Path: utzoo!genat!mnetor!george From: george@mnetor.UUCP (George Hart) Newsgroups: comp.lang.c Subject: Re: unofficial X3J11 meeting notes Keywords: ANSI C standard Message-ID: <4385@mnetor.UUCP> Date: 15 Dec 87 13:39:39 GMT References: <9770@mimsy.UUCP> <6833@brl-smoke.ARPA> Reply-To: george@mnetor.UUCP (George Hart) Organization: Computer X (CANADA) Ltd., Toronto, Ontario, Canada Lines: 29 In article <6833@brl-smoke.ARPA> gwyn@brl.arpa (Doug Gwyn (VLD/VMB)) writes: >The "noalias" type qualifier promises that the object can only be >modified by a single handle (as I said), thereby permitting the >optimizer to do things that are not safe otherwise; for example, >for pointers that could be used as aliases accessing the same >object, without "noalias" qualifying the object, every time it >was modified via one pointer the compiler would have to assume >that the modification might affect what is seen via the other >pointer. With "noalias", the compiler is entitled to treat the >two access paths as referring to non-overlapping objects, which >means that it can assume that the result of a previous dereference >(which may be in an active register) is not invalidated by a store >through another pointer, so it does not need to reload the value >already in the register just to be safe. Will the standard also specify that attempts to create or use alternate handles for an object declared "noalias" are to generate compiler warnings/errors? -- Regards, George Hart, Computer X Canada Ltd. NOW REAL SOON NOW UUCP: utzoo UUCP: utzoo >!mnetor!george > cxhi!george uunet uunet BELL: (416)475-8980