llvm/llvm/lib/Transforms/Coroutines/CoroElide.cpp

//===- CoroElide.cpp - Coroutine Frame Allocation Elision Pass ------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Coroutines/CoroElide.h"
#include "CoroInternal.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FileSystem.h"
#include <optional>

usingnamespacellvm;

#define DEBUG_TYPE …

STATISTIC(NumOfCoroElided, "The # of coroutine get elided.");

#ifndef NDEBUG
static cl::opt<std::string> CoroElideInfoOutputFilename(
    "coro-elide-info-output-file", cl::value_desc("filename"),
    cl::desc("File to record the coroutines got elided"), cl::Hidden);
#endif

namespace {
// Created on demand if the coro-elide pass has work to do.
class FunctionElideInfo { … };

class CoroIdElider { … };
} // end anonymous namespace

// Go through the list of coro.subfn.addr intrinsics and replace them with the
// provided constant.
static void replaceWithConstant(Constant *Value,
                                SmallVectorImpl<CoroSubFnInst *> &Users) { … }

// See if any operand of the call instruction references the coroutine frame.
static bool operandReferences(CallInst *CI, AllocaInst *Frame, AAResults &AA) { … }

// Look for any tail calls referencing the coroutine frame and remove tail
// attribute from them, since now coroutine frame resides on the stack and tail
// call implies that the function does not references anything on the stack.
// However if it's a musttail call, we cannot remove the tailcall attribute.
// It's safe to keep it there as the musttail call is for symmetric transfer,
// and by that point the frame should have been destroyed and hence not
// interfering with operands.
static void removeTailCallAttribute(AllocaInst *Frame, AAResults &AA) { … }

// Given a resume function @f.resume(%f.frame* %frame), returns the size
// and expected alignment of %f.frame type.
static std::optional<std::pair<uint64_t, Align>>
getFrameLayout(Function *Resume) { … }

// Finds first non alloca instruction in the entry block of a function.
static Instruction *getFirstNonAllocaInTheEntryBlock(Function *F) { … }

#ifndef NDEBUG
static std::unique_ptr<raw_fd_ostream> getOrCreateLogFile() {
  assert(!CoroElideInfoOutputFilename.empty() &&
         "coro-elide-info-output-file shouldn't be empty");
  std::error_code EC;
  auto Result = std::make_unique<raw_fd_ostream>(CoroElideInfoOutputFilename,
                                                 EC, sys::fs::OF_Append);
  if (!EC)
    return Result;
  llvm::errs() << "Error opening coro-elide-info-output-file '"
               << CoroElideInfoOutputFilename << " for appending!\n";
  return std::make_unique<raw_fd_ostream>(2, false); // stderr.
}
#endif

void FunctionElideInfo::collectPostSplitCoroIds() { … }

CoroIdElider::CoroIdElider(CoroIdInst *CoroId, FunctionElideInfo &FEI,
                           AAResults &AA, DominatorTree &DT,
                           OptimizationRemarkEmitter &ORE)
    : … { … }

// To elide heap allocations we need to suppress code blocks guarded by
// llvm.coro.alloc and llvm.coro.free instructions.
void CoroIdElider::elideHeapAllocations(uint64_t FrameSize, Align FrameAlign) { … }

bool CoroIdElider::canCoroBeginEscape(
    const CoroBeginInst *CB, const SmallPtrSetImpl<BasicBlock *> &TIs) const { … }

bool CoroIdElider::lifetimeEligibleForElide() const { … }

bool CoroIdElider::attemptElide() { … }

PreservedAnalyses CoroElidePass::run(Function &F, FunctionAnalysisManager &AM) { … }