[InstSimplify] Test select bit test with trunc to i1 (NFC)

Author: andjo403

llvm/test/Transforms/InstSimplify/select.ll

@@ -1749,3 +1749,31 @@ define <4 x i32> @select_vector_cmp_with_bitcasts(<2 x i64> %x, <4 x i32> %y) {
   %sel = select <4 x i1> %cmp, <4 x i32> %sub.bc, <4 x i32> zeroinitializer
   ret <4 x i32> %sel
 }
+
+define i8 @bittest_trunc_or(i8 %x) {
+; CHECK-LABEL: @bittest_trunc_or(
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i8 [[X1:%.*]] to i1
+; CHECK-NEXT:    [[OR:%.*]] = or i8 [[X1]], 1
+; CHECK-NEXT:    [[X:%.*]] = select i1 [[TRUNC]], i8 [[OR]], i8 [[X1]]
+; CHECK-NEXT:    ret i8 [[X]]
+;
+  %trunc = trunc i8 %x to i1
+  %or = or i8 %x, 1
+  %cond = select i1 %trunc, i8 %or, i8 %x
+  ret i8 %cond
+}
+
+define i8 @bittest_trunc_not_or(i8 %x) {
+; CHECK-LABEL: @bittest_trunc_not_or(
+; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i8 [[X:%.*]] to i1
+; CHECK-NEXT:    [[NOT:%.*]] = xor i1 [[TRUNC]], true
+; CHECK-NEXT:    [[OR:%.*]] = or i8 [[X]], 1
+; CHECK-NEXT:    [[COND:%.*]] = select i1 [[NOT]], i8 [[OR]], i8 [[X]]
+; CHECK-NEXT:    ret i8 [[COND]]
+;
+  %trunc = trunc i8 %x to i1
+  %not = xor i1 %trunc, true
+  %or = or i8 %x, 1
+  %cond = select i1 %not, i8 %or, i8 %x
+  ret i8 %cond
+}