IndirectCallPromotionAnalysis.cpp
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//===-- IndirectCallPromotionAnalysis.cpp - Find promotion candidates ===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Helper methods for identifying profitable indirect call promotion
// candidates for an instruction when the indirect-call value profile metadata
// is available.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/IndirectCallPromotionAnalysis.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/IndirectCallVisitor.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/ProfileData/InstrProf.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include <string>
#include <utility>
#include <vector>
using namespace llvm;
#define DEBUG_TYPE "pgo-icall-prom-analysis"
// The percent threshold for the direct-call target (this call site vs the
// remaining call count) for it to be considered as the promotion target.
static cl::opt<unsigned> ICPRemainingPercentThreshold(
"icp-remaining-percent-threshold", cl::init(30), cl::Hidden, cl::ZeroOrMore,
cl::desc("The percentage threshold against remaining unpromoted indirect "
"call count for the promotion"));
// The percent threshold for the direct-call target (this call site vs the
// total call count) for it to be considered as the promotion target.
static cl::opt<unsigned>
ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5),
cl::Hidden, cl::ZeroOrMore,
cl::desc("The percentage threshold against total "
"count for the promotion"));
// Set the maximum number of targets to promote for a single indirect-call
// callsite.
static cl::opt<unsigned>
MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, cl::ZeroOrMore,
cl::desc("Max number of promotions for a single indirect "
"call callsite"));
ICallPromotionAnalysis::ICallPromotionAnalysis() {
ValueDataArray = std::make_unique<InstrProfValueData[]>(MaxNumPromotions);
}
bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
uint64_t TotalCount,
uint64_t RemainingCount) {
return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
Count * 100 >= ICPTotalPercentThreshold * TotalCount;
}
// Indirect-call promotion heuristic. The direct targets are sorted based on
// the count. Stop at the first target that is not promoted. Returns the
// number of candidates deemed profitable.
uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
<< " Num_targets: " << NumVals << "\n");
uint32_t I = 0;
uint64_t RemainingCount = TotalCount;
for (; I < MaxNumPromotions && I < NumVals; I++) {
uint64_t Count = ValueDataRef[I].Count;
assert(Count <= RemainingCount);
LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
<< " Target_func: " << ValueDataRef[I].Value << "\n");
if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n");
return I;
}
RemainingCount -= Count;
}
return I;
}
ArrayRef<InstrProfValueData>
ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
uint32_t &NumCandidates) {
bool Res =
getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
ValueDataArray.get(), NumVals, TotalCount);
if (!Res) {
NumCandidates = 0;
return ArrayRef<InstrProfValueData>();
}
NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
}