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Subject: Re: Is VIEW_CONVERT_EXPR an lvalue? (was Re: RFA (fold): PATCH for c++/49290 (folding *(T*)(ar+10)))
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Date: Mon, 13 Jun 2011 06:12:00 -0000
Cc: Jason Merrill <jason@redhat.com>, Richard Guenther <rguenther@suse.de>, gcc-patches List <gcc-patches@gcc.gnu.org>, GCC <gcc@gcc.gnu.org>
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To: Richard Guenther <richard.guenther@gmail.com>
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On Jun 12, 2011, at 4:03 AM, Richard Guenther wrote:
> Btw, see tree.def which says
>=20
> /* Represents viewing something of one type as being of a second type.
>   This corresponds to an "Unchecked Conversion" in Ada and roughly to
>   the idiom *(type2 *)&X in C.  The only operand is the value to be
>   viewed as being of another type.  It is undefined if the type of the
>   input and of the expression have different sizes.
>=20
>   This code may also be used within the LHS of a MODIFY_EXPR, in which
>   case no actual data motion may occur.  TREE_ADDRESSABLE will be set in
>   this case and GCC must abort if it could not do the operation without
>   generating insns.  */

I wasn't able to follow what this was trying to say.  :-(  No actual data m=
otion may occur?  The wording is weasely.  Does it mean: Data motion does n=
ot occur when used on the LHS of a MODIFY_EXPR?  If so, it should just dire=
ctly state it.