[Bug c++/7503] (x < Y ? X : Y) as an lvalue and assignment

[Bug c++/7503] (x < Y ? X : Y) as an lvalue and assignment

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2003-05-03 00:00:00         |2003-08-19 04:13:37
               date|                            |


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-08-19 04:13 -------
Related to bug 11427.  I think this extension should be removed as the C front-end 
rejects this.

[Bug c++/7503] (x < Y ? X : Y) as an lvalue and assignment

[falk at debian dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503



------- Additional Comments From falk at debian dot org  2003-08-19 07:02 -------
It's not an extension, the C++ language allows this.

[Bug c++/7503] (x < Y ? X : Y) as an lvalue and assignment

[moore_mn at cobra dot cs dot mercer dot edu]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503



------- Additional Comments From moore_mn at cobra dot cs dot mercer dot edu  2003-08-19 08:23 -------
Subject:  (x < Y ? X : Y) as an lvalue and assignment

I believe that C allows it too.
I also believe that C99 allows all of
the short-cut versions ( ?> and friends).

I might have made an attempt to fix it
myself (in g++) if it could easily be converted
to an equivalent if/else stmt, but that gets
complex and I don't know the internals well
enough.  Converting it to evaluate to a
reference to the "winner" would break
for register variables.  Always converting
(with or without the assignment) would
break if there were a constant as one of
the contestants (contestants meaning possible
results of the ?: ).
I think that ?: and friends are almost more
trouble than they are worth, with conditional
exacution and conditional assignments.
What still bothers me is that the second
test program I sent works(or did when I sent it),
while the first didn't.  The only real difference
was that the result of the operation in the version
that didn't work could be determined at compile
time while the other asks for input which is used
to determine the outcome.
It probably should be disabled and an error issued
because there may be some code somewhere out there
that uses this and expects it to work, since it
compiles without a hitch.  Well, either people
are assuming that it works (and their code behaves
badly, but not such that they notice) or they are
not using it.  Either way, an error should be reported
if it might be broken.  (my guess, no one is using it
except for CS students and professors, and then in
test code to see if it works)

Nathan Moore

[Bug c++/7503] (x < Y ? X : Y) as an lvalue and assignment

[schwab at suse dot de]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503



------- Additional Comments From schwab at suse dot de  2003-08-19 08:58 -------
In C the result of ?: is never an lvalue.

[Bug c++/7503] (x < Y ? X : Y) used for assignment causes wrong code

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-05-22 22:55 -------
The problem is how MAX_EXPR is expanded, as (x < 0) ? X : Y = 1 works.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503

[Bug c++/7503] (x < Y ? X : Y) used for assignment causes wrong code

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-06-20 15:17 -------
*** Bug 16102 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ofiravni99 at walla dot co
                   |                            |dot il


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503

[Bug c++/7503] (x < Y ? X : Y) used for assignment causes wrong code

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-06-21 15:01 -------
One (possibly good) question: does a ?: operator involve sequence 
points? If we have an expression like 
  (a>b ? a : b) = 1; 
with a,b being references, then we use some of the variables both 
for evaluation and for assignment, and the question is if any of these 
operations need to be ordered. 
 
W. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503

[Bug c++/7503] (x < Y ? X : Y) used for assignment causes wrong code

[schwab at suse dot de]

------- Additional Comments From schwab at suse dot de  2004-06-21 15:56 -------
There is a sequence point after the evaluation of the condition (6.5.15#4). 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503

[Bug c++/7503] (x < Y ? X : Y) used for assignment causes wrong code

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-09-12 05:38 -------
Patch posted here: <http://gcc.gnu.org/ml/gcc-patches/2004-09/msg01130.html>.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503

[Bug c++/7503] (x < Y ? X : Y) used for assignment causes wrong code

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2004-09-21 16:20 -------
Subject: Bug 7503

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	sayle@gcc.gnu.org	2004-09-21 16:20:12

Modified files:
	gcc/cp         : ChangeLog tree.c typeck.c 
	gcc/testsuite  : ChangeLog 
Added files:
	gcc/testsuite/g++.dg/opt: pr7503-1.C pr7503-2.C pr7503-3.C 
	                          pr7503-4.C pr7503-5.C 

Log message:
	PR c++/7503
	* tree.c (lvalue_p_1):  Disallow MIN_EXPR and MAX_EXPR as lvalues
	if either operand has side-effects.
	* typeck.c (rationalize_conditional_expr): Assert that neither
	operand of MIN_EXPR or MAX_EXPR has side-effects.
	(build_modify_expr):  Add support for MIN_EXPR and MAX_EXPR.
	Check that the "lhs" is a valid lvalue, i.e. that neither operand
	of a MIN_EXPR or MAX_EXPR has a side-effect.
	
	* g++.dg/opt/pr7503-1.C: New testcase for COND_EXPR lvalues.
	* g++.dg/opt/pr7503-2.C: New testcase for <? and >? lvalues.
	* g++.dg/opt/pr7503-3.C: New testcase for invalid <? lvalue errors.
	* g++.dg/opt/pr7503-4.C: New testcase for <?= and >?= assignments.
	* g++.dg/opt/pr7503-5.C: New testcase for side-effects with <?=.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/ChangeLog.diff?cvsroot=gcc&r1=1.4371&r2=1.4372
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/tree.c.diff?cvsroot=gcc&r1=1.410&r2=1.411
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/typeck.c.diff?cvsroot=gcc&r1=1.577&r2=1.578
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.4325&r2=1.4326
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/opt/pr7503-1.C.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/opt/pr7503-2.C.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/opt/pr7503-3.C.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/opt/pr7503-4.C.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/opt/pr7503-5.C.diff?cvsroot=gcc&r1=NONE&r2=1.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503

[Bug c++/7503] (x < Y ? X : Y) used for assignment causes wrong code

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-09-21 18:43 -------
Fixed for 4.0.0.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=7503