This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Live range shrinkage in pre-reload scheduling

On 15/05/14 09:52, Ramana Radhakrishnan wrote:
On Thu, May 15, 2014 at 8:36 AM, Maxim Kuvyrkov
<> wrote:
On May 15, 2014, at 6:46 PM, Ramana Radhakrishnan <> wrote:
I'm not claiming it's a great heuristic or anything.  There's bound to
be room for improvement.  But it was based on "reality" and real results.

Of course, if it turns out not be a win for ARM or s390x any more then it
should be disabled.
The current situation that Kyrill is investigating is a case where we
notice the first scheduler pass being a bit too aggressive with
creating ILP opportunities with the A15 scheduler that causes
performance differences with not turning on the first scheduler pass
vs using the defaults.
Charles has a work-in-progress patch that fixes a bug in SCHED_PRESSURE_MODEL that causes the above symptoms.  The bug causes 1st scheduler to unnecessarily increase live ranges of pseudo registers when there are a lot of instructions in the ready list.
Is this something that you've seen shows up in general integer code as
well ? Do you or Charles have an example for us to look at ? I'm not
sure what "lot of instructions in the ready list" really means here.
The specific case Kyrill's been looking into is Dhrystone Proc_8 when
tuned for a Cortex-A15 with neon and float-abi=hard but I am not sure
if that has "too many instructions" :) .

Kyrill, could you also look into the other cases we have from SPEC2k
where we see this as well and come back with any specific testcases
that Charles / Richard could also take a look into.
Hi all,

From what I can see the most significant regression from this pre-regalloc scheduling on SPEC2k is in 171.swim. It seems to suffer from similar symptoms to Proc_8 (lots of extra spills on the stack)

Looking forward to the patch :). Let me know if I can help with any testing/validation.

Charles, can you finish your patch in the next several days and post it for review?
I think we'll await this but we'll go look into some of the benchmarks.


Thank you,

Maxim Kuvyrkov

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]