[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/Vectorize/VPlan.cpp b/llvm/lib/Transforms/Vectorize/VPlan.cpp
index dad733b4651..05a5400beb4 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlan.cpp
@@ -468,7 +468,7 @@ void VPlan::updateDominatorTree(DominatorTree *DT, BasicBlock *LoopPreHeaderBB,
            "One successor of a basic block does not lead to the other.");
     assert(InterimSucc->getSinglePredecessor() &&
            "Interim successor has more than one predecessor.");
-    assert(pred_size(PostDomSucc) == 2 &&
+    assert(PostDomSucc->hasNPredecessors(2) &&
            "PostDom successor has more than two predecessors.");
     DT->addNewBlock(InterimSucc, BB);
     DT->addNewBlock(PostDomSucc, BB);