> There's a name for a kind of change that makes a previously correct program incorrect: "compiler bug".
No. The only thing that matters is that the language rules are respected. Or maybe you'd want programs that were correct with the first C compilers to still work today ? Because for instance they didn't do type checks at all. `void f(float, float); int x = f;` you say ? no problem! `char c; c[-15];` ? no problem! Everything did compile, sure. Is it the world we want ? Most certainly not.
Trigraphs used to be part of the standard and are now removed. So really old programs that used them now would fail to compile. Granted, that is a bit of a low hanging fruit.
No. The only thing that matters is that the language rules are respected. Or maybe you'd want programs that were correct with the first C compilers to still work today ? Because for instance they didn't do type checks at all. `void f(float, float); int x = f;` you say ? no problem! `char c; c[-15];` ? no problem! Everything did compile, sure. Is it the world we want ? Most certainly not.