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//===- InlineAlways.cpp - Code to inline always_inline functions ----------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements a custom inliner that handles only functions that
// are marked as "always inline".
#include "llvm/Transforms/IPO/AlwaysInliner.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/InlineCost.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/CallingConv.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/InitializePasses.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Transforms/IPO/Inliner.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
using namespace llvm;
#define DEBUG_TYPE "inline"
PreservedAnalyses AlwaysInlinerPass::run(Module &M,
ModuleAnalysisManager &MAM) {
// Add inline assumptions during code generation.
FunctionAnalysisManager &FAM =
auto GetAssumptionCache = [&](Function &F) -> AssumptionCache & {
return FAM.getResult<AssumptionAnalysis>(F);
auto &PSI = MAM.getResult<ProfileSummaryAnalysis>(M);
SmallSetVector<CallBase *, 16> Calls;
bool Changed = false;
SmallVector<Function *, 16> InlinedFunctions;
for (Function &F : M) {
// When callee coroutine function is inlined into caller coroutine function
// before coro-split pass,
// coro-early pass can not handle this quiet well.
// So we won't inline the coroutine function if it have not been unsplited
if (F.isPresplitCoroutine())
if (!F.isDeclaration() && F.hasFnAttribute(Attribute::AlwaysInline) &&
isInlineViable(F).isSuccess()) {
for (User *U : F.users())
if (auto *CB = dyn_cast<CallBase>(U))
if (CB->getCalledFunction() == &F)
for (CallBase *CB : Calls) {
Function *Caller = CB->getCaller();
OptimizationRemarkEmitter ORE(Caller);
auto OIC = shouldInline(
[&](CallBase &CB) {
return InlineCost::getAlways("always inline attribute");
emitInlinedInto(ORE, CB->getDebugLoc(), CB->getParent(), F, *Caller,
*OIC, false, DEBUG_TYPE);
InlineFunctionInfo IFI(
/*cg=*/nullptr, GetAssumptionCache, &PSI,
InlineResult Res = InlineFunction(
*CB, IFI, &FAM.getResult<AAManager>(F), InsertLifetime);
assert(Res.isSuccess() && "unexpected failure to inline");
// Merge the attributes based on the inlining.
AttributeFuncs::mergeAttributesForInlining(*Caller, F);
Changed = true;
// Remember to try and delete this function afterward. This both avoids
// re-walking the rest of the module and avoids dealing with any iterator
// invalidation issues while deleting functions.
// Remove any live functions.
erase_if(InlinedFunctions, [&](Function *F) {
return !F->isDefTriviallyDead();
// Delete the non-comdat ones from the module and also from our vector.
auto NonComdatBegin = partition(
InlinedFunctions, [&](Function *F) { return F->hasComdat(); });
for (Function *F : make_range(NonComdatBegin, InlinedFunctions.end()))
InlinedFunctions.erase(NonComdatBegin, InlinedFunctions.end());
if (!InlinedFunctions.empty()) {
// Now we just have the comdat functions. Filter out the ones whose comdats
// are not actually dead.
filterDeadComdatFunctions(M, InlinedFunctions);
// The remaining functions are actually dead.
for (Function *F : InlinedFunctions)
return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
namespace {
/// Inliner pass which only handles "always inline" functions.
/// Unlike the \c AlwaysInlinerPass, this uses the more heavyweight \c Inliner
/// base class to provide several facilities such as array alloca merging.
class AlwaysInlinerLegacyPass : public LegacyInlinerBase {
AlwaysInlinerLegacyPass() : LegacyInlinerBase(ID, /*InsertLifetime*/ true) {
AlwaysInlinerLegacyPass(bool InsertLifetime)
: LegacyInlinerBase(ID, InsertLifetime) {
/// Main run interface method. We override here to avoid calling skipSCC().
bool runOnSCC(CallGraphSCC &SCC) override { return inlineCalls(SCC); }
static char ID; // Pass identification, replacement for typeid
InlineCost getInlineCost(CallBase &CB) override;
using llvm::Pass::doFinalization;
bool doFinalization(CallGraph &CG) override {
return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/true);
char AlwaysInlinerLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(AlwaysInlinerLegacyPass, "always-inline",
"Inliner for always_inline functions", false, false)
INITIALIZE_PASS_END(AlwaysInlinerLegacyPass, "always-inline",
"Inliner for always_inline functions", false, false)
Pass *llvm::createAlwaysInlinerLegacyPass(bool InsertLifetime) {
return new AlwaysInlinerLegacyPass(InsertLifetime);
/// Get the inline cost for the always-inliner.
/// The always inliner *only* handles functions which are marked with the
/// attribute to force inlining. As such, it is dramatically simpler and avoids
/// using the powerful (but expensive) inline cost analysis. Instead it uses
/// a very simple and boring direct walk of the instructions looking for
/// impossible-to-inline constructs.
/// Note, it would be possible to go to some lengths to cache the information
/// computed here, but as we only expect to do this for relatively few and
/// small functions which have the explicit attribute to force inlining, it is
/// likely not worth it in practice.
InlineCost AlwaysInlinerLegacyPass::getInlineCost(CallBase &CB) {
Function *Callee = CB.getCalledFunction();
// Only inline direct calls to functions with always-inline attributes
// that are viable for inlining.
if (!Callee)
return InlineCost::getNever("indirect call");
// When callee coroutine function is inlined into caller coroutine function
// before coro-split pass,
// coro-early pass can not handle this quiet well.
// So we won't inline the coroutine function if it have not been unsplited
if (Callee->isPresplitCoroutine())
return InlineCost::getNever("unsplited coroutine call");
// FIXME: We shouldn't even get here for declarations.
if (Callee->isDeclaration())
return InlineCost::getNever("no definition");
if (!CB.hasFnAttr(Attribute::AlwaysInline))
return InlineCost::getNever("no alwaysinline attribute");
auto IsViable = isInlineViable(*Callee);
if (!IsViable.isSuccess())
return InlineCost::getNever(IsViable.getFailureReason());
return InlineCost::getAlways("always inliner");