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The question here isn't whether it's easier to write correct C programs than Java programs, it's whether C is a simple language. Subtle UB, as much of a headac

The question here isn't whether it's easier to write correct C programs than Java programs, it's whether C is a simple language. Subtle UB, as much of a headache as it can be to a programmer using the language, in this case leads to simpler implementation of a compiler.

kevinmgranger 9y ago
I think you've pointed out the distinction many miss when talking about simplicity, which results in talking past each other: simplicity for the user and simplicity for the compiler writer are totally different things. Java is simpler for the user but more complex for the implementer, and C is more complex for the user but simpler for the implementer.
pcwalton 9y ago
No, it doesn't. Maybe it did in 1978, but modern C compilers have to go to heroic lengths to do things like alias analysis that would be easier if the aliasing rules of C weren't so subtle. In Java the question of "can pointer A alias pointer B" is simple (unless typeof A derives typeof B or vice versa, the answer is no). In C, due to TBAA, it's hideously complex.
- jcranmer 9y ago
  If you look at software engineering and static analysis papers for a language like Java, there's often a discussion about using stuff like 2-object, 3-call site context sensitive alias analyses built on more or less fairly standardized Datalog rules. If you look at C or C++, the response is generally "you want a precise alias analysis? fall down in riotous laughter". The rules for TBAA are complex, and many C/C++ programs violate those rules because it's so hard to actually make sure you're not violating them, and half of the purpose of using C/C++ is actually to be able to do the kind of type-punning that TBAA prohibits.
- boomlinde 9y ago
  I mean writing a compiler that fulfills the specification. Whether a design complicates the implementation of alias analysis doesn't really change whether it is simple.

kevinmgranger 9y ago

I think you've pointed out the distinction many miss when talking about simplicity, which results in talking past each other: simplicity for the user and simplicity for the compiler writer are totally different things. Java is simpler for the user but more complex for the implementer, and C is more complex for the user but simpler for the implementer.

pcwalton 9y ago

No, it doesn't. Maybe it did in 1978, but modern C compilers have to go to heroic lengths to do things like alias analysis that would be easier if the aliasing rules of C weren't so subtle. In Java the question of "can pointer A alias pointer B" is simple (unless typeof A derives typeof B or vice versa, the answer is no). In C, due to TBAA, it's hideously complex.

jcranmer 9y ago
If you look at software engineering and static analysis papers for a language like Java, there's often a discussion about using stuff like 2-object, 3-call site context sensitive alias analyses built on more or less fairly standardized Datalog rules. If you look at C or C++, the response is generally "you want a precise alias analysis? fall down in riotous laughter". The rules for TBAA are complex, and many C/C++ programs violate those rules because it's so hard to actually make sure you're not violating them, and half of the purpose of using C/C++ is actually to be able to do the kind of type-punning that TBAA prohibits.
boomlinde 9y ago
I mean writing a compiler that fulfills the specification. Whether a design complicates the implementation of alias analysis doesn't really change whether it is simple.