Use unary CreateShuffleVector if possible

As mentioned in D93793, there are quite a few places where unary `IRBuilder::CreateShuffleVector(X, Mask)` can be used
instead of `IRBuilder::CreateShuffleVector(X, Undef, Mask)`.
Let's update them.

Actually, it would have been more natural if the patches were made in this order:
(1) let them use unary CreateShuffleVector first
(2) update IRBuilder::CreateShuffleVector to use poison as a placeholder value (D93793)

The order is swapped, but in terms of correctness it is still fine.

Reviewed By: spatel

Differential Revision: https://reviews.llvm.org/D93923

1 files changed, 1 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index 0698c3c..3ea758a 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -6723,8 +6723,7 @@ bool CodeGenPrepare::optimizeShuffleVectorInst(ShuffleVectorInst *SVI) {
       cast<Instruction>(SVI->getOperand(0))->getOperand(1), NewType);
   Value *Insert = Builder.CreateInsertElement(UndefValue::get(NewVecType), BC1,
                                               (uint64_t)0);
-  Value *Shuffle = Builder.CreateShuffleVector(
-      Insert, UndefValue::get(NewVecType), SVI->getShuffleMask());
+  Value *Shuffle = Builder.CreateShuffleVector(Insert, SVI->getShuffleMask());
   Value *BC2 = Builder.CreateBitCast(Shuffle, SVIVecType);
 
   SVI->replaceAllUsesWith(BC2);