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NNTP-Posting-Date: Mon, 14 Nov 2016 12:42:55 -0600
From: Gareth Owen <gwowen@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Compiler design in C?
References: <nvsmpq$noi$2@dont-email.me> <o02hqq$ndk$1@dont-email.me> <d5d5655d-ff29-4273-8791-1d09c6fbf385@googlegroups.com> <o02q7a$oca$1@dont-email.me> <23d0f58e-a17c-4ef7-8db6-9cc5b7bcaf04@googlegroups.com> <o040re$d5a$1@dont-email.me> <9e27a17d-aaab-48e1-9139-95114dea0da6@googlegroups.com> <o05b51$81t$1@dont-email.me> <3121b7be-aca1-44b0-9dc9-6b23611bbfba@googlegroups.com> <o074os$61m$1@dont-email.me> <300e8fda-56cf-476f-9bd7-257791357090@googlegroups.com> <8760nsr02s.fsf@gmail.com> <0dc796fe-911c-4dc0-952a-7b9e3ed54eae@googlegroups.com> <87mvh4kytv.fsf@bsb.me.uk> <7f59dd53-a2fd-4e61-85b9-308790eeab7d@googlegroups.com> <877f87llzn.fsf@bsb.me.uk> <7309d801-64fc-4d2b-961e-1e8b50f11389@googlegroups.com> <878tsn2e8z.fsf@gmail.com> <65a37d5b-1c93-41ad-95f4-321c05397d43@googlegroups.com> <87vavqh6zf.fsf@gmail.com> <f4ce9545-c5e7-4db8-8e46-dcaafa2bbd01@googlegroups.com>
Date: Mon, 14 Nov 2016 18:42:55 +0000
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supercat@casperkitty.com writes:

> On Monday, November 14, 2016 at 1:10:35 AM UTC-6, gwowen wrote:
>> supercat writes:
>> 
>> > On Sunday, November 13, 2016 at 4:42:44 PM UTC-6, gwowen wrote:
>> > Since neither x nor y has its address taken, a compiler could easily
>> > recognize that there is no possible means by which x can hold anything other
>> > than 3, or y can hold anything other than 6, when the printf is executed.
>> 
>> This entirely at odds with your previous description of how variable
>> reads / writes should map to loads and stores.
>
> They should behave *as if* they are being read from and written to memory.

I don't understand.
How does

printf("7\n");

behave as if x=3 and y=4 have been read and written from memory
(in a sense not already covered by C's as if rule, which you reject as
 not being the correct model for optimisation)