This is the mail archive of the
mailing list for the GCC project.
Re: [PATCH, Pointer Bounds Checker 14/x] Passes [12/n] Optimize string functions
- From: Jeff Law <law at redhat dot com>
- To: Ilya Enkovich <enkovich dot gnu at gmail dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Fri, 10 Oct 2014 10:25:07 -0600
- Subject: Re: [PATCH, Pointer Bounds Checker 14/x] Passes [12/n] Optimize string functions
- Authentication-results: sourceware.org; auth=none
- References: <20141008191815 dot GL13454 at msticlxl57 dot ims dot intel dot com> <5436BF8A dot 1030200 at redhat dot com> <20141010141953 dot GA61068 at msticlxl57 dot ims dot intel dot com>
On 10/10/14 08:19, Ilya Enkovich wrote:
So is the purpose here to expose the checks that would normally be
done in the mem* routines to their caller in the hopes that doing
so will expose redundant checks? Or is there some other reason?
There are few reasons to replace instrumented string functions:
1. As you said following redundant checks elimination may remove
checks for some string functions
2. By default functions like memcpy
should assume pointers are copied and copy bounds. If we know
pointers are not copied, we may use faster version with no bounds
3. If we avoid both checks and bounds copy then it is a
candidate for existing string function calls inlining in expand pass
Perfect. So this belongs in a comment in the code.
Did you already post them? There's been so many patches I'm starting to
lose track :-)
I thought tests will be added later.
For future reference, when you break a submission down into logical
hunks, including the tests in those logical hunks helps. I realize the
MPX work isn't as well suited for that kind of breakdown, but it's worth
keeping in mind.
I have ~250 tests to commit.
Will check I have tests for optimizations.
BTW this particular
optimization cann't work until we have instrumented builtin calls.
Yea, hopefully we'll get to that before close of stage1.
I had assumed the gimple_call_set_fndecl was a nop if we didn't change
the fndecl. Is that not the case?
It's a nit, but I'd tend to write that as:
if (!fndecl_nochk) continue;
fndecl = fndecl_nochk gimple_call_set_fndecl (stmt, fndecl);
There is one more assignment to fndecl above which makes your version
Thanks. I suspect everyone has just done their own implementation
inline like you did. It's something I'll be keeping my eye out for in
others' code so we can funnel everyone into your new function. ISTM
many speculative optimizations are going to need that kind of helper.
I'm a bit surprised we don't have this kind of capability already
broken out. But assuming that's the case, can you go ahead and
break that out into its own little helper function? You don't
need to find all the cases where we're doing this kind of thing
today, just create the helper function and use it in your new
I could miss such function (looked in cfg hooks and tree-cfg.h).
Hopefully someone will correct me if it is so.
Taking into account not instrumented builtin calls I suppose this
patch goes into a next builtin related series. But here is a version
Yea, I think you're right. I think this is OK when the builtins are done.