diff options
| -rw-r--r-- | lib/CodeGen/TailDuplication.cpp | 26 |
1 files changed, 13 insertions, 13 deletions
diff --git a/lib/CodeGen/TailDuplication.cpp b/lib/CodeGen/TailDuplication.cpp index a2af8b3b7d..d6860bcd17 100644 --- a/lib/CodeGen/TailDuplication.cpp +++ b/lib/CodeGen/TailDuplication.cpp @@ -433,28 +433,28 @@ bool TailDuplicatePass::TailDuplicate(MachineBasicBlock *TailBB, MachineFunction &MF, SmallVector<MachineBasicBlock*, 8> &TDBBs, SmallVector<MachineInstr*, 16> &Copies) { - // 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 // of one less than the tail-merge threshold. When optimizing for size, // duplicate only one, because one branch instruction can be eliminated to // compensate for the duplication. unsigned MaxDuplicateCount; - if (hasIndirectBranch) + if (MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize)) + MaxDuplicateCount = 1; + else + MaxDuplicateCount = TailDuplicateSize; + + if (PreRegAlloc) { + // Pre-regalloc tail duplication hurts compile time and doesn't help + // much except for indirect branches. + if (TailBB->empty() || !TailBB->back().getDesc().isIndirectBranch()) + return false; // 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 - // to allow undoing the effects of tail merging. + // to allow undoing the effects of tail merging and other optimizations + // that rearrange the predecessors of the indirect branch. MaxDuplicateCount = 20; - else if (MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize)) - MaxDuplicateCount = 1; - else - MaxDuplicateCount = TailDuplicateSize; + } // Don't try to tail-duplicate single-block loops. if (TailBB->isSuccessor(TailBB)) |