Likely code generation bug in GCC 4.0.1

[Claus Fischer]

On Mon, May 14, 2007 at 10:35:57AM +0100, Andrew Haley wrote:
: Claus Fischer writes:
:  > On Mon, May 14, 2007 at 10:18:26AM +0100, Andrew Haley wrote:
:  > : Claus Fischer writes:
:  > :  > 
:  > :  > I think I found a code generation bug in GCC 4.0.1.
:  > :  > 
:  > :  > I'm sending this mail to make sure this bug is known and
:  > :  > is or will be removed in newer versions.
:  > :  > On a quick glance I couldn't find it in the bug database,
:  > :  > so it may not be known.
:  > : 
:  > : Redirected to gcc-help.
:  > : 
:  > : Please send a full test case that can be run, with full information
:  > : about the expected effect.
:  > 
:  > 
:  > The full test case is way too big to run and contains data
:  > which I don't have authority to disclose publicly.
: 
: I'm not asking for your full code.  If you believe that the bug is in
: the code generated for the source you posted, presumably you can
: create a test wrapper.


I can, but it's likely to take me more than five times as long
as someone who knows assembler to take a (quick) glance. If that
quick glance doesn't get us further, I'm very willing to do my
homework/test case, even though just switching to gcc 4.1 would
probably solve MY problem completely. It's just out of desire to
help gcc people keep gcc bug-free that I have tried to "isolate"
this bug.

I have already spent a lot of time tracking this down, and I feel
I have reached a point where the imbalance of time I'd have to
spend to create a complete test case, and of the time required to
look at the assembly, is grossly in favor of learning assembly
myself :-)

[ Unfortunately, creating the MINGW cross compilation environment
  itself is a task that would probably keep most gcc developers from
  examining the case, even if I posted the instructions. ]

: Experience over meny years has shown us that this is the bet way to
: find and fix bugs in gcc.  It's much more productive than staring at
: thousands of lines of assembly language.

I know and understand. I typically try to do that. But that's easier
for a recent GCC as shipped with Linux, than for a cross-compilation
environment that involves Mingw and an older GCC.

: The problem is that gcc reorders and reorganizes code to such an
: extent that it can be exceedingly hard to find the equivalent code.

I understand that.

Claus

-- 
Claus Fischer <claus.fischer@clausfischer.com>
http://www.clausfischer.com/