On 10/11/13 11:23, Andreas Krebbel wrote:
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
http://gcc.gnu.org/ml/gcc-patches/2013-04/msg00993.html
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:
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.
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
operates correctly.
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.
jeff
