[InstSimplify] Add test for #77320 (NFC)

Author: nikic

llvm/test/Transforms/InstSimplify/select.ll

@@ -1733,3 +1733,17 @@ define i8 @select_or_disjoint_eq(i8 %x, i8 %y) {
   %sel = select i1 %cmp, i8 %x, i8 %or
   ret i8 %sel
 }
+
+; FIXME: This is a miscompile.
+define <4 x i32> @select_vector_cmp_with_bitcasts(<2 x i64> %x, <4 x i32> %y) {
+; CHECK-LABEL: @select_vector_cmp_with_bitcasts(
+; CHECK-NEXT:    ret <4 x i32> zeroinitializer
+;
+  %x.bc = bitcast <2 x i64> %x to <4 x i32>
+  %y.bc = bitcast <4 x i32> %y to <2 x i64>
+  %sub = sub <2 x i64> %x, %y.bc
+  %sub.bc = bitcast <2 x i64> %sub to <4 x i32>
+  %cmp = icmp eq <4 x i32> %y, %x.bc
+  %sel = select <4 x i1> %cmp, <4 x i32> %sub.bc, <4 x i32> zeroinitializer
+  ret <4 x i32> %sel
+}