using namespace llvm::PatternMatch;
STATISTIC(NumBlocksElim, "Number of blocks eliminated");
-STATISTIC(NumPHIsElim, "Number of trivial PHIs eliminated");
-STATISTIC(NumGEPsElim, "Number of GEPs converted to casts");
+STATISTIC(NumPHIsElim, "Number of trivial PHIs eliminated");
+STATISTIC(NumGEPsElim, "Number of GEPs converted to casts");
STATISTIC(NumCmpUses, "Number of uses of Cmp expressions replaced with uses of "
"sunken Cmps");
STATISTIC(NumCastUses, "Number of uses of Cast expressions replaced with uses "
"of sunken Casts");
STATISTIC(NumMemoryInsts, "Number of memory instructions whose address "
"computations were sunk");
-STATISTIC(NumExtsMoved, "Number of [s|z]ext instructions combined with loads");
-STATISTIC(NumExtUses, "Number of uses of [s|z]ext instructions optimized");
+STATISTIC(NumExtsMoved, "Number of [s|z]ext instructions combined with loads");
+STATISTIC(NumExtUses, "Number of uses of [s|z]ext instructions optimized");
+STATISTIC(NumRetsDup, "Number of return instructions duplicated");
-static cl::opt<bool>
-CriticalEdgeSplit("cgp-critical-edge-splitting",
- cl::desc("Split critical edges during codegen prepare"),
- cl::init(false), cl::Hidden);
+static cl::opt<bool> DisableBranchOpts(
+ "disable-cgp-branch-opts", cl::Hidden, cl::init(false),
+ cl::desc("Disable branch optimizations in CodeGenPrepare"));
namespace {
class CodeGenPrepare : public FunctionPass {
/// update it.
BasicBlock::iterator CurInstIterator;
- /// BackEdges - Keep a set of all the loop back edges.
- ///
- SmallSet<std::pair<const BasicBlock*, const BasicBlock*>, 8> BackEdges;
-
- // Keeps track of non-local addresses that have been sunk into a block. This
- // allows us to avoid inserting duplicate code for blocks with multiple
- // load/stores of the same address.
+ /// Keeps track of non-local addresses that have been sunk into a block.
+ /// This allows us to avoid inserting duplicate code for blocks with
+ /// multiple load/stores of the same address.
DenseMap<Value*, Value*> SunkAddrs;
+ /// ModifiedDT - If CFG is modified in anyway, dominator tree may need to
+ /// be updated.
+ bool ModifiedDT;
+
public:
static char ID; // Pass identification, replacement for typeid
explicit CodeGenPrepare(const TargetLowering *tli = 0)
AU.addPreserved<ProfileInfo>();
}
- virtual void releaseMemory() {
- BackEdges.clear();
- }
-
private:
bool EliminateMostlyEmptyBlocks(Function &F);
bool CanMergeBlocks(const BasicBlock *BB, const BasicBlock *DestBB) const;
bool OptimizeCallInst(CallInst *CI);
bool MoveExtToFormExtLoad(Instruction *I);
bool OptimizeExtUses(Instruction *I);
- void findLoopBackEdges(const Function &F);
+ bool DupRetToEnableTailCallOpts(ReturnInst *RI);
};
}
return new CodeGenPrepare(TLI);
}
-/// findLoopBackEdges - Do a DFS walk to find loop back edges.
-///
-void CodeGenPrepare::findLoopBackEdges(const Function &F) {
- SmallVector<std::pair<const BasicBlock*,const BasicBlock*>, 32> Edges;
- FindFunctionBackedges(F, Edges);
-
- BackEdges.insert(Edges.begin(), Edges.end());
-}
-
-
bool CodeGenPrepare::runOnFunction(Function &F) {
bool EverMadeChange = false;
+ ModifiedDT = false;
DT = getAnalysisIfAvailable<DominatorTree>();
PFI = getAnalysisIfAvailable<ProfileInfo>();
+
// First pass, eliminate blocks that contain only PHI nodes and an
// unconditional branch.
EverMadeChange |= EliminateMostlyEmptyBlocks(F);
- // Now find loop back edges, but only if they are being used to decide which
- // critical edges to split.
- if (CriticalEdgeSplit)
- findLoopBackEdges(F);
-
bool MadeChange = true;
while (MadeChange) {
MadeChange = false;
- for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+ for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
+ BasicBlock *BB = I++;
MadeChange |= OptimizeBlock(*BB);
+ }
EverMadeChange |= MadeChange;
}
SunkAddrs.clear();
+ if (!DisableBranchOpts) {
+ MadeChange = false;
+ for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+ MadeChange |= ConstantFoldTerminator(BB);
+
+ if (MadeChange)
+ ModifiedDT = true;
+ EverMadeChange |= MadeChange;
+ }
+
+ if (ModifiedDT && DT)
+ DT->DT->recalculate(F);
+
return EverMadeChange;
}
// The PHIs are now updated, change everything that refers to BB to use
// DestBB and remove BB.
BB->replaceAllUsesWith(DestBB);
- if (DT) {
+ if (DT && !ModifiedDT) {
BasicBlock *BBIDom = DT->getNode(BB)->getIDom()->getBlock();
BasicBlock *DestBBIDom = DT->getNode(DestBB)->getIDom()->getBlock();
BasicBlock *NewIDom = DT->findNearestCommonDominator(BBIDom, DestBBIDom);
DEBUG(dbgs() << "AFTER:\n" << *DestBB << "\n\n\n");
}
-/// FindReusablePredBB - Check all of the predecessors of the block DestPHI
-/// lives in to see if there is a block that we can reuse as a critical edge
-/// from TIBB.
-static BasicBlock *FindReusablePredBB(PHINode *DestPHI, BasicBlock *TIBB) {
- BasicBlock *Dest = DestPHI->getParent();
-
- /// TIPHIValues - This array is lazily computed to determine the values of
- /// PHIs in Dest that TI would provide.
- SmallVector<Value*, 32> TIPHIValues;
-
- /// TIBBEntryNo - This is a cache to speed up pred queries for TIBB.
- unsigned TIBBEntryNo = 0;
-
- // Check to see if Dest has any blocks that can be used as a split edge for
- // this terminator.
- for (unsigned pi = 0, e = DestPHI->getNumIncomingValues(); pi != e; ++pi) {
- BasicBlock *Pred = DestPHI->getIncomingBlock(pi);
- // To be usable, the pred has to end with an uncond branch to the dest.
- BranchInst *PredBr = dyn_cast<BranchInst>(Pred->getTerminator());
- if (!PredBr || !PredBr->isUnconditional())
- continue;
- // Must be empty other than the branch and debug info.
- BasicBlock::iterator I = Pred->begin();
- while (isa<DbgInfoIntrinsic>(I))
- I++;
- if (&*I != PredBr)
- continue;
- // Cannot be the entry block; its label does not get emitted.
- if (Pred == &Dest->getParent()->getEntryBlock())
- continue;
-
- // Finally, since we know that Dest has phi nodes in it, we have to make
- // sure that jumping to Pred will have the same effect as going to Dest in
- // terms of PHI values.
- PHINode *PN;
- unsigned PHINo = 0;
- unsigned PredEntryNo = pi;
-
- bool FoundMatch = true;
- for (BasicBlock::iterator I = Dest->begin();
- (PN = dyn_cast<PHINode>(I)); ++I, ++PHINo) {
- if (PHINo == TIPHIValues.size()) {
- if (PN->getIncomingBlock(TIBBEntryNo) != TIBB)
- TIBBEntryNo = PN->getBasicBlockIndex(TIBB);
- TIPHIValues.push_back(PN->getIncomingValue(TIBBEntryNo));
- }
-
- // If the PHI entry doesn't work, we can't use this pred.
- if (PN->getIncomingBlock(PredEntryNo) != Pred)
- PredEntryNo = PN->getBasicBlockIndex(Pred);
-
- if (TIPHIValues[PHINo] != PN->getIncomingValue(PredEntryNo)) {
- FoundMatch = false;
- break;
- }
- }
-
- // If we found a workable predecessor, change TI to branch to Succ.
- if (FoundMatch)
- return Pred;
- }
- return 0;
-}
-
-
-/// SplitEdgeNicely - Split the critical edge from TI to its specified
-/// successor if it will improve codegen. We only do this if the successor has
-/// phi nodes (otherwise critical edges are ok). If there is already another
-/// predecessor of the succ that is empty (and thus has no phi nodes), use it
-/// instead of introducing a new block.
-static void SplitEdgeNicely(TerminatorInst *TI, unsigned SuccNum,
- SmallSet<std::pair<const BasicBlock*,
- const BasicBlock*>, 8> &BackEdges,
- Pass *P) {
- BasicBlock *TIBB = TI->getParent();
- BasicBlock *Dest = TI->getSuccessor(SuccNum);
- assert(isa<PHINode>(Dest->begin()) &&
- "This should only be called if Dest has a PHI!");
- PHINode *DestPHI = cast<PHINode>(Dest->begin());
-
- // Do not split edges to EH landing pads.
- if (InvokeInst *Invoke = dyn_cast<InvokeInst>(TI))
- if (Invoke->getSuccessor(1) == Dest)
- return;
-
- // As a hack, never split backedges of loops. Even though the copy for any
- // PHIs inserted on the backedge would be dead for exits from the loop, we
- // assume that the cost of *splitting* the backedge would be too high.
- if (BackEdges.count(std::make_pair(TIBB, Dest)))
- return;
-
- if (BasicBlock *ReuseBB = FindReusablePredBB(DestPHI, TIBB)) {
- ProfileInfo *PFI = P->getAnalysisIfAvailable<ProfileInfo>();
- if (PFI)
- PFI->splitEdge(TIBB, Dest, ReuseBB);
- Dest->removePredecessor(TIBB);
- TI->setSuccessor(SuccNum, ReuseBB);
- return;
- }
-
- SplitCriticalEdge(TI, SuccNum, P, true);
-}
-
-
/// OptimizeNoopCopyExpression - If the specified cast instruction is a noop
/// copy (e.g. it's casting from one pointer type to another, i32->i8 on PPC),
/// sink it into user blocks to reduce the number of virtual
// happens.
WeakVH IterHandle(CurInstIterator);
- ReplaceAndSimplifyAllUses(CI, RetVal, TLI ? TLI->getTargetData() : 0, DT);
+ ReplaceAndSimplifyAllUses(CI, RetVal, TLI ? TLI->getTargetData() : 0,
+ ModifiedDT ? 0 : DT);
// If the iterator instruction was recursively deleted, start over at the
// start of the block.
- if (IterHandle != CurInstIterator)
+ if (IterHandle != CurInstIterator) {
CurInstIterator = BB->begin();
+ SunkAddrs.clear();
+ }
return true;
}
return Simplifier.fold(CI, TD);
}
+/// DupRetToEnableTailCallOpts - Look for opportunities to duplicate return
+/// instructions to the predecessor to enable tail call optimizations. The
+/// case it is currently looking for is:
+/// bb0:
+/// %tmp0 = tail call i32 @f0()
+/// br label %return
+/// bb1:
+/// %tmp1 = tail call i32 @f1()
+/// br label %return
+/// bb2:
+/// %tmp2 = tail call i32 @f2()
+/// br label %return
+/// return:
+/// %retval = phi i32 [ %tmp0, %bb0 ], [ %tmp1, %bb1 ], [ %tmp2, %bb2 ]
+/// ret i32 %retval
+///
+/// =>
+///
+/// bb0:
+/// %tmp0 = tail call i32 @f0()
+/// ret i32 %tmp0
+/// bb1:
+/// %tmp1 = tail call i32 @f1()
+/// ret i32 %tmp1
+/// bb2:
+/// %tmp2 = tail call i32 @f2()
+/// ret i32 %tmp2
+///
+bool CodeGenPrepare::DupRetToEnableTailCallOpts(ReturnInst *RI) {
+ if (!TLI)
+ return false;
+
+ Value *V = RI->getReturnValue();
+ PHINode *PN = V ? dyn_cast<PHINode>(V) : NULL;
+ if (V && !PN)
+ return false;
+
+ BasicBlock *BB = RI->getParent();
+ if (PN && PN->getParent() != BB)
+ return false;
+
+ // It's not safe to eliminate the sign / zero extension of the return value.
+ // See llvm::isInTailCallPosition().
+ const Function *F = BB->getParent();
+ unsigned CallerRetAttr = F->getAttributes().getRetAttributes();
+ if ((CallerRetAttr & Attribute::ZExt) || (CallerRetAttr & Attribute::SExt))
+ return false;
+
+ // Make sure there are no instructions between the PHI and return, or that the
+ // return is the first instruction in the block.
+ if (PN) {
+ BasicBlock::iterator BI = BB->begin();
+ do { ++BI; } while (isa<DbgInfoIntrinsic>(BI));
+ if (&*BI != RI)
+ return false;
+ } else {
+ BasicBlock::iterator BI = BB->begin();
+ while (isa<DbgInfoIntrinsic>(BI)) ++BI;
+ if (&*BI != RI)
+ return false;
+ }
+
+ /// Only dup the ReturnInst if the CallInst is likely to be emitted as a tail
+ /// call.
+ SmallVector<CallInst*, 4> TailCalls;
+ if (PN) {
+ for (unsigned I = 0, E = PN->getNumIncomingValues(); I != E; ++I) {
+ CallInst *CI = dyn_cast<CallInst>(PN->getIncomingValue(I));
+ // Make sure the phi value is indeed produced by the tail call.
+ if (CI && CI->hasOneUse() && CI->getParent() == PN->getIncomingBlock(I) &&
+ TLI->mayBeEmittedAsTailCall(CI))
+ TailCalls.push_back(CI);
+ }
+ } else {
+ SmallPtrSet<BasicBlock*, 4> VisitedBBs;
+ for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE; ++PI) {
+ if (!VisitedBBs.insert(*PI))
+ continue;
+
+ BasicBlock::InstListType &InstList = (*PI)->getInstList();
+ BasicBlock::InstListType::reverse_iterator RI = InstList.rbegin();
+ BasicBlock::InstListType::reverse_iterator RE = InstList.rend();
+ do { ++RI; } while (RI != RE && isa<DbgInfoIntrinsic>(&*RI));
+ if (RI == RE)
+ continue;
+
+ CallInst *CI = dyn_cast<CallInst>(&*RI);
+ if (CI && CI->use_empty() && TLI->mayBeEmittedAsTailCall(CI))
+ TailCalls.push_back(CI);
+ }
+ }
+
+ bool Changed = false;
+ for (unsigned i = 0, e = TailCalls.size(); i != e; ++i) {
+ CallInst *CI = TailCalls[i];
+ CallSite CS(CI);
+
+ // Conservatively require the attributes of the call to match those of the
+ // return. Ignore noalias because it doesn't affect the call sequence.
+ unsigned CalleeRetAttr = CS.getAttributes().getRetAttributes();
+ if ((CalleeRetAttr ^ CallerRetAttr) & ~Attribute::NoAlias)
+ continue;
+
+ // Make sure the call instruction is followed by an unconditional branch to
+ // the return block.
+ BasicBlock *CallBB = CI->getParent();
+ BranchInst *BI = dyn_cast<BranchInst>(CallBB->getTerminator());
+ if (!BI || !BI->isUnconditional() || BI->getSuccessor(0) != BB)
+ continue;
+
+ // Duplicate the return into CallBB.
+ (void)FoldReturnIntoUncondBranch(RI, BB, CallBB);
+ ModifiedDT = Changed = true;
+ ++NumRetsDup;
+ }
+
+ // If we eliminated all predecessors of the block, delete the block now.
+ if (Changed && pred_begin(BB) == pred_end(BB))
+ BB->eraseFromParent();
+
+ return Changed;
+}
+
//===----------------------------------------------------------------------===//
// Memory Optimization
//===----------------------------------------------------------------------===//
// the addressing mode obtained from the non-PHI roots of the graph
// are equivalent.
Value *Consensus = 0;
- unsigned NumUses = 0;
+ unsigned NumUsesConsensus = 0;
+ bool IsNumUsesConsensusValid = false;
SmallVector<Instruction*, 16> AddrModeInsts;
ExtAddrMode AddrMode;
while (!worklist.empty()) {
ExtAddrMode NewAddrMode =
AddressingModeMatcher::Match(V, AccessTy,MemoryInst,
NewAddrModeInsts, *TLI);
-
- // Ensure that the obtained addressing mode is equivalent to that obtained
- // for all other roots of the PHI traversal. Also, when choosing one
- // such root as representative, select the one with the most uses in order
- // to keep the cost modeling heuristics in AddressingModeMatcher applicable.
- if (!Consensus || NewAddrMode == AddrMode) {
- if (V->getNumUses() > NumUses) {
+
+ // This check is broken into two cases with very similar code to avoid using
+ // getNumUses() as much as possible. Some values have a lot of uses, so
+ // calling getNumUses() unconditionally caused a significant compile-time
+ // regression.
+ if (!Consensus) {
+ Consensus = V;
+ AddrMode = NewAddrMode;
+ AddrModeInsts = NewAddrModeInsts;
+ continue;
+ } else if (NewAddrMode == AddrMode) {
+ if (!IsNumUsesConsensusValid) {
+ NumUsesConsensus = Consensus->getNumUses();
+ IsNumUsesConsensusValid = true;
+ }
+
+ // Ensure that the obtained addressing mode is equivalent to that obtained
+ // for all other roots of the PHI traversal. Also, when choosing one
+ // such root as representative, select the one with the most uses in order
+ // to keep the cost modeling heuristics in AddressingModeMatcher
+ // applicable.
+ unsigned NumUses = V->getNumUses();
+ if (NumUses > NumUsesConsensus) {
Consensus = V;
- NumUses = V->getNumUses();
- AddrMode = NewAddrMode;
+ NumUsesConsensus = NumUses;
AddrModeInsts = NewAddrModeInsts;
}
continue;
MemoryInst->replaceUsesOfWith(Repl, SunkAddr);
+ // If we have no uses, recursively delete the value and all dead instructions
+ // using it.
if (Repl->use_empty()) {
+ // This can cause recursive deletion, which can invalidate our iterator.
+ // Use a WeakVH to hold onto it in case this happens.
+ WeakVH IterHandle(CurInstIterator);
+ BasicBlock *BB = CurInstIterator->getParent();
+
RecursivelyDeleteTriviallyDeadInstructions(Repl);
- // This address is now available for reassignment, so erase the table entry;
- // we don't want to match some completely different instruction.
- SunkAddrs[Addr] = 0;
+
+ if (IterHandle != CurInstIterator) {
+ // If the iterator instruction was recursively deleted, start over at the
+ // start of the block.
+ CurInstIterator = BB->begin();
+ SunkAddrs.clear();
+ } else {
+ // This address is now available for reassignment, so erase the table
+ // entry; we don't want to match some completely different instruction.
+ SunkAddrs[Addr] = 0;
+ }
}
++NumMemoryInsts;
return true;
if (CallInst *CI = dyn_cast<CallInst>(I))
return OptimizeCallInst(CI);
+ if (ReturnInst *RI = dyn_cast<ReturnInst>(I))
+ return DupRetToEnableTailCallOpts(RI);
+
return false;
}
// across basic blocks and rewrite them to improve basic-block-at-a-time
// selection.
bool CodeGenPrepare::OptimizeBlock(BasicBlock &BB) {
- bool MadeChange = false;
-
- // Split all critical edges where the dest block has a PHI.
- if (CriticalEdgeSplit) {
- TerminatorInst *BBTI = BB.getTerminator();
- if (BBTI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(BBTI)) {
- for (unsigned i = 0, e = BBTI->getNumSuccessors(); i != e; ++i) {
- BasicBlock *SuccBB = BBTI->getSuccessor(i);
- if (isa<PHINode>(SuccBB->begin()) && isCriticalEdge(BBTI, i, true))
- SplitEdgeNicely(BBTI, i, BackEdges, this);
- }
- }
- }
-
SunkAddrs.clear();
+ bool MadeChange = false;
CurInstIterator = BB.begin();
for (BasicBlock::iterator E = BB.end(); CurInstIterator != E; )
projects / oota-llvm.git / blobdiff