[Bug c/13711] New: double assignment results in incorrect assembly

[Bug c/13711] New: double assignment results in incorrect assembly

[satter at synplicity dot com]

Tested and failed on i686-linux-gcc3.3 (32bit) and on opteron-linux-gcc3.2 (64bit)

I will attach the failing testcase to this bug.  Essentially, what is going on
is this:

In this line of code:

globalArray[i] = value = do_something(i);

globalArray is a pointer to a dynamically allocated chunk of memory.  Inside
the do_something function globalArray is reallocated to be larger.  Normally, if
the code is written like this:

globalArray[i] = do_something(i);

or even this:

value = globalArray[i] = do_something(i);

then GCC understands that it cannot calculate the address for 
globalArray[i] until after the do_something function returns.  However,
in the bad case above, the assembly code that is generated calculates
the globalArray[i] address then calls do_something and then stores
the return value in the wrong (old) location.

I have also tried this test case using gcc 2.96 on the same i686-linux
machine and it works correctly, the problem only exists for gcc 3.2 and
3.3 (I don't have 3.4 to test).

tom

-- 
           Summary: double assignment results in incorrect assembly
           Product: gcc
           Version: 3.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: satter at synplicity dot com
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13711

[Bug c/13711] double assignment results in incorrect assembly

[satter at synplicity dot com]

------- Additional Comments From satter at synplicity dot com  2004-01-16 21:06 -------
Created an attachment (id=5504)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=5504&action=view)
shows a problem that occurs on gcc3.2 and gcc3.3

To test:

gcc -g -o gcc32bug gcc32bug.c
./gcc32bug


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13711

[Bug c/13711] double assignment results in incorrect assembly

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-01-16 23:38 -------
Invalid as you cannot depend on the order of calculation.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13711