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

[Balázs Kéri via Phabricator via cfe-commits]

balazske 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)),
----------------
martong wrote:
> NoQ wrote:
> > 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).
> Alright, I agree, I'll remove these cases. 
> 
> Generally speaking I realized that it is hard to create these cases, and it is very rare when we can come up with a meaningful case set for any function. So while we are at it, could you please take a look at another patch, where I add no cases just argument constraints: D82288 ?
But it could make sense that if the input of the function is known before the call, we can compute the output? For `abs(x)` if we know that `x == 0` is true the checker could assume `abs(x) == 0` too. These "cases" provide data for this functionality.


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https://reviews.llvm.org/D79432