include/swift/SILOptimizer/Differentiation/Common.h

//===--- Common.h - Automatic differentiation common utils ----*- C++ -*---===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2019 - 2020 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// Automatic differentiation common utilities.
//
//===----------------------------------------------------------------------===//

#ifndef SWIFT_SILOPTIMIZER_UTILS_DIFFERENTIATION_COMMON_H
#define SWIFT_SILOPTIMIZER_UTILS_DIFFERENTIATION_COMMON_H

#include "swift/AST/DiagnosticsSIL.h"
#include "swift/AST/Expr.h"
#include "swift/AST/SemanticAttrs.h"
#include "swift/SIL/SILDifferentiabilityWitness.h"
#include "swift/SIL/SILFunction.h"
#include "swift/SIL/Projection.h"
#include "swift/SIL/SILModule.h"
#include "swift/SIL/TypeSubstCloner.h"
#include "swift/SILOptimizer/Analysis/ArraySemantic.h"
#include "swift/SILOptimizer/Analysis/DifferentiableActivityAnalysis.h"
#include "swift/SILOptimizer/Differentiation/DifferentiationInvoker.h"

namespace swift {

namespace autodiff {

class ADContext;

//===----------------------------------------------------------------------===//
// Helpers
//===----------------------------------------------------------------------===//

/// Prints an "[AD] " prefix to `llvm::dbgs()` and returns the debug stream.
/// This is being used to print short debug messages within the AD pass.
raw_ostream &getADDebugStream();

/// Given an element address from an `array.uninitialized_intrinsic` `apply`
/// instruction, returns the `apply` instruction. The element address is either
/// a `pointer_to_address` or `index_addr` instruction to the `RawPointer`
/// result of the instrinsic:
///
///     %result = apply %array.uninitialized_intrinsic : $(Array<T>, RawPointer)
///     (%array, %ptr) = destructure_tuple %result
///     %elt0 = pointer_to_address %ptr to $*T       // element address
///     %index_1 = integer_literal $Builtin.Word, 1
///     %elt1 = index_addr %elt0, %index_1           // element address
///     ...
// TODO(SR-12894): Find a better name and move this general utility to
// ArraySemantic.h.
ApplyInst *getAllocateUninitializedArrayIntrinsicElementAddress(SILValue v);

/// Given a value, finds its single `destructure_tuple` user if the value is
/// tuple-typed and such a user exists.
DestructureTupleInst *getSingleDestructureTupleUser(SILValue value);

/// Returns true if the given original function is a "semantic member accessor".
///
/// "Semantic member accessors" are attached to member properties that have a
/// corresponding tangent stored property in the parent `TangentVector` type.
/// These accessors have special-case pullback generation based on their
/// semantic behavior.
///
/// "Semantic member accessors" currently include:
/// - Stored property accessors. These are implicitly generated.
/// - Property wrapper wrapped value accessors. These are implicitly generated
///   and internally call `var wrappedValue`.
bool isSemanticMemberAccessor(SILFunction *original);

/// Returns true if the given apply site has a "semantic member accessor"
/// callee.
bool hasSemanticMemberAccessorCallee(ApplySite applySite);

/// Given a full apply site, apply the given callback to each of its
/// "direct results".
///
/// - `apply`
/// Special case because `apply` returns a single (possibly tuple-typed) result
/// instead of multiple results. If the `apply` has a single
/// `destructure_tuple` user, treat the `destructure_tuple` results as the
/// `apply` direct results.
///
/// - `begin_apply`
/// Apply callback to each `begin_apply` direct result.
///
/// - `try_apply`
/// Apply callback to each `try_apply` successor basic block argument.
void forEachApplyDirectResult(
    FullApplySite applySite, llvm::function_ref<void(SILValue)> resultCallback);

/// Given a function, gathers all of its formal results (both direct and
/// indirect) in an order defined by its result type. Note that "formal results"
/// refer to result values in the body of the function, not at call sites.
void collectAllFormalResultsInTypeOrder(SILFunction &function,
                                        SmallVectorImpl<SILValue> &results);

/// Given a function, gathers all of its direct results in an order defined by
/// its result type. Note that "formal results" refer to result values in the
/// body of the function, not at call sites.
void collectAllDirectResultsInTypeOrder(SILFunction &function,
                                        SmallVectorImpl<SILValue> &results);

/// Given a function call site, gathers all of its actual results (both direct
/// and indirect) in an order defined by its result type.
void collectAllActualResultsInTypeOrder(
    ApplyInst *ai, ArrayRef<SILValue> extractedDirectResults,
    SmallVectorImpl<SILValue> &results);

/// For an `apply` instruction with active results, compute:
/// - The results of the `apply` instruction, in type order.
/// - The set of minimal parameter and result indices for differentiating the
///   `apply` instruction.
void collectMinimalIndicesForFunctionCall(
    ApplyInst *ai, AutoDiffConfig parentConfig,
    const DifferentiableActivityInfo &activityInfo,
    SmallVectorImpl<SILValue> &results, SmallVectorImpl<unsigned> &paramIndices,
    SmallVectorImpl<unsigned> &resultIndices);

/// Returns the underlying instruction for the given SILValue, if it exists,
/// peering through function conversion instructions.
template <class Inst> Inst *peerThroughFunctionConversions(SILValue value) {
  if (auto *inst = dyn_cast<Inst>(value))
    return inst;
  if (auto *cvi = dyn_cast<CopyValueInst>(value))
    return peerThroughFunctionConversions<Inst>(cvi->getOperand());
  if (auto *bbi = dyn_cast<BeginBorrowInst>(value))
    return peerThroughFunctionConversions<Inst>(bbi->getOperand());
  if (auto *tttfi = dyn_cast<ThinToThickFunctionInst>(value))
    return peerThroughFunctionConversions<Inst>(tttfi->getOperand());
  if (auto *cfi = dyn_cast<ConvertFunctionInst>(value))
    return peerThroughFunctionConversions<Inst>(cfi->getOperand());
  if (auto *pai = dyn_cast<PartialApplyInst>(value))
    return peerThroughFunctionConversions<Inst>(pai->getCallee());
  return nullptr;
}

//===----------------------------------------------------------------------===//
// Diagnostic utilities
//===----------------------------------------------------------------------===//

// Returns `v`'s location if it is valid. Otherwise, returns `v`'s function's
// location as as a fallback. Used for diagnostics.
SILLocation getValidLocation(SILValue v);

// Returns `inst`'s location if it is valid. Otherwise, returns `inst`'s
// function's location as as a fallback. Used for diagnostics.
SILLocation getValidLocation(SILInstruction *inst);

//===----------------------------------------------------------------------===//
// Tangent property lookup utilities
//===----------------------------------------------------------------------===//

/// Returns the tangent stored property of the given original stored property
/// and base type. On error, emits diagnostic and returns nullptr.
VarDecl *getTangentStoredProperty(ADContext &context, VarDecl *originalField,
                                  CanType baseType, SILLocation loc,
                                  DifferentiationInvoker invoker);

/// Returns the tangent stored property of the original stored property
/// referenced by the given projection instruction with the given base type.
/// On error, emits diagnostic and returns nullptr.
///
/// NOTE: Asserts if \p projectionInst is not one of: struct_extract,
/// struct_element_addr, or ref_element_addr.
VarDecl *getTangentStoredProperty(ADContext &context,
                                  SingleValueInstruction *projectionInst,
                                  CanType baseType,
                                  DifferentiationInvoker invoker);

//===----------------------------------------------------------------------===//
// Code emission utilities
//===----------------------------------------------------------------------===//

/// Given a range of elements, joins these into a single value. If there's
/// exactly one element, returns that element. Otherwise, creates a tuple using
/// a `tuple` instruction.
SILValue joinElements(ArrayRef<SILValue> elements, SILBuilder &builder,
                      SILLocation loc);

/// Given a value, extracts all elements to `results` from this value if it has
/// a tuple type. Otherwise, add this value directly to `results`.
void extractAllElements(SILValue value, SILBuilder &builder,
                        SmallVectorImpl<SILValue> &results);

/// Emit a zero value into the given buffer access by calling
/// `AdditiveArithmetic.zero`. The given type must conform to
/// `AdditiveArithmetic`.
void emitZeroIntoBuffer(SILBuilder &builder, CanType type,
                        SILValue bufferAccess, SILLocation loc);

/// Emit a `Builtin.Word` value that represents the given type's memory layout
/// size.
SILValue emitMemoryLayoutSize(
    SILBuilder &builder, SILLocation loc, CanType type);

/// Emit a projection of the top-level subcontext from the context object.
SILValue emitProjectTopLevelSubcontext(
    SILBuilder &builder, SILLocation loc, SILValue context,
    SILType subcontextType);

//===----------------------------------------------------------------------===//
// Utilities for looking up derivatives of functions
//===----------------------------------------------------------------------===//

/// Returns a differentiability witness (definition or declaration) exactly
/// matching the specified indices. If none are found in the given `module`,
/// returns `nullptr`.
///
/// \param parameterIndices must be lowered to SIL.
/// \param resultIndices must be lowered to SIL.
SILDifferentiabilityWitness *
getExactDifferentiabilityWitness(SILModule &module, SILFunction *original,
                                 IndexSubset *parameterIndices,
                                 IndexSubset *resultIndices);

/// Finds the derivative configuration (from `@differentiable` and
/// `@derivative` attributes) for `original` whose parameter indices are a
/// minimal superset of the specified AST parameter indices. Returns `None` if
/// no such configuration is found.
///
/// \param parameterIndices must be lowered to SIL.
/// \param minimalASTParameterIndices is an output parameter that is set to the
/// AST indices of the minimal configuration, or to `nullptr` if no such
/// configuration exists.
Optional<AutoDiffConfig>
findMinimalDerivativeConfiguration(AbstractFunctionDecl *original,
                                   IndexSubset *parameterIndices,
                                   IndexSubset *&minimalASTParameterIndices);

/// Returns a differentiability witness for `original` whose parameter indices
/// are a minimal superset of the specified parameter indices and whose result
/// indices match the given result indices, out of all
/// differentiability witnesses that come from AST "@differentiable" or
/// "@differentiating" attributes.
///
/// This function never creates new differentiability witness definitions.
/// However, this function may create new differentiability witness declarations
/// referring to definitions in other modules when these witnesses have not yet
/// been declared in the current module.
///
/// \param module is the SILModule in which to get or create the witnesses.
/// \param parameterIndices must be lowered to SIL.
/// \param resultIndices must be lowered to SIL.
SILDifferentiabilityWitness *getOrCreateMinimalASTDifferentiabilityWitness(
    SILModule &module, SILFunction *original, IndexSubset *parameterIndices,
    IndexSubset *resultIndices);

} // end namespace autodiff

/// Creates arguments in the entry block based on the function type.
inline void createEntryArguments(SILFunction *f) {
  auto *entry = f->getEntryBlock();
  auto conv = f->getConventions();
  auto &ctx = f->getASTContext();
  auto moduleDecl = f->getModule().getSwiftModule();
  assert((entry->getNumArguments() == 0 || conv.getNumSILArguments() == 0) &&
         "Entry already has arguments?!");
  auto createFunctionArgument = [&](SILType type) {
    // Create a dummy parameter declaration.
    // Necessary to prevent crash during argument explosion optimization.
    auto loc = f->getLocation().getSourceLoc();
    auto *decl = new (ctx)
        ParamDecl(loc, loc, Identifier(), loc, Identifier(), moduleDecl);
    decl->setSpecifier(ParamDecl::Specifier::Default);
    entry->createFunctionArgument(type, decl);
  };
  for (auto indResTy :
       conv.getIndirectSILResultTypes(f->getTypeExpansionContext())) {
    if (indResTy.hasArchetype())
      indResTy = indResTy.mapTypeOutOfContext();
    createFunctionArgument(f->mapTypeIntoContext(indResTy).getAddressType());
  }
  for (auto paramTy : conv.getParameterSILTypes(f->getTypeExpansionContext())) {
    if (paramTy.hasArchetype())
      paramTy = paramTy.mapTypeOutOfContext();
    createFunctionArgument(f->mapTypeIntoContext(paramTy));
  }
}

/// Cloner that remaps types using the target function's generic environment.
class BasicTypeSubstCloner final
    : public TypeSubstCloner<BasicTypeSubstCloner, SILOptFunctionBuilder> {

  static SubstitutionMap getSubstitutionMap(SILFunction *target) {
    if (auto *targetGenEnv = target->getGenericEnvironment())
      return targetGenEnv->getForwardingSubstitutionMap();
    return SubstitutionMap();
  }

public:
  explicit BasicTypeSubstCloner(SILFunction *original, SILFunction *target)
      : TypeSubstCloner(*target, *original, getSubstitutionMap(target)) {}

  void postProcess(SILInstruction *orig, SILInstruction *cloned) {
    SILClonerWithScopes::postProcess(orig, cloned);
  }

  void cloneFunction() {
    auto &newFunction = Builder.getFunction();
    auto *entry = newFunction.createBasicBlock();
    createEntryArguments(&newFunction);
    SmallVector<SILValue, 8> entryArguments(newFunction.getArguments().begin(),
                                            newFunction.getArguments().end());
    cloneFunctionBody(&Original, entry, entryArguments);
  }
};

} // end namespace swift

#endif // SWIFT_SILOPTIMIZER_MANDATORY_DIFFERENTIATION_COMMON_H