[Bug middle-end/106008] New: [12 Regression] warning: ‘(((char *)loadcmds.113_68 + _933 + 16))[329406144173384849].mapend’ may be used uninitialized [-Wmaybe-uninitialized]

["hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106008

            Bug ID: 106008
           Summary: [12 Regression] warning: ‘(((char *)loadcmds.113_68 +
                    _933 + 16))[329406144173384849].mapend’ may be used
                    uninitialized [-Wmaybe-uninitialized]
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
  Target Milestone: ---

Created attachment 53156
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53156&action=edit
A testcase

When building glibc master branch with -mavx512f, I got

[hjl@gnu-tgl-2 tmp]$ gcc -O2 -march=x86-64 -S -Wall x.i -mavx512f 
dl-load.c: In function ‘_dl_map_object_from_fd.constprop’:
dl-load.c:1158:30: warning: ‘(((char *)loadcmds.113_68 + _933 +
16))[329406144173384849].mapend’ may be used uninitialized
[-Wmaybe-uninitialized]
[hjl@gnu-tgl-2 tmp]$ 

The code looks like

          struct loadcmd *c = &loadcmds[nloadcmds++];
          c->mapstart = ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize));
          c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
          c->dataend = ph->p_vaddr + ph->p_filesz;
          c->allocend = ph->p_vaddr + ph->p_memsz;
          /* Remember the maximum p_align.  */
          if (powerof2 (ph->p_align) && ph->p_align > p_align_max)
            p_align_max = ph->p_align;
          c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));

          /* Determine whether there is a gap between the last segment
             and this one.  */
          if (nloadcmds > 1 && c[-1].mapend != c->mapstart)
            has_holes = true;

c[-1].mapend should always be initialized.