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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174915 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Vectorize/BBVectorize.cpp b/lib/Transforms/Vectorize/BBVectorize.cpp
index b14d91dd8e6eb98ee55962d19bf2bd6cbf37c93a..c11d9f679d4f59e6456f993cb0d2d2cd820ea05c 100644 (file)
--- a/lib/Transforms/Vectorize/BBVectorize.cpp
+++ b/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;
     }
   }