[PATCH] D79432: [analyzer] StdLibraryFunctionsChecker: Add summaries for libc

[Artem Dergachev via Phabricator via cfe-commits]

NoQ added inline comments.


================
Comment at: clang/lib/StaticAnalyzer/Checkers/StdLibraryFunctionsChecker.cpp:1123-1124
+      "abs", Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure)
+                 .Case({ArgumentCondition(0, WithinRange, SingleValue(0)),
+                        ReturnValueCondition(WithinRange, SingleValue(0))})
+                 .Case({ArgumentCondition(0, WithinRange, Range(1, IntMax)),
----------------
NoQ wrote:
> The three-way state split is unjustified here. Usage of `abs` is not a sufficient indication that the value may be 0, otherwise:
> ```lang=c++
> int foo(int x, int y) {
>   int z = abs(y);   // Assuming 'abs' has taken branch on which y == 0...
>   return x / z;     // ... we'll be forced to emit a division by zero warning here.
> }
> ```
> 
> Generally, there are very few cases when state splits upon function calls are justified. The common cases are:
> - The function returns bool and finding that bool is the only reason to ever call this function. Eg., `isalpha()` and such.
> - The function can at any time completely unpredictably take any of the branches, in other words, taint is involved. Eg., `scanf()` can always fail simply because the user of the program wrote something special into stdin.
> returns bool

Or something that kinda resembles bool (eg., `isalpha()` returns a variety of different ints in practice due to its static lookup table implementation strategy but the user only cares about whether it's zero or non-zero).


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D79432/new/

https://reviews.llvm.org/D79432