Szelethus added a comment.
In D72705#2143405 <https://reviews.llvm.org/D72705#2143405>, @balazske wrote:
> We must check on every execution path that a specific condition on a value is
> satisfied (or: find one where the condition is not satisfied). This would be
> the most simple form of this checker. This can be done with the path
> sensitive check and `checkDeadSymbols`. If the symbol becomes dead with
> unsatisfied condition a warning is emitted. The "condition" is a
> syntactic-like check that looks for code like "`X != EOF`". This is probably
> done best by using `StmtVisitor` if a value is evaluated (at assignment or
> condition in `if` or other statements), different than the current form.
Pathsensitivity is about checking **one** specific path of execution with
rather great precision, we really need dataflow to argue about **all** paths.
Syntactic checking and pathsensitive analysis fundamentally lacks a lot of
information that dataflow by design has. With that said, asking whether a
symbol is dead is a part of liveness analysis which is a dataflow algorithm,
but what that interface lacks is //why// a symbol is live/dead. I think what
you need here is a set of reads reachable from the return value point. For this
example, you are interested in which reads are reachable from b9, and you could
analyze them one-by-one (which could be done syntactically at that point):
c = fgetc(fd); // [b9]
if (c == '+' || c == '*' || c == '|' || c == '>' || c == '@' || c == EOF || c
== '\n') { [b1] }
// [b8] [b7] [b6] [b5] [b4] [b3]
[b2]
// [b0 (EXIT)]
Repository:
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https://reviews.llvm.org/D72705
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