carbon-lang/toolchain/lower/file_context.h

// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#ifndef CARBON_TOOLCHAIN_LOWER_FILE_CONTEXT_H_
#define CARBON_TOOLCHAIN_LOWER_FILE_CONTEXT_H_

#include "clang/Basic/CodeGenOptions.h"
#include "clang/CodeGen/ModuleBuilder.h"
#include "clang/Lex/PreprocessorOptions.h"
#include "llvm/Support/BLAKE3.h"
#include "toolchain/lower/context.h"
#include "toolchain/parse/tree_and_subtrees.h"
#include "toolchain/sem_ir/file.h"
#include "toolchain/sem_ir/ids.h"
#include "toolchain/sem_ir/inst_namer.h"

namespace Carbon::Lower {

// Context and shared functionality for lowering within a SemIR file.
class FileContext {
 public:
  using LoweredConstantStore =
      FixedSizeValueStore<SemIR::InstId, llvm::Constant*>;

  // Describes a specific function's body fingerprint.
  struct SpecificFunctionFingerprint {
    // Fingerprint with all specific-dependent instructions, except specific
    // calls. This is built by the `FunctionContext` while lowering each
    // instruction in the definition of a specific function.
    // TODO: This can be merged with the function type fingerprint, for a
    // single upfront non-equivalence check, and hash bucketing for deeper
    // equivalence evaluation.
    llvm::BLAKE3Result<32> common_fingerprint;
    // Fingerprint for all calls to specific functions (hashes all calls to
    // other specifics). This is built by the `FunctionContext` while lowering.
    llvm::BLAKE3Result<32> specific_fingerprint;
    // All non-hashed specific_ids of functions called.
    llvm::SmallVector<SemIR::SpecificId> calls;
  };

  explicit FileContext(Context& context, const SemIR::File& sem_ir,
                       const SemIR::InstNamer* inst_namer,
                       llvm::raw_ostream* vlog_stream);

  // Creates the Clang `CodeGenerator` to generate LLVM module from imported C++
  // code. Returns null when not importing C++.
  auto CreateCppCodeGenerator() -> std::unique_ptr<clang::CodeGenerator>;

  // Prepares to lower code in this IR, by precomputing needed LLVM types,
  // constants, declarations, etc. Should only be called once, before we lower
  // anything in this file.
  auto PrepareToLower() -> void;

  // Lowers all the definitions provided by the SemIR::File to LLVM IR.
  auto LowerDefinitions() -> void;

  // Perform final cleanup tasks once all lowering has been completed.
  auto Finalize() -> void;

  // Gets a callable's function. Returns nullptr for a builtin or a function we
  // have not lowered.
  auto GetFunction(SemIR::FunctionId function_id,
                   SemIR::SpecificId specific_id = SemIR::SpecificId::None)
      -> llvm::Function* {
    return *GetFunctionAddr(function_id, specific_id);
  }

  // Gets a or creates callable's function. Returns nullptr for a builtin.
  auto GetOrCreateFunction(SemIR::FunctionId function_id,
                           SemIR::SpecificId specific_id) -> llvm::Function*;

  // Returns a lowered type for the given type_id.
  auto GetType(SemIR::TypeId type_id) -> llvm::Type* {
    CARBON_CHECK(type_id.has_value(), "Should not be called with `None`");
    CARBON_CHECK(type_id.is_concrete(), "Lowering symbolic type {0}: {1}",
                 type_id, sem_ir().types().GetAsInst(type_id));
    CARBON_CHECK(types_.Get(type_id), "Missing type {0}: {1}", type_id,
                 sem_ir().types().GetAsInst(type_id));
    return types_.Get(type_id);
  }

  // Returns location information for use with DebugInfo.
  auto GetLocForDI(SemIR::InstId inst_id) -> Context::LocForDI;

  // Returns a lowered value to use for a value of type `type`.
  auto GetTypeAsValue() -> llvm::Constant* {
    return context().GetTypeAsValue();
  }

  // Returns a lowered value to use for a value of int literal type.
  auto GetIntLiteralAsValue() -> llvm::Constant* {
    return context().GetIntLiteralAsValue();
  }

  // Returns a value for the given constant. If specified, `use_inst_id` is the
  // instruction that is using this constant.
  auto GetConstant(SemIR::ConstantId const_id, SemIR::InstId use_inst_id)
      -> llvm::Value*;

  // Returns the empty LLVM struct type used to represent the type `type`.
  auto GetTypeType() -> llvm::StructType* { return context().GetTypeType(); }

  auto context() -> Context& { return *context_; }
  auto llvm_context() -> llvm::LLVMContext& { return context().llvm_context(); }
  auto llvm_module() -> llvm::Module& { return context().llvm_module(); }
  auto sem_ir() -> const SemIR::File& { return *sem_ir_; }
  auto cpp_ast() -> const clang::ASTUnit* { return sem_ir().cpp_ast(); }
  auto inst_namer() -> const SemIR::InstNamer* { return inst_namer_; }
  auto global_variables() -> const Map<SemIR::InstId, llvm::GlobalVariable*>& {
    return global_variables_;
  }
  auto printf_int_format_string() -> llvm::Value* {
    return context().printf_int_format_string();
  }
  auto SetPrintfIntFormatString(llvm::Value* printf_int_format_string) {
    context().SetPrintfIntFormatString(printf_int_format_string);
  }

  struct FunctionTypeInfo {
    llvm::FunctionType* type;
    llvm::SmallVector<SemIR::InstId> param_inst_ids;
    llvm::Type* return_type = nullptr;
    SemIR::InstId return_param_id = SemIR::InstId::None;
  };

  // Retrieve various features of the function's type useful for constructing
  // the `llvm::Type` for the `llvm::Function`. If any part of the type can't be
  // manifest (eg: incomplete return or parameter types), then the result is as
  // if the type was `void()`.
  auto BuildFunctionTypeInfo(const SemIR::Function& function,
                             SemIR::SpecificId specific_id) -> FunctionTypeInfo;

  // Builds the global for the given instruction, which should then be cached by
  // the caller.
  auto BuildGlobalVariableDecl(SemIR::VarStorage var_storage)
      -> llvm::GlobalVariable*;

  // Builds the definition for the given function. If the function is only a
  // declaration with no definition, does nothing. If this is a generic it'll
  // only be lowered if the specific_id is specified. During this lowering of
  // a generic, more generic functions may be added for lowering.
  auto BuildFunctionDefinition(
      SemIR::FunctionId function_id,
      SemIR::SpecificId specific_id = SemIR::SpecificId::None) -> void;

 private:
  // Gets the location in which a callable's function is stored.
  auto GetFunctionAddr(SemIR::FunctionId function_id,
                       SemIR::SpecificId specific_id) -> llvm::Function** {
    return specific_id.has_value() ? &specific_functions_.Get(specific_id)
                                   : &functions_.Get(function_id);
  }

  // Notes that a C++ function has been referenced for the first time, so we
  // should ask Clang to generate a definition for it if possible.
  auto HandleReferencedCppFunction(clang::FunctionDecl* cpp_decl) -> void;

  // Notes that a specific function has been referenced for the first time.
  // Updates the fingerprint to include the function's type, and adds the
  // function to the list of specific functions whose definitions should be
  // lowered.
  auto HandleReferencedSpecificFunction(SemIR::FunctionId function_id,
                                        SemIR::SpecificId specific_id,
                                        llvm::Type* llvm_type) -> void;

  // Builds the declaration for the given function, which should then be cached
  // by the caller.
  auto BuildFunctionDecl(SemIR::FunctionId function_id,
                         SemIR::SpecificId specific_id =
                             SemIR::SpecificId::None) -> llvm::Function*;

  // Builds a function's body. Common functionality for all functions.
  //
  // The `function_id` and `specific_id` identify the function within this
  // context's file. If the function was defined in a different file,
  // `definition_context` is a `FileContext` for that other file.
  // `definition_function` is the `Function` object within the file that owns
  // the definition.
  auto BuildFunctionBody(SemIR::FunctionId function_id,
                         SemIR::SpecificId specific_id,
                         const SemIR::Function& declaration_function,
                         FileContext& definition_context,
                         const SemIR::Function& definition_function) -> void;

  // Build the DISubprogram metadata for the given function.
  auto BuildDISubprogram(const SemIR::Function& function,
                         const llvm::Function* llvm_function)
      -> llvm::DISubprogram*;

  // Builds the type for the given instruction, which should then be cached by
  // the caller.
  auto BuildType(SemIR::InstId inst_id) -> llvm::Type*;

  auto BuildVtable(const SemIR::Class& class_info) -> llvm::GlobalVariable*;

  // Records a specific that was lowered for a generic. These are added one
  // by one while lowering their definitions.
  auto AddLoweredSpecificForGeneric(SemIR::GenericId generic_id,
                                    SemIR::SpecificId specific_id) {
    lowered_specifics_.Get(generic_id).push_back(specific_id);
  }

  // Initializes and returns a SpecificFunctionFingerprint* instance for a
  // specific. The internal of the fingerprint are populated during and after
  // lowering the function body of that specific.
  auto InitializeFingerprintForSpecific(SemIR::SpecificId specific_id)
      -> SpecificFunctionFingerprint* {
    if (!specific_id.has_value()) {
      return nullptr;
    }
    return &lowered_specific_fingerprint_.Get(specific_id);
  }

  // Entry point for coalescing equivalent specifics. Two function definitions,
  // from the same generic, with different specific_ids are considered
  // equivalent if, at the LLVM level, one can be replaced with the other, with
  // no change in behavior. All LLVM types and instructions must be equivalent.
  auto CoalesceEquivalentSpecifics() -> void;

  // While coalescing specifics, returns whether the function types for two
  // specifics are equivalent. This uses a fingerprint generated for each
  // function type.
  auto AreFunctionTypesEquivalent(SemIR::SpecificId specific_id1,
                                  SemIR::SpecificId specific_id2) -> bool;

  // While coalescing specifics, compare the function bodies for two specifics.
  // This uses fingerprints generated during lowering of the function body.
  // The `visited_equivalent_specifics` parameter is used to track cycles in
  // the function callgraph, and will also return equivalent pairs of specifics
  // found, if the two specifics given as arguments are found to be equivalent.
  auto AreFunctionBodiesEquivalent(
      SemIR::SpecificId specific_id1, SemIR::SpecificId specific_id2,
      Set<std::pair<SemIR::SpecificId, SemIR::SpecificId>>&
          visited_equivalent_specifics) -> bool;

  // Given an equivalent pair of specifics, updates the canonical specific to
  // use for each of the two Specifics found to be equivalent.
  auto ProcessSpecificEquivalence(
      std::pair<SemIR::SpecificId, SemIR::SpecificId> pair) -> void;

  // Checks if two specific_ids are equivalent and also reduces the equivalence
  // chains/paths. This update ensures the canonical specific is always "one
  // hop away".
  auto IsKnownEquivalence(SemIR::SpecificId specific_id1,
                          SemIR::SpecificId specific_id2) -> bool;

  // Update the tracked equivalent specific for the `SpecificId`. This may
  // occur a replacement was performed and a chain of such replacements needs
  // to be followed to discover the canonical specific for the given argument.
  auto UpdateEquivalentSpecific(SemIR::SpecificId specific_id) -> void;

  // Update the LLVM function to use for a `SpecificId` that has been found to
  // have another equivalent LLVM function. Replace all uses of the original
  // LLVM function with the equivalent one found, and delete the previous LLVM
  // function body.
  auto UpdateAndDeleteLLVMFunction(SemIR::SpecificId specific_id) -> void;

  // Inserts a pair into a set of pairs in canonical form. Also implicitly
  // checks entry already existed if it cannot be inserted.
  auto InsertPair(
      SemIR::SpecificId specific_id1, SemIR::SpecificId specific_id2,
      Set<std::pair<SemIR::SpecificId, SemIR::SpecificId>>& set_of_pairs)
      -> bool;

  // Checks if a pair is contained into a set of pairs, in canonical form.
  auto ContainsPair(
      SemIR::SpecificId specific_id1, SemIR::SpecificId specific_id2,
      const Set<std::pair<SemIR::SpecificId, SemIR::SpecificId>>& set_of_pairs)
      -> bool;

  // The overall lowering context.
  Context* context_;

  // The input SemIR.
  const SemIR::File* const sem_ir_;

  // The options used to create the Clang Code Generator.
  clang::HeaderSearchOptions cpp_header_search_options_;
  clang::PreprocessorOptions cpp_preprocessor_options_;
  clang::CodeGenOptions cpp_code_gen_options_;

  // The Clang `CodeGenerator` to generate LLVM module from imported C++
  // code. Should be initialized using `CreateCppCodeGenerator()`. Can be null
  // if no C++ code is imported.
  std::unique_ptr<clang::CodeGenerator> cpp_code_generator_;

  // The instruction namer, if given.
  const SemIR::InstNamer* const inst_namer_;

  // The optional vlog stream.
  llvm::raw_ostream* vlog_stream_;

  // Maps callables to lowered functions. SemIR treats callables as the
  // canonical form of a function, so lowering needs to do the same.
  using LoweredFunctionStore =
      FixedSizeValueStore<SemIR::FunctionId, llvm::Function*>;
  LoweredFunctionStore functions_;

  // Maps specific callables to lowered functions.
  FixedSizeValueStore<SemIR::SpecificId, llvm::Function*> specific_functions_;

  // Provides lowered versions of types. Entries are non-symbolic types.
  using LoweredTypeStore = FixedSizeValueStore<SemIR::TypeId, llvm::Type*>;
  LoweredTypeStore types_;

  // Maps constants to their lowered values. Indexes are the `InstId` for
  // constant instructions.
  LoweredConstantStore constants_;

  // Maps global variables to their lowered variant.
  Map<SemIR::InstId, llvm::GlobalVariable*> global_variables_;

  // For a generic function, keep track of the specifics for which LLVM
  // function declarations were created. Those can be retrieved then from
  // `specific_functions_`.
  FixedSizeValueStore<SemIR::GenericId, llvm::SmallVector<SemIR::SpecificId>>
      lowered_specifics_;

  // For specifics that exist in lowered_specifics, a hash of their function
  // type information: return and parameter types.
  // TODO: Hashing all members of `FunctionTypeInfo` may not be necessary.
  FixedSizeValueStore<SemIR::SpecificId, llvm::BLAKE3Result<32>>
      lowered_specifics_type_fingerprint_;

  // This is initialized and populated while lowering a specific.
  FixedSizeValueStore<SemIR::SpecificId, SpecificFunctionFingerprint>
      lowered_specific_fingerprint_;

  // Equivalent specifics that have been found. For each specific, this points
  // to the canonical equivalent specific, which may also be self. We currently
  // define the canonical specific as the one with the lowest
  // `SpecificId.index`.
  //
  // Entries are initialized to `SpecificId::None`, which defines that there is
  // no other equivalent specific to this `SpecificId`.
  FixedSizeValueStore<SemIR::SpecificId, SemIR::SpecificId>
      equivalent_specifics_;

  // Non-equivalent specifics found.
  // TODO: Revisit this due to its quadratic space growth.
  Set<std::pair<SemIR::SpecificId, SemIR::SpecificId>>
      non_equivalent_specifics_;
};

}  // namespace Carbon::Lower

#endif  // CARBON_TOOLCHAIN_LOWER_FILE_CONTEXT_H_