Optimization: bitcast (<1 x ...> insertelement ..., X, ...) to ... ==> bitcast X to ...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174905 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 16 insertions, 5 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 98fd05a..fbc259b 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -1738,11 +1738,22 @@ Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
   }
 
   if (VectorType *SrcVTy = dyn_cast<VectorType>(SrcTy)) {
-    if (SrcVTy->getNumElements() == 1 && !DestTy->isVectorTy()) {
-      Value *Elem =
-        Builder->CreateExtractElement(Src,
-                   Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
-      return CastInst::Create(Instruction::BitCast, Elem, DestTy);
+    if (SrcVTy->getNumElements() == 1) {
+      // If our destination is not a vector, then make this a straight
+      // scalar-scalar cast.
+      if (!DestTy->isVectorTy()) {
+        Value *Elem =
+          Builder->CreateExtractElement(Src,
+                     Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
+        return CastInst::Create(Instruction::BitCast, Elem, DestTy);
+      }
+
+      // Otherwise, see if our source is an insert. If so, then use the scalar
+      // component directly.
+      if (InsertElementInst *IEI =
+            dyn_cast<InsertElementInst>(CI.getOperand(0)))
+        return CastInst::Create(Instruction::BitCast, IEI->getOperand(1),
+                                DestTy);
     }
   }