISTIC(NumPostRAHoisted,
+ "Number of machine instructions hoisted out of loops post regalloc");
namespace {
class MachineLICM : public MachineFunctionPass {
- MachineConstantPool *MCP;
+ bool PreRegAlloc;
+
const TargetMachine *TM;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
- BitVector AllocatableSet;
+ const MachineFrameInfo *MFI;
+ MachineRegisterInfo *RegInfo;
// Various analyses that we use...
AliasAnalysis *AA; // Alias analysis info.
- MachineLoopInfo *LI; // Current MachineLoopInfo
+ MachineLoopInfo *MLI; // Current MachineLoopInfo
MachineDominatorTree *DT; // Machine dominator tree for the cur loop
- MachineRegisterInfo *RegInfo; // Machine register information
// State that is updated as we process loops
bool Changed; // True if a loop is changed.
- bool FirstInLoop; // True if it's the first LICM in the loop.
MachineLoop *CurLoop; // The current loop we are working on.
MachineBasicBlock *CurPreheader; // The preheader for CurLoop.
+ BitVector AllocatableSet;
+
// For each opcode, keep a list of potentail CSE instructions.
DenseMap<unsigned, std::vector<const MachineInstr*> > CSEMap;
+
public:
static char ID; // Pass identification, replacement for typeid
- MachineLICM() : MachineFunctionPass(&ID) {}
+ MachineLICM() :
+ MachineFunctionPass(&ID), PreRegAlloc(true) {}
+
+ explicit MachineLICM(bool PreRA) :
+ MachineFunctionPass(&ID), PreRegAlloc(PreRA) {}
virtual bool runOnMachineFunction(MachineFunction &MF);
@@ -88,6 +98,39 @@ namespace {
}
private:
+ /// CandidateInfo - Keep track of information about hoisting candidates.
+ struct CandidateInfo {
+ MachineInstr *MI;
+ unsigned Def;
+ int FI;
+ CandidateInfo(MachineInstr *mi, unsigned def, int fi)
+ : MI(mi), Def(def), FI(fi) {}
+ };
+
+ /// HoistRegionPostRA - Walk the specified region of the CFG and hoist loop
+ /// invariants out to the preheader.
+ void HoistRegionPostRA();
+
+ /// HoistPostRA - When an instruction is found to only use loop invariant
+ /// operands that is safe to hoist, this instruction is called to do the
+ /// dirty work.
+ void HoistPostRA(MachineInstr *MI, unsigned Def);
+
+ /// ProcessMI - Examine the instruction for potentai LICM candidate. Also
+ /// gather register def and frame object update information.
+ void ProcessMI(MachineInstr *MI, unsigned *PhysRegDefs,
+ SmallSet<int, 32> &StoredFIs,
+ SmallVector<CandidateInfo, 32> &Candidates);
+
+ /// AddToLiveIns - Add register 'Reg' to the livein sets of BBs in the
+ /// current loop.
+ void AddToLiveIns(unsigned Reg);
+
+ /// IsLICMCandidate - Returns true if the instruction may be a suitable
+ /// candidate for LICM. e.g. If the instruction is a call, then it's obviously
+ /// not safe to hoist it.
+ bool IsLICMCandidate(MachineInstr &I);
+
/// IsLoopInvariantInst - Returns true if the instruction is loop
/// invariant. I.e., all virtual register operands are defined outside of
/// the loop, physical registers aren't accessed (explicitly or implicitly),
@@ -145,7 +188,9 @@ char MachineLICM::ID = 0;
static RegisterPass<MachineLICM>
X("machinelicm", "Machine Loop Invariant Code Motion");
-FunctionPass *llvm::createMachineLICMPass() { return new MachineLICM(); }
+FunctionPass *llvm::createMachineLICMPass(bool PreRegAlloc) {
+ return new MachineLICM(PreRegAlloc);
+}
/// LoopIsOuterMostWithPreheader - Test if the given loop is the outer-most
/// loop that has a preheader.
@@ -156,31 +201,31 @@ static bool LoopIsOuterMostWithPreheader(MachineLoop *CurLoop) {
return true;
}
-/// Hoist expressions out of the specified loop. Note, alias info for inner loop
-/// is not preserved so it is not a good idea to run LICM multiple times on one
-/// loop.
-///
bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
- DEBUG(dbgs() << "******** Machine LICM ********\n");
+ if (PreRegAlloc)
+ DEBUG(dbgs() << "******** Pre-regalloc Machine LICM ********\n");
+ else
+ DEBUG(dbgs() << "******** Post-regalloc Machine LICM ********\n");
- Changed = FirstInLoop = false;
- MCP = MF.getConstantPool();
+ Changed = false;
TM = &MF.getTarget();
TII = TM->getInstrInfo();
TRI = TM->getRegisterInfo();
+ MFI = MF.getFrameInfo();
RegInfo = &MF.getRegInfo();
AllocatableSet = TRI->getAllocatableSet(MF);
// Get our Loop information...
- LI = &getAnalysis<MachineLoopInfo>();
- DT = &getAnalysis<MachineDominatorTree>();
- AA = &getAnalysis<AliasAnalysis>();
+ MLI = &getAnalysis<MachineLoopInfo>();
+ DT = &getAnalysis<MachineDominatorTree>();
+ AA = &getAnalysis<AliasAnalysis>();
- for (MachineLoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) {
+ for (MachineLoopInfo::iterator I = MLI->begin(), E = MLI->end(); I != E; ++I){
CurLoop = *I;
- // Only visit outer-most preheader-sporting loops.
- if (!LoopIsOuterMostWithPreheader(CurLoop))
+ // If this is done before regalloc, only visit outer-most preheader-sporting
+ // loops.
+ if (PreRegAlloc && !LoopIsOuterMostWithPreheader(CurLoop))
continue;
// Determine the block to which to hoist instructions. If we can't find a
@@ -193,16 +238,230 @@ bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
if (!CurPreheader)
continue;
- // CSEMap is initialized for loop header when the first instruction is
- // being hoisted.
- FirstInLoop = true;
- HoistRegion(DT->getNode(CurLoop->getHeader()));
- CSEMap.clear();
+ if (!PreRegAlloc)
+ HoistRegionPostRA();
+ else {
+ // CSEMap is initialized for loop header when the first instruction is
+ // being hoisted.
+ MachineDomTreeNode *N = DT->getNode(CurLoop->getHeader());
+ HoistRegion(N);
+ CSEMap.clear();
+ }
}
return Changed;
}
+/// InstructionStoresToFI - Return true if instruction stores to the
+/// specified frame.
+static bool InstructionStoresToFI(const MachineInstr *MI, int FI) {
+ for (MachineInstr::mmo_iterator o = MI->memoperands_begin(),
+ oe = MI->memoperands_end(); o != oe; ++o) {
+ if (!(*o)->isStore() || !(*o)->getValue())
+ continue;
+ if (const FixedStackPseudoSourceValue *Value =
+ dyn_cast<const FixedStackPseudoSourceValue>((*o)->getValue())) {
+ if (Value->getFrameIndex() == FI)
+ return true;
+ }
+ }
+ return false;
+}
+
+/// ProcessMI - Examine the instruction for potentai LICM candidate. Also
+/// gather register def and frame object update information.
+void MachineLICM::ProcessMI(MachineInstr *MI,
+ unsigned *PhysRegDefs,
+ SmallSet<int, 32> &StoredFIs,
+ SmallVector<CandidateInfo, 32> &Candidates) {
+ bool RuledOut = false;
+ bool HasNonInvariantUse = false;
+ unsigned Def = 0;
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (MO.isFI()) {
+ // Remember if the instruction stores to the frame index.
+ int FI = MO.getIndex();
+ if (!StoredFIs.count(FI) &&
+ MFI->isSpillSlotObjectIndex(FI) &&
+ InstructionStoresToFI(MI, FI))
+ StoredFIs.insert(FI);
+ HasNonInvariantUse = true;
+ continue;
+ }
+
+ if (!MO.isReg())
+ continue;
+ unsigned Reg = MO.getReg();
+ if (!Reg)
+ continue;
+ assert(TargetRegisterInfo::isPhysicalRegister(Reg) &&
+ "Not expecting virtual register!");
+
+ if (!MO.isDef()) {
+ if (Reg && PhysRegDefs[Reg])
+ // If it's using a non-loop-invariant register, then it's obviously not
+ // safe to hoist.
+ HasNonInvariantUse = true;
+ continue;
+ }
+
+ if (MO.isImplicit()) {
+ ++PhysRegDefs[Reg];
+ for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
+ ++PhysRegDefs[*AS];
+ if (!MO.isDead())
+ // Non-dead implicit def? This cannot be hoisted.
+ RuledOut = true;
+ // No need to check if a dead implicit def is also defined by
+ // another instruction.
+ continue;
+ }
+
+ // FIXME: For now, avoid instructions with multiple defs, unless
+ // it's a dead implicit def.
+ if (Def)
+ RuledOut = true;
+ else
+ Def = Reg;
+
+ // If we have already seen another instruction that defines the same
+ // register, then this is not safe.
+ if (++PhysRegDefs[Reg] > 1)
+ // MI defined register is seen defined by another instruction in
+ // the loop, it cannot be a LICM candidate.
+ RuledOut = true;
+ for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
+ if (++PhysRegDefs[*AS] > 1)
+ RuledOut = true;
+ }
+
+ // Only consider reloads for now and remats which do not have register
+ // operands. FIXME: Consider unfold load folding instructions.
+ if (Def && !RuledOut) {
+ int FI = INT_MIN;
+ if ((!HasNonInvariantUse && IsLICMCandidate(*MI)) ||
+ (TII->isLoadFromStackSlot(MI, FI) && MFI->isSpillSlotObjectIndex(FI)))
+ Candidates.push_back(CandidateInfo(MI, Def, FI));
+ }
+}
+
+/// HoistRegionPostRA - Walk the specified region of the CFG and hoist loop
+/// invariants out to the preheader.
+void MachineLICM::HoistRegionPostRA() {
+ unsigned NumRegs = TRI->getNumRegs();
+ unsigned *PhysRegDefs = new unsigned[NumRegs];
+ std::fill(PhysRegDefs, PhysRegDefs + NumRegs, 0);
+
+ SmallVector<CandidateInfo, 32> Candidates;
+ SmallSet<int, 32> StoredFIs;
+
+ // Walk the entire region, count number of defs for each register, and
+ // collect potential LICM candidates.
+ const std::vector<MachineBasicBlock*> Blocks = CurLoop->getBlocks();
+ for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
+ MachineBasicBlock *BB = Blocks[i];
+ // Conservatively treat live-in's as an external def.
+ // FIXME: That means a reload that're reused in successor block(s) will not
+ // be LICM'ed.
+ for (MachineBasicBlock::livein_iterator I = BB->livein_begin(),
+ E = BB->livein_end(); I != E; ++I) {
+ unsigned Reg = *I;
+ ++PhysRegDefs[Reg];
+ for (const unsigned *AS = TRI->getAliasSet(Reg); *AS; ++AS)
+ ++PhysRegDefs[*AS];
+ }
+
+ for (MachineBasicBlock::iterator
+ MII = BB->begin(), E = BB->end(); MII != E; ++MII) {
+ MachineInstr *MI = &*MII;
+ ProcessMI(MI, PhysRegDefs, StoredFIs, Candidates);
+ }
+ }
+
+ // Now evaluate whether the potential candidates qualify.
+ // 1. Check if the candidate defined register is defined by another
+ // instruction in the loop.
+ // 2. If the candidate is a load from stack slot (always true for now),
+ // check if the slot is stored anywhere in the loop.
+ for (unsigned i = 0, e = Candidates.size(); i != e; ++i) {
+ if (Candidates[i].FI != INT_MIN &&
+ StoredFIs.count(Candidates[i].FI))
+ continue;
+
+ if (PhysRegDefs[Candidates[i].Def] == 1) {
+ bool Safe = true;
+ MachineInstr *MI = Candidates[i].MI;
+ for (unsigned j = 0, ee = MI->getNumOperands(); j != ee; ++j) {
+ const MachineOperand &MO = MI->getOperand(j);
+ if (!MO.isReg() || MO.isDef() || !MO.getReg())
+ continue;
+ if (PhysRegDefs[MO.getReg()]) {
+ // If it's using a non-loop-invariant register, then it's obviously
+ // not safe to hoist.
+ Safe = false;
+ break;
+ }
+ }
+ if (Safe)
+ HoistPostRA(MI, Candidates[i].Def);
+ }
+ }
+
+ delete[] PhysRegDefs;
+}
+
+/// AddToLiveIns - Add register 'Reg' to the livein sets of BBs in the current
+/// loop, and make sure it is not killed by any instructions in the loop.
+void MachineLICM::AddToLiveIns(unsigned Reg) {
+ const std::vector<MachineBasicBlock*> Blocks = CurLoop->getBlocks();
+ for (unsigned i = 0, e = Blocks.size(); i != e; ++i) {
+ MachineBasicBlock *BB = Blocks[i];
+ if (!BB->isLiveIn(Reg))
+ BB->addLiveIn(Reg);
+ for (MachineBasicBlock::iterator
+ MII = BB->begin(), E = BB->end(); MII != E; ++MII) {
+ MachineInstr *MI = &*MII;
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isReg() || !MO.getReg() || MO.isDef()) continue;
+ if (MO.getReg() == Reg || TRI->isSuperRegister(Reg, MO.getReg()))
+ MO.setIsKill(false);
+ }
+ }
+ }
+}
+
+/// HoistPostRA - When an instruction is found to only use loop invariant
+/// operands that is safe to hoist, this instruction is called to do the
+/// dirty work.
+void MachineLICM::HoistPostRA(MachineInstr *MI, unsigned Def) {
+ // Now move the instructions to the predecessor, inserting it before any
+ // terminator instructions.
+ DEBUG({
+ dbgs() << "Hoisting " << *MI;
+ if (CurPreheader->getBasicBlock())
+ dbgs() << " to MachineBasicBlock "
+ << CurPreheader->getName();
+ if (MI->getParent()->getBasicBlock())
+ dbgs() << " from MachineBasicBlock "
+ << MI->getParent()->getName();
+ dbgs() << "\n";
+ });
+
+ // Splice the instruction to the preheader.
+ MachineBasicBlock *MBB = MI->getParent();
+ CurPreheader->splice(CurPreheader->getFirstTerminator(), MBB, MI);
+
+ // Add register to livein list to all the BBs in the current loop since a
+ // loop invariant must be kept live throughout the whole loop. This is
+ // important to ensure later passes do not scavenge the def register.
+ AddToLiveIns(Def);
+
+ ++NumPostRAHoisted;
+ Changed = true;
+}
+
/// HoistRegion - Walk the specified region of the CFG (defined by all blocks
/// dominated by the specified block, and that are in the current loop) in depth
/// first order w.r.t the DominatorTree. This allows us to visit definitions
@@ -223,17 +482,17 @@ void MachineLICM::HoistRegion(MachineDomTreeNode *N) {
}
const std::vector<MachineDomTreeNode*> &Children = N->getChildren();
-
for (unsigned I = 0, E = Children.size(); I != E; ++I)
HoistRegion(Children[I]);
}
-/// IsLoopInvariantInst - Returns true if the instruction is loop
-/// invariant. I.e., all virtual register operands are defined outside of the
-/// loop, physical registers aren't accessed explicitly, and there are no side
-/// effects that aren't captured by the operands or other flags.
-///
-bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
+/// IsLICMCandidate - Returns true if the instruction may be a suitable
+/// candidate for LICM. e.g. If the instruction is a call, then it's obviously
+/// not safe to hoist it.
+bool MachineLICM::IsLICMCandidate(MachineInstr &I) {
+ if (I.isImplicitDef())
+ return false;
+
const TargetInstrDesc &TID = I.getDesc();
// Ignore stuff that we obviously can't hoist.
@@ -251,6 +510,17 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
// This is a trivial form of alias analysis.
return false;
}
+ return true;
+}
+
+/// IsLoopInvariantInst - Returns true if the instruction is loop
+/// invariant. I.e., all virtual register operands are defined outside of the
+/// loop, physical registers aren't accessed explicitly, and there are no side
+/// effects that aren't captured by the operands or other flags.
+///
+bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
+ if (!IsLICMCandidate(I))
+ return false;
// The instruction is loop invariant if all of its operands are.
for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
@@ -341,9 +611,6 @@ bool MachineLICM::isLoadFromConstantMemory(MachineInstr *MI) {
/// IsProfitableToHoist - Return true if it is potentially profitable to hoist
/// the given loop invariant.
bool MachineLICM::IsProfitableToHoist(MachineInstr &MI) {
- if (MI.isImplicitDef())
- return false;
-
// FIXME: For now, only hoist re-materilizable instructions. LICM will
// increase register pressure. We want to make sure it doesn't increase
// spilling.
generated by cgit v1.2.3 (git 2.25.1) at 2025-02-24 23:27:09 +0000