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//===- CoroAnnotationElide.cpp - Elide attributed safe coroutine calls ----===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// \file
// This pass transforms all Call or Invoke instructions that are annotated
// "coro_elide_safe" to call the `.noalloc` variant of coroutine instead.
// The frame of the callee coroutine is allocated inside the caller. A pointer
// to the allocated frame will be passed into the `.noalloc` ramp function.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Coroutines/CoroAnnotationElide.h"
#include "llvm/Analysis/CGSCCPassManager.h"
#include "llvm/Analysis/LazyCallGraph.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/IR/Analysis.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Transforms/Utils/CallGraphUpdater.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include <cassert>
using namespace llvm;
#define DEBUG_TYPE "coro-annotation-elide"
static Instruction *getFirstNonAllocaInTheEntryBlock(Function *F) {
for (Instruction &I : F->getEntryBlock())
if (!isa<AllocaInst>(&I))
return &I;
llvm_unreachable("no terminator in the entry block");
}
// Create an alloca in the caller, using FrameSize and FrameAlign as the callee
// coroutine's activation frame.
static Value *allocateFrameInCaller(Function *Caller, uint64_t FrameSize,
Align FrameAlign) {
LLVMContext &C = Caller->getContext();
BasicBlock::iterator InsertPt =
getFirstNonAllocaInTheEntryBlock(Caller)->getIterator();
const DataLayout &DL = Caller->getDataLayout();
auto FrameTy = ArrayType::get(Type::getInt8Ty(C), FrameSize);
auto *Frame = new AllocaInst(FrameTy, DL.getAllocaAddrSpace(), "", InsertPt);
Frame->setAlignment(FrameAlign);
return Frame;
}
// Given a call or invoke instruction to the elide safe coroutine, this function
// does the following:
// - Allocate a frame for the callee coroutine in the caller using alloca.
// - Replace the old CB with a new Call or Invoke to `NewCallee`, with the
// pointer to the frame as an additional argument to NewCallee.
static void processCall(CallBase *CB, Function *Caller, Function *NewCallee,
uint64_t FrameSize, Align FrameAlign) {
// TODO: generate the lifetime intrinsics for the new frame. This will require
// introduction of two pesudo lifetime intrinsics in the frontend around the
// `co_await` expression and convert them to real lifetime intrinsics here.
auto *FramePtr = allocateFrameInCaller(Caller, FrameSize, FrameAlign);
auto NewCBInsertPt = CB->getIterator();
llvm::CallBase *NewCB = nullptr;
SmallVector<Value *, 4> NewArgs;
NewArgs.append(CB->arg_begin(), CB->arg_end());
NewArgs.push_back(FramePtr);
if (auto *CI = dyn_cast<CallInst>(CB)) {
auto *NewCI = CallInst::Create(NewCallee->getFunctionType(), NewCallee,
NewArgs, "", NewCBInsertPt);
NewCI->setTailCallKind(CI->getTailCallKind());
NewCB = NewCI;
} else if (auto *II = dyn_cast<InvokeInst>(CB)) {
NewCB = InvokeInst::Create(NewCallee->getFunctionType(), NewCallee,
II->getNormalDest(), II->getUnwindDest(),
NewArgs, {}, "", NewCBInsertPt);
} else {
llvm_unreachable("CallBase should either be Call or Invoke!");
}
NewCB->setCalledFunction(NewCallee->getFunctionType(), NewCallee);
NewCB->setCallingConv(CB->getCallingConv());
NewCB->setAttributes(CB->getAttributes());
NewCB->setDebugLoc(CB->getDebugLoc());
std::copy(CB->bundle_op_info_begin(), CB->bundle_op_info_end(),
NewCB->bundle_op_info_begin());
NewCB->removeFnAttr(llvm::Attribute::CoroElideSafe);
CB->replaceAllUsesWith(NewCB);
InlineFunctionInfo IFI;
InlineResult IR = InlineFunction(*NewCB, IFI);
if (IR.isSuccess()) {
CB->eraseFromParent();
} else {
NewCB->replaceAllUsesWith(CB);
NewCB->eraseFromParent();
}
}
PreservedAnalyses CoroAnnotationElidePass::run(LazyCallGraph::SCC &C,
CGSCCAnalysisManager &AM,
LazyCallGraph &CG,
CGSCCUpdateResult &UR) {
bool Changed = false;
CallGraphUpdater CGUpdater;
CGUpdater.initialize(CG, C, AM, UR);
auto &FAM =
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C, CG).getManager();
for (LazyCallGraph::Node &N : C) {
Function *Callee = &N.getFunction();
Function *NewCallee = Callee->getParent()->getFunction(
(Callee->getName() + ".noalloc").str());
if (!NewCallee)
continue;
SmallVector<CallBase *, 4> Users;
for (auto *U : Callee->users()) {
if (auto *CB = dyn_cast<CallBase>(U)) {
if (CB->getCalledFunction() == Callee)
Users.push_back(CB);
}
}
auto FramePtrArgPosition = NewCallee->arg_size() - 1;
auto FrameSize =
NewCallee->getParamDereferenceableBytes(FramePtrArgPosition);
auto FrameAlign =
NewCallee->getParamAlign(FramePtrArgPosition).valueOrOne();
auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(*Callee);
for (auto *CB : Users) {
auto *Caller = CB->getFunction();
if (!Caller)
continue;
bool IsCallerPresplitCoroutine = Caller->isPresplitCoroutine();
bool HasAttr = CB->hasFnAttr(llvm::Attribute::CoroElideSafe);
if (IsCallerPresplitCoroutine && HasAttr) {
auto *CallerN = CG.lookup(*Caller);
auto *CallerC = CallerN ? CG.lookupSCC(*CallerN) : nullptr;
// If CallerC is nullptr, it means LazyCallGraph hasn't visited Caller
// yet. Skip the call graph update.
auto ShouldUpdateCallGraph = !!CallerC;
processCall(CB, Caller, NewCallee, FrameSize, FrameAlign);
ORE.emit([&]() {
return OptimizationRemark(DEBUG_TYPE, "CoroAnnotationElide", Caller)
<< "'" << ore::NV("callee", Callee->getName())
<< "' elided in '" << ore::NV("caller", Caller->getName())
<< "'";
});
FAM.invalidate(*Caller, PreservedAnalyses::none());
Changed = true;
if (ShouldUpdateCallGraph)
updateCGAndAnalysisManagerForCGSCCPass(CG, *CallerC, *CallerN, AM, UR,
FAM);
} else {
ORE.emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "CoroAnnotationElide",
Caller)
<< "'" << ore::NV("callee", Callee->getName())
<< "' not elided in '" << ore::NV("caller", Caller->getName())
<< "' (caller_presplit="
<< ore::NV("caller_presplit", IsCallerPresplitCoroutine)
<< ", elide_safe_attr=" << ore::NV("elide_safe_attr", HasAttr)
<< ")";
});
}
}
}
return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
}
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