[PATCH] D112296: [Analyzer][solver] Handle adjustments in constraint assignor remainder

[Gabor Marton via Phabricator via cfe-commits]

martong added inline comments.


================
Comment at: clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp:1623
     if (!Constraint.containsZero()) {
-      State = RCM.assumeSymNE(State, LHS, Zero, Zero);
+      State = RCM.assumeSymRel(State, LHS, BO_NE, Zero);
       if (!State)
----------------
martong wrote:
> ASDenysPetrov wrote:
> > martong wrote:
> > > ASDenysPetrov wrote:
> > > > What I see, you're still trying to avoid using `State->assume`, which I recommend in a parent revision, but coming closer using its guts.
> > > So, it would look like this:
> > > ```
> > > State = State->assume(Builder.makeSymbolVal(LHS).castAs<nonloc::SymbolVal>(), true);
> > > ```
> > > The main  reason why we cannot use `State->assume` is that it boils down to `RangedConstraintManager::assumeSym` that has a specific logic for the `boolean` assumption. I.e. the operator is being negated in a case:
> > > ```
> > >     if (BinaryOperator::isComparisonOp(op) && op != BO_Cmp) {
> > >       if (!Assumption)
> > >         op = BinaryOperator::negateComparisonOp(op);
> > > 
> > >       return assumeSymRel(State, SIE->getLHS(), op, SIE->getRHS());
> > >     }
> > > ```
> > > You can try it for yourself, and see that the test case added in this patch will not pass if we were to use `State->assume`. Essentially, we have to evade the special "bool" logic, and the closest we can get is using `assumeSymRel`.
> > > 
> > > Besides that, by using `State->assume` we would have a superfluous conversion chain `Symbol->SVal->Symbol` until we reach `assumeSymRel`. 
> > >You can try it for yourself, and see that the test case added in this patch will not pass if we were to use `State->assume.`
> > I can't confirm. Your test case passed when I replaced with `State = State->assume(Builder.makeSymbolVal(LHS).castAs<nonloc::SymbolVal>(), true);`.
> > > specific logic for the boolean assumption. I.e. the operator is being negated in a case:
> > That just simplifies the expression, say, you want to find whether `x > 5 is false`, than the Solver finds for you whether 
> > `x <= 5 is true`, which is an equivalent.
> > > Essentially, we have to evade the special "bool" logic
> > There is no problem with //bool// logic. It's an equivalent of `SVal != 0` when //true//, and `SVal == 0` when //false//. Nothing more.
> > 
> > All in all I see the problem to use `assume`. Not because of this function itself, but because you do it incorrect by getting an `SVal` from `LHS` with `makeSymbolVal`. We should get it with `State->getSVal` which needs `LocationContext` as a second parameter. And that's the challenge, to pass `LocationContext` here, since `RangedConstraintManager` doesn't use it, at least for now.
> > I can't confirm. Your test case passed when I replaced with `State = State->assume(Builder.makeSymbolVal(LHS).castAs<nonloc::SymbolVal>(), true);`.
> 
> Actually, since the last time I tried with `State->assume` we merged D110913. If you revert the changes of that patch you'll see that this test case indeed fails. However, here is a slightly modified case that fails even on the current llvm/main branch with `State->assume` but passes with `assumeSymRel`:
> ```
> void rem_constant_adj(int x, int y) {
>   if ((x + y + 1) % 3 == 0) // (x + y + 1) % 3 != 0 -> x + y + 1 != 0 -> x != -1
>     return;
>   clang_analyzer_eval(x + y + 1 != 0); // expected-warning{{TRUE}}
>   clang_analyzer_eval(x + y != -1);    // expected-warning{{TRUE}}
>   (void)(x * y); // keep the constraints alive.
> }
> ```
> 
> The only change is that we have `x + y` instead of `x`. 
> 
> Now, the explanation for the original test case when we have `(x + 1) % 3`: When we ask the value of `x != -1` then `assumeDual` evaluates the TRUE case which is feasible and then it tries to evaluate the FALSE case, so it queries `x == -1` is true. However, this kicks in the simplification, which simplifies the previous constraint of `x+1, [not 0]` to `-1 + 1, [not 0]` which is a contradiction, thus an infeasible state is returned.
> When we have `x + y` in the test case, then simplification cannot simplify `x + y + 1`, thus the situation is different.
> 
> So, the main problem with `State->assume` is that it does not compute the adjustment. I.e. when we have `x + 1` as LHS then `assumeSym(LHS)` calls into `assumeSymUnsupported` and that does not compute the adjustment. The only functions that compute the adjustment are `assumeSymRel` and `assumeSymInclusiveRange`.
BTW, if D103317 was merged, then I'd have to find another test case that fails here, but I think I could find one. Anyway, the point is that we need a function here, that handles the adjustments.


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https://reviews.llvm.org/D112296