[NFC][mlgo] Add feature declarations for the ML regalloc advisor

This just adds feature declarations and some boilerplate.

Differential Revision: https://reviews.llvm.org/D116076

llvm/include/llvm/Analysis/MLModelRunner.h

@@ -41,6 +41,11 @@ class MLModelRunner {
         getTensorUntyped(static_cast<size_t>(FeatureID)));
   }
 
+  virtual void *getTensorUntyped(size_t Index) = 0;
+  const void *getTensorUntyped(size_t Index) const {
+    return (const_cast<MLModelRunner *>(this))->getTensorUntyped(Index);
+  }
+
   enum class Kind : int { Unknown, Release, Development, NoOp };
   Kind getKind() const { return Type; }
 
@@ -49,10 +54,6 @@ class MLModelRunner {
     assert(Type != Kind::Unknown);
   }
   virtual void *evaluateUntyped() = 0;
-  virtual void *getTensorUntyped(size_t Index) = 0;
-  const void *getTensorUntyped(size_t Index) const {
-    return (const_cast<MLModelRunner *>(this))->getTensorUntyped(Index);
-  }
 
   LLVMContext &Ctx;
   const Kind Type;

llvm/lib/CodeGen/CMakeLists.txt

@@ -113,6 +113,7 @@ add_llvm_component_library(LLVMCodeGen
   MIRFSDiscriminator.cpp
   MIRSampleProfile.cpp
   MIRYamlMapping.cpp
+  MLRegallocEvictAdvisor.cpp
   ModuloSchedule.cpp
   MultiHazardRecognizer.cpp
   PatchableFunction.cpp

llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp

@@ -0,0 +1,173 @@
+//===- MLRegAllocEvictAdvisor.cpp - ML eviction advisor -------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Implementation of the ML eviction advisor and reward injection pass
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Config/config.h"
+
+#if defined(LLVM_HAVE_TF_AOT) || defined(LLVM_HAVE_TF_API)
+
+#include "RegAllocEvictionAdvisor.h"
+#include "llvm/Analysis/MLModelRunner.h"
+#include "llvm/Analysis/ModelUnderTrainingRunner.h"
+#include "llvm/Analysis/NoInferenceModelRunner.h"
+#include "llvm/Analysis/Utils/TFUtils.h"
+#include "llvm/CodeGen/CalcSpillWeights.h"
+#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/CodeGen/RegisterClassInfo.h"
+#include "llvm/CodeGen/VirtRegMap.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Pass.h"
+#include "llvm/PassRegistry.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Target/TargetMachine.h"
+
+#include <memory>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "ml-regalloc"
+
+namespace {
+// This is the maximum number of interfererring ranges. That's the number of
+// distinct AllocationOrder values, which comes from MCRegisterClass::RegsSize.
+// For X86, that's 32.
+// TODO: find a way to get this, statically, in a programmatic way.
+static const int64_t MaxInterferences = 32;
+
+// Logically, we can think of the feature set given to the evaluator as a 2D
+// matrix. The rows are the features (see next). The columns correspond to the
+// interferences. We treat the candidate virt reg as an 'interference', too, as
+// its feature set is the same as that of the interferring ranges. So we'll have
+// MaxInterferences + 1 columns and by convention, we will use the last column
+// for the virt reg seeking allocation.
+static const int64_t CandidateVirtRegPos = MaxInterferences;
+static const int64_t NumberOfInterferences = CandidateVirtRegPos + 1;
+
+// Most features are as described above, so we'll reuse this vector in defining
+// them.
+static const std::vector<int64_t> PerLiveRangeShape{1, NumberOfInterferences};
+
+// --------------
+// Features table
+// --------------
+// For each interfering live range (incl. the candidate) we collect a number of
+// features. However, because the features are of different types (and because
+// of ML best practices), we organize the tensors per feature, not per
+// candidate. Each such tensor has a scalar value corresponding to the
+// interferring live range at that position, in the order in AllocationOrder.
+// The last position corresponds to the virt reg seeking allocation.
+// Exception to all that is the progression feature, which is just a scalar (see
+// its documentation for details).
+// Note on naming: the "_by_max" are normalized using the largest value of that
+// tensor, as observed in the current decision making stage (i.e. for the
+// current call to the advisor's tryFindEvictionCandidate)
+//
+// The feature list format: type, name, shape, documentation.
+// Note: we can really just use int64 and float, hence the modeling of some
+// bools as int64 values.
+#define RA_EVICT_FEATURES_LIST(M)                                              \
+  M(int64_t, mask, PerLiveRangeShape,                                          \
+    "boolean values, 0 for unavailable candidates (i.e. if a position is 0, "  \
+    "it "                                                                      \
+    "can't be evicted)")                                                       \
+  M(int64_t, is_free, PerLiveRangeShape,                                       \
+    "boolean values, 1 if this phys reg is actually free (no interferences)")  \
+  M(float, nr_urgent, PerLiveRangeShape,                                       \
+    "number of 'urgent' intervals, normalized. Urgent are those that are OK "  \
+    "to break cascades")                                                       \
+  M(float, nr_broken_hints, PerLiveRangeShape,                                 \
+    "if this position were evicted, how many broken hints would there be")     \
+  M(int64_t, is_hint, PerLiveRangeShape,                                       \
+    "is this a preferred phys reg for the candidate")                          \
+  M(int64_t, is_local, PerLiveRangeShape,                                      \
+    "is this live range local to a basic block")                               \
+  M(float, nr_rematerializable, PerLiveRangeShape,                             \
+    "nr rematerializable ranges")                                              \
+  M(float, nr_defs_and_uses, PerLiveRangeShape,                                \
+    "bb freq - weighed nr defs and uses")                                      \
+  M(float, weighed_reads_by_max, PerLiveRangeShape,                            \
+    "bb freq - weighed nr of reads, normalized")                               \
+  M(float, weighed_writes_by_max, PerLiveRangeShape,                           \
+    "bb feq - weighed nr of writes, normalized")                               \
+  M(float, weighed_read_writes_by_max, PerLiveRangeShape,                      \
+    "bb freq - weighed nr of uses that are both read and writes, normalized")  \
+  M(float, weighed_indvars_by_max, PerLiveRangeShape,                          \
+    "bb freq - weighed nr of uses that are indvars, normalized")               \
+  M(float, hint_weights_by_max, PerLiveRangeShape,                             \
+    "bb freq - weighed nr of uses that are hints, normalized")                 \
+  M(float, start_bb_freq_by_max, PerLiveRangeShape,                            \
+    "the freq in the start block, normalized")                                 \
+  M(float, end_bb_freq_by_max, PerLiveRangeShape,                              \
+    "freq of end block, normalized")                                           \
+  M(float, hottest_bb_freq_by_max, PerLiveRangeShape,                          \
+    "hottest BB freq, normalized")                                             \
+  M(float, liverange_size, PerLiveRangeShape,                                  \
+    "size (instr index diff) of the LR")                                       \
+  M(float, use_def_density, PerLiveRangeShape,                                 \
+    "the max weight, as computed by the manual heuristic")                     \
+  M(int64_t, max_stage, PerLiveRangeShape,                                     \
+    "largest stage of an interval in this LR")                                 \
+  M(int64_t, min_stage, PerLiveRangeShape,                                     \
+    "lowest stage of an interval in this LR")                                  \
+  M(float, progress, {1}, "ratio of current queue size to initial size")
+
+// The model learns to pick one of the mask == 1 interferences. This is the name
+// of the output tensor.
+// The contract with the model is that the output will be guaranteed to be to a
+// mask == 1 position.
+const char *const DecisionName = "index_to_evict";
+
+// Named features index.
+enum FeatureIDs {
+#define _FEATURE_IDX(_, name, __, ___) name,
+  RA_EVICT_FEATURES_LIST(_FEATURE_IDX)
+#undef _FEATURE_IDX
+      FeatureCount
+};
+
+// The ML advisor will typically have a sparse input to the evaluator, because
+// various phys regs won't be available. It's easier (maintenance-wise) to
+// bulk-reset the state of the evaluator each time we are about to use it again.
+template <typename T> size_t getTotalSize(const std::vector<int64_t> &Shape) {
+  size_t Ret = sizeof(T);
+  for (const auto V : Shape)
+    Ret *= V;
+  return Ret;
+}
+
+void resetInputs(MLModelRunner &Runner) {
+#define _RESET(TYPE, NAME, SHAPE, __)                                          \
+  std::memset(Runner.getTensorUntyped(FeatureIDs::NAME), 0,                    \
+              getTotalSize<TYPE>(SHAPE));
+  RA_EVICT_FEATURES_LIST(_RESET)
+#undef _RESET
+}
+
+// Development mode-specifics
+#ifdef LLVM_HAVE_TF_API
+#define _DECL_FEATURES(type, name, shape, _)                                   \
+  TensorSpec::createSpec<type>(#name, shape),
+
+static const std::vector<TensorSpec> InputFeatures{
+    {RA_EVICT_FEATURES_LIST(_DECL_FEATURES)}};
+#undef _DECL_FEATURES
+static const TensorSpec Output =
+    TensorSpec::createSpec<int64_t>(DecisionName, {1});
+const char *const RewardName = "reward";
+static const TensorSpec Reward =
+    TensorSpec::createSpec<int64_t>(RewardName, {1});
+
+#endif //#ifdef LLVM_HAVE_TF_API
+} // namespace
+#endif // defined(LLVM_HAVE_TF_AOT) || defined(LLVM_HAVE_TF_API)