ba6c5f8e4e
This is the first PR to enable the prefetch optimization via Propeller based on our [RFC](https://discourse.llvm.org/t/rfc-code-prefetch-insertion/88668/22). It enables emitting special symbols prefixed with `__llvm_prefetch_target` to point to the prefetch targets as specified via directives in the profile. A prefetch target is uniquely identified by its function name, basic block ID, and the subblock index (used when the target is after a call instruction). A new pass is added which sets a field in basic blocks which have prefetch targets. The next PR will add the prefetch insertion logic into the same pass.
102 lines
3.8 KiB
C++
102 lines
3.8 KiB
C++
//===-- InsertCodePrefetch.cpp ---=========--------------------------------===//
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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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/// \file
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/// Code Prefetch Insertion Pass.
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//===----------------------------------------------------------------------===//
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/// This pass inserts code prefetch instructions according to the prefetch
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/// directives in the basic block section profile. The target of a prefetch can
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/// be the beginning of any dynamic basic block, that is the beginning of a
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/// machine basic block, or immediately after a callsite. A global symbol is
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/// emitted at the position of the target so it can be addressed from the
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/// prefetch instruction from any module.
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/StringExtras.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/CodeGen/BasicBlockSectionUtils.h"
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#include "llvm/CodeGen/BasicBlockSectionsProfileReader.h"
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/InitializePasses.h"
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using namespace llvm;
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#define DEBUG_TYPE "insert-code-prefetch"
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namespace {
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class InsertCodePrefetch : public MachineFunctionPass {
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public:
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static char ID;
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InsertCodePrefetch() : MachineFunctionPass(ID) {
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initializeInsertCodePrefetchPass(*PassRegistry::getPassRegistry());
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}
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StringRef getPassName() const override {
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return "Code Prefetch Inserter Pass";
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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// Sets prefetch targets based on the bb section profile.
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bool runOnMachineFunction(MachineFunction &MF) override;
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};
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} // end anonymous namespace
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//===----------------------------------------------------------------------===//
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// Implementation
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//===----------------------------------------------------------------------===//
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char InsertCodePrefetch::ID = 0;
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INITIALIZE_PASS_BEGIN(InsertCodePrefetch, DEBUG_TYPE, "Code prefetch insertion",
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true, false)
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INITIALIZE_PASS_DEPENDENCY(BasicBlockSectionsProfileReaderWrapperPass)
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INITIALIZE_PASS_END(InsertCodePrefetch, DEBUG_TYPE, "Code prefetch insertion",
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true, false)
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bool InsertCodePrefetch::runOnMachineFunction(MachineFunction &MF) {
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assert(MF.getTarget().getBBSectionsType() == BasicBlockSection::List &&
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"BB Sections list not enabled!");
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if (hasInstrProfHashMismatch(MF))
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return false;
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// Set each block's prefetch targets so AsmPrinter can emit a special symbol
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// there.
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SmallVector<CallsiteID> PrefetchTargets =
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getAnalysis<BasicBlockSectionsProfileReaderWrapperPass>()
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.getPrefetchTargetsForFunction(MF.getName());
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DenseMap<UniqueBBID, SmallVector<unsigned>> PrefetchTargetsByBBID;
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for (const auto &Target : PrefetchTargets)
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PrefetchTargetsByBBID[Target.BBID].push_back(Target.CallsiteIndex);
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// Sort and uniquify the callsite indices for every block.
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for (auto &[K, V] : PrefetchTargetsByBBID) {
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llvm::sort(V);
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V.erase(llvm::unique(V), V.end());
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}
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for (auto &MBB : MF) {
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auto R = PrefetchTargetsByBBID.find(*MBB.getBBID());
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if (R == PrefetchTargetsByBBID.end())
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continue;
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MBB.setPrefetchTargetCallsiteIndexes(R->second);
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}
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return false;
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}
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void InsertCodePrefetch::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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AU.addRequired<BasicBlockSectionsProfileReaderWrapperPass>();
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MachineFunctionPass::getAnalysisUsage(AU);
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}
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MachineFunctionPass *llvm::createInsertCodePrefetchPass() {
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return new InsertCodePrefetch();
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}
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