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Throttle tail merging; handling blocks with large numbers of predecessors
is too slow. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37509 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -564,6 +564,9 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
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return MadeChange;
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}
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// Throttle for huge numbers of predecessors (compile speed problems)
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#define THRESHOLD 100
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bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
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if (!EnableTailMerge) return false;
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@ -577,7 +580,8 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
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MergePotentials.push_back(std::make_pair(HashEndOfMBB(I, 2U), I));
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}
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// See if we can do any tail merging on those.
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MadeChange |= TryMergeBlocks(NULL, NULL);
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if (MergePotentials.size() < THRESHOLD)
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MadeChange |= TryMergeBlocks(NULL, NULL);
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// Look at blocks (IBB) with multiple predecessors (PBB).
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// We change each predecessor to a canonical form, by
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@ -599,7 +603,7 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
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// transformations.)
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for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
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if (!I->succ_empty() && I->pred_size() >= 2) {
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if (!I->succ_empty() && I->pred_size() >= 2 && I->pred_size() < THRESHOLD) {
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MachineBasicBlock *IBB = I;
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MachineBasicBlock *PredBB = prior(I);
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MergePotentials.clear();
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