To be bread it must have toar lechem, "the appearance of bread". So noodles are definitely out, as are cooked grains, which do not even necessarily require bishul yisrael (to be cooked by a Jew), but batter-based cakes etc. are in. Beyond that things get hard to pin down, and I have not seen any responsa on the subject. Rav Yitzchok Berkovits says they showed Rav Shlomo Zalman Cheerios, and he said, "אה, קליינע בייגעלאך" - literally, "Small baigels!" but in Israeli parlance, "Small pretzels!" He held that Cheerios have the appearance of bread and would therefore not be pas yisrael. Similarly, I believe I saw a chart from the Star-K which said that if one eats Cheerios to satiety one would be Biblically obligated to say birkat hamazon. However, the Lakewood minhag seems to be to treat Cheerios as a noodle and not require them to be pas yisrael, though I have seen no source for this. I asked Rav Gedaliah Anemer if bran flakes had toar lechem and would therefore be forbidden to eat during the 10 Days of Repentence (OC 603:1) and he replied he didn't think so.
The concept of toar lechem, "the appearance of bread," comes from OC 168:10, where the Shulchan Aruch approximately says that if you crumble your matzah, wet it and make it into a matzah ball, it loses its "hamotzi" and becomes a "mezonot". Rav Alexander Mandelbaum in V'Zot haBracha mentions the the gemara says grains which are ma'aseh kedeira ("cooked in a pot") are always mezonot, not hamotzi (Brachot 37a). He quotes several authorities who thought noodles did have toar lechem, but Rav Akiva Eiger rejects them and infers that the Rambam agrees with him: even though they are made from dough, since they are not baked, they are not bread-like, and so is the conclusion of the Mishna Brura.
Rav Mandelbaum quotes Rav Mordechai Eliyahu that pancakes and melawach have toar lechem. He says breakfast cereals consisting of various baked shapes of some thickness - he mentions Grape Nuts and several Israeli brands - have toar lechem according to Rav Shlomo Zalman and Rav Elyashiv, however Rav Scheinberg disagreed. Rav Shlomo Zalman agreed that bran flakes do not have toar lechem, but Rav Elyashiv held they did.
I do not know of any source that links YD 112 to OC 168; I think it's taken as self-evident, given that YD 113:1 states that any food which is not eaten raw and which is "suitable for a king's table" is forbidden if cooked by a non-Jew.