optimization/5422: powerpc -O2 -fssa -fdce misoptimization

optimization/5422: powerpc -O2 -fssa -fdce misoptimization

[haruki.kodera]

>Number:         5422
>Category:       optimization
>Synopsis:       powerpc -O2 -fssa -fdce misoptimization
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          wrong-code
>Submitter-Id:   net
>Arrival-Date:   Fri Jan 18 01:36:00 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     haruki.kodera@nifty.com
>Release:        3.0.3
>Organization:
>Environment:
Configured with: ./configure --target=ppc-eabi --enable-languages=c,c++ --disable-multilib
>Description:
gcc-3.0.3 miscompiles code with -O2 -fssa -fdce

The testcase:
------------ BEGIN -------------
volatile int check = 0;

extern void waitcheck ()
{
  while (!check) {}
}
-------------- END ----------------

Since volatilization specification of
the "check" is carried out, it is a meaningful code.
However, if optimization is applied, it will become
 the function ended immediately.
>How-To-Repeat:
compile with -O2 (or higher) and -fssa and -fdce options.

---
I am sorry that it is poor at English.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:

Re: optimization/5422: powerpc -O2 -fssa -fdce misoptimization

[dje]

Synopsis: powerpc -O2 -fssa -fdce misoptimization

Responsible-Changed-From-To: unassigned->dje
Responsible-Changed-By: dje
Responsible-Changed-When: Wed Mar 13 14:26:38 2002
Responsible-Changed-Why:
    powerpc
State-Changed-From-To: open->closed
State-Changed-By: dje
State-Changed-When: Wed Mar 13 14:26:38 2002
State-Changed-Why:
    @item -fssa
    @opindex fssa
    Perform optimizations in static single assignment form.  Each function's
    flow graph is translated into SSA form, optimizations are performed, and
    the flow graph is translated back from SSA form.  Users should not
    specify this option, since it is not yet ready for production use.
    
    @item -fdce
    @opindex fdce
    Perform dead-code elimination in SSA form.  Requires @option{-fssa}.  Like
    @option{-fssa}, this is an experimental feature.
    
    The SSA optimizations are experimental and should not be
    used.  The options are known to produce incorrect results.
    Until these options are supported for production use, bug
    reports cannot be addressed.  If you want to help with the
    development of these types of optimizations, please contact
    the developers directly.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5422