MI-Sched: handle latency of in-order operations with the new machine model.

The per-operand machine model allows the target to define "unbuffered"
processor resources. This change is a quick, cheap way to model stalls
caused by the latency of operations that use such resources. This only
applies when the processor's micro-op buffer size is non-zero
(Out-of-Order). We can't precisely model in-order stalls during
out-of-order execution, but this is an easy and effective
heuristic. It benefits cortex-a9 scheduling when using the new
machine model, which is not yet on by default.

MI-Sched for armv7 was evaluated on Swift (and only not enabled because
of a performance bug related to predication). However, we never
evaluated Cortex-A9 performance on MI-Sched in its current form. This
change adds MI-Sched functionality to reach performance goals on
A9. The only remaining change is to allow MI-Sched to run as a PostRA
pass.

I evaluated performance using a set of options to estimate the performance impact once MI sched is default on armv7:
-mcpu=cortex-a9 -disable-post-ra -misched-bench -scheditins=false

For a simple saxpy loop I see a 1.7x speedup. Here are the llvm-testsuite results:
(min run time over 2 runs, filtering tiny changes)

Speedups:
| Benchmarks/BenchmarkGame/recursive         |  52.39% |
| Benchmarks/VersaBench/beamformer           |  20.80% |
| Benchmarks/Misc/pi                         |  19.97% |
| Benchmarks/Misc/mandel-2                   |  19.95% |
| SPEC/CFP2000/188.ammp                      |  18.72% |
| Benchmarks/McCat/08-main/main              |  18.58% |
| Benchmarks/Misc-C++/Large/sphereflake      |  18.46% |
| Benchmarks/Olden/power                     |  17.11% |
| Benchmarks/Misc-C++/mandel-text            |  16.47% |
| Benchmarks/Misc/oourafft                   |  15.94% |
| Benchmarks/Misc/flops-7                    |  14.99% |
| Benchmarks/FreeBench/distray               |  14.26% |
| SPEC/CFP2006/470.lbm                       |  14.00% |
| mediabench/mpeg2/mpeg2dec/mpeg2decode      |  12.28% |
| Benchmarks/SmallPT/smallpt                 |  10.36% |
| Benchmarks/Misc-C++/Large/ray              |   8.97% |
| Benchmarks/Misc/fp-convert                 |   8.75% |
| Benchmarks/Olden/perimeter                 |   7.10% |
| Benchmarks/Bullet/bullet                   |   7.03% |
| Benchmarks/Misc/mandel                     |   6.75% |
| Benchmarks/Olden/voronoi                   |   6.26% |
| Benchmarks/Misc/flops-8                    |   5.77% |
| Benchmarks/Misc/matmul_f64_4x4             |   5.19% |
| Benchmarks/MiBench/security-rijndael       |   5.15% |
| Benchmarks/Misc/flops-6                    |   5.10% |
| Benchmarks/Olden/tsp                       |   4.46% |
| Benchmarks/MiBench/consumer-lame           |   4.28% |
| Benchmarks/Misc/flops-5                    |   4.27% |
| Benchmarks/mafft/pairlocalalign            |   4.19% |
| Benchmarks/Misc/himenobmtxpa               |   4.07% |
| Benchmarks/Misc/lowercase                  |   4.06% |
| SPEC/CFP2006/433.milc                      |   3.99% |
| Benchmarks/tramp3d-v4                      |   3.79% |
| Benchmarks/FreeBench/pifft                 |   3.66% |
| Benchmarks/Ptrdist/ks                      |   3.21% |
| Benchmarks/Adobe-C++/loop_unroll           |   3.12% |
| SPEC/CINT2000/175.vpr                      |   3.12% |
| Benchmarks/nbench                          |   2.98% |
| SPEC/CFP2000/183.equake                    |   2.91% |
| Benchmarks/Misc/perlin                     |   2.85% |
| Benchmarks/Misc/flops-1                    |   2.82% |
| Benchmarks/Misc-C++-EH/spirit              |   2.80% |
| Benchmarks/Misc/flops-2                    |   2.77% |
| Benchmarks/NPB-serial/is                   |   2.42% |
| Benchmarks/ASC_Sequoia/CrystalMk           |   2.33% |
| Benchmarks/BenchmarkGame/n-body            |   2.28% |
| Benchmarks/SciMark2-C/scimark2             |   2.27% |
| Benchmarks/Olden/bh                        |   2.03% |
| skidmarks10/skidmarks                      |   1.81% |
| Benchmarks/Misc/flops                      |   1.72% |

Slowdowns:
| Benchmarks/llubenchmark/llu                | -14.14% |
| Benchmarks/Polybench/stencils/seidel-2d    |  -5.67% |
| Benchmarks/Adobe-C++/functionobjects       |  -5.25% |
| Benchmarks/Misc-C++/oopack_v1p8            |  -5.00% |
| Benchmarks/Shootout/hash                   |  -2.35% |
| Benchmarks/Prolangs-C++/ocean              |  -2.01% |
| Benchmarks/Polybench/medley/floyd-warshall |  -1.98% |
| Polybench/linear-algebra/kernels/3mm       |  -1.95% |
| Benchmarks/McCat/09-vor/vor                |  -1.68% |

llvm-svn: 196516

2 files changed, 52 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/MachineScheduler.cpp b/llvm/lib/CodeGen/MachineScheduler.cpp
index f8c4a893c12..3296149afa8 100644
--- a/llvm/lib/CodeGen/MachineScheduler.cpp
+++ b/llvm/lib/CodeGen/MachineScheduler.cpp
@@ -1330,7 +1330,7 @@ public:
   /// Represent the type of SchedCandidate found within a single queue.
   /// pickNodeBidirectional depends on these listed by decreasing priority.
   enum CandReason {
-    NoCand, PhysRegCopy, RegExcess, RegCritical, Cluster, Weak, RegMax,
+    NoCand, PhysRegCopy, RegExcess, RegCritical, Stall, Cluster, Weak, RegMax,
     ResourceReduce, ResourceDemand, BotHeightReduce, BotPathReduce,
     TopDepthReduce, TopPathReduce, NextDefUse, NodeOrder};
 
@@ -1583,6 +1583,10 @@ public:
                       MaxExecutedResCount);
     }
 
+    /// Get the difference between the given SUnit's ready time and the current
+    /// cycle.
+    unsigned getLatencyStallCycles(SUnit *SU);
+
     bool checkHazard(SUnit *SU);
 
     unsigned findMaxLatency(ArrayRef<SUnit*> ReadySUs);
@@ -1869,6 +1873,23 @@ void GenericScheduler::registerRoots() {
   }
 }
 
+/// Compute the stall cycles based on this SUnit's ready time. Heuristics treat
+/// these "soft stalls" differently than the hard stall cycles based on CPU
+/// resources and computed by checkHazard(). A fully in-order model
+/// (MicroOpBufferSize==0) will not make use of this since instructions are not
+/// available for scheduling until they are ready. However, a weaker in-order
+/// model may use this for heuristics. For example, if a processor has in-order
+/// behavior when reading certain resources, this may come into play.
+unsigned GenericScheduler::SchedBoundary::getLatencyStallCycles(SUnit *SU) {
+  if (!SU->isUnbuffered)
+    return 0;
+
+  unsigned ReadyCycle = (isTop() ? SU->TopReadyCycle : SU->BotReadyCycle);
+  if (ReadyCycle > CurrCycle)
+    return ReadyCycle - CurrCycle;
+  return 0;
+}
+
 /// Does this SU have a hazard within the current instruction group.
 ///
 /// The scheduler supports two modes of hazard recognition. The first is the
@@ -1948,9 +1969,9 @@ getOtherResourceCount(unsigned &OtherCritIdx) {
 /// inside and outside the zone.
 void GenericScheduler::SchedBoundary::setPolicy(CandPolicy &Policy,
                                                    SchedBoundary &OtherZone) {
-  // Now that potential stalls have been considered, apply preemptive heuristics
-  // based on the the total latency and resources inside and outside this
-  // zone.
+  // Apply preemptive heuristics based on the the total latency and resources
+  // inside and outside this zone. Potential stalls should be considered before
+  // following this policy.
 
   // Compute remaining latency. We need this both to determine whether the
   // overall schedule has become latency-limited and whether the instructions
@@ -2141,7 +2162,11 @@ void GenericScheduler::SchedBoundary::bumpNode(SUnit *SU) {
     break;
   default:
     // We don't currently model the OOO reorder buffer, so consider all
-    // scheduled MOps to be "retired".
+    // scheduled MOps to be "retired". We do loosely model in-order resource
+    // latency. If this instruction uses an in-order resource, account for any
+    // likely stall cycles.
+    if (SU->isUnbuffered && ReadyCycle > NextCycle)
+      NextCycle = ReadyCycle;
     break;
   }
   RetiredMOps += IncMOps;
@@ -2514,6 +2539,11 @@ void GenericScheduler::tryCandidate(SchedCandidate &Cand,
       && tryLatency(TryCand, Cand, Zone))
     return;
 
+  // Prioritize instructions that read unbuffered resources by stall cycles.
+  if (tryLess(Zone.getLatencyStallCycles(TryCand.SU),
+              Zone.getLatencyStallCycles(Cand.SU), TryCand, Cand, Stall))
+    return;
+
   // Keep clustered nodes together to encourage downstream peephole
   // optimizations which may reduce resource requirements.
   //
@@ -2577,6 +2607,7 @@ const char *GenericScheduler::getReasonStr(
   case PhysRegCopy:    return "PREG-COPY";
   case RegExcess:      return "REG-EXCESS";
   case RegCritical:    return "REG-CRIT  ";
+  case Stall:          return "STALL     ";
   case Cluster:        return "CLUSTER   ";
   case Weak:           return "WEAK      ";
   case RegMax:         return "REG-MAX   ";
diff --git a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
index 7d9160ab1f4..eeae6ec03d8 100644
--- a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -687,6 +687,22 @@ void ScheduleDAGInstrs::initSUnits() {
 
     // Assign the Latency field of SU using target-provided information.
     SU->Latency = SchedModel.computeInstrLatency(SU->getInstr());
+
+    // If this SUnit uses an unbuffered resource, mark it as such.
+    // These resources are used for in-order execution pipelines within an
+    // out-of-order core and are identified by BufferSize=1. BufferSize=0 is
+    // used for dispatch/issue groups and is not considered here.
+    if (SchedModel.hasInstrSchedModel()) {
+      const MCSchedClassDesc *SC = getSchedClass(SU);
+      for (TargetSchedModel::ProcResIter
+             PI = SchedModel.getWriteProcResBegin(SC),
+             PE = SchedModel.getWriteProcResEnd(SC); PI != PE; ++PI) {
+        if (SchedModel.getProcResource(PI->ProcResourceIdx)->BufferSize == 1) {
+          SU->isUnbuffered = true;
+          break;
+        }
+      }
+    }
   }
 }