diff options
Diffstat (limited to 'lib/CodeGen/BranchFolding.cpp')
| -rw-r--r-- | lib/CodeGen/BranchFolding.cpp | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp index dc67593c33..2d7836f4f3 100644 --- a/lib/CodeGen/BranchFolding.cpp +++ b/lib/CodeGen/BranchFolding.cpp @@ -451,7 +451,10 @@ static bool MergeCompare(const std::pair<unsigned,MachineBasicBlock*> &p, bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB, MachineBasicBlock* PredBB) { - unsigned minCommonTailLength = (SuccBB ? 1 : 2); + // It doesn't make sense to save a single instruction since tail merging + // will add a jump. + // FIXME: Ask the target to provide the threshold? + unsigned minCommonTailLength = (SuccBB ? 1 : 2) + 1; MadeChange = false; // Sort by hash value so that blocks with identical end sequences sort @@ -476,9 +479,9 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB, // 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 + // Since instructions may get combined later (e.g. single stores into // store multiple) this measure is not particularly accurate. - MachineBasicBlock::iterator BBI1, BBI2; + MachineBasicBlock::iterator BBI1, BBI2; unsigned FoundI = ~0U, FoundJ = ~0U; unsigned maxCommonTailLength = 0U; @@ -541,6 +544,12 @@ bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB, continue; } + MachineBasicBlock::iterator TrialBBI1, TrialBBI2; + unsigned CommonTailLen = ComputeCommonTailLength(CurMBB, MBB2, + TrialBBI1, TrialBBI2); + if (CommonTailLen < minCommonTailLength) + continue; + // Decide whether we want to split CurMBB or MBB2. if (ShouldSplitFirstBlock(CurMBB, BBI1, MBB2, BBI2, PredBB)) { CurMBB = SplitMBBAt(*CurMBB, BBI1); |