llvm/clang/lib/CodeGen/CGCoroutine.cpp

//===----- CGCoroutine.cpp - Emit LLVM Code for C++ coroutines ------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This contains code dealing with C++ code generation of coroutines.
//
//===----------------------------------------------------------------------===//

#include "CGCleanup.h"
#include "CodeGenFunction.h"
#include "llvm/ADT/ScopeExit.h"
#include "clang/AST/StmtCXX.h"
#include "clang/AST/StmtVisitor.h"

usingnamespaceclang;
usingnamespaceCodeGen;

Value;
BasicBlock;

namespace {
enum class AwaitKind { … };
static constexpr llvm::StringLiteral AwaitKindStr[] = …;
}

struct clang::CodeGen::CGCoroData { … };

// Defining these here allows to keep CGCoroData private to this file.
clang::CodeGen::CodeGenFunction::CGCoroInfo::CGCoroInfo() { … }
CodeGenFunction::CGCoroInfo::~CGCoroInfo() { … }

static void createCoroData(CodeGenFunction &CGF,
                           CodeGenFunction::CGCoroInfo &CurCoro,
                           llvm::CallInst *CoroId,
                           CallExpr const *CoroIdExpr = nullptr) { … }

// Synthesize a pretty name for a suspend point.
static SmallString<32> buildSuspendPrefixStr(CGCoroData &Coro, AwaitKind Kind) { … }

// Check if function can throw based on prototype noexcept, also works for
// destructors which are implicitly noexcept but can be marked noexcept(false).
static bool FunctionCanThrow(const FunctionDecl *D) { … }

static bool StmtCanThrow(const Stmt *S) { … }

// Emit suspend expression which roughly looks like:
//
//   auto && x = CommonExpr();
//   if (!x.await_ready()) {
//      llvm_coro_save();
//      llvm_coro_await_suspend(&x, frame, wrapper) (*) (**)
//      llvm_coro_suspend(); (***)
//   }
//   x.await_resume();
//
// where the result of the entire expression is the result of x.await_resume()
//
//   (*) llvm_coro_await_suspend_{void, bool, handle} is lowered to
//      wrapper(&x, frame) when it's certain not to interfere with
//      coroutine transform. await_suspend expression is
//      asynchronous to the coroutine body and not all analyses
//      and transformations can handle it correctly at the moment.
//
//      Wrapper function encapsulates x.await_suspend(...) call and looks like:
//
//      auto __await_suspend_wrapper(auto& awaiter, void* frame) {
//        std::coroutine_handle<> handle(frame);
//        return awaiter.await_suspend(handle);
//      }
//
//  (**) If x.await_suspend return type is bool, it allows to veto a suspend:
//      if (x.await_suspend(...))
//        llvm_coro_suspend();
//
//  (***) llvm_coro_suspend() encodes three possible continuations as
//       a switch instruction:
//
//  %where-to = call i8 @llvm.coro.suspend(...)
//  switch i8 %where-to, label %coro.ret [ ; jump to epilogue to suspend
//    i8 0, label %yield.ready   ; go here when resumed
//    i8 1, label %yield.cleanup ; go here when destroyed
//  ]
//
//  See llvm's docs/Coroutines.rst for more details.
//
namespace {
  struct LValueOrRValue { … };
}
static LValueOrRValue emitSuspendExpression(CodeGenFunction &CGF, CGCoroData &Coro,
                                    CoroutineSuspendExpr const &S,
                                    AwaitKind Kind, AggValueSlot aggSlot,
                                    bool ignoreResult, bool forLValue) { … }

RValue CodeGenFunction::EmitCoawaitExpr(const CoawaitExpr &E,
                                        AggValueSlot aggSlot,
                                        bool ignoreResult) { … }
RValue CodeGenFunction::EmitCoyieldExpr(const CoyieldExpr &E,
                                        AggValueSlot aggSlot,
                                        bool ignoreResult) { … }

void CodeGenFunction::EmitCoreturnStmt(CoreturnStmt const &S) { … }


#ifndef NDEBUG
static QualType getCoroutineSuspendExprReturnType(const ASTContext &Ctx,
  const CoroutineSuspendExpr *E) {
  const auto *RE = E->getResumeExpr();
  // Is it possible for RE to be a CXXBindTemporaryExpr wrapping
  // a MemberCallExpr?
  assert(isa<CallExpr>(RE) && "unexpected suspend expression type");
  return cast<CallExpr>(RE)->getCallReturnType(Ctx);
}
#endif

llvm::Function *
CodeGenFunction::generateAwaitSuspendWrapper(Twine const &CoroName,
                                             Twine const &SuspendPointName,
                                             CoroutineSuspendExpr const &S) { … }

LValue
CodeGenFunction::EmitCoawaitLValue(const CoawaitExpr *E) { … }

LValue
CodeGenFunction::EmitCoyieldLValue(const CoyieldExpr *E) { … }

// Hunts for the parameter reference in the parameter copy/move declaration.
namespace {
struct GetParamRef : public StmtVisitor<GetParamRef> { … };
}

// This class replaces references to parameters to their copies by changing
// the addresses in CGF.LocalDeclMap and restoring back the original values in
// its destructor.

namespace {
  struct ParamReferenceReplacerRAII { … };
}

// For WinEH exception representation backend needs to know what funclet coro.end
// belongs to. That information is passed in a funclet bundle.
static SmallVector<llvm::OperandBundleDef, 1>
getBundlesForCoroEnd(CodeGenFunction &CGF) { … }

namespace {
// We will insert coro.end to cut any of the destructors for objects that
// do not need to be destroyed once the coroutine is resumed.
// See llvm/docs/Coroutines.rst for more details about coro.end.
struct CallCoroEnd final : public EHScopeStack::Cleanup { … };
}

namespace {
// Make sure to call coro.delete on scope exit.
struct CallCoroDelete final : public EHScopeStack::Cleanup { … };
}

namespace {
struct GetReturnObjectManager { … };
} // namespace

static void emitBodyAndFallthrough(CodeGenFunction &CGF,
                                   const CoroutineBodyStmt &S, Stmt *Body) { … }

void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) { … }

// Emit coroutine intrinsic and patch up arguments of the token type.
RValue CodeGenFunction::EmitCoroutineIntrinsic(const CallExpr *E,
                                               unsigned int IID) { … }