diff options
| -rw-r--r-- | lib/CodeGen/TailDuplication.cpp | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/lib/CodeGen/TailDuplication.cpp b/lib/CodeGen/TailDuplication.cpp index c99c74c0f4..f51f74d506 100644 --- a/lib/CodeGen/TailDuplication.cpp +++ b/lib/CodeGen/TailDuplication.cpp @@ -253,7 +253,7 @@ bool TailDuplicatePass::TailDuplicateBlocks(MachineFunction &MF) { SSAUpdateVals.clear(); } - // Eliminate some of the copies inserted tail duplication to maintain + // Eliminate some of the copies inserted by tail duplication to maintain // SSA form. for (unsigned i = 0, e = Copies.size(); i != e; ++i) { MachineInstr *Copy = Copies[i]; @@ -437,8 +437,11 @@ bool TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF, SmallVector<MachineBasicBlock*, 8> &TDBBs, SmallVector<MachineInstr*, 16> &Copies) { - // Don't try to tail-duplicate single-block loops. - if (TailBB->isSuccessor(TailBB)) + // Pre-regalloc tail duplication hurts compile time and doesn't help + // much except for indirect branches. + bool hasIndirectBranch = (!TailBB->empty() && + TailBB->back().getDesc().isIndirectBranch()); + if (PreRegAlloc && !hasIndirectBranch) return false; // Set the limit on the number of instructions to duplicate, with a default @@ -446,7 +449,7 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF, // duplicate only one, because one branch instruction can be eliminated to // compensate for the duplication. unsigned MaxDuplicateCount; - if (!TailBB->empty() && TailBB->back().getDesc().isIndirectBranch()) + if (hasIndirectBranch) // If the target has hardware branch prediction that can handle indirect // branches, duplicating them can often make them predictable when there // are common paths through the code. The limit needs to be high enough @@ -457,6 +460,10 @@ TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF, else MaxDuplicateCount = TailDuplicateSize; + // Don't try to tail-duplicate single-block loops. + if (TailBB->isSuccessor(TailBB)) + return false; + // Check the instructions in the block to determine whether tail-duplication // is invalid or unlikely to be profitable. unsigned InstrCount = 0; |