[Bug middle-end/95903] New: gcc 10: wrong code with -fwrapv

[markus at oberhumer dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95903

            Bug ID: 95903
           Summary: gcc 10: wrong code with -fwrapv
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: markus at oberhumer dot com
  Target Milestone: ---

Link at Compiler Explorer: https://godbolt.org/z/VgNLcX


The following 2 functions should generate identical code when using "-fwrapv",
but
the second function is missing the sign extension after the add.


// compile with: gcc-10 -m64 -O2 -fwrapv

char get_byte_use_add(const char* ptr, int off)
{
    off += 1;
    return ptr[off];
}

char get_byte_use_plus(const char* ptr, int off)
{
    return ptr[off + 1]; // gcc: BUG
}