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Move PHIElimination's SplitCriticalEdge for MachineBasicBlocks out 

into a utility routine, teach it how to update MachineLoopInfo, and
make use of it in MachineLICM to split critical edges on demand.

llvm-svn: 106555
This commit is contained in:
Dan Gohman 2010-06-22 17:25:57 +00:00
parent a9f90275cc
commit 3570f81b1e
5 changed files with 141 additions and 77 deletions
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9
llvm/include/llvm/CodeGen/MachineBasicBlock.h
View File

@ -19,6 +19,7 @@
namespace llvm {
class Pass;
class BasicBlock;
class MachineFunction;
class MCSymbol;
@ -281,6 +282,14 @@ public:
/// it returns end()
iterator getFirstTerminator();
/// SplitCriticalEdge - Split the critical edge from this block to the
/// given successor block, and return the newly created block, or null
/// if splitting is not possible.
///
/// This function updates LiveVariables, MachineDominatorTree, and
/// MachineLoopInfo, as applicable.
MachineBasicBlock *SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P);
void pop_front() { Insts.pop_front(); }
void pop_back() { Insts.pop_back(); }
void push_back(MachineInstr *MI) { Insts.push_back(MI); }

4
llvm/include/llvm/CodeGen/MachineLoopInfo.h
View File

@ -64,13 +64,13 @@ class MachineLoopInfo : public MachineFunctionPass {
void operator=(const MachineLoopInfo &); // do not implement
MachineLoopInfo(const MachineLoopInfo &); // do not implement
LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
public:
static char ID; // Pass identification, replacement for typeid
MachineLoopInfo() : MachineFunctionPass(&ID) {}
LoopInfoBase<MachineBasicBlock, MachineLoop>& getBase() { return LI; }
/// iterator/begin/end - The interface to the top-level loops in the current
/// function.
///

79
llvm/lib/CodeGen/MachineBasicBlock.cpp
View File

@ -13,7 +13,10 @@
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/BasicBlock.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCContext.h"
#include "llvm/Target/TargetRegisterInfo.h"
@ -396,6 +399,82 @@ bool MachineBasicBlock::canFallThrough() {
return FBB == 0;
}
MachineBasicBlock *
MachineBasicBlock::SplitCriticalEdge(MachineBasicBlock *Succ, Pass *P) {
MachineFunction *MF = getParent();
DebugLoc dl; // FIXME: this is nowhere
// We may need to update this's terminator, but we can't do that if AnalyzeBranch
// fails. If this uses a jump table, we won't touch it.
const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
MachineBasicBlock *TBB = 0, *FBB = 0;
SmallVector<MachineOperand, 4> Cond;
if (TII->AnalyzeBranch(*this, TBB, FBB, Cond))
return NULL;
MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
MF->insert(llvm::next(MachineFunction::iterator(this)), NMBB);
DEBUG(dbgs() << "PHIElimination splitting critical edge:"
" BB#" << getNumber()
<< " -- BB#" << NMBB->getNumber()
<< " -- BB#" << Succ->getNumber() << '\n');
ReplaceUsesOfBlockWith(Succ, NMBB);
updateTerminator();
// Insert unconditional "jump Succ" instruction in NMBB if necessary.
NMBB->addSuccessor(Succ);
if (!NMBB->isLayoutSuccessor(Succ)) {
Cond.clear();
MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, Succ, NULL, Cond, dl);
}
// Fix PHI nodes in Succ so they refer to NMBB instead of this
for (MachineBasicBlock::iterator i = Succ->begin(), e = Succ->end();
i != e && i->isPHI(); ++i)
for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
if (i->getOperand(ni+1).getMBB() == this)
i->getOperand(ni+1).setMBB(NMBB);
if (LiveVariables *LV =
P->getAnalysisIfAvailable<LiveVariables>())
LV->addNewBlock(NMBB, this, Succ);
if (MachineDominatorTree *MDT =
P->getAnalysisIfAvailable<MachineDominatorTree>())
MDT->addNewBlock(NMBB, this);
if (MachineLoopInfo *MLI =
P->getAnalysisIfAvailable<MachineLoopInfo>())
if (MachineLoop *TIL = MLI->getLoopFor(this)) {
// If one or the other blocks were not in a loop, the new block is not
// either, and thus LI doesn't need to be updated.
if (MachineLoop *DestLoop = MLI->getLoopFor(Succ)) {
if (TIL == DestLoop) {
// Both in the same loop, the NMBB joins loop.
DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
} else if (TIL->contains(DestLoop)) {
// Edge from an outer loop to an inner loop. Add to the outer loop.
TIL->addBasicBlockToLoop(NMBB, MLI->getBase());
} else if (DestLoop->contains(TIL)) {
// Edge from an inner loop to an outer loop. Add to the outer loop.
DestLoop->addBasicBlockToLoop(NMBB, MLI->getBase());
} else {
// Edge from two loops with no containment relation. Because these
// are natural loops, we know that the destination block must be the
// header of its loop (adding a branch into a loop elsewhere would
// create an irreducible loop).
assert(DestLoop->getHeader() == Succ &&
"Should not create irreducible loops!");
if (MachineLoop *P = DestLoop->getParentLoop())
P->addBasicBlockToLoop(NMBB, MLI->getBase());
}
}
}
return NMBB;
}
/// removeFromParent - This method unlinks 'this' from the containing function,
/// and returns it, but does not delete it.
MachineBasicBlock *MachineBasicBlock::removeFromParent() {

73
llvm/lib/CodeGen/MachineLICM.cpp
View File

@ -83,7 +83,6 @@ namespace {
const char *getPassName() const { return "Machine Instruction LICM"; }
// FIXME: Loop preheaders?
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<MachineLoopInfo>();
@ -182,6 +181,10 @@ namespace {
/// current loop preheader that may become duplicates of instructions that
/// are hoisted out of the loop.
void InitCSEMap(MachineBasicBlock *BB);
/// getCurPreheader - Get the preheader for the current loop, splitting
/// a critical edge if needed.
MachineBasicBlock *getCurPreheader();
};
} // end anonymous namespace
@ -193,11 +196,11 @@ FunctionPass *llvm::createMachineLICMPass(bool PreRegAlloc) {
return new MachineLICM(PreRegAlloc);
}
/// LoopIsOuterMostWithPreheader - Test if the given loop is the outer-most
/// loop that has a preheader.
static bool LoopIsOuterMostWithPreheader(MachineLoop *CurLoop) {
/// LoopIsOuterMostWithPredecessor - Test if the given loop is the outer-most
/// loop that has a unique predecessor.
static bool LoopIsOuterMostWithPredecessor(MachineLoop *CurLoop) {
for (MachineLoop *L = CurLoop->getParentLoop(); L; L = L->getParentLoop())
if (L->getLoopPreheader())
if (L->getLoopPredecessor())
return false;
return true;
}
@ -223,20 +226,11 @@ bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
for (MachineLoopInfo::iterator I = MLI->begin(), E = MLI->end(); I != E; ++I){
CurLoop = *I;
CurPreheader = 0;
// 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
// suitable loop preheader, we can't do any hoisting.
//
// FIXME: We are only hoisting if the basic block coming into this loop
// has only one successor. This isn't the case in general because we haven't
// broken critical edges or added preheaders.
CurPreheader = CurLoop->getLoopPreheader();
if (!CurPreheader)
if (PreRegAlloc && !LoopIsOuterMostWithPredecessor(CurLoop))
continue;
if (!PreRegAlloc)
@ -438,13 +432,16 @@ void MachineLICM::AddToLiveIns(unsigned Reg) {
/// operands that is safe to hoist, this instruction is called to do the
/// dirty work.
void MachineLICM::HoistPostRA(MachineInstr *MI, unsigned Def) {
MachineBasicBlock *Preheader = getCurPreheader();
if (!Preheader) return;
// Now move the instructions to the predecessor, inserting it before any
// terminator instructions.
DEBUG({
dbgs() << "Hoisting " << *MI;
if (CurPreheader->getBasicBlock())
if (Preheader->getBasicBlock())
dbgs() << " to MachineBasicBlock "
<< CurPreheader->getName();
<< Preheader->getName();
if (MI->getParent()->getBasicBlock())
dbgs() << " from MachineBasicBlock "
<< MI->getParent()->getName();
@ -453,7 +450,7 @@ void MachineLICM::HoistPostRA(MachineInstr *MI, unsigned Def) {
// Splice the instruction to the preheader.
MachineBasicBlock *MBB = MI->getParent();
CurPreheader->splice(CurPreheader->getFirstTerminator(), MBB, MI);
Preheader->splice(Preheader->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
@ -756,6 +753,9 @@ bool MachineLICM::EliminateCSE(MachineInstr *MI,
/// that are safe to hoist, this instruction is called to do the dirty work.
///
void MachineLICM::Hoist(MachineInstr *MI) {
MachineBasicBlock *Preheader = getCurPreheader();
if (!Preheader) return;
// First check whether we should hoist this instruction.
if (!IsLoopInvariantInst(*MI) || !IsProfitableToHoist(*MI)) {
// If not, try unfolding a hoistable load.
@ -767,9 +767,9 @@ void MachineLICM::Hoist(MachineInstr *MI) {
// terminator instructions.
DEBUG({
dbgs() << "Hoisting " << *MI;
if (CurPreheader->getBasicBlock())
if (Preheader->getBasicBlock())
dbgs() << " to MachineBasicBlock "
<< CurPreheader->getName();
<< Preheader->getName();
if (MI->getParent()->getBasicBlock())
dbgs() << " from MachineBasicBlock "
<< MI->getParent()->getName();
@ -779,7 +779,7 @@ void MachineLICM::Hoist(MachineInstr *MI) {
// If this is the first instruction being hoisted to the preheader,
// initialize the CSE map with potential common expressions.
if (FirstInLoop) {
InitCSEMap(CurPreheader);
InitCSEMap(Preheader);
FirstInLoop = false;
}
@ -789,7 +789,7 @@ void MachineLICM::Hoist(MachineInstr *MI) {
CI = CSEMap.find(Opcode);
if (!EliminateCSE(MI, CI)) {
// Otherwise, splice the instruction to the preheader.
CurPreheader->splice(CurPreheader->getFirstTerminator(),MI->getParent(),MI);
Preheader->splice(Preheader->getFirstTerminator(),MI->getParent(),MI);
// Clear the kill flags of any register this instruction defines,
// since they may need to be live throughout the entire loop
@ -813,3 +813,30 @@ void MachineLICM::Hoist(MachineInstr *MI) {
++NumHoisted;
Changed = true;
}
MachineBasicBlock *MachineLICM::getCurPreheader() {
// Determine the block to which to hoist instructions. If we can't find a
// suitable loop predecessor, we can't do any hoisting.
// If we've tried to get a preheader and failed, don't try again.
if (CurPreheader == reinterpret_cast<MachineBasicBlock *>(-1))
return 0;
if (!CurPreheader) {
CurPreheader = CurLoop->getLoopPreheader();
if (!CurPreheader) {
MachineBasicBlock *Pred = CurLoop->getLoopPredecessor();
if (!Pred) {
CurPreheader = reinterpret_cast<MachineBasicBlock *>(-1);
return 0;
}
CurPreheader = Pred->SplitCriticalEdge(CurLoop->getHeader(), this);
if (!CurPreheader) {
CurPreheader = reinterpret_cast<MachineBasicBlock *>(-1);
return 0;
}
}
}
return CurPreheader;
}

53
llvm/lib/CodeGen/PHIElimination.cpp
View File

@ -34,7 +34,6 @@
using namespace llvm;
STATISTIC(NumAtomic, "Number of atomic phis lowered");
STATISTIC(NumSplits, "Number of critical edges split on demand");
STATISTIC(NumReused, "Number of reused lowered phis");
char PHIElimination::ID = 0;
@ -391,58 +390,8 @@ bool llvm::PHIElimination::SplitPHIEdges(MachineFunction &MF,
// (not considering PHI nodes). If the register is live in to this block
// anyway, we would gain nothing from splitting.
if (!LV.isLiveIn(Reg, MBB) && LV.isLiveOut(Reg, *PreMBB))
SplitCriticalEdge(PreMBB, &MBB);
PreMBB->SplitCriticalEdge(&MBB, this);
}
}
return true;
}
MachineBasicBlock *PHIElimination::SplitCriticalEdge(MachineBasicBlock *A,
MachineBasicBlock *B) {
assert(A && B && "Missing MBB end point");
MachineFunction *MF = A->getParent();
DebugLoc dl; // FIXME: this is nowhere
// We may need to update A's terminator, but we can't do that if AnalyzeBranch
// fails. If A uses a jump table, we won't touch it.
const TargetInstrInfo *TII = MF->getTarget().getInstrInfo();
MachineBasicBlock *TBB = 0, *FBB = 0;
SmallVector<MachineOperand, 4> Cond;
if (TII->AnalyzeBranch(*A, TBB, FBB, Cond))
return NULL;
++NumSplits;
MachineBasicBlock *NMBB = MF->CreateMachineBasicBlock();
MF->insert(llvm::next(MachineFunction::iterator(A)), NMBB);
DEBUG(dbgs() << "PHIElimination splitting critical edge:"
" BB#" << A->getNumber()
<< " -- BB#" << NMBB->getNumber()
<< " -- BB#" << B->getNumber() << '\n');
A->ReplaceUsesOfBlockWith(B, NMBB);
A->updateTerminator();
// Insert unconditional "jump B" instruction in NMBB if necessary.
NMBB->addSuccessor(B);
if (!NMBB->isLayoutSuccessor(B)) {
Cond.clear();
MF->getTarget().getInstrInfo()->InsertBranch(*NMBB, B, NULL, Cond, dl);
}
// Fix PHI nodes in B so they refer to NMBB instead of A
for (MachineBasicBlock::iterator i = B->begin(), e = B->end();
i != e && i->isPHI(); ++i)
for (unsigned ni = 1, ne = i->getNumOperands(); ni != ne; ni += 2)
if (i->getOperand(ni+1).getMBB() == A)
i->getOperand(ni+1).setMBB(NMBB);
if (LiveVariables *LV=getAnalysisIfAvailable<LiveVariables>())
LV->addNewBlock(NMBB, A, B);
if (MachineDominatorTree *MDT=getAnalysisIfAvailable<MachineDominatorTree>())
MDT->addNewBlock(NMBB, A);
return NMBB;
}