SROA: Generate selects instead of shuffles when blending values because this is the cannonical form.

Shuffles are more difficult to lower and we usually don't touch them, while we do optimize selects more often.

llvm-svn: 180875

1 files changed, 6 insertions, 8 deletions

diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index c383e2f8ed8..d073e789dcb 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -2322,17 +2322,15 @@ static Value *insertVector(IRBuilderTy &IRB, Value *Old, Value *V,
   V = IRB.CreateShuffleVector(V, UndefValue::get(V->getType()),
                               ConstantVector::get(Mask),
                               Name + ".expand");
-  DEBUG(dbgs() << "    shuffle1: " << *V << "\n");
+  DEBUG(dbgs() << "    shuffle: " << *V << "\n");
 
   Mask.clear();
   for (unsigned i = 0; i != VecTy->getNumElements(); ++i)
-    if (i >= BeginIndex && i < EndIndex)
-      Mask.push_back(IRB.getInt32(i));
-    else
-      Mask.push_back(IRB.getInt32(i + VecTy->getNumElements()));
-  V = IRB.CreateShuffleVector(V, Old, ConstantVector::get(Mask),
-                              Name + "insert");
-  DEBUG(dbgs() << "    shuffle2: " << *V << "\n");
+    Mask.push_back(IRB.getInt1(i >= BeginIndex && i < EndIndex));
+
+  V = IRB.CreateSelect(ConstantVector::get(Mask), V, Old, Name + "blend");
+
+  DEBUG(dbgs() << "    blend: " << *V << "\n");
   return V;
 }