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From: guy%gorodish@Sun.COM (Guy Harris)
Newsgroups: comp.lang.c
Subject: Re: constant expression rules
Message-ID: <29194@sun.uucp>
Date: Sat, 26-Sep-87 00:45:41 EDT
Article-I.D.: sun.29194
Posted: Sat Sep 26 00:45:41 1987
Date-Received: Sun, 27-Sep-87 09:44:18 EDT
References: <3018@ulysses.homer.nj.att.com>
Sender: news@sun.uucp
Lines: 20
Keywords: portability

> The question is - what is a reasonable level of constant folding that
> I can assume when trying to write portable code?  Is this a bug or a
> gotcha?

This is a bug.  Any reasonable and correct compiler will certainly include
float -> int conversions, and *vice versa*, as operations that can be
performed at compile time, as well as the usual sorts of floating-point and
integer operations.

The trouble is that PCC's code for doing folding of conversions of constants at
compile time is very fragile, and if you don't arrange to have things done at
the proper times, PCC ends up seeing trees with conversion operators, rather
than constants, at the root and gets all ticked off at you.  I have seen this
sort of thing break several flavors of PCC (including CCI's 68K compiler; that
one I fixed, for at least some of the cases).  Unfortunately, fixes to one
version may not fix other versions; some of the code in question lives in the
machine-dependent portions of PCC.
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.c);g