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//===- AMDGPUInline.cpp - Code to perform simple function inlining --------===//
// 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
/// \file
/// This is AMDGPU specific replacement of the standard inliner.
/// The main purpose is to account for the fact that calls not only expensive
/// on the AMDGPU, but much more expensive if a private memory pointer is
/// passed to a function as an argument. In this situation, we are unable to
/// eliminate private memory in the caller unless inlined and end up with slow
/// and expensive scratch access. Thus, we boost the inline threshold for such
/// functions here.
#include "AMDGPU.h"
#include "llvm/Transforms/IPO.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/CallGraph.h"
#include "llvm/Analysis/InlineCost.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/IPO/Inliner.h"
using namespace llvm;
#define DEBUG_TYPE "inline"
static cl::opt<int>
ArgAllocaCost("amdgpu-inline-arg-alloca-cost", cl::Hidden, cl::init(1500),
cl::desc("Cost of alloca argument"));
// If the amount of scratch memory to eliminate exceeds our ability to allocate
// it into registers we gain nothing by aggressively inlining functions for that
// heuristic.
static cl::opt<unsigned>
ArgAllocaCutoff("amdgpu-inline-arg-alloca-cutoff", cl::Hidden, cl::init(256),
cl::desc("Maximum alloca size to use for inline cost"));
// Inliner constraint to achieve reasonable compilation time
static cl::opt<size_t>
MaxBB("amdgpu-inline-max-bb", cl::Hidden, cl::init(1100),
cl::desc("Maximum BB number allowed in a function after inlining"
" (compile time constraint)"));
namespace {
class AMDGPUInliner : public LegacyInlinerBase {
AMDGPUInliner() : LegacyInlinerBase(ID) {
Params = getInlineParams();
static char ID; // Pass identification, replacement for typeid
unsigned getInlineThreshold(CallSite CS) const;
InlineCost getInlineCost(CallSite CS) override;
bool runOnSCC(CallGraphSCC &SCC) override;
void getAnalysisUsage(AnalysisUsage &AU) const override;
TargetTransformInfoWrapperPass *TTIWP;
InlineParams Params;
} // end anonymous namespace
char AMDGPUInliner::ID = 0;
INITIALIZE_PASS_BEGIN(AMDGPUInliner, "amdgpu-inline",
"AMDGPU Function Integration/Inlining", false, false)
INITIALIZE_PASS_END(AMDGPUInliner, "amdgpu-inline",
"AMDGPU Function Integration/Inlining", false, false)
Pass *llvm::createAMDGPUFunctionInliningPass() { return new AMDGPUInliner(); }
bool AMDGPUInliner::runOnSCC(CallGraphSCC &SCC) {
TTIWP = &getAnalysis<TargetTransformInfoWrapperPass>();
return LegacyInlinerBase::runOnSCC(SCC);
void AMDGPUInliner::getAnalysisUsage(AnalysisUsage &AU) const {
unsigned AMDGPUInliner::getInlineThreshold(CallSite CS) const {
int Thres = Params.DefaultThreshold;
Function *Caller = CS.getCaller();
// Listen to the inlinehint attribute when it would increase the threshold
// and the caller does not need to minimize its size.
Function *Callee = CS.getCalledFunction();
bool InlineHint = Callee && !Callee->isDeclaration() &&
if (InlineHint && Params.HintThreshold && Params.HintThreshold > Thres
&& !Caller->hasFnAttribute(Attribute::MinSize))
Thres = Params.HintThreshold.getValue() *
const DataLayout &DL = Caller->getParent()->getDataLayout();
if (!Callee)
return (unsigned)Thres;
// If we have a pointer to private array passed into a function
// it will not be optimized out, leaving scratch usage.
// Increase the inline threshold to allow inliniting in this case.
uint64_t AllocaSize = 0;
SmallPtrSet<const AllocaInst *, 8> AIVisited;
for (Value *PtrArg : CS.args()) {
PointerType *Ty = dyn_cast<PointerType>(PtrArg->getType());
if (!Ty || (Ty->getAddressSpace() != AMDGPUAS::PRIVATE_ADDRESS &&
Ty->getAddressSpace() != AMDGPUAS::FLAT_ADDRESS))
PtrArg = GetUnderlyingObject(PtrArg, DL);
if (const AllocaInst *AI = dyn_cast<AllocaInst>(PtrArg)) {
if (!AI->isStaticAlloca() || !AIVisited.insert(AI).second)
AllocaSize += DL.getTypeAllocSize(AI->getAllocatedType());
// If the amount of stack memory is excessive we will not be able
// to get rid of the scratch anyway, bail out.
if (AllocaSize > ArgAllocaCutoff) {
AllocaSize = 0;
if (AllocaSize)
Thres += ArgAllocaCost;
return (unsigned)Thres;
// Check if call is just a wrapper around another call.
// In this case we only have call and ret instructions.
static bool isWrapperOnlyCall(CallSite CS) {
Function *Callee = CS.getCalledFunction();
if (!Callee || Callee->size() != 1)
return false;
const BasicBlock &BB = Callee->getEntryBlock();
if (const Instruction *I = BB.getFirstNonPHI()) {
if (!isa<CallInst>(I)) {
return false;
if (isa<ReturnInst>(*std::next(I->getIterator()))) {
LLVM_DEBUG(dbgs() << " Wrapper only call detected: "
<< Callee->getName() << '\n');
return true;
return false;
InlineCost AMDGPUInliner::getInlineCost(CallSite CS) {
Function *Callee = CS.getCalledFunction();
Function *Caller = CS.getCaller();
if (!Callee || Callee->isDeclaration())
return llvm::InlineCost::getNever("undefined callee");
if (CS.isNoInline())
return llvm::InlineCost::getNever("noinline");
TargetTransformInfo &TTI = TTIWP->getTTI(*Callee);
if (!TTI.areInlineCompatible(Caller, Callee))
return llvm::InlineCost::getNever("incompatible");
if (CS.hasFnAttr(Attribute::AlwaysInline)) {
auto IsViable = isInlineViable(*Callee);
if (IsViable)
return llvm::InlineCost::getAlways("alwaysinline viable");
return llvm::InlineCost::getNever(IsViable.message);
if (isWrapperOnlyCall(CS))
return llvm::InlineCost::getAlways("wrapper-only call");
InlineParams LocalParams = Params;
LocalParams.DefaultThreshold = (int)getInlineThreshold(CS);
bool RemarksEnabled = false;
const auto &BBs = Caller->getBasicBlockList();
if (!BBs.empty()) {
auto DI = OptimizationRemark(DEBUG_TYPE, "", DebugLoc(), &BBs.front());
if (DI.isEnabled())
RemarksEnabled = true;
OptimizationRemarkEmitter ORE(Caller);
std::function<AssumptionCache &(Function &)> GetAssumptionCache =
[this](Function &F) -> AssumptionCache & {
return ACT->getAssumptionCache(F);
auto IC = llvm::getInlineCost(cast<CallBase>(*CS.getInstruction()), Callee,
LocalParams, TTI, GetAssumptionCache, None, PSI,
RemarksEnabled ? &ORE : nullptr);
if (IC && !IC.isAlways() && !Callee->hasFnAttribute(Attribute::InlineHint)) {
// Single BB does not increase total BB amount, thus subtract 1
size_t Size = Caller->size() + Callee->size() - 1;
if (MaxBB && Size > MaxBB)
return llvm::InlineCost::getNever("max number of bb exceeded");
return IC;