[Bug middle-end/68855] New: PAREN_EXPR not "ignored" where possible

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68855

            Bug ID: 68855
           Summary: PAREN_EXPR not "ignored" where possible
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

In 465.tonto we end up with

  [shell2.fppized.f90:975:0] _967 = COMPLEX_EXPR <_178, _201>;
  [shell2.fppized.f90:975:0] _968 = ((_967));
  _3980 = REALPART_EXPR <_968>;

and _201/_967 otherwise unused.  REALPART_EXPR should look through
PAREN_EXPR here and wrap its simplification result in PAREN_EXPR
instead (or PAREN_EXPRs should be pushed into operands of non-associatable
stmts).

Not sure if one can devise other interesting examples.