Re: c++/5504: Optimization breaks wei-ku-1 from blitz (fwd)

Re: c++/5504: Optimization breaks wei-ku-1 from blitz (fwd)

[Diego Novillo]

The following reply was made to PR c++/5504; it has been noted by GNATS.

From: Diego Novillo <dnovillo@redhat.com>
To: gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: c++/5504: Optimization breaks wei-ku-1 from blitz (fwd)
Date: Tue, 26 Mar 2002 08:30:11 -0500

 Jason,
 
 Although the PR indicates that g++ ICEs, the program actually
 compiles.  However, it takes about 7 hours and cc1plus grows to
 ~650 Mb.
 
 The problem seems to be in the expansion of EH cleanups.  I've
 been comparing gcc 3.0.4 with the 3.1 branch.  This is what I
 found so far:
 
 - Both compilers seem to generate roughly the same number of
   trees.  They both grow to about 47 Mb right before the call to
   expand_stmt() in semantics.c:expand_body().
 
 - However, when expand_stmt() is called to expand the body of
   main(), the 3.1 compiler grows to 415Mb, while the 3.0.4.
   compiler grows to about 53 Mb.
 
 - The difference is in the calls to expand_eh_region_end_cleanup()
   The 3.0.4 compiler calls it 76 times.  The 3.1 compiler calls
   it 59,212 times.
   
   Not surprisingly, we spend no more than a couple of minutes
   generating the initial RTL, and 7 hours trying to optimize it.
   We seem to be generating mostly fluff because the final .s file
   doesn't look overly large (a couple of Mb, IIRC).
 
 - The program seems to compile fine with -fno-exceptions.
 
 Jakub tracked the problem to your destructor cleanup patch from
 Dec01:
 
 http://gcc.gnu.org/ml/gcc-patches/2001-12/msg01532.html
 
 I don't know enough C++ to determine whether this is to be
 expected or not.  The test case is rather large, so it may well
 be that 3.0.4 was not doing the right thing.
 
 Any ideas on what to try next?
 
 
 Thanks.  Diego.