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sample loader pass. In https://reviews.llvm.org/rG5fb65c02ca5e91e7e1a00e0efdb8edc899f3e4b9, to prevent repeated indirect call promotion for the same indirect call and the same target, we used zero-count value profile to indicate an indirect call has been promoted for a certain target. We removed PromotedInsns cache in the same patch. However, there was a problem in that patch described below, and that problem led me to add PromotedInsns back as a mitigation in https://reviews.llvm.org/rG4ffad1fb489f691825d6c7d78e1626de142f26cf. When we get value profile from metadata by calling getValueProfDataFromInst, we need to specify the maximum possible number of values we expect to read. We uses MaxNumPromotions in the last patch so the maximum number of value information extracted from metadata is MaxNumPromotions. If we have many values including zero-count values when we write the metadata, some of them will be dropped when we read them because we only read MaxNumPromotions values. It will allow repeated indirect call promotion again. We need to make sure if there are values indicating promoted targets, those values need to be saved in metadata with higher priority than other values. The patch fixed that problem. We change to use -1 to represent the count of a promoted target instead of 0 so it is easier to sort the values. When we prepare to update the metadata in updateIDTMetaData, we will sort the values in the descending count order and extract only MaxNumPromotions values to write into metadata. Since -1 is the max uint64_t number, if we have equal to or less than MaxNumPromotions of -1 count values, they will all be kept in metadata. If we have more than MaxNumPromotions of -1 count values, we will only save MaxNumPromotions such values maximally. In such case, we have logic in place in doesHistoryAllowICP to guarantee no more promotion in sample loader pass will happen for the indirect call, because it has been promoted enough. With this change, now we can remove PromotedInsns without problem. Differential Revision: https://reviews.llvm.org/D97350
105 lines
4.3 KiB
C++
105 lines
4.3 KiB
C++
//===-- IndirectCallPromotionAnalysis.cpp - Find promotion candidates ===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Helper methods for identifying profitable indirect call promotion
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// candidates for an instruction when the indirect-call value profile metadata
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// is available.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/IndirectCallPromotionAnalysis.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Analysis/IndirectCallVisitor.h"
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#include "llvm/IR/InstIterator.h"
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#include "llvm/IR/InstVisitor.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/ProfileData/InstrProf.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include <memory>
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using namespace llvm;
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#define DEBUG_TYPE "pgo-icall-prom-analysis"
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// The percent threshold for the direct-call target (this call site vs the
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// remaining call count) for it to be considered as the promotion target.
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static cl::opt<unsigned> ICPRemainingPercentThreshold(
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"icp-remaining-percent-threshold", cl::init(30), cl::Hidden, cl::ZeroOrMore,
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cl::desc("The percentage threshold against remaining unpromoted indirect "
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"call count for the promotion"));
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// The percent threshold for the direct-call target (this call site vs the
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// total call count) for it to be considered as the promotion target.
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static cl::opt<unsigned>
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ICPTotalPercentThreshold("icp-total-percent-threshold", cl::init(5),
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cl::Hidden, cl::ZeroOrMore,
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cl::desc("The percentage threshold against total "
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"count for the promotion"));
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// Set the maximum number of targets to promote for a single indirect-call
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// callsite.
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static cl::opt<unsigned>
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MaxNumPromotions("icp-max-prom", cl::init(3), cl::Hidden, cl::ZeroOrMore,
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cl::desc("Max number of promotions for a single indirect "
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"call callsite"));
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ICallPromotionAnalysis::ICallPromotionAnalysis() {
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ValueDataArray = std::make_unique<InstrProfValueData[]>(MaxNumPromotions);
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}
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bool ICallPromotionAnalysis::isPromotionProfitable(uint64_t Count,
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uint64_t TotalCount,
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uint64_t RemainingCount) {
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return Count * 100 >= ICPRemainingPercentThreshold * RemainingCount &&
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Count * 100 >= ICPTotalPercentThreshold * TotalCount;
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}
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// Indirect-call promotion heuristic. The direct targets are sorted based on
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// the count. Stop at the first target that is not promoted. Returns the
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// number of candidates deemed profitable.
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uint32_t ICallPromotionAnalysis::getProfitablePromotionCandidates(
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const Instruction *Inst, uint32_t NumVals, uint64_t TotalCount) {
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ArrayRef<InstrProfValueData> ValueDataRef(ValueDataArray.get(), NumVals);
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LLVM_DEBUG(dbgs() << " \nWork on callsite " << *Inst
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<< " Num_targets: " << NumVals << "\n");
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uint32_t I = 0;
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uint64_t RemainingCount = TotalCount;
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for (; I < MaxNumPromotions && I < NumVals; I++) {
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uint64_t Count = ValueDataRef[I].Count;
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assert(Count <= RemainingCount);
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LLVM_DEBUG(dbgs() << " Candidate " << I << " Count=" << Count
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<< " Target_func: " << ValueDataRef[I].Value << "\n");
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if (!isPromotionProfitable(Count, TotalCount, RemainingCount)) {
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LLVM_DEBUG(dbgs() << " Not promote: Cold target.\n");
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return I;
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}
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RemainingCount -= Count;
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}
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return I;
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}
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ArrayRef<InstrProfValueData>
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ICallPromotionAnalysis::getPromotionCandidatesForInstruction(
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const Instruction *I, uint32_t &NumVals, uint64_t &TotalCount,
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uint32_t &NumCandidates) {
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bool Res =
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getValueProfDataFromInst(*I, IPVK_IndirectCallTarget, MaxNumPromotions,
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ValueDataArray.get(), NumVals, TotalCount);
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if (!Res) {
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NumCandidates = 0;
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return ArrayRef<InstrProfValueData>();
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}
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NumCandidates = getProfitablePromotionCandidates(I, NumVals, TotalCount);
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return ArrayRef<InstrProfValueData>(ValueDataArray.get(), NumVals);
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}
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