Thanks David.
I thought -mmininal-toc might have been a better workaround as well :-) .
Is there a Bugzilla number for this issue?
-Original Message-
From: David Edelsohn [mailto:dje@gmail.com]
Sent: Tuesday, July 28, 2009 9:46 AM
To: Tim Crook
Subject: Re: How to figure out the gcc -dP output?
Tim,
I do not fully understand the complete explanation of the original problem.
You mention extraneous lwz and TOC. I think you are referring to a bug in GCC
4.1 that incorrectly emitted loads after the TOC already had been changed for
an indirect call. GCSE probably is producing code that requires a constant and
GCC needs to place that constant in the TOC. The late creation of the TOC
reference is not scheduled correctly.
GCSE is an optimization. -mminimal-toc is an option to avoid TOC overflow.
Both of these are work-arounds to the problem. Disabling GCSE probably will
slow down the application. -mminimal-toc probably will have less of a
performance impact.
As I mentioned to Chris when I spoke with him last week, I would recomment
upgrading to a newer version of GCC because GCC 4.1 no longer is maintained.
Many bug fixes, such as one for the problem you are encountering, are
incorporated into newer releases.
David
> I found a possible compiler workaround, compiling with -mminimal-toc. Would
> I get better performance by using this, instead of turning off gcse?
On Fri, Jul 24, 2009 at 4:34 PM, Tim Crook wrote:
> Hello there.
>
> I am trying to track down a problem with gcc 4.1 which has to do with
> inlining and templates on PowerPC. Is there any documentation I can look
> related to the output generated with -fdump? I am getting extraneous lwz
> (load word and zero extend) instructions inserted when calling various
> methods - after $toc (r2) has been switched to the destination method's
> global data, just before the method call with the bctrl instruction. This lwz
> instruction causes a crash on IBM AIX when 32-bit shared libraries are loaded
> non-contiguously in memory. It looks like various code blocks are not being
> combined correctly when code is inlined - the extra lwz is being left behind.
>
> I have figured out that turning off gcse optimizations will stop this
> behavior, but doing this causes a performance hit. I would prefer not to
> upgrade the compiler at this time. With the compiler dump using -fdump, I am
> looking for a better way to work around this problem.
>
> Tim Crook.
>
