[InstCombine] avoid crashing on shuffle shrinkage when input type is not same as result type

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297280 91177308-0d34-0410-b5e6-96231b3b80d8

Author: rotateright

lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -470,7 +470,8 @@ static Instruction *shrinkSplatShuffle(TruncInst &Trunc,
                                        InstCombiner::BuilderTy &Builder) {
   auto *Shuf = dyn_cast<ShuffleVectorInst>(Trunc.getOperand(0));
   if (Shuf && Shuf->hasOneUse() && isa<UndefValue>(Shuf->getOperand(1)) &&
-      Shuf->getMask()->getSplatValue()) {
+      Shuf->getMask()->getSplatValue() &&
+      Shuf->getType() == Shuf->getOperand(0)->getType()) {
     // trunc (shuf X, Undef, SplatMask) --> shuf (trunc X), Undef, SplatMask
     Constant *NarrowUndef = UndefValue::get(Trunc.getType());
     Value *NarrowOp = Builder.CreateTrunc(Shuf->getOperand(0), Trunc.getType());

test/Transforms/InstCombine/trunc.ll

@@ -520,3 +520,16 @@ define <3 x i31> @wide_splat3(<3 x i33> %x) {
   ret <3 x i31> %trunc
 }
 
+; TODO: The shuffle extends the length of the input vector. Should we shrink this?
+
+define <8 x i8> @wide_lengthening_splat(<4 x i16> %v) {
+; CHECK-LABEL: @wide_lengthening_splat(
+; CHECK-NEXT:    [[SHUF:%.*]] = shufflevector <4 x i16> %v, <4 x i16> undef, <8 x i32> zeroinitializer
+; CHECK-NEXT:    [[TR:%.*]] = trunc <8 x i16> [[SHUF]] to <8 x i8>
+; CHECK-NEXT:    ret <8 x i8> [[TR]]
+;
+  %shuf = shufflevector <4 x i16> %v, <4 x i16> %v, <8 x i32> zeroinitializer
+  %tr = trunc <8 x i16> %shuf to <8 x i8>
+  ret <8 x i8> %tr
+}
+