This is the mail archive of the
mailing list for the GCC project.
Re: [PING] 3 patches waiting for approval/review
- From: Jeff Law <law at redhat dot com>
- To: Andreas Krebbel <krebbel at linux dot vnet dot ibm dot com>, gcc-patches at gcc dot gnu dot org
- Date: Wed, 16 Oct 2013 14:25:05 -0600
- Subject: Re: [PING] 3 patches waiting for approval/review
- Authentication-results: sourceware.org; auth=none
- References: <20130821092143 dot GA19762 at bart> <5255B296 dot 6000405 at redhat dot com> <52567AAB dot 3050709 at linux dot vnet dot ibm dot com> <5256D8A7 dot 8090402 at redhat dot com> <525833F7 dot 9000609 at linux dot vnet dot ibm dot com>
On 10/11/13 11:23, Andreas Krebbel wrote:
It's not about PROFILE_HOOKS vs FUNCTION_PROFILER, but the ABI and how
the backend changes its behavior on the return value of leaf_function_p.
On 10/10/13 18:41, Jeff Law wrote:
On 10/10/13 04:00, Andreas Krebbel wrote:
On 09/10/13 21:46, Jeff Law wrote:
On 08/21/13 03:21, Andreas Krebbel wrote:
[RFC] Allow functions calling mcount before prologue to be leaf functions
I don't think this is necessarily correct for all targets. ISTM the
ability to consider a function calling mcount as a leaf needs to be a
property of the target.
We have already "profile_before_prologue" as a target property. Shouldn't this be enough to decide
upon this? When a function calls mcount before the prologue it shouldn't matter whether the function
is leaf or not.
I don't think so, I think it'd break the PA's 32 bit ABI, maybe the 64
bit ABI as well. It's the caller's responsibility to build a mini stack
frame if the function makes any calls. If the code in the prologue
expander uses "leafness" to make the decision about whether or not to
allocate the mini frame, then it'd do the wrong thing here.
Since it seems to be about PROFILE_HOOKS vs FUNCTION_PROFILER targets what about the following patch:
Effectively you want to have functions which are not leaf functions
(they call mcount) be treated as leaf functions. I have great concerns
about the safety of allowing that without exports on each port weighing
in on its correctness for their port.
I still really feel this should be a target hook that is off by default
so that the target maintainers can audit their target to ensure it
Maybe I'm missing something, so perhaps another approach. Can you
explain why you think it is safe to ignore calls to mcount when trying
to determine if a function is a leaf or not?
BTW, there is a hunk of this patch that can and should go forward now
rather than later. Specifically removing the profile_arc_flag part of
the test. If you wanted to push that forward immediately, I'd support
that and you should consider it pre-approved.