diff options
Diffstat (limited to 'llvm/lib/CodeGen/MachineBlockPlacement.cpp')
| -rw-r--r-- | llvm/lib/CodeGen/MachineBlockPlacement.cpp | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp index 08fe3d4..2dbabfe 100644 --- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp +++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp @@ -104,6 +104,12 @@ static cl::opt<unsigned> MaxBytesForAlignmentOverride( "alignment"), cl::init(0), cl::Hidden); +static cl::opt<unsigned> PredecessorLimit( + "block-placement-predecessor-limit", + cl::desc("For blocks with more predecessors, certain layout optimizations" + "will be disabled to prevent quadratic compile time."), + cl::init(1000), cl::Hidden); + // FIXME: Find a good default for this flag and remove the flag. static cl::opt<unsigned> ExitBlockBias( "block-placement-exit-block-bias", @@ -1030,6 +1036,11 @@ bool MachineBlockPlacement::isTrellis( SmallPtrSet<const MachineBasicBlock *, 8> SeenPreds; for (MachineBasicBlock *Succ : ViableSuccs) { + // Compile-time optimization: runtime is quadratic in the number of + // predecessors. For such uncommon cases, exit early. + if (Succ->pred_size() > PredecessorLimit) + return false; + int PredCount = 0; for (auto *SuccPred : Succ->predecessors()) { // Allow triangle successors, but don't count them. @@ -1472,6 +1483,11 @@ bool MachineBlockPlacement::hasBetterLayoutPredecessor( if (SuccChain.UnscheduledPredecessors == 0) return false; + // Compile-time optimization: runtime is quadratic in the number of + // predecessors. For such uncommon cases, exit early. + if (Succ->pred_size() > PredecessorLimit) + return false; + // There are two basic scenarios here: // ------------------------------------- // Case 1: triangular shape CFG (if-then): |