clang/lib/CodeGen/CGCoroutine.cpp

//===----- CGCoroutine.cpp - Emit LLVM Code for C++ coroutines ------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This contains code dealing with C++ code generation of coroutines.
//
//===----------------------------------------------------------------------===//

#include "CodeGenFunction.h"
#include "clang/AST/StmtCXX.h"

using namespace clang;
using namespace CodeGen;

namespace clang {
namespace CodeGen {

struct CGCoroData {

  // Stores the jump destination just before the final suspend. Coreturn
  // statements jumps to this point after calling return_xxx promise member.
  CodeGenFunction::JumpDest FinalJD;

  unsigned CoreturnCount = 0;

  // Stores the llvm.coro.id emitted in the function so that we can supply it
  // as the first argument to coro.begin, coro.alloc and coro.free intrinsics.
  // Note: llvm.coro.id returns a token that cannot be directly expressed in a
  // builtin.
  llvm::CallInst *CoroId = nullptr;
  // If coro.id came from the builtin, remember the expression to give better
  // diagnostic. If CoroIdExpr is nullptr, the coro.id was created by
  // EmitCoroutineBody.
  CallExpr const *CoroIdExpr = nullptr;
};
}
}

clang::CodeGen::CodeGenFunction::CGCoroInfo::CGCoroInfo() {}
CodeGenFunction::CGCoroInfo::~CGCoroInfo() {}

static void createCoroData(CodeGenFunction &CGF,
                           CodeGenFunction::CGCoroInfo &CurCoro,
                           llvm::CallInst *CoroId,
                           CallExpr const *CoroIdExpr = nullptr) {
  if (CurCoro.Data) {
    if (CurCoro.Data->CoroIdExpr)
      CGF.CGM.Error(CoroIdExpr->getLocStart(),
                    "only one __builtin_coro_id can be used in a function");
    else if (CoroIdExpr)
      CGF.CGM.Error(CoroIdExpr->getLocStart(),
                    "__builtin_coro_id shall not be used in a C++ coroutine");
    else
      llvm_unreachable("EmitCoroutineBodyStatement called twice?");

    return;
  }

  CurCoro.Data = std::unique_ptr<CGCoroData>(new CGCoroData);
  CurCoro.Data->CoroId = CoroId;
  CurCoro.Data->CoroIdExpr = CoroIdExpr;
}

void CodeGenFunction::EmitCoreturnStmt(CoreturnStmt const &S) {
  ++CurCoro.Data->CoreturnCount;
  EmitStmt(S.getPromiseCall());
  EmitBranchThroughCleanup(CurCoro.Data->FinalJD);
}

void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
  auto *NullPtr = llvm::ConstantPointerNull::get(Builder.getInt8PtrTy());
  auto &TI = CGM.getContext().getTargetInfo();
  unsigned NewAlign = TI.getNewAlign() / TI.getCharWidth();

  auto *FinalBB = createBasicBlock("coro.final");

  auto *CoroId = Builder.CreateCall(
      CGM.getIntrinsic(llvm::Intrinsic::coro_id),
      {Builder.getInt32(NewAlign), NullPtr, NullPtr, NullPtr});
  createCoroData(*this, CurCoro, CoroId);

  EmitScalarExpr(S.getAllocate());

  // FIXME: Setup cleanup scopes.

  EmitStmt(S.getPromiseDeclStmt());

  CurCoro.Data->FinalJD = getJumpDestInCurrentScope(FinalBB);

  // FIXME: Emit initial suspend and more before the body.

  EmitStmt(S.getBody());

  // See if we need to generate final suspend.
  const bool CanFallthrough = Builder.GetInsertBlock();
  const bool HasCoreturns = CurCoro.Data->CoreturnCount > 0;
  if (CanFallthrough || HasCoreturns) {
    EmitBlock(FinalBB);
    // FIXME: Emit final suspend.
  }
  EmitStmt(S.getDeallocate());

  // FIXME: Emit return for the coroutine return object.
}

// Emit coroutine intrinsic and patch up arguments of the token type.
RValue CodeGenFunction::EmitCoroutineIntrinsic(const CallExpr *E,
                                               unsigned int IID) {
  SmallVector<llvm::Value *, 8> Args;
  switch (IID) {
  default:
    break;
  // The following three intrinsics take a token parameter referring to a token
  // returned by earlier call to @llvm.coro.id. Since we cannot represent it in
  // builtins, we patch it up here.
  case llvm::Intrinsic::coro_alloc:
  case llvm::Intrinsic::coro_begin:
  case llvm::Intrinsic::coro_free: {
    if (CurCoro.Data && CurCoro.Data->CoroId) {
      Args.push_back(CurCoro.Data->CoroId);
      break;
    }
    CGM.Error(E->getLocStart(), "this builtin expect that __builtin_coro_id has"
                                " been used earlier in this function");
    // Fallthrough to the next case to add TokenNone as the first argument.
  }
  // @llvm.coro.suspend takes a token parameter. Add token 'none' as the first
  // argument.
  case llvm::Intrinsic::coro_suspend:
    Args.push_back(llvm::ConstantTokenNone::get(getLLVMContext()));
    break;
  }
  for (auto &Arg : E->arguments())
    Args.push_back(EmitScalarExpr(Arg));

  llvm::Value *F = CGM.getIntrinsic(IID);
  llvm::CallInst *Call = Builder.CreateCall(F, Args);

  // If we see @llvm.coro.id remember it in the CoroData. We will update
  // coro.alloc, coro.begin and coro.free intrinsics to refer to it.
  if (IID == llvm::Intrinsic::coro_id) {
    createCoroData(*this, CurCoro, Call, E);
  }
  return RValue::get(Call);
}