+ else if (p.second->getNumber() > q.second->getNumber())
+ return false;
+ else {
+ // _GLIBCXX_DEBUG checks strict weak ordering, which involves comparing
+ // an object with itself.
+#ifndef _GLIBCXX_DEBUG
+ assert(0 && "Predecessor appears twice");
+#endif
+ return(false);
+ }
+}
+
+// See if any of the blocks in MergePotentials (which all have a common single
+// successor, or all have no successor) can be tail-merged. If there is a
+// successor, any blocks in MergePotentials that are not tail-merged and
+// are not immediately before Succ must have an unconditional branch to
+// Succ added (but the predecessor/successor lists need no adjustment).
+// The lone predecessor of Succ that falls through into Succ,
+// if any, is given in PredBB.
+
+bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
+ MachineBasicBlock* PredBB) {
+ unsigned minCommonTailLength = (SuccBB ? 1 : 2);
+ MadeChange = false;
+
+ // Sort by hash value so that blocks with identical end sequences sort
+ // together.
+ std::stable_sort(MergePotentials.begin(), MergePotentials.end(), MergeCompare);
+
+ // Walk through equivalence sets looking for actual exact matches.
+ while (MergePotentials.size() > 1) {
+ unsigned CurHash = (MergePotentials.end()-1)->first;
+ unsigned PrevHash = (MergePotentials.end()-2)->first;
+ MachineBasicBlock *CurMBB = (MergePotentials.end()-1)->second;
+
+ // If there is nothing that matches the hash of the current basic block,
+ // give up.
+ if (CurHash != PrevHash) {
+ if (SuccBB && CurMBB != PredBB)
+ FixTail(CurMBB, SuccBB, TII);
+ MergePotentials.pop_back();
+ continue;
+ }
+
+ // Look through all the pairs of blocks that have the same hash as this
+ // one, and find the pair that has the largest number of instructions in
+ // common.
+ // Since instructions may get combined later (e.g. single stores into
+ // store multiple) this measure is not particularly accurate.
+ MachineBasicBlock::iterator BBI1, BBI2;
+
+ unsigned FoundI = ~0U, FoundJ = ~0U;
+ unsigned maxCommonTailLength = 0U;
+ for (int i = MergePotentials.size()-1;
+ i != -1 && MergePotentials[i].first == CurHash; --i) {
+ for (int j = i-1;
+ j != -1 && MergePotentials[j].first == CurHash; --j) {
+ MachineBasicBlock::iterator TrialBBI1, TrialBBI2;
+ unsigned CommonTailLen = ComputeCommonTailLength(
+ MergePotentials[i].second,
+ MergePotentials[j].second,
+ TrialBBI1, TrialBBI2);
+ if (CommonTailLen >= minCommonTailLength &&
+ CommonTailLen > maxCommonTailLength) {
+ FoundI = i;
+ FoundJ = j;
+ maxCommonTailLength = CommonTailLen;
+ BBI1 = TrialBBI1;
+ BBI2 = TrialBBI2;
+ }
+ }
+ }
+
+ // If we didn't find any pair that has at least minCommonTailLength
+ // instructions in common, bail out. All entries with this
+ // hash code can go away now.
+ if (FoundI == ~0U) {
+ for (int i = MergePotentials.size()-1;
+ i != -1 && MergePotentials[i].first == CurHash; --i) {
+ // Put the unconditional branch back, if we need one.
+ CurMBB = MergePotentials[i].second;
+ if (SuccBB && CurMBB != PredBB)
+ FixTail(CurMBB, SuccBB, TII);
+ MergePotentials.pop_back();
+ }
+ continue;
+ }
+
+ // Otherwise, move the block(s) to the right position(s). So that
+ // BBI1/2 will be valid, the last must be I and the next-to-last J.
+ if (FoundI != MergePotentials.size()-1)
+ std::swap(MergePotentials[FoundI], *(MergePotentials.end()-1));
+ if (FoundJ != MergePotentials.size()-2)
+ std::swap(MergePotentials[FoundJ], *(MergePotentials.end()-2));
+
+ CurMBB = (MergePotentials.end()-1)->second;
+ MachineBasicBlock *MBB2 = (MergePotentials.end()-2)->second;
+
+ // If neither block is the entire common tail, split the tail of one block
+ // to make it redundant with the other tail. Also, we cannot jump to the
+ // entry block, so if one block is the entry block, split the other one.
+ MachineBasicBlock *Entry = CurMBB->getParent()->begin();
+ if (CurMBB->begin() == BBI1 && CurMBB != Entry)
+ ; // CurMBB is common tail
+ else if (MBB2->begin() == BBI2 && MBB2 != Entry)
+ ; // MBB2 is common tail
+ else {
+ if (0) { // Enable this to disable partial tail merges.
+ MergePotentials.pop_back();
+ continue;
+ }
+
+ // Decide whether we want to split CurMBB or MBB2.
+ if (ShouldSplitFirstBlock(CurMBB, BBI1, MBB2, BBI2, PredBB)) {
+ CurMBB = SplitMBBAt(*CurMBB, BBI1);
+ BBI1 = CurMBB->begin();
+ MergePotentials.back().second = CurMBB;
+ } else {
+ MBB2 = SplitMBBAt(*MBB2, BBI2);
+ BBI2 = MBB2->begin();
+ (MergePotentials.end()-2)->second = MBB2;
+ }
+ }
+
+ if (MBB2->begin() == BBI2 && MBB2 != Entry) {
+ // Hack the end off CurMBB, making it jump to MBBI@ instead.
+ ReplaceTailWithBranchTo(BBI1, MBB2);
+ // This modifies CurMBB, so remove it from the worklist.
+ MergePotentials.pop_back();
+ } else {
+ assert(CurMBB->begin() == BBI1 && CurMBB != Entry &&
+ "Didn't split block correctly?");
+ // Hack the end off MBB2, making it jump to CurMBB instead.
+ ReplaceTailWithBranchTo(BBI2, CurMBB);
+ // This modifies MBB2, so remove it from the worklist.
+ MergePotentials.erase(MergePotentials.end()-2);
+ }
+ MadeChange = true;
+ }
+ return MadeChange;
+}
+
+bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
+
+ if (!EnableTailMerge) return false;
+
+ MadeChange = false;
+
+ // First find blocks with no successors.
+ MergePotentials.clear();
+ for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
+ if (I->succ_empty())
+ MergePotentials.push_back(std::make_pair(HashEndOfMBB(I, 2U), I));
+ }
+ // See if we can do any tail merging on those.
+ if (MergePotentials.size() < TailMergeThreshold)
+ MadeChange |= TryMergeBlocks(NULL, NULL);
+
+ // Look at blocks (IBB) with multiple predecessors (PBB).
+ // We change each predecessor to a canonical form, by
+ // (1) temporarily removing any unconditional branch from the predecessor
+ // to IBB, and
+ // (2) alter conditional branches so they branch to the other block
+ // not IBB; this may require adding back an unconditional branch to IBB
+ // later, where there wasn't one coming in. E.g.
+ // Bcc IBB
+ // fallthrough to QBB
+ // here becomes
+ // Bncc QBB
+ // with a conceptual B to IBB after that, which never actually exists.
+ // With those changes, we see whether the predecessors' tails match,
+ // and merge them if so. We change things out of canonical form and
+ // back to the way they were later in the process. (OptimizeBranches
+ // would undo some of this, but we can't use it, because we'd get into
+ // a compile-time infinite loop repeatedly doing and undoing the same
+ // transformations.)
+
+ for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
+ if (!I->succ_empty() && I->pred_size() >= 2 &&
+ I->pred_size() < TailMergeThreshold) {
+ MachineBasicBlock *IBB = I;
+ MachineBasicBlock *PredBB = prior(I);
+ MergePotentials.clear();
+ for (MachineBasicBlock::pred_iterator P = I->pred_begin(),
+ E2 = I->pred_end();
+ P != E2; ++P) {
+ MachineBasicBlock* PBB = *P;
+ // Skip blocks that loop to themselves, can't tail merge these.
+ if (PBB==IBB)
+ continue;
+ MachineBasicBlock *TBB = 0, *FBB = 0;
+ std::vector<MachineOperand> Cond;
+ if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond)) {
+ // Failing case: IBB is the target of a cbr, and
+ // we cannot reverse the branch.
+ std::vector<MachineOperand> NewCond(Cond);
+ if (Cond.size() && TBB==IBB) {
+ if (TII->ReverseBranchCondition(NewCond))
+ continue;
+ // This is the QBB case described above
+ if (!FBB)
+ FBB = next(MachineFunction::iterator(PBB));
+ }
+ // Failing case: the only way IBB can be reached from PBB is via
+ // exception handling. Happens for landing pads. Would be nice
+ // to have a bit in the edge so we didn't have to do all this.
+ if (IBB->isLandingPad()) {
+ MachineFunction::iterator IP = PBB; IP++;
+ MachineBasicBlock* PredNextBB = NULL;
+ if (IP!=MF.end())
+ PredNextBB = IP;
+ if (TBB==NULL) {
+ if (IBB!=PredNextBB) // fallthrough
+ continue;
+ } else if (FBB) {
+ if (TBB!=IBB && FBB!=IBB) // cbr then ubr
+ continue;
+ } else if (Cond.empty()) {
+ if (TBB!=IBB) // ubr
+ continue;
+ } else {
+ if (TBB!=IBB && IBB!=PredNextBB) // cbr
+ continue;
+ }
+ }
+ // Remove the unconditional branch at the end, if any.
+ if (TBB && (Cond.size()==0 || FBB)) {
+ TII->RemoveBranch(*PBB);
+ if (Cond.size())
+ // reinsert conditional branch only, for now
+ TII->InsertBranch(*PBB, (TBB==IBB) ? FBB : TBB, 0, NewCond);
+ }
+ MergePotentials.push_back(std::make_pair(HashEndOfMBB(PBB, 1U), *P));
+ }
+ }
+ if (MergePotentials.size() >= 2)
+ MadeChange |= TryMergeBlocks(I, PredBB);
+ // Reinsert an unconditional branch if needed.
+ // The 1 below can be either an original single predecessor, or a result
+ // of removing blocks in TryMergeBlocks.
+ PredBB = prior(I); // this may have been changed in TryMergeBlocks
+ if (MergePotentials.size()==1 &&
+ (MergePotentials.begin())->second != PredBB)
+ FixTail((MergePotentials.begin())->second, I, TII);