[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/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 670168bf537..e2f54606f2d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1526,7 +1526,7 @@ bool InstCombiner::mergeStoreIntoSuccessor(StoreInst &SI) {
   // Check if the successor block has exactly 2 incoming edges.
   BasicBlock *StoreBB = SI.getParent();
   BasicBlock *DestBB = StoreBB->getTerminator()->getSuccessor(0);
-  if (pred_size(DestBB) != 2)
+  if (!DestBB->hasNPredecessors(2))
     return false;
 
   // Capture the other block (the block that doesn't contain our store).