Re: [PATCH] Fix PR middle-end/17746

[Jason Merrill <jason at redhat dot com>]

Again, my question is: what behavior do we expect from this code?
Given the quoted code

    ADDR_EXPR
      COMPONENT_REF
        VIEW_CONVERT_EXPR <record_type1 ... align-ok>
          INDIRECT_REF <record_type2>
            VAR_DECL <pointer_type <record_type2>>

where the VIEW_CONVERT_EXPR is increasing the alignment, either
1) we know that the pointer already has the proper alignment, or
2) the pointer might not have the proper alignment, so we might need to
   copy into a record_type1 temporary with the appropriate alignment.

I suspect that the get_inner_reference change was needed because #2 is
true.  In that case, the gimplifier should allocate a temporary for the
VIEW_CONVERT_EXPR on platforms where a temporary is needed.

Perhaps the right fix is to make handled_component_p match
get_inner_reference and tweak gimplify_compound_lval to set fallback =
fb_either if the base expression is a VIEW_CONVERT_EXPR.

Incidentally, the expand_expr_real/VIEW_CONVERT_EXPR code doesn't seem to
try to use 'target' in the alignment mismatch case; it seems to me that it
should do that before it allocates a temporary.

Jason