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* [Bug c++/108537] New: constexpr UB pointer dereference compiles if the dereferenced value is not used
@ 2023-01-25 10:35 ed at edwardrosten dot com
  0 siblings, 0 replies; only message in thread
From: ed at edwardrosten dot com @ 2023-01-25 10:35 UTC (permalink / raw)
  To: gcc-bugs

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108537

            Bug ID: 108537
           Summary: constexpr UB pointer dereference compiles if the
                    dereferenced value is not used
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ed at edwardrosten dot com
  Target Milestone: ---

The following code compiles successfully:

constexpr int a(){
    int* b = new int[1];
    int r= &b[100]-b; //UB
    b[100];  //UB
    delete[] b;
    return r;
}


template<int X> int N=0;

int foo(){
    return N<a()>;
}


b[100] is unconditionally undefined behaviour, even though the value is never
used.

Tested on a scattering of versions (10.3, 11.2, 12.2) with -std=c++2a -O2

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2023-01-25 10:35 [Bug c++/108537] New: constexpr UB pointer dereference compiles if the dereferenced value is not used ed at edwardrosten dot com

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