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Re: c++/9440: [3.4 regression] error message about non-lvalue
- From: Ansgar Esztermann <ansgar at thphy dot uni-duesseldorf dot de>
- To: nobody at gcc dot gnu dot org
- Cc: gcc-prs at gcc dot gnu dot org,
- Date: 25 Feb 2003 12:36:00 -0000
- Subject: Re: c++/9440: [3.4 regression] error message about non-lvalue
- Reply-to: Ansgar Esztermann <ansgar at thphy dot uni-duesseldorf dot de>
The following reply was made to PR c++/9440; it has been noted by GNATS.
From: Ansgar Esztermann <ansgar at thphy dot uni-duesseldorf dot de>
To: gcc-gnats at gcc dot gnu dot org, <gcc-bugs at gcc dot gnu dot org>, <nobody at gcc dot gnu dot org>,
<gcc-prs at gcc dot gnu dot org>, <andrew at andypo dot net>
Cc:
Subject: Re: c++/9440: [3.4 regression] error message about non-lvalue
Date: Tue, 25 Feb 2003 13:33:00 +0100 (CET)
As far as I can see, this is what happens:
The compiler creates temporaries for args 2 and 3 of the conditional
operator (i.e. A() and a in Andrew's example) by calling A(const A&).
The parameter to the copy constructor is calculated by build_this()
in cp/call.c. This function, however, only knows one way to calculate
the this pointer: it uses ADDR_EXPR, which does not work for non-
lvalues - hence the error message concerning "unary &".
This problem did not occur prior to the patch cited by Craig, because
the compiler would simply neglect to build temporaries for non-lvalues
occurring as arguments to the conditional operator.
I think the best way to fix PR 9440 (and probably 9537) is to fix
build_this(), i.e. crawl along the tree (at least for non-lvalues)
to find /this/ rather than blindly use ADDR_EXPR.
I can try to implement this, but my knowledge about the internals
of cc1plus is rather scarce, so if you a quick solution is needed,
someone else might want to step forward.
Ansgar
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