BBVectorize: Don't over-search when building the dependency map

When building the pairable-instruction dependency map, don't search
past the last pairable instruction. For large blocks that have been
divided into multiple instruction groups, searching past the last
instruction in each group is very wasteful. This gives a 32% speedup
on the csa.ll test case from PR15222 (when using 50 instructions
in each group).

No functionality change intended.

llvm-svn: 174915

1 files changed, 10 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Vectorize/BBVectorize.cpp b/llvm/lib/Transforms/Vectorize/BBVectorize.cpp
index b14d91dd8e6..c11d9f679d4 100644
--- a/llvm/lib/Transforms/Vectorize/BBVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/BBVectorize.cpp
@@ -1380,20 +1380,28 @@ namespace {
     // Iterate through the basic block, recording all users of each
     // pairable instruction.
 
-    BasicBlock::iterator E = BB.end();
+    BasicBlock::iterator E = BB.end(), EL =
+      BasicBlock::iterator(cast<Instruction>(PairableInsts.back()));
     for (BasicBlock::iterator I = BB.getFirstInsertionPt(); I != E; ++I) {
       if (IsInPair.find(I) == IsInPair.end()) continue;
 
       DenseSet<Value *> Users;
       AliasSetTracker WriteSet(*AA);
-      for (BasicBlock::iterator J = llvm::next(I); J != E; ++J)
+      for (BasicBlock::iterator J = llvm::next(I); J != E; ++J) {
         (void) trackUsesOfI(Users, WriteSet, I, J);
 
+        if (J == EL)
+          break;
+      }
+
       for (DenseSet<Value *>::iterator U = Users.begin(), E = Users.end();
            U != E; ++U) {
         if (IsInPair.find(*U) == IsInPair.end()) continue;
         PairableInstUsers.insert(ValuePair(I, *U));
       }
+
+      if (I == EL)
+        break;
     }
   }