On Thu, May 3, 2012 at 10:21 AM, Olivier Hainque <hain...@adacore.com> wrote: > > On Apr 30, 2012, at 16:18 , Olivier Hainque wrote: >>> Can you formally relate those three representations and tell me why >>> VIEW_CONVERT_EXPR is useful (not only convenient because of less operands) >>> to use on lvalues (thus memory, compared to registers or constants)? >> >> I have ideas on how they are supposed to relate (corresponding to your >> intuitive understanding, what is documented), but MEM_REF and BIT_FIELD_REF >> were introduced much more recently though, so I'm pretty sure that there are >> details that escape me. > > One area of potential difference came to mind yesterday: regarding the > processing of type alignment differences. VCE to more aligned (of the > same size) would make a temp copy to yield a correctly aligned object. > > Would MEM_REF do that as well ?
A temporary copy? You mean if I do VIEW_CONVERT_EXPR <double> (longlong) on x86 with -malign-double (so long long is 4 byte aligned and double is 8 byte aligned) the access guarantees only 4 byte alignment but if we "spill" that to a temporary the temporary will use double as type and thus get larger alignment of 8 bytes? MEM_REF <double> (&longlong) would assume 8-byte alignment of longlong unless you use a double type variant with 4-byte alignment. Richard.
