[Bug tree-optimization/110434] New: tree-nrv introduces incorrect CLOBBER(eol)

["kristerw at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110434

            Bug ID: 110434
           Summary: tree-nrv introduces incorrect CLOBBER(eol)
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
  Target Milestone: ---

The tree-nrv pass may introduce incorrect CLOBBER(eol) of the form
  <retval> ={v} {CLOBBER(eol)};
  return <retval>;

One example of this can be seen by compiling gcc.c-torture/execute/921204-1.c
for x86 using the flags "-O -m32", where it changes the IR

  union bu o;
  ...
  o = i;
  MEM[(union  *)&o].b18 = _11;
  MEM[(union  *)&o].b20 = _11;
  <retval> = o;
  o ={v} {CLOBBER(eol)};
  return <retval>;

to just use <retval> instead of o

  union bu o [value-expr: <retval>];
  ...
  <retval> = i;
  MEM[(union  *)&<retval>].b18 = _11;
  MEM[(union  *)&<retval>].b20 = _11;
  <retval> ={v} {CLOBBER(eol)};
  return <retval>;

so the CLOBBER(eol) now refers to <retval>.