[IR] Add hasNPredecessors, hasNPredecessorsOrMore to BasicBlock

Add methods to BasicBlock which make it easier to efficiently check
whether a block has N (or more) predecessors.

This can be more efficient than using pred_size(), which is a linear
time operation.

We might consider adding similar methods for successors. I haven't done
so in this patch because succ_size() is already O(1).

With this patch applied, I measured a 0.065% compile-time reduction in
user time for running `opt -O3` on the sqlite3 amalgamation (30 trials).
The change in mergeStoreIntoSuccessor alone saves 45 million linked list
iterations in a stage2 Release build of llc.

See llvm.org/PR39702 for a harder but more general way of achieving
similar results.

Differential Revision: https://reviews.llvm.org/D54686

llvm-svn: 347256

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/MemorySSAUpdater.cpp b/llvm/lib/Analysis/MemorySSAUpdater.cpp
index 1ac58188bd9..6c817d20368 100644
--- a/llvm/lib/Analysis/MemorySSAUpdater.cpp
+++ b/llvm/lib/Analysis/MemorySSAUpdater.cpp
@@ -1022,7 +1022,7 @@ void MemorySSAUpdater::wireOldPredecessorsToNewImmediatePredecessor(
   MemoryPhi *Phi = MSSA->getMemoryAccess(Old);
   if (!Phi)
     return;
-  if (pred_size(Old) == 1) {
+  if (Old->hasNPredecessors(1)) {
     assert(pred_size(New) == Preds.size() &&
            "Should have moved all predecessors.");
     MSSA->moveTo(Phi, New, MemorySSA::Beginning);