[Bug c++/23794] New: C++ frontend passes invalid COND_EXPR to the middle-end

[rguenth at gcc dot gnu dot org]

Split out from PR23624.

For

template<int>
void f()
{
    int *t, i;
    t[i ? 0 : i];
}

the C++ frontend creates i ? 0 : i, i.e. an integer type conditional,
instead of i != 0 ? 0 : i in case of a template only. Causing this is

build_x_conditional_expr
...
  expr = build_conditional_expr (ifexp, op1, op2);
  if (processing_template_decl && expr != error_mark_node)
    return build_min_non_dep (COND_EXPR, expr,
                              orig_ifexp, orig_op1, orig_op2);

where in the case of a template decl, the valid expr i != 0 ? 0 : i is
thrown away and rebuilt as i ? 0 : i, where the default conversion is no
longer applied.  That could be fixed using perform_implicit_conversion
(boolean_type_node, orig_ifexp) - but I don't know if that would succeed
in case of i being a template param.  We use this (potentially dependent)
expr later to create a non-dependent expr where we fail to apply the
default conversion, too, in

pt.c:build_non_dependent_expr

we could fix that there, too, performing default conversion if the type
is not correct.  And later in

typeck.c:build_array_ref

we happen to call fold on the invalid(?) COND_EXPR.

patch:
http://gcc.gnu.org/ml/gcc-patches/2005-08/msg01740.html

-- 
           Summary: C++ frontend passes invalid COND_EXPR to the middle-end
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23794