java/1401: += semantics not correct

java/1401: += semantics not correct

[tromey]

>Number:         1401
>Category:       java
>Synopsis:       += semantics not correct
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    apbianco
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Dec 20 12:19:38 PST 2000
>Closed-Date:    
>Last-Modified:  Sun Nov 19 22:30:00 PST 2000
>Originator:     Tom Tromey
>Release:        unknown-1.0
>Organization:
>Environment:

>Description:
Consider the program below.
It prints `2'.
However, it should print `1'.
The problem is that we evaluate the left-hand side
of the `+=' twice, contradicting JLS 15.26.2.
Maybe using a SAVE_EXPR in build_assignment()
would be good enough?



public class fp
{
  public static void main (String[] args)
  {
    int i = 0;
    int[] foo = {2, 3, 4};
    foo[i++] += 7;
    System.out.println (i);
  }
}
>How-To-Repeat:

>Fix:

>Release-Note:
>Audit-Trail:

Formerly PR gcj/371


From: Alexandre Petit-Bianco <apbianco@cygnus.com>
To: java-gnats@sourceware.cygnus.com
Cc:  
Subject: Re: gcj/371: += semantics not correct
Date: Sun, 19 Nov 2000 22:22:40 -0800 (PST)

 tromey@redhat.com writes:
 
 > Consider the program below.  It prints `2'.  However, it should
 > print `1'.  The problem is that we evaluate the left-hand side of
 > the `+=' twice, contradicting JLS 15.26.2.  Maybe using a SAVE_EXPR
 > in build_assignment() would be good enough?
 
 Most likely. Note that this could be a regression -- we spent quite
 some time in the past getting these cases right but it might have
 broken again at some point :-(
 
 ./A
>Unformatted: