diff options
Diffstat (limited to 'llvm/lib/CodeGen/BranchFolding.cpp')
| -rw-r--r-- | llvm/lib/CodeGen/BranchFolding.cpp | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp index fb8d98f228e..2d01301402f 100644 --- a/llvm/lib/CodeGen/BranchFolding.cpp +++ b/llvm/lib/CodeGen/BranchFolding.cpp @@ -600,6 +600,22 @@ ProfitableToMerge(MachineBasicBlock *MBB1, MachineBasicBlock *MBB2, if (MBB2->isLayoutSuccessor(MBB1) && I1 == MBB1->begin()) return true; + // If both blocks are identical and end in a branch, merge them unless they + // both have a fallthrough predecessor and successor. + // We can only do this after block placement because it depends on whether + // there are fallthroughs, and we don't know until after layout. + if (AfterPlacement && I1 == MBB1->begin() && I2 == MBB2->begin()) { + auto BothFallThrough = [](MachineBasicBlock *MBB) { + if (MBB->succ_size() != 0 && !MBB->canFallThrough()) + return false; + MachineFunction::iterator I(MBB); + MachineFunction *MF = MBB->getParent(); + return (MBB != &*MF->begin()) && std::prev(I)->canFallThrough(); + }; + if (!BothFallThrough(MBB1) || !BothFallThrough(MBB2)) + return true; + } + // If both blocks have an unconditional branch temporarily stripped out, // count that as an additional common instruction for the following // heuristics. This heuristic is only accurate for single-succ blocks, so to |
