This adds the ability to use the GCNRPTrackers during scheduling. These trackers have several advantages over the generic trackers: 1. global live-thru trackers, 2. subregister based RP deltas, and 3. flexible vreg -> PressureSet mappings.
This feature is off-by-default to ease with the roll-out process. In particular, when using the optional trackers, the scheduler will still maintain the generic trackers leading to unnecessary compile time.
PressureDiff is reliable most of the time, and it's pretty much free
compared to RPTracker. We can use it whenever there is no subregister
definitions, or physregs invovled. No subregs because PDiff doesn't take
into account lane liveness, and no Physreg because it seems to get
PhysReg liveness completely wrong. Sometimes it adds a diff, sometimes
itt doesn't - I didn't look at that one for long so maybe there is
something we can eventually do to make it better.
This allows us to save a ton of calls to RPTracker and LIS too. On a
huge IR module (100+MB), it went from about 20M calls to RPTracker in this
function down to 3.4, with the rest being PressureDiffs.
I also added an expensive check to verify correctness of PressureDiff.
Unlike older ASICs GFX10+ have a lot of VGPRs. Therefore, it is possible
to achieve high occupancy even with all or almost all addressable VGPRs
used. Our scheduler was never tuned for this scenario. The VGPR Critical
Limit threshold always comes very high, even if maximum occupancy is
targeted. For example on gfx1100 it is set to 192 registers even with
the requested occupancy 16. As a result scheduler starts prioritizing
register pressure reduction very late and we easily end up spilling.
This patch makes VGPR critical limit similar to what we would have on
pre-gfx10 targets with much more limited VGPR budget while still trying
to maintain occupancy as it does now.
Pre-gfx10 ASICs shall not be affected as the limit shall be the same
as before, and on gfx10+ it shall only affect regions where we have
to spill.
Fixes: SWDEV-377300
Differential Revision: https://reviews.llvm.org/D141876
Current implementation abuses ErrorMargin to apply an additional
bias to VGPR and SGPR limits under a high register pressure. The
ErrorMargin exists to account for inaccuracies of the RP tracker
and not to tackle an excess pressure. Introduce separate bias for
this purpose and also make it different for SGPRs and VGPRs as we
may want to use different values in the future.
This is supposed to be NFC, however there is a subtle difference
when subtracting a margin overflows the limit. Doing two subtractions
makes it less probable, although manifests only in mir tests with
an artificially small register budget.
Differential Revision: https://reviews.llvm.org/D142051
Since the divergence-driven ISel was fully enabled we have more VGPRs available.
MachineScheduler trying to take advantage of that bumps up the occupancy sacrificing
the hiding of memory access latency. This really spoils the initially good schedule.
A new metric that reflects the latency hiding quality of the schedule has been created
to make it to balance between occupancy and latency. The metric is based on the latency
model which computes the bubble to working cycles ratio. Then we use this ratio to decide
if the higher occupancy schedule is profitable as follows:
Profit = NewOccupancy/OldOccupancy * OldMetric/NewMetric
Reviewed By: rampitec
Differential Revision: https://reviews.llvm.org/D139710
Adds a builtin that serves as an optimization hint to apply specific optimized
DAG mutations during scheduling. This also disables any other mutations or
clustering that may interfere with the desired pipeline. The first optimization
strategy that is added here is designed to improve the performance of small gemm
kernels on gfx90a.
Reviewed By: jrbyrnes
Differential Revision: https://reviews.llvm.org/D132079
Creates a new scheduling strategy that attempts to maximize ILP for a single
wave.
Reviewed By: rampitec
Differential Revision: https://reviews.llvm.org/D130869
By not clustering loads and adjusting heuristics to more aggressively reduce
register pressure we may be able to increase occupancy for the function if it
was dropped in a first pass scheduling.
Similarly, try to reduce spilling if register usage exceeds lower bound
occupancy.
Reviewed By: rampitec
Differential Revision: https://reviews.llvm.org/D130329
Tries to make the different scheduling stages a bit more self contained and
modifiable. Intended to be NFC. Preface to other changes.
Reviewed By: rampitec
Differential Revision: https://reviews.llvm.org/D130147
This was stored in LiveIntervals, but not actually used for anything
related to LiveIntervals. It was only used in one check for if a load
instruction is rematerializable. I also don't think this was entirely
correct, since it was implicitly assuming constant loads are also
dereferenceable.
Remove this and rely only on the invariant+dereferenceable flags in
the memory operand. Set the flag based on the AA query upfront. This
should have the same net benefit, but has the possible disadvantage of
making this AA query nonlazy.
Preserve the behavior of assuming pointsToConstantMemory implying
dereferenceable for now, but maybe this should be changed.
Enable the PreRARematerialize pass when there are multiple high RP scheduling
regions present. Require the occupancy in all high RP regions be improved
before finalizing sinking. If any high RP region did not improve in occupancy
then un-do all sinking and restore the state to before the pass.
Reviewed By: rampitec
Differential Revision: https://reviews.llvm.org/D122501
Add a new pass in the pre-ra AMDGPU scheduler to check if sinking trivially rematerializable defs that only has one use outside of the defining block will increase occupancy. If we can determine that occupancy can be increased, then rematerialize only the minimum amount of defs required to increase occupancy. Also re-schedule all regions that had occupancy matching the previous min occupancy using the new occupancy.
This is based off of the discussion in https://reviews.llvm.org/D117562.
The logic to determine the defs we should collect and determining if sinking would be beneficial is mostly the same. Main differences is that we are no longer limiting it to immediate defs and the def and use does not have to be part of a loop.
Reviewed By: rampitec
Differential Revision: https://reviews.llvm.org/D119475
Nonfunctional commit fixing several minor spelling errors in llvm/lib/Target/AMDGPU header files.
Testing workflow as a new contributor.
Differential Revision: https://reviews.llvm.org/D109733
If a region was not constrained by a high register pressure
and was not rescheduled without clustering we can skip
rescheduling it ClusteredLowOccupancyReschedule stage.
This improves scheduling speed by 25% on some kernels.
Differential Revision: https://reviews.llvm.org/D97506
We are attempting rescheduling without load store clustering
if occupancy limits were not met with clustering. Skip this
for regions which do not have any loads or stores at all.
In a set of kernels I am experimenting with this improves
scheduling time by ~30%.
Differential Revision: https://reviews.llvm.org/D97342
We want to have more load/store clustering but we also want
to maintain low register pressure which are oposit targets.
Allow scheduler to reschedule regions without mutations
applied if we hit a register limit.
Differential Revision: https://reviews.llvm.org/D73386
Approximately 30% of the time was spent in the std::vector
constructor. In one testcase this pushes the scheduler to being the
second slowest pass.
I'm not sure I understand why these vector are necessary. The default
scheduler initCandidate seems to use some pre-existing vectors for the
pressure.
llvm-svn: 371136
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
Summary:
This is a follow-up to r335942.
- Merge SISubtarget into AMDGPUSubtarget and rename to GCNSubtarget
- Rename AMDGPUCommonSubtarget to AMDGPUSubtarget
- Merge R600Subtarget::Generation and GCNSubtarget::Generation into
AMDGPUSubtarget::Generation.
Reviewers: arsenm, jvesely
Subscribers: kzhuravl, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, javed.absar, llvm-commits
Differential Revision: https://reviews.llvm.org/D49037
llvm-svn: 336851
Keep track of achieved occupancy in SIMachineFunctionInfo.
At the moment we have a lot of duplicated or even missed code to
query and maintain occupancy info. Record it in the MFI and
query in a single call. Interfaces:
- getOccupancy() - returns current recorded achieved occupancy.
- getMinAllowedOccupancy() - returns lesser of the achieved occupancy
and the lowest occupancy we are ready to tolerate. For example if
a kernel is memory bound we are ready to tolerate 4 waves.
- limitOccupancy() - record occupancy level if we have to lower it.
- increaseOccupancy() - record occupancy if scheduler managed to
increase the occupancy.
MFI takes care of integrating different checks affecting occupancy,
including LDS use and waves-per-eu attribute. Note that scheduler
starts with not yet known register pressure, so has to record either
limit or increase in occupancy after it is done. Later passes can
just query a resulting value.
New interface is used in the active scheduler and NFC wrt its work.
Changes are also made to experimental schedulers to use it and record
an occupancy after they are done. Before the change waves-per-eu was
ignored by experimental schedulers and tolerance window for memory
bound kernels was not used.
Differential Revision: https://reviews.llvm.org/D47509
llvm-svn: 333629
Using LIS can be quite expensive, so caching of calculated region
live-ins and pressure is implemented. It does two things:
1. Caches the info for the second stage when we schedule with
decreased target occupancy.
2. Tracks the basic block from top to bottom thus eliminating the
need to scan whole register file liveness at every region split
in the middle of the block.
The scheduling is now done in 3 stages instead of two, with the first
one being really a no-op and only used to collect scheduling regions
as sent by the scheduler driver.
There is no functional change to the current behavior, only compilation
speed is affected. In general computeBlockPressure() could be simplified
if we switch to backward RP tracker, because scheduler sends regions
within a block starting from the last upward. We could use a natural
order of upward tracker to seamlessly change between regions of the same
block, since live reg set of a previous tracked region would become a
live-out of the next region. That however requires fixing upward tracker
to properly account defs and uses of the same instruction as both are
contributing to the current pressure. When we converge on the produced
pressure we should be able to switch between them back and forth. In
addition, backward tracker is less expensive as it uses LIS in recede
less often than forward uses it in advance.
At the moment the worst known case compilation time has improved from 26
minutes to 8.5.
Differential Revision: https://reviews.llvm.org/D33117
llvm-svn: 303184
This factors register pressure estimation mechanism from the
GCNSchedStrategy into the forward tracker to unify interface
with other strategies and expose it to other interested phases.
Differential Revision: https://reviews.llvm.org/D33105
llvm-svn: 303179
This is incorrect to record region boundaries before scheduling,
it may change after scheduling. As a result second pass may see less
instructions to schedule than it should.
Differential Revision: https://reviews.llvm.org/D31434
llvm-svn: 298945
If during scheduling we have identified that we cannot keep optimistic
occupancy increase critical register pressure limit and try scheduling
of the whole function again. In this case blocks with smaller pressure
will have a chance for better scheduling.
Differential Revision: https://reviews.llvm.org/D30442
llvm-svn: 296506
This change introduces new method to estimate register pressure in
GCNScheduler. Standard RPTracker gives huge error due to the following
reasons:
1. It does not account for live-ins or live-outs if value is not used
in the region itself. That creates a huge error in a very common case
if there are a lot of live-thu registers.
2. It does not properly count subregs.
3. It assumes a register used as an input operand can be reused as an
output. This is not always possible by itself, this is not what RA
will finally do in many cases for various reasons not limited to RA's
inability to do so, and this is not so if the value is actually a
live-thu.
In addition we can now see clear separation between live-in pressure
which we cannot change with the scheduling and tentative pressure
which we can change.
Differential Revision: https://reviews.llvm.org/D30439
llvm-svn: 296491
This patch reverts region's scheduling to the original untouched state
in case if we have have decreased occupancy.
In addition it switches to use TargetRegisterInfo occupancy callback
for pressure limits instead of gradually increasing limits which were
just passed by. We are going to stay with the best schedule so we do
not need to tolerate worsened scheduling anymore.
Differential Revision: https://reviews.llvm.org/D29971
llvm-svn: 295206
