gcj/107: Bad array or type conversion bug when compiling bytecode

[mdw at cs dot berkeley dot edu]

>Number:         107
>Category:       gcj
>Synopsis:       Bad array or type conversion bug when compiling bytecode
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    apbianco
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Nov 21 21:50:00 PST 1999
>Closed-Date:
>Last-Modified:
>Originator:     Matt Welsh <mdw@cs.berkeley.edu>
>Release:        gcc 2.95.2
>Organization:
>Environment:
Linux x86 Red Hat 6.0
>Description:
Apparently there is a bug in either array references or type
conversion which occurs only when compiling Java bytecode,
and varies depending on the level of optimization used. In 
this example, code compiled with -O2 exhibits the bug, but
-O does not. 

The code which exhibits this bug is rather simple; it is a
routine which takes a 'short' and writes two bytes of the
short into a byte array (it is part of a hand-coded 
serialization routine). Note the use of a loop to do the
array reference as well as the ugly type-casting; I realize
that this is not beautiful code but it does show the bug
in a simple test case.
>How-To-Repeat:
Compile the given test program with 'javac' or 'jikes' to
bytecode. Compile with gcj 2.95.2 with:
'gcj -O2 --main=PutShort -o PutShort PutShort.class'
Then run 'PutShort'. 

The program calls 'put_short' in a loop to write the
values 0..50 to a byte array containing 100 bytes, and
then prints out the contents of the byte array. Correct
output should be the hex values for the shorts 0..50 in
sequence; incorrect output is usually random bytes.
>Fix:
Unknown. Possible workaround is to disable optimization 
during compilation, however, this doesn't work in all cases!
>Release-Note:
>Audit-Trail:
>Unformatted:
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