using namespace llvm;
namespace {
- Statistic<> NumUnswitched("loop-unswitch", "Number of loops unswitched");
+ Statistic<> NumBranches("loop-unswitch", "Number of branches unswitched");
+ Statistic<> NumSwitches("loop-unswitch", "Number of switches unswitched");
+ Statistic<> NumSelects ("loop-unswitch", "Number of selects unswitched");
+ Statistic<> NumTrivial ("loop-unswitch",
+ "Number of unswitches that are trivial");
+ Statistic<> NumSimplify("loop-unswitch",
+ "Number of simplifications of unswitched code");
cl::opt<unsigned>
Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
cl::init(10), cl::Hidden);
}
private:
+ bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L);
unsigned getLoopUnswitchCost(Loop *L, Value *LIC);
- void VersionLoop(Value *LIC, Loop *L, Loop *&Out1, Loop *&Out2);
- BasicBlock *SplitBlock(BasicBlock *BB, bool SplitAtTop);
- void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC, bool Val);
- void UnswitchTrivialCondition(Loop *L, Value *Cond, bool EntersLoopOnCond,
- BasicBlock *ExitBlock);
+ void VersionLoop(Value *LIC, Constant *OnVal,
+ Loop *L, Loop *&Out1, Loop *&Out2);
+ BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To);
+ BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt);
+ void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,Constant *Val,
+ bool isEqual);
+ void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
+ bool EntersWhenTrue, BasicBlock *ExitBlock);
};
RegisterOpt<LoopUnswitch> X("loop-unswitch", "Unswitch loops");
}
return false;
}
-/// FindTrivialLoopExitBlock - We know that we have a branch from the loop
-/// header to the specified latch block. See if one of the successors of the
-/// latch block is an exit, and if so what block it is.
-static BasicBlock *FindTrivialLoopExitBlock(Loop *L, BasicBlock *Latch) {
+/// isTrivialLoopExitBlock - Check to see if all paths from BB either:
+/// 1. Exit the loop with no side effects.
+/// 2. Branch to the latch block with no side-effects.
+///
+/// If these conditions are true, we return true and set ExitBB to the block we
+/// exit through.
+///
+static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
+ BasicBlock *&ExitBB,
+ std::set<BasicBlock*> &Visited) {
BasicBlock *Header = L->getHeader();
- BranchInst *LatchBranch = dyn_cast<BranchInst>(Latch->getTerminator());
- if (!LatchBranch || !LatchBranch->isConditional()) return 0;
-
- // Simple case, the latch block is a conditional branch. The target that
- // doesn't go to the loop header is our block if it is not in the loop.
- if (LatchBranch->getSuccessor(0) == Header) {
- if (L->contains(LatchBranch->getSuccessor(1))) return false;
- return LatchBranch->getSuccessor(1);
- } else {
- assert(LatchBranch->getSuccessor(1) == Header);
- if (L->contains(LatchBranch->getSuccessor(0))) return false;
- return LatchBranch->getSuccessor(0);
+ for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI) {
+ if (!Visited.insert(*SI).second) {
+ // Already visited and Ok, end of recursion.
+ } else if (L->contains(*SI)) {
+ // Check to see if the successor is a trivial loop exit.
+ if (!isTrivialLoopExitBlockHelper(L, *SI, ExitBB, Visited))
+ return false;
+ } else {
+ // Otherwise, this is a loop exit, this is fine so long as this is the
+ // first exit.
+ if (ExitBB != 0) return false;
+ ExitBB = *SI;
+ }
}
+
+ // Okay, everything after this looks good, check to make sure that this block
+ // doesn't include any side effects.
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
+ if (I->mayWriteToMemory())
+ return false;
+
+ return true;
}
+static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
+ std::set<BasicBlock*> Visited;
+ Visited.insert(L->getHeader()); // Branches to header are ok.
+ Visited.insert(BB); // Don't revisit BB after we do.
+ BasicBlock *ExitBB = 0;
+ if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
+ return ExitBB;
+ return 0;
+}
/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
/// trivial: that is, that the condition controls whether or not the loop does
/// runs when the condition is true, False if the loop body executes when the
/// condition is false. Otherwise, return null to indicate a complex condition.
static bool IsTrivialUnswitchCondition(Loop *L, Value *Cond,
- bool *CondEntersLoop = 0,
+ Constant **Val = 0,
+ bool *EntersWhenTrue = 0,
BasicBlock **LoopExit = 0) {
BasicBlock *Header = L->getHeader();
- BranchInst *HeaderTerm = dyn_cast<BranchInst>(Header->getTerminator());
-
- // If the header block doesn't end with a conditional branch on Cond, we can't
- // handle it.
- if (!HeaderTerm || !HeaderTerm->isConditional() ||
- HeaderTerm->getCondition() != Cond)
- return false;
+ TerminatorInst *HeaderTerm = Header->getTerminator();
+
+ BasicBlock *LoopExitBB = 0;
+ if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
+ // If the header block doesn't end with a conditional branch on Cond, we
+ // can't handle it.
+ if (!BI->isConditional() || BI->getCondition() != Cond)
+ return false;
- // Check to see if the conditional branch goes to the latch block. If not,
- // it's not trivial. This also determines the value of Cond that will execute
- // the loop.
- BasicBlock *Latch = L->getLoopLatch();
- if (HeaderTerm->getSuccessor(1) == Latch) {
- if (CondEntersLoop) *CondEntersLoop = true;
- } else if (HeaderTerm->getSuccessor(0) == Latch)
- if (CondEntersLoop) *CondEntersLoop = false;
- else
- return false; // Doesn't branch to latch block.
+ // Check to see if a successor of the branch is guaranteed to go to the
+ // latch block or exit through a one exit block without having any
+ // side-effects. If so, determine the value of Cond that causes it to do
+ // this.
+ if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(0)))) {
+ if (Val) *Val = ConstantBool::False;
+ } else if ((LoopExitBB = isTrivialLoopExitBlock(L, BI->getSuccessor(1)))) {
+ if (Val) *Val = ConstantBool::True;
+ }
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
+ // If this isn't a switch on Cond, we can't handle it.
+ if (SI->getCondition() != Cond) return false;
+
+ // Check to see if a successor of the switch is guaranteed to go to the
+ // latch block or exit through a one exit block without having any
+ // side-effects. If so, determine the value of Cond that causes it to do
+ // this. Note that we can't trivially unswitch on the default case.
+ for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
+ if ((LoopExitBB = isTrivialLoopExitBlock(L, SI->getSuccessor(i)))) {
+ // Okay, we found a trivial case, remember the value that is trivial.
+ if (Val) *Val = SI->getCaseValue(i);
+ if (EntersWhenTrue) *EntersWhenTrue = false;
+ break;
+ }
+ }
+
+ if (!LoopExitBB)
+ return false; // Can't handle this.
- // The latch block must end with a conditional branch where one edge goes to
- // the header (this much we know) and one edge goes OUT of the loop.
- BasicBlock *LoopExitBlock = FindTrivialLoopExitBlock(L, Latch);
- if (!LoopExitBlock) return 0;
- if (LoopExit) *LoopExit = LoopExitBlock;
+ if (LoopExit) *LoopExit = LoopExitBB;
// We already know that nothing uses any scalar values defined inside of this
// loop. As such, we just have to check to see if this loop will execute any
// side-effecting instructions (e.g. stores, calls, volatile loads) in the
- // part of the loop that the code *would* execute.
+ // part of the loop that the code *would* execute. We already checked the
+ // tail, check the header now.
for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
if (I->mayWriteToMemory())
return false;
- for (BasicBlock::iterator I = Latch->begin(), E = Latch->end(); I != E; ++I)
- if (I->mayWriteToMemory())
- return false;
return true;
}
// loop.
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I) {
- for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
- BBI != E; ++BBI)
TerminatorInst *TI = (*I)->getTerminator();
- // FIXME: Handle invariant select instructions.
-
- if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
- if (!isa<Constant>(SI) && L->isLoopInvariant(SI->getCondition()))
- DEBUG(std::cerr << "TODO: Implement unswitching 'switch' loop %"
- << L->getHeader()->getName() << ", cost = "
- << L->getBlocks().size() << "\n" << **I);
- continue;
+ if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+ // If this isn't branching on an invariant condition, we can't unswitch
+ // it.
+ if (BI->isConditional()) {
+ // See if this, or some part of it, is loop invariant. If so, we can
+ // unswitch on it if we desire.
+ Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed);
+ if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L)) {
+ ++NumBranches;
+ return true;
+ }
+ }
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+ Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
+ if (LoopCond && SI->getNumCases() > 1) {
+ // Find a value to unswitch on:
+ // FIXME: this should chose the most expensive case!
+ Constant *UnswitchVal = SI->getCaseValue(1);
+ if (UnswitchIfProfitable(LoopCond, UnswitchVal, L)) {
+ ++NumSwitches;
+ return true;
+ }
+ }
}
- BranchInst *BI = dyn_cast<BranchInst>(TI);
- if (!BI) continue;
-
- // If this isn't branching on an invariant condition, we can't unswitch it.
- if (!BI->isConditional())
- continue;
-
- // See if this, or some part of it, is loop invariant. If so, we can
- // unswitch on it if we desire.
- Value *LoopCond = FindLIVLoopCondition(BI->getCondition(), L, Changed);
- if (LoopCond == 0) continue;
+ // Scan the instructions to check for unswitchable values.
+ for (BasicBlock::iterator BBI = (*I)->begin(), E = (*I)->end();
+ BBI != E; ++BBI)
+ if (SelectInst *SI = dyn_cast<SelectInst>(BBI)) {
+ Value *LoopCond = FindLIVLoopCondition(SI->getCondition(), L, Changed);
+ if (LoopCond && UnswitchIfProfitable(LoopCond, ConstantBool::True, L)) {
+ ++NumSelects;
+ return true;
+ }
+ }
+ }
- // Check to see if it would be profitable to unswitch this loop.
- if (getLoopUnswitchCost(L, LoopCond) > Threshold) {
- // FIXME: this should estimate growth by the amount of code shared by the
- // resultant unswitched loops. This should have no code growth:
- // for () { if (iv) {...} }
- // as one copy of the loop will be empty.
- //
- DEBUG(std::cerr << "NOT unswitching loop %"
- << L->getHeader()->getName() << ", cost too high: "
- << L->getBlocks().size() << "\n");
- continue;
- }
+ return Changed;
+}
+
+/// UnswitchIfProfitable - We have found that we can unswitch L when
+/// LoopCond == Val to simplify the loop. If we decide that this is profitable,
+/// unswitch the loop, reprocess the pieces, then return true.
+bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,Loop *L){
+ // Check to see if it would be profitable to unswitch this loop.
+ if (getLoopUnswitchCost(L, LoopCond) > Threshold) {
+ // FIXME: this should estimate growth by the amount of code shared by the
+ // resultant unswitched loops.
+ //
+ DEBUG(std::cerr << "NOT unswitching loop %"
+ << L->getHeader()->getName() << ", cost too high: "
+ << L->getBlocks().size() << "\n");
+ return false;
+ }
- // If this loop has live-out values, we can't unswitch it. We need something
- // like loop-closed SSA form in order to know how to insert PHI nodes for
- // these values.
- if (LoopValuesUsedOutsideLoop(L)) {
- DEBUG(std::cerr << "NOT unswitching loop %"
- << L->getHeader()->getName()
- << ", a loop value is used outside loop!\n");
- continue;
- }
+ // If this loop has live-out values, we can't unswitch it. We need something
+ // like loop-closed SSA form in order to know how to insert PHI nodes for
+ // these values.
+ if (LoopValuesUsedOutsideLoop(L)) {
+ DEBUG(std::cerr << "NOT unswitching loop %" << L->getHeader()->getName()
+ << ", a loop value is used outside loop!\n");
+ return false;
+ }
- //std::cerr << "BEFORE:\n"; LI->dump();
- Loop *NewLoop1 = 0, *NewLoop2 = 0;
+ //std::cerr << "BEFORE:\n"; LI->dump();
+ Loop *NewLoop1 = 0, *NewLoop2 = 0;
- // If this is a trivial condition to unswitch (which results in no code
- // duplication), do it now.
- bool EntersLoopOnCond;
- BasicBlock *ExitBlock;
- if (IsTrivialUnswitchCondition(L, LoopCond, &EntersLoopOnCond, &ExitBlock)){
- UnswitchTrivialCondition(L, LoopCond, EntersLoopOnCond, ExitBlock);
- NewLoop1 = L;
- } else {
- VersionLoop(LoopCond, L, NewLoop1, NewLoop2);
- }
-
- //std::cerr << "AFTER:\n"; LI->dump();
-
- // Try to unswitch each of our new loops now!
- if (NewLoop1) visitLoop(NewLoop1);
- if (NewLoop2) visitLoop(NewLoop2);
- return true;
+ // If this is a trivial condition to unswitch (which results in no code
+ // duplication), do it now.
+ Constant *CondVal;
+ bool EntersWhenTrue = true;
+ BasicBlock *ExitBlock;
+ if (IsTrivialUnswitchCondition(L, LoopCond, &CondVal,
+ &EntersWhenTrue, &ExitBlock)) {
+ UnswitchTrivialCondition(L, LoopCond, CondVal, EntersWhenTrue, ExitBlock);
+ NewLoop1 = L;
+ } else {
+ VersionLoop(LoopCond, Val, L, NewLoop1, NewLoop2);
}
-
- return Changed;
+
+ //std::cerr << "AFTER:\n"; LI->dump();
+
+ // Try to unswitch each of our new loops now!
+ if (NewLoop1) visitLoop(NewLoop1);
+ if (NewLoop2) visitLoop(NewLoop2);
+ return true;
}
-/// SplitBlock - Split the specified basic block into two pieces. If SplitAtTop
-/// is false, this splits the block so the second half only has an unconditional
-/// branch. If SplitAtTop is true, it makes it so the first half of the block
-/// only has an unconditional branch in it.
+/// SplitBlock - Split the specified block at the specified instruction - every
+/// thing before SplitPt stays in Old and everything starting with SplitPt moves
+/// to a new block. The two blocks are joined by an unconditional branch and
+/// the loop info is updated.
///
-/// This method updates the LoopInfo for this function to correctly reflect the
-/// CFG changes made.
-///
-/// This routine returns the new basic block that was inserted, which is always
-/// the later part of the block.
-BasicBlock *LoopUnswitch::SplitBlock(BasicBlock *BB, bool SplitAtTop) {
- BasicBlock::iterator SplitPoint;
- if (!SplitAtTop)
- SplitPoint = BB->getTerminator();
- else {
- SplitPoint = BB->begin();
- while (isa<PHINode>(SplitPoint)) ++SplitPoint;
- }
-
- BasicBlock *New = BB->splitBasicBlock(SplitPoint, BB->getName()+".tail");
- // New now lives in whichever loop that BB used to.
- if (Loop *L = LI->getLoopFor(BB))
+BasicBlock *LoopUnswitch::SplitBlock(BasicBlock *Old, Instruction *SplitPt) {
+ BasicBlock::iterator SplitIt = SplitPt;
+ while (isa<PHINode>(SplitIt))
+ ++SplitIt;
+ BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
+
+ // The new block lives in whichever loop the old one did.
+ if (Loop *L = LI->getLoopFor(Old))
L->addBasicBlockToLoop(New, *LI);
+
return New;
}
+BasicBlock *LoopUnswitch::SplitEdge(BasicBlock *BB, BasicBlock *Succ) {
+ TerminatorInst *LatchTerm = BB->getTerminator();
+ unsigned SuccNum = 0;
+ for (unsigned i = 0, e = LatchTerm->getNumSuccessors(); ; ++i) {
+ assert(i != e && "Didn't find edge?");
+ if (LatchTerm->getSuccessor(i) == Succ) {
+ SuccNum = i;
+ break;
+ }
+ }
+
+ // If this is a critical edge, let SplitCriticalEdge do it.
+ if (SplitCriticalEdge(BB->getTerminator(), SuccNum, this))
+ return LatchTerm->getSuccessor(SuccNum);
+
+ // If the edge isn't critical, then BB has a single successor or Succ has a
+ // single pred. Split the block.
+ BasicBlock::iterator SplitPoint;
+ if (BasicBlock *SP = Succ->getSinglePredecessor()) {
+ // If the successor only has a single pred, split the top of the successor
+ // block.
+ assert(SP == BB && "CFG broken");
+ return SplitBlock(Succ, Succ->begin());
+ } else {
+ // Otherwise, if BB has a single successor, split it at the bottom of the
+ // block.
+ assert(BB->getTerminator()->getNumSuccessors() == 1 &&
+ "Should have a single succ!");
+ return SplitBlock(BB, BB->getTerminator());
+ }
+}
+
+
+
// RemapInstruction - Convert the instruction operands from referencing the
// current values into those specified by ValueMap.
//
return New;
}
+/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
+/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
+/// code immediately before InsertPt.
+static void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
+ BasicBlock *TrueDest,
+ BasicBlock *FalseDest,
+ Instruction *InsertPt) {
+ // Insert a conditional branch on LIC to the two preheaders. The original
+ // code is the true version and the new code is the false version.
+ Value *BranchVal = LIC;
+ if (!isa<ConstantBool>(Val)) {
+ BranchVal = BinaryOperator::createSetEQ(LIC, Val, "tmp", InsertPt);
+ } else if (Val != ConstantBool::True) {
+ // We want to enter the new loop when the condition is true.
+ std::swap(TrueDest, FalseDest);
+ }
+
+ // Insert the new branch.
+ new BranchInst(TrueDest, FalseDest, BranchVal, InsertPt);
+}
+
+
/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
/// condition in it (a cond branch from its header block to its latch block,
/// where the path through the loop that doesn't execute its body has no
/// side-effects), unswitch it. This doesn't involve any code duplication, just
/// moving the conditional branch outside of the loop and updating loop info.
void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
- bool EnterOnCond,
+ Constant *Val, bool EntersWhenTrue,
BasicBlock *ExitBlock) {
DEBUG(std::cerr << "loop-unswitch: Trivial-Unswitch loop %"
<< L->getHeader()->getName() << " [" << L->getBlocks().size()
<< " blocks] in Function " << L->getHeader()->getParent()->getName()
- << " on cond:" << *Cond << "\n");
+ << " on cond: " << *Val << (EntersWhenTrue ? " == " : " != ") <<
+ *Cond << "\n");
- // First step, split the preahder, so that we know that there is a safe place
+ // First step, split the preheader, so that we know that there is a safe place
// to insert the conditional branch. We will change 'OrigPH' to have a
// conditional branch on Cond.
BasicBlock *OrigPH = L->getLoopPreheader();
- BasicBlock *NewPH = SplitBlock(OrigPH, false);
+ BasicBlock *NewPH = SplitEdge(OrigPH, L->getHeader());
// Now that we have a place to insert the conditional branch, create a place
// to branch to: this is the exit block out of the loop that we should
// short-circuit to.
- // Split this block now, so that the loop maintains its exit block.
+ // Split this block now, so that the loop maintains its exit block, and so
+ // that the jump from the preheader can execute the contents of the exit block
+ // without actually branching to it (the exit block should be dominated by the
+ // loop header, not the preheader).
assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
- BasicBlock *NewExit;
- if (BasicBlock *SinglePred = ExitBlock->getSinglePredecessor()) {
- assert(SinglePred == L->getLoopLatch() && "Unexpected case");
- NewExit = SplitBlock(ExitBlock, true);
- } else {
- // Otherwise, this is a critical edge. Split block would split the wrong
- // edge here, so we use SplitCriticalEdge, which allows us to specify the
- // edge to split, not just the block.
- TerminatorInst *LatchTerm = L->getLoopLatch()->getTerminator();
- unsigned SuccNum = 0;
- for (unsigned i = 0, e = LatchTerm->getNumSuccessors(); ; ++i) {
- assert(i != e && "Didn't find edge?");
- if (LatchTerm->getSuccessor(i) == ExitBlock) {
- SuccNum = i;
- break;
- }
- }
- SplitCriticalEdge(LatchTerm, SuccNum, this);
- NewExit = LatchTerm->getSuccessor(SuccNum);
- assert(NewExit != ExitBlock && "Edge not split!");
- }
-
+ BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin());
+
// Okay, now we have a position to branch from and a position to branch to,
// insert the new conditional branch.
- new BranchInst(EnterOnCond ? NewPH : NewExit, EnterOnCond ? NewExit : NewPH,
- Cond, OrigPH->getTerminator());
+ {
+ BasicBlock *TrueDest = NewPH, *FalseDest = NewExit;
+ if (!EntersWhenTrue) std::swap(TrueDest, FalseDest);
+ EmitPreheaderBranchOnCondition(Cond, Val, TrueDest, FalseDest,
+ OrigPH->getTerminator());
+ }
OrigPH->getTerminator()->eraseFromParent();
// Now that we know that the loop is never entered when this condition is a
// particular value, rewrite the loop with this info. We know that this will
// at least eliminate the old branch.
- RewriteLoopBodyWithConditionConstant(L, Cond, EnterOnCond);
-
- ++NumUnswitched;
+ RewriteLoopBodyWithConditionConstant(L, Cond, Val, EntersWhenTrue);
+ ++NumTrivial;
}
-/// VersionLoop - We determined that the loop is profitable to unswitch and
-/// contains a branch on a loop invariant condition. Split it into loop
-/// versions and test the condition outside of either loop. Return the loops
-/// created as Out1/Out2.
-void LoopUnswitch::VersionLoop(Value *LIC, Loop *L, Loop *&Out1, Loop *&Out2) {
+/// VersionLoop - We determined that the loop is profitable to unswitch when LIC
+/// equal Val. Split it into loop versions and test the condition outside of
+/// either loop. Return the loops created as Out1/Out2.
+void LoopUnswitch::VersionLoop(Value *LIC, Constant *Val, Loop *L,
+ Loop *&Out1, Loop *&Out2) {
Function *F = L->getHeader()->getParent();
DEBUG(std::cerr << "loop-unswitch: Unswitching loop %"
- << L->getHeader()->getName() << " [" << L->getBlocks().size()
- << " blocks] in Function " << F->getName()
- << " on cond:" << *LIC << "\n");
+ << L->getHeader()->getName() << " [" << L->getBlocks().size()
+ << " blocks] in Function " << F->getName()
+ << " when '" << *Val << "' == " << *LIC << "\n");
+ // LoopBlocks contains all of the basic blocks of the loop, including the
+ // preheader of the loop, the body of the loop, and the exit blocks of the
+ // loop, in that order.
std::vector<BasicBlock*> LoopBlocks;
// First step, split the preheader and exit blocks, and add these blocks to
// the LoopBlocks list.
BasicBlock *OrigPreheader = L->getLoopPreheader();
- LoopBlocks.push_back(SplitBlock(OrigPreheader, false));
+ LoopBlocks.push_back(SplitEdge(OrigPreheader, L->getHeader()));
// We want the loop to come after the preheader, but before the exit blocks.
LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
std::sort(ExitBlocks.begin(), ExitBlocks.end());
ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
ExitBlocks.end());
+
+ // Split all of the edges from inside the loop to their exit blocks. This
+ // unswitching trivial: no phi nodes to update.
+ unsigned NumBlocks = L->getBlocks().size();
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
- SplitBlock(ExitBlocks[i], true);
- LoopBlocks.push_back(ExitBlocks[i]);
+ BasicBlock *ExitBlock = ExitBlocks[i];
+ std::vector<BasicBlock*> Preds(pred_begin(ExitBlock), pred_end(ExitBlock));
+
+ for (unsigned j = 0, e = Preds.size(); j != e; ++j) {
+ assert(L->contains(Preds[j]) &&
+ "All preds of loop exit blocks must be the same loop!");
+ SplitEdge(Preds[j], ExitBlock);
+ }
}
+
+ // The exit blocks may have been changed due to edge splitting, recompute.
+ ExitBlocks.clear();
+ L->getExitBlocks(ExitBlocks);
+ std::sort(ExitBlocks.begin(), ExitBlocks.end());
+ ExitBlocks.erase(std::unique(ExitBlocks.begin(), ExitBlocks.end()),
+ ExitBlocks.end());
+
+ // Add exit blocks to the loop blocks.
+ LoopBlocks.insert(LoopBlocks.end(), ExitBlocks.begin(), ExitBlocks.end());
// Next step, clone all of the basic blocks that make up the loop (including
// the loop preheader and exit blocks), keeping track of the mapping between
NewBlocks.reserve(LoopBlocks.size());
std::map<const Value*, Value*> ValueMap;
for (unsigned i = 0, e = LoopBlocks.size(); i != e; ++i) {
- NewBlocks.push_back(CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F));
- ValueMap[LoopBlocks[i]] = NewBlocks.back(); // Keep the BB mapping.
+ BasicBlock *New = CloneBasicBlock(LoopBlocks[i], ValueMap, ".us", F);
+ NewBlocks.push_back(New);
+ ValueMap[LoopBlocks[i]] = New; // Keep the BB mapping.
}
// Splice the newly inserted blocks into the function right before the
// Now we create the new Loop object for the versioned loop.
Loop *NewLoop = CloneLoop(L, L->getParentLoop(), ValueMap, LI);
- if (Loop *Parent = L->getParentLoop()) {
+ Loop *ParentLoop = L->getParentLoop();
+ if (ParentLoop) {
// Make sure to add the cloned preheader and exit blocks to the parent loop
// as well.
- Parent->addBasicBlockToLoop(NewBlocks[0], *LI);
- for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
- Parent->addBasicBlockToLoop(cast<BasicBlock>(ValueMap[ExitBlocks[i]]),
- *LI);
+ ParentLoop->addBasicBlockToLoop(NewBlocks[0], *LI);
+ }
+
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
+ BasicBlock *NewExit = cast<BasicBlock>(ValueMap[ExitBlocks[i]]);
+ if (ParentLoop)
+ ParentLoop->addBasicBlockToLoop(cast<BasicBlock>(NewExit), *LI);
+
+ assert(NewExit->getTerminator()->getNumSuccessors() == 1 &&
+ "Exit block should have been split to have one successor!");
+ BasicBlock *ExitSucc = NewExit->getTerminator()->getSuccessor(0);
+
+ // If the successor of the exit block had PHI nodes, add an entry for
+ // NewExit.
+ PHINode *PN;
+ for (BasicBlock::iterator I = ExitSucc->begin();
+ (PN = dyn_cast<PHINode>(I)); ++I) {
+ Value *V = PN->getIncomingValueForBlock(ExitBlocks[i]);
+ std::map<const Value *, Value*>::iterator It = ValueMap.find(V);
+ if (It != ValueMap.end()) V = It->second;
+ PN->addIncoming(V, NewExit);
+ }
}
// Rewrite the code to refer to itself.
RemapInstruction(I, ValueMap);
// Rewrite the original preheader to select between versions of the loop.
- assert(isa<BranchInst>(OrigPreheader->getTerminator()) &&
- cast<BranchInst>(OrigPreheader->getTerminator())->isUnconditional() &&
- OrigPreheader->getTerminator()->getSuccessor(0) == LoopBlocks[0] &&
+ BranchInst *OldBR = cast<BranchInst>(OrigPreheader->getTerminator());
+ assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == LoopBlocks[0] &&
"Preheader splitting did not work correctly!");
- // Remove the unconditional branch to LoopBlocks[0].
- OrigPreheader->getInstList().pop_back();
- // Insert a conditional branch on LIC to the two preheaders. The original
- // code is the true version and the new code is the false version.
- new BranchInst(LoopBlocks[0], NewBlocks[0], LIC, OrigPreheader);
+ // Emit the new branch that selects between the two versions of this loop.
+ EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
+ OldBR->eraseFromParent();
// Now we rewrite the original code to know that the condition is true and the
// new code to know that the condition is false.
- RewriteLoopBodyWithConditionConstant(L, LIC, true);
- RewriteLoopBodyWithConditionConstant(NewLoop, LIC, false);
- ++NumUnswitched;
+ RewriteLoopBodyWithConditionConstant(L, LIC, Val, false);
+ RewriteLoopBodyWithConditionConstant(NewLoop, LIC, Val, true);
Out1 = L;
Out2 = NewLoop;
}
-// RewriteLoopBodyWithConditionConstant - We know that the boolean value LIC has
-// the value specified by Val in the specified loop. Rewrite any uses of LIC or
-// of properties correlated to it.
+/// RemoveFromWorklist - Remove all instances of I from the worklist vector
+/// specified.
+static void RemoveFromWorklist(Instruction *I,
+ std::vector<Instruction*> &Worklist) {
+ std::vector<Instruction*>::iterator WI = std::find(Worklist.begin(),
+ Worklist.end(), I);
+ while (WI != Worklist.end()) {
+ unsigned Offset = WI-Worklist.begin();
+ Worklist.erase(WI);
+ WI = std::find(Worklist.begin()+Offset, Worklist.end(), I);
+ }
+}
+
+/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
+/// program, replacing all uses with V and update the worklist.
+static void ReplaceUsesOfWith(Instruction *I, Value *V,
+ std::vector<Instruction*> &Worklist) {
+ DEBUG(std::cerr << "Replace with '" << *V << "': " << *I);
+
+ // Add uses to the worklist, which may be dead now.
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
+ Worklist.push_back(Use);
+
+ // Add users to the worklist which may be simplified now.
+ for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
+ UI != E; ++UI)
+ Worklist.push_back(cast<Instruction>(*UI));
+ I->replaceAllUsesWith(V);
+ I->eraseFromParent();
+ RemoveFromWorklist(I, Worklist);
+ ++NumSimplify;
+}
+
+
+
+// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
+// the value specified by Val in the specified loop, or we know it does NOT have
+// that value. Rewrite any uses of LIC or of properties correlated to it.
void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
- bool Val) {
+ Constant *Val,
+ bool IsEqual) {
assert(!isa<Constant>(LIC) && "Why are we unswitching on a constant?");
+
// FIXME: Support correlated properties, like:
// for (...)
// if (li1 < li2)
// ...
// if (li1 > li2)
// ...
- ConstantBool *BoolVal = ConstantBool::get(Val);
+ // NotVal - If Val is a bool, this contains its inverse.
+ Constant *NotVal = 0;
+ if (ConstantBool *CB = dyn_cast<ConstantBool>(Val))
+ NotVal = ConstantBool::get(!CB->getValue());
+
// FOLD boolean conditions (X|LIC), (X&LIC). Fold conditional branches,
// selects, switches.
std::vector<User*> Users(LIC->use_begin(), LIC->use_end());
- for (unsigned i = 0, e = Users.size(); i != e; ++i)
- if (Instruction *U = cast<Instruction>(Users[i]))
- if (L->contains(U->getParent()))
- U->replaceUsesOfWith(LIC, BoolVal);
+
+ std::vector<Instruction*> Worklist;
+
+ // If we know that LIC == Val, or that LIC == NotVal, just replace uses of LIC
+ // in the loop with the appropriate one directly.
+ if (IsEqual || NotVal) {
+ Value *Replacement = NotVal ? NotVal : Val;
+
+ for (unsigned i = 0, e = Users.size(); i != e; ++i)
+ if (Instruction *U = cast<Instruction>(Users[i])) {
+ if (!L->contains(U->getParent()))
+ continue;
+ U->replaceUsesOfWith(LIC, Replacement);
+ Worklist.push_back(U);
+ }
+ } else {
+ // Otherwise, we don't know the precise value of LIC, but we do know that it
+ // is certainly NOT "Val". As such, simplify any uses in the loop that we
+ // can. This case occurs when we unswitch switch statements.
+ for (unsigned i = 0, e = Users.size(); i != e; ++i)
+ if (Instruction *U = cast<Instruction>(Users[i])) {
+ if (!L->contains(U->getParent()))
+ continue;
+
+ Worklist.push_back(U);
+
+ // If we know that LIC is not Val, use this info to simplify code.
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(U)) {
+ for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
+ if (SI->getCaseValue(i) == Val) {
+ // Found a dead case value. Don't remove PHI nodes in the
+ // successor if they become single-entry, those PHI nodes may
+ // be in the Users list.
+ SI->getSuccessor(i)->removePredecessor(SI->getParent(), true);
+ SI->removeCase(i);
+ break;
+ }
+ }
+ }
+
+ // TODO: We could do other simplifications, for example, turning
+ // LIC == Val -> false.
+ }
+ }
+
+ // Okay, now that we have simplified some instructions in the loop, walk over
+ // it and constant prop, dce, and fold control flow where possible. Note that
+ // this is effectively a very simple loop-structure-aware optimizer.
+ while (!Worklist.empty()) {
+ Instruction *I = Worklist.back();
+ Worklist.pop_back();
+
+ // Simple constant folding.
+ if (Constant *C = ConstantFoldInstruction(I)) {
+ ReplaceUsesOfWith(I, C, Worklist);
+ continue;
+ }
+
+ // Simple DCE.
+ if (isInstructionTriviallyDead(I)) {
+ DEBUG(std::cerr << "Remove dead instruction '" << *I);
+
+ // Add uses to the worklist, which may be dead now.
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ if (Instruction *Use = dyn_cast<Instruction>(I->getOperand(i)))
+ Worklist.push_back(Use);
+ I->eraseFromParent();
+ RemoveFromWorklist(I, Worklist);
+ ++NumSimplify;
+ continue;
+ }
+
+ // Special case hacks that appear commonly in unswitched code.
+ switch (I->getOpcode()) {
+ case Instruction::Select:
+ if (ConstantBool *CB = dyn_cast<ConstantBool>(I->getOperand(0))) {
+ ReplaceUsesOfWith(I, I->getOperand(!CB->getValue()+1), Worklist);
+ continue;
+ }
+ break;
+ case Instruction::And:
+ if (isa<ConstantBool>(I->getOperand(0))) // constant -> RHS
+ cast<BinaryOperator>(I)->swapOperands();
+ if (ConstantBool *CB = dyn_cast<ConstantBool>(I->getOperand(1))) {
+ if (CB->getValue()) // X & 1 -> X
+ ReplaceUsesOfWith(I, I->getOperand(0), Worklist);
+ else // X & 0 -> 0
+ ReplaceUsesOfWith(I, I->getOperand(1), Worklist);
+ continue;
+ }
+ break;
+ case Instruction::Or:
+ if (isa<ConstantBool>(I->getOperand(0))) // constant -> RHS
+ cast<BinaryOperator>(I)->swapOperands();
+ if (ConstantBool *CB = dyn_cast<ConstantBool>(I->getOperand(1))) {
+ if (CB->getValue()) // X | 1 -> 1
+ ReplaceUsesOfWith(I, I->getOperand(1), Worklist);
+ else // X | 0 -> X
+ ReplaceUsesOfWith(I, I->getOperand(0), Worklist);
+ continue;
+ }
+ break;
+ case Instruction::Br: {
+ BranchInst *BI = cast<BranchInst>(I);
+ if (BI->isUnconditional()) {
+ // If BI's parent is the only pred of the successor, fold the two blocks
+ // together.
+ BasicBlock *Pred = BI->getParent();
+ BasicBlock *Succ = BI->getSuccessor(0);
+ BasicBlock *SinglePred = Succ->getSinglePredecessor();
+ if (!SinglePred) continue; // Nothing to do.
+ assert(SinglePred == Pred && "CFG broken");
+
+ DEBUG(std::cerr << "Merging blocks: " << Pred->getName() << " <- "
+ << Succ->getName() << "\n");
+
+ // Resolve any single entry PHI nodes in Succ.
+ while (PHINode *PN = dyn_cast<PHINode>(Succ->begin()))
+ ReplaceUsesOfWith(PN, PN->getIncomingValue(0), Worklist);
+
+ // Move all of the successor contents from Succ to Pred.
+ Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
+ Succ->end());
+ BI->eraseFromParent();
+ RemoveFromWorklist(BI, Worklist);
+
+ // If Succ has any successors with PHI nodes, update them to have
+ // entries coming from Pred instead of Succ.
+ Succ->replaceAllUsesWith(Pred);
+
+ // Remove Succ from the loop tree.
+ LI->removeBlock(Succ);
+ Succ->eraseFromParent();
+ break;
+ }
+ break;
+ }
+ }
+ }
}
projects / oota-llvm.git / blobdiff