linux-kernel - Re: [PATCH 16/16] fix handling of integer constant expressions

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Message-ID: <20070627155425.GX21478@ftp.linux.org.uk>
Date:	Wed, 27 Jun 2007 16:54:25 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	Neil Booth <neil@...kokuya.co.uk>
Cc:	Josh Triplett <josh@...edesktop.org>,
	Segher Boessenkool <segher@...nel.crashing.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-sparse@...r.kernel.org
Subject: Re: [PATCH 16/16] fix handling of integer constant expressions

On Wed, Jun 27, 2007 at 03:06:36PM +0100, Al Viro wrote:
> *unprintable*
> 
> Yes, I see...  OK, null pointer constants handling (next patch in the
> queue) introduces is_zero_constant() (silent evaluation of integer
> constant expression, with division by 0/too large shift/- on lowest
> value of signed integer type leaving the branch as-is, so that later
> expand would generate a proper error on it; then checking if we'd
> reduced the sucker to EXPR_VALUE[0]).  I'll pull it into a separate
> patch, along with is_nonzero_constant(), and change rules for potential
> ICE on parser stage to
> 	maybe-ICE && y => maybe-ICE
> 	maybe-ICE || y => maybe-ICE
> 	maybe-ICE ? x : y => maybe-ICE if at least one of x and y is maybe-ICE
> 	maybe-ICE ? : y => maybe-ICE
> letting evaluate_expression() on such suckers use them if the first argument
> turns out to be ICE after its evaluate_expression()...
> 
> It really stinks, especially since we can't say "oh, parent it known to
> be non-ICE, no need to bother" - subexpression might be shared.

... or it could be done simpler, if we keep the current logics for
Int_const_expr flag at parse time and add a 'const expression' one
with rules as above.  Anyway, I'm going to get some sleep before
dealing with that crap.
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