Bug in Tree to RTL expansion?

[Bingfeng Mei]

Michael,
Thanks for your help. I struggled to understand tree-ssa-ter.c.
Please see questions below. 

I also tried the tree-ssa-ter.c from the trunk. Same results.

Bingfeng

> -----Original Message-----
> From: Michael Matz [mailto:matz@suse.de]
> Sent: 08 December 2011 13:50
> To: Richard Guenther
> Cc: Bingfeng Mei; gcc@gcc.gnu.org
> Subject: Re: Bug in Tree to RTL expansion?
> 
> Hi,
> 
> On Thu, 8 Dec 2011, Richard Guenther wrote:
> 
> > > What I am not sure is whether the coalescing algorithm or the
> > > expanding procedure is wrong here.
> 
> The forwarding of _218 is wrong.  TER shouldn't have marked it as being
> able to forward (check the expand-detailed dump for the "Replacing
> Expressions" section).  Obviously it does think it can forward it, so
> something is wrong in tree-ssa-ter.c.
> 
> If you can't come up with a testcase that fails with some available
> cross
> compiler (though I wonder why, the tree-ssa parts of the compiler are
> not
> that target dependend, so maybe you can show similar forwarding with an
> adjusted testcase for something publically available) you have to debug
> it
> yourself (I'm right now not aware of any known bug in 4.5 regarding
> this
> particular situation).
> 
> There should be a call to kill_expr on the statement
>   ptr_h2_310 = ptr_h2_493 + 16;

I tracked into how TER is executed. 
kill_expr is called but the kill_list are already all empty because

mark_replaceable -> finished_with_expr  clear all the kill_list.

In addition, once replaceable_expressions is set by mark_replaceable. It doesn't seem
it is ever cleared due to kill_expr or any other function. replaceable_expression
is the only data structure passed to expand pass.  


> which should have killed the expression MEM[ptr_h2_493] (and hence _218)
> from the available expressions.
> 
> 
> Ciao,
> Michael.