Re: c/10143: Post increment doesn work more than once per statement

[Neil Booth <neil@daikokuya.co.uk>]

The following reply was made to PR c/10143; it has been noted by GNATS.

From: Neil Booth <neil@daikokuya.co.uk>
To: Nick Macdonald <macdonn@nortelnetworks.com>
Cc: "Joseph S. Myers" <jsm28@cam.ac.uk>,
	Falk Hueffner <falk.hueffner@student.uni-tuebingen.de>,
	gcc-gnats@gcc.gnu.org, gcc-bugs@gcc.gnu.org
Subject: Re: c/10143: Post increment doesn work more than once per statement
Date: Thu, 20 Mar 2003 00:08:04 +0000

 Nick Macdonald wrote:-
 
 > I was just trying to make the product better...  I feel the answer of
 > "not a bug" to be a bit pedantic...  sure, technically it may not be a
 > bug...  however, logically, the current behaviour is less than stellar
 > and it should be addressed to make post and pre increment behave more or
 > less similarly...  I have learned a valuable lesson from all this, and I
 
 Things aren't that clearcut - effectively, the compiler passes the
 code to the optimizer with a set of restrictions indicating what the
 optimizer can and cannot assume.  Because of guarantees afforded by the
 standard, the optimizer is given pretty free reign, and munges your code.
 But that's only because it's wrong.  It's not a matter of treating a or
 b consistently; just consider it a fluke that you observed the result
 you did.  If you move a line of code you might see a different result,
 or GCC in 2 months time might, for any of a million reasons, decide to
 optimize it differently.
 
 Now, -Wsequence-point should have warned, but its algorithm is based on
 GCC trees, so consider me unsurprised at its fragility.  None of this
 existed in 2.95, but it does in 3.2.
 
 Neil.