[cfe-dev] Potentially expensive analysis for missing `[]` in delete expression

[Rafael Auler]

This is an interesting analysis that would really help a lot of people.
However, if the analysis intend to be truly accurate, I think it should be
implemented in the static analyzer.

For example:

if (cond)
  a = new int[5];
else
  a = (int*) malloc(sizeof(int)*5);

would easily trick a CFG-based analysis because it can't know at
compile-time whether cond is true or false.

Nevertheless, I still believe that a front-end analysis can help in simpler
cases, but we can't expect to be 100% accurate.


On Tue, Jul 8, 2014 at 1:57 PM, Ismail Pazarbasi <ismail.pazarbasi at gmail.com
> wrote:

> Hi,
>
> During a demo, audience caught that I forgot [] in delete expression.
> clang didn't warn about it. I was wondering whether this is due to the cost
> of analysis. My sample was something like:
>
>   class A {
>     int *a;
>   public:
>     A() : a(new int[5]) { }
>     ~A() { delete /*[]*/ a; }
>   };
>
> but following doesn't seem like to analyze missing [] either:
>
>   % clang++ -fsyntax-only -x c++ -pedantic -Wall -Wextra -
>   void f() {
>     int *a = new int[5];
>     delete a;
>   }
>   %
>
> Is this analysis omitted due to performance concerns or simply an
> oversight?
>
> Analyzing my sample requires clang to analyze all ctor-initializers, then
> in-class initializers, to check whether member was new[]'ed each time it
> sees delete expression where pointee is a MemberExpr. For the latter case,
> I think checking whether VarDecl initialized with new[] is enough. Did I
> get this right? I already have a patch for this, but I didn't test its
> performance impact on a sufficiently large code base. Do we have previous
> implementation experience with this?
>
> Ismail
>
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>
>
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