[Bug c++/52954] New: Missing bounds check warning

[Bug c++/52954] New: Missing bounds check warning

[xinliangli at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52954

             Bug #: 52954
           Summary: Missing bounds check warning
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: xinliangli@gmail.com


int foo() {
  int arr[100];
  // ...
 return arr[100];
 }

 /*  From clang:

 array.cpp:4:10: warning: array index 100 is past the end of the array
(which contains 100 elements) [-Warray-bounds]
 return arr[100];
        ^   ~~~
array.cpp:2:3: note: array 'arr' declared here
 int arr[100];
 ^
1 warning generated.

*/

[Bug c++/52954] Missing bounds check warning

[xinliangli at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52954

--- Comment #1 from davidxl <xinliangli at gmail dot com> 2012-04-12 21:56:07 UTC ---
Another example:

constexpr int arr_size = 42;
 constexpr int N = 44;
 void f(int);
 int test() {
   int arr[arr_size];
  // ...
   f(arr[N]);
   // ...
  if (N < arr_size) return arr[N];
  return 0;
 }

/*

deadcode.cpp:7:5: warning: array index 44 is past the end of the array
(which contains 42 elements) [-Warray-bounds]
 f(arr[N]);
   ^   ~
deadcode.cpp:5:3: note: array 'arr' declared here
 int arr[arr_size];
 ^
1 warning generated.

*/

[Bug c++/52954] Missing bounds check warning without optimization

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52954

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-04-13
            Summary|Missing bounds check        |Missing bounds check
                   |warning                     |warning without
                   |                            |optimization
     Ever Confirmed|0                           |1

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-04-13 09:51:38 UTC ---
We only perform array-bounds warnings when we optimize and the VRP pass is
turned on.  We completely miss this kind of warning in the frontend(s),
though they for sure can only detect very simple cases.

[Bug c++/52954] Missing bounds check warning without optimization

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52954

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |manu at gcc dot gnu.org
         Resolution|---                         |DUPLICATE

--- Comment #4 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
Duplicate

*** This bug has been marked as a duplicate of bug 3587 ***
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3587

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xinliangli at gmail dot com

--- Comment #11 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
*** Bug 52954 has been marked as a duplicate of this bug. ***
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Subject: [Bug c++/66962] [concepts] overloaded function causing memory blow-up and ICE
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idf962

--- Comment #13 from Andrew Sutton <andrew.n.sutton at gmail dot com> ---
There are a couple of other problems in the minimized example (concept int
shows up a couple of times, there's a variable template whose initializer is a
requires expression). I doubt those contribute to the observed problem.

I suspect there's something else at work. There was a performance problem
related earlier this year where (either) normalization or decomposition was
being applied for each subexpression multiple times.

The total number of elements in a decomposition should be linear w.r.t. to the
number of disjunctions. I'll try to look through this tomorrow.

A possible optimization is to store specializations of each concept being
normalized, so we don't expand to the same expressions over and over again --
basically, helping to ensure that we don't have lots of duplicate cases that
we're proving over and over again. It would probably be a good idea to prove
that's logically sound before implementing :/