[PATCH] D82381: [analyzer] Introduce small improvements to the solver infra

[Denys Petrov via Phabricator via cfe-commits]

ASDenysPetrov added a comment.

@vsavchenko
Thank you.
Despite of all of my nits, LGTM!



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Comment at: clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp:367-378
+RangeSet RangeSet::Delete(BasicValueFactory &BV, Factory &F,
+                          const llvm::APSInt &Point) const {
+  llvm::APSInt Upper = Point;
+  llvm::APSInt Lower = Point;
+
+  ++Upper;
+  --Lower;
----------------
vsavchenko wrote:
> ASDenysPetrov wrote:
> > Useful function. But I'd better rename it to `subtract` as we are working with sets (as a mathimatical collection). We should have a such one for the Ranges not only for Points.
> > We have `intersect`, `delete` aka `subtract`. And we also need to have functions `union` and `symmetricDifference` to cover full palette of common operations on sets.
> I agree that we should have a full set of functions.  I don't agree however, that this function is a `subtract`.  Subtract is an operation on two sets and here we have a set and a point.  One might argue that a point is just a very simple set, that's true, but real `subtract` would be more complex in its implementation.
> 
> Naming it `delete`, on the other hand, I was coming from a notion of deleting points or neighbourhoods (https://en.wikipedia.org/wiki/Neighbourhood_(mathematics)#Deleted_neighbourhood).
>One might argue that a point is just a very simple set
That's actually what I mean :) and for this particular case you may leave the implementation as is. And for me it still does what `subtract` does. But I'm OK,  I don't insist.


================
Comment at: clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp:734
   //        expressions which we currently do not know how to negate.
-  const RangeSet *getRangeForMinusSymbol(ProgramStateRef State, SymbolRef Sym) {
+  Optional<RangeSet> getRangeForInvertedSub(SymbolRef Sym) {
     if (const SymSymExpr *SSE = dyn_cast<SymSymExpr>(Sym)) {
----------------
vsavchenko wrote:
> ASDenysPetrov wrote:
> > As for me, I'd call this like `getRangeForNegatedSymSymExpr`, since you do Negate operation inside.
> I'm not super happy about my name either, but I feel like it describes it better than the previous name and your version.  That function doesn't work for any `SymSymExpr` and it doesn't simply negate whatever we gave it.  It works specifically for symbolic subtractions and this is the information I want to be reflected in the name.
Oh, I just assumed //...Sub// at the end as a //subexpression// but you mean //subtraction//. What I'm trying to say is that we can rename it like `getRangeFor...`//the expression which this function can handle//. E.g. `getRangeForNegatedSubtractionSymSymExpr`. My point is in a speaking name.

I think //invertion// is not something appropriate in terms of applying minus operator. I think invertion of zero should be something opposite but not a zero. Because when you would like to implement the function which turns [A, B] into [MIN, A)U(B, MAX], what would be the name of it? I think this is an //invertion//.

But this is not a big deal, it's just my thoughts.


================
Comment at: clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp:841-844
+  RangeSet getTrueRange(QualType T) {
+    RangeSet TypeRange = infer(T);
+    return assumeNonZero(TypeRange, T);
+  }
----------------
vsavchenko wrote:
> ASDenysPetrov wrote:
> > Don't you think this is too complicated for such a simple getter?
> > Maybe we can just construct the range using smth about `RangeSet(RangeFactory, ++Zero, --Zero);` ?
> It is more complex than a false range but there is a reason for it.
> 
> First of all, `RangeSet` can't have ranges where the end is greater than its start.  Only `Intersect` can handle such ranges correctly.  Another thing is that ranges like that mean `[MIN, --Zero], [++Zero, MAX]` and without a type we can't really say what `MIN` and `MAX` are, so such constructor for `RangeSet` simply cannot exist.
> 
> Another point is that we do need to have `[MIN, -1], [+1, MAX]` as opposed to `[-1, -1], [+1, +1]` because of C language (it doesn't have boolean type), and because of the cases like `a - b` where we know that `a != b`.
> 
> I hope that answers the question.
I just want this function has low complexity and be more lightweight as `getFalseRange`. And if we have any chance to simplify it (and you have all the data to get MIN and MAX), it'd be cool.


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https://reviews.llvm.org/D82381