From da24f2f8e175e3561e9a523fa5dd70a448a6b369 Mon Sep 17 00:00:00 2001 From: Rafael Espindola Date: Tue, 14 Jun 2011 04:41:17 +0000 Subject: Make the threshold used by branch folding softer. Before we would get a sharp all or nothing transition when one extra predecessor was added. Now we still test first ones for merging. llvm-svn: 132974 --- llvm/lib/CodeGen/BranchFolding.cpp | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-) (limited to 'llvm/lib/CodeGen/BranchFolding.cpp') diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp index 719cd264f68..b43884ebf2f 100644 --- a/llvm/lib/CodeGen/BranchFolding.cpp +++ b/llvm/lib/CodeGen/BranchFolding.cpp @@ -799,14 +799,22 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { // First find blocks with no successors. MergePotentials.clear(); - for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) { + for (MachineFunction::iterator I = MF.begin(), E = MF.end(); + I != E && MergePotentials.size() < TailMergeThreshold; ++I) { + if (TriedMerging.count(I)) + continue; if (I->succ_empty()) MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(I), I)); } + // If this is a large problem, avoid visiting the same basic blocks + // multiple times. + if (MergePotentials.size() == TailMergeThreshold) + for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) + TriedMerging.insert(MergePotentials[i].getBlock()); + // See if we can do any tail merging on those. - if (MergePotentials.size() < TailMergeThreshold && - MergePotentials.size() >= 2) + if (MergePotentials.size() >= 2) MadeChange |= TryTailMergeBlocks(NULL, NULL); // Look at blocks (IBB) with multiple predecessors (PBB). @@ -830,15 +838,17 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { for (MachineFunction::iterator I = llvm::next(MF.begin()), E = MF.end(); I != E; ++I) { - if (I->pred_size() >= 2 && I->pred_size() < TailMergeThreshold) { + if (I->pred_size() >= 2) { SmallPtrSet UniquePreds; MachineBasicBlock *IBB = I; MachineBasicBlock *PredBB = prior(I); MergePotentials.clear(); for (MachineBasicBlock::pred_iterator P = I->pred_begin(), E2 = I->pred_end(); - P != E2; ++P) { + P != E2 && MergePotentials.size() < TailMergeThreshold; ++P) { MachineBasicBlock *PBB = *P; + if (TriedMerging.count(PBB)) + continue; // Skip blocks that loop to themselves, can't tail merge these. if (PBB == IBB) continue; @@ -891,6 +901,12 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) { MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(PBB), *P)); } } + // If this is a large problem, avoid visiting the same basic blocks + // multiple times. + if (MergePotentials.size() == TailMergeThreshold) + for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i) + TriedMerging.insert(MergePotentials[i].getBlock()); + if (MergePotentials.size() >= 2) MadeChange |= TryTailMergeBlocks(IBB, PredBB); // Reinsert an unconditional branch if needed. -- cgit v1.2.3