[InstCombine] add possible bswap as widening shuffle test; NFC

Goes with the proposal in D66965.

llvm-svn: 370407

Author: rotateright

llvm/test/Transforms/InstCombine/bswap.ll

@@ -283,8 +283,8 @@ define i32 @shuf_4bytes_extra_use(<4 x i8> %x) {
   ret i32 %cast
 }
 
-define i128 @shuf_load_16bytes(<16 x i8> %x) {
-; CHECK-LABEL: @shuf_load_16bytes(
+define i128 @shuf_16bytes(<16 x i8> %x) {
+; CHECK-LABEL: @shuf_16bytes(
 ; CHECK-NEXT:    [[BSWAP:%.*]] = shufflevector <16 x i8> [[X:%.*]], <16 x i8> undef, <16 x i32> <i32 15, i32 14, i32 13, i32 12, i32 11, i32 10, i32 9, i32 8, i32 7, i32 6, i32 5, i32 4, i32 3, i32 2, i32 1, i32 0>
 ; CHECK-NEXT:    [[CAST:%.*]] = bitcast <16 x i8> [[BSWAP]] to i128
 ; CHECK-NEXT:    ret i128 [[CAST]]
@@ -293,3 +293,14 @@ define i128 @shuf_load_16bytes(<16 x i8> %x) {
   %cast = bitcast <16 x i8> %bswap to i128
   ret i128 %cast
 }
+
+define i32 @shuf_2bytes_widening(<2 x i8> %x) {
+; CHECK-LABEL: @shuf_2bytes_widening(
+; CHECK-NEXT:    [[BSWAP:%.*]] = shufflevector <2 x i8> [[X:%.*]], <2 x i8> undef, <4 x i32> <i32 1, i32 0, i32 undef, i32 undef>
+; CHECK-NEXT:    [[CAST:%.*]] = bitcast <4 x i8> [[BSWAP]] to i32
+; CHECK-NEXT:    ret i32 [[CAST]]
+;
+  %bswap = shufflevector <2 x i8> %x, <2 x i8> undef, <4 x i32> <i32 1, i32 0, i32 undef, i32 undef>
+  %cast = bitcast <4 x i8> %bswap to i32
+  ret i32 %cast
+}