[Bug c++/81901] New: false-positive -Warray-bounds

[webrown.cpp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81901

            Bug ID: 81901
           Summary: false-positive -Warray-bounds
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vermaelen.wouter at gmail dot com
                CC: webrown.cpp at gmail dot com
  Target Milestone: ---
                CC: webrown.cpp at gmail dot com

When switching from gcc-6 to gcc-7 my application triggers some new compiler
warnings (with -Wall). I believe these warnings are false-positives. But I
don't see an easy way to work around them. I also tested with a gcc-8 snapshot
(2017/08/19) and the problem persists.

I managed to reduce my program to the following:

        int a[8];

        extern void f2();

        void f() {
            for (int i = 0x3F; i >= 0x10; --i) {
                switch (i & 0xF0) {
                    case 0x00:
                        if ((i & 0x0F) < 8) a[i] = 0;
                        break;
                    case 0x10:
                        f2();
                }
            }
        }

Compile with
    g++ -O2 -Wall test.cpp

warning: array subscript is above array bounds [-Warray-bounds]