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https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232993 91177308-0d34-0410-b5e6-96231b3b80d8
603 lines
21 KiB
C++
603 lines
21 KiB
C++
//===- MergedLoadStoreMotion.cpp - merge and hoist/sink load/stores -------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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//! \file
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//! \brief This pass performs merges of loads and stores on both sides of a
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// diamond (hammock). It hoists the loads and sinks the stores.
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//
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// The algorithm iteratively hoists two loads to the same address out of a
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// diamond (hammock) and merges them into a single load in the header. Similar
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// it sinks and merges two stores to the tail block (footer). The algorithm
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// iterates over the instructions of one side of the diamond and attempts to
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// find a matching load/store on the other side. It hoists / sinks when it
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// thinks it safe to do so. This optimization helps with eg. hiding load
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// latencies, triggering if-conversion, and reducing static code size.
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//
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//===----------------------------------------------------------------------===//
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//
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//
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// Example:
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// Diamond shaped code before merge:
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//
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// header:
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// br %cond, label %if.then, label %if.else
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// + +
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// + +
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// + +
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// if.then: if.else:
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// %lt = load %addr_l %le = load %addr_l
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// <use %lt> <use %le>
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// <...> <...>
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// store %st, %addr_s store %se, %addr_s
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// br label %if.end br label %if.end
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// + +
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// + +
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// + +
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// if.end ("footer"):
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// <...>
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//
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// Diamond shaped code after merge:
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//
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// header:
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// %l = load %addr_l
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// br %cond, label %if.then, label %if.else
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// + +
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// + +
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// + +
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// if.then: if.else:
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// <use %l> <use %l>
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// <...> <...>
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// br label %if.end br label %if.end
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// + +
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// + +
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// + +
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// if.end ("footer"):
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// %s.sink = phi [%st, if.then], [%se, if.else]
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// <...>
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// store %s.sink, %addr_s
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// <...>
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//
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//
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//===----------------------- TODO -----------------------------------------===//
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//
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// 1) Generalize to regions other than diamonds
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// 2) Be more aggressive merging memory operations
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// Note that both changes require register pressure control
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/CFG.h"
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#include "llvm/Analysis/Loads.h"
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#include "llvm/Analysis/MemoryBuiltins.h"
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#include "llvm/Analysis/MemoryDependenceAnalysis.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/IR/PatternMatch.h"
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#include "llvm/Support/Allocator.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/SSAUpdater.h"
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#include <vector>
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using namespace llvm;
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#define DEBUG_TYPE "mldst-motion"
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//===----------------------------------------------------------------------===//
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// MergedLoadStoreMotion Pass
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//===----------------------------------------------------------------------===//
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namespace {
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class MergedLoadStoreMotion : public FunctionPass {
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AliasAnalysis *AA;
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MemoryDependenceAnalysis *MD;
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public:
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static char ID; // Pass identification, replacement for typeid
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explicit MergedLoadStoreMotion(void)
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: FunctionPass(ID), MD(nullptr), MagicCompileTimeControl(250) {
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initializeMergedLoadStoreMotionPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F) override;
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private:
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// This transformation requires dominator postdominator info
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<TargetLibraryInfoWrapperPass>();
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AU.addRequired<MemoryDependenceAnalysis>();
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AU.addRequired<AliasAnalysis>();
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AU.addPreserved<AliasAnalysis>();
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}
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// Helper routines
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///
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/// \brief Remove instruction from parent and update memory dependence
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/// analysis.
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///
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void removeInstruction(Instruction *Inst);
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BasicBlock *getDiamondTail(BasicBlock *BB);
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bool isDiamondHead(BasicBlock *BB);
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// Routines for hoisting loads
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bool isLoadHoistBarrierInRange(const Instruction& Start,
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const Instruction& End,
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LoadInst* LI);
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LoadInst *canHoistFromBlock(BasicBlock *BB, LoadInst *LI);
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void hoistInstruction(BasicBlock *BB, Instruction *HoistCand,
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Instruction *ElseInst);
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bool isSafeToHoist(Instruction *I) const;
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bool hoistLoad(BasicBlock *BB, LoadInst *HoistCand, LoadInst *ElseInst);
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bool mergeLoads(BasicBlock *BB);
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// Routines for sinking stores
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StoreInst *canSinkFromBlock(BasicBlock *BB, StoreInst *SI);
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PHINode *getPHIOperand(BasicBlock *BB, StoreInst *S0, StoreInst *S1);
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bool isStoreSinkBarrierInRange(const Instruction& Start,
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const Instruction& End,
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AliasAnalysis::Location Loc);
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bool sinkStore(BasicBlock *BB, StoreInst *SinkCand, StoreInst *ElseInst);
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bool mergeStores(BasicBlock *BB);
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// The mergeLoad/Store algorithms could have Size0 * Size1 complexity,
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// where Size0 and Size1 are the #instructions on the two sides of
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// the diamond. The constant chosen here is arbitrary. Compiler Time
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// Control is enforced by the check Size0 * Size1 < MagicCompileTimeControl.
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const int MagicCompileTimeControl;
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};
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char MergedLoadStoreMotion::ID = 0;
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}
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///
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/// \brief createMergedLoadStoreMotionPass - The public interface to this file.
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///
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FunctionPass *llvm::createMergedLoadStoreMotionPass() {
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return new MergedLoadStoreMotion();
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}
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INITIALIZE_PASS_BEGIN(MergedLoadStoreMotion, "mldst-motion",
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"MergedLoadStoreMotion", false, false)
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INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis)
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INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
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INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
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INITIALIZE_PASS_END(MergedLoadStoreMotion, "mldst-motion",
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"MergedLoadStoreMotion", false, false)
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///
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/// \brief Remove instruction from parent and update memory dependence analysis.
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///
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void MergedLoadStoreMotion::removeInstruction(Instruction *Inst) {
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// Notify the memory dependence analysis.
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if (MD) {
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MD->removeInstruction(Inst);
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if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
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MD->invalidateCachedPointerInfo(LI->getPointerOperand());
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if (Inst->getType()->getScalarType()->isPointerTy()) {
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MD->invalidateCachedPointerInfo(Inst);
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}
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}
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Inst->eraseFromParent();
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}
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///
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/// \brief Return tail block of a diamond.
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///
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BasicBlock *MergedLoadStoreMotion::getDiamondTail(BasicBlock *BB) {
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assert(isDiamondHead(BB) && "Basic block is not head of a diamond");
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BranchInst *BI = (BranchInst *)(BB->getTerminator());
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BasicBlock *Succ0 = BI->getSuccessor(0);
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BasicBlock *Tail = Succ0->getTerminator()->getSuccessor(0);
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return Tail;
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}
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///
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/// \brief True when BB is the head of a diamond (hammock)
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///
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bool MergedLoadStoreMotion::isDiamondHead(BasicBlock *BB) {
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if (!BB)
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return false;
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if (!isa<BranchInst>(BB->getTerminator()))
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return false;
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if (BB->getTerminator()->getNumSuccessors() != 2)
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return false;
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BranchInst *BI = (BranchInst *)(BB->getTerminator());
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BasicBlock *Succ0 = BI->getSuccessor(0);
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BasicBlock *Succ1 = BI->getSuccessor(1);
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if (!Succ0->getSinglePredecessor() ||
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Succ0->getTerminator()->getNumSuccessors() != 1)
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return false;
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if (!Succ1->getSinglePredecessor() ||
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Succ1->getTerminator()->getNumSuccessors() != 1)
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return false;
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BasicBlock *Tail = Succ0->getTerminator()->getSuccessor(0);
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// Ignore triangles.
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if (Succ1->getTerminator()->getSuccessor(0) != Tail)
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return false;
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return true;
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}
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///
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/// \brief True when instruction is a hoist barrier for a load
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///
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/// Whenever an instruction could possibly modify the value
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/// being loaded or protect against the load from happening
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/// it is considered a hoist barrier.
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///
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bool MergedLoadStoreMotion::isLoadHoistBarrierInRange(const Instruction& Start,
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const Instruction& End,
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LoadInst* LI) {
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AliasAnalysis::Location Loc = AA->getLocation(LI);
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return AA->canInstructionRangeModRef(Start, End, Loc, AliasAnalysis::Mod);
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}
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///
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/// \brief Decide if a load can be hoisted
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///
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/// When there is a load in \p BB to the same address as \p LI
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/// and it can be hoisted from \p BB, return that load.
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/// Otherwise return Null.
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///
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LoadInst *MergedLoadStoreMotion::canHoistFromBlock(BasicBlock *BB1,
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LoadInst *Load0) {
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for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end(); BBI != BBE;
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++BBI) {
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Instruction *Inst = BBI;
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// Only merge and hoist loads when their result in used only in BB
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if (!isa<LoadInst>(Inst) || Inst->isUsedOutsideOfBlock(BB1))
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continue;
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LoadInst *Load1 = dyn_cast<LoadInst>(Inst);
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BasicBlock *BB0 = Load0->getParent();
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AliasAnalysis::Location Loc0 = AA->getLocation(Load0);
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AliasAnalysis::Location Loc1 = AA->getLocation(Load1);
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if (AA->isMustAlias(Loc0, Loc1) && Load0->isSameOperationAs(Load1) &&
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!isLoadHoistBarrierInRange(BB1->front(), *Load1, Load1) &&
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!isLoadHoistBarrierInRange(BB0->front(), *Load0, Load0)) {
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return Load1;
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}
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}
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return nullptr;
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}
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///
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/// \brief Merge two equivalent instructions \p HoistCand and \p ElseInst into
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/// \p BB
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///
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/// BB is the head of a diamond
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///
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void MergedLoadStoreMotion::hoistInstruction(BasicBlock *BB,
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Instruction *HoistCand,
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Instruction *ElseInst) {
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DEBUG(dbgs() << " Hoist Instruction into BB \n"; BB->dump();
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dbgs() << "Instruction Left\n"; HoistCand->dump(); dbgs() << "\n";
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dbgs() << "Instruction Right\n"; ElseInst->dump(); dbgs() << "\n");
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// Hoist the instruction.
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assert(HoistCand->getParent() != BB);
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// Intersect optional metadata.
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HoistCand->intersectOptionalDataWith(ElseInst);
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HoistCand->dropUnknownMetadata();
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// Prepend point for instruction insert
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Instruction *HoistPt = BB->getTerminator();
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// Merged instruction
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Instruction *HoistedInst = HoistCand->clone();
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// Notify AA of the new value.
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if (isa<LoadInst>(HoistCand))
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AA->copyValue(HoistCand, HoistedInst);
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// Hoist instruction.
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HoistedInst->insertBefore(HoistPt);
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HoistCand->replaceAllUsesWith(HoistedInst);
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removeInstruction(HoistCand);
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// Replace the else block instruction.
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ElseInst->replaceAllUsesWith(HoistedInst);
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removeInstruction(ElseInst);
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}
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///
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/// \brief Return true if no operand of \p I is defined in I's parent block
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///
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bool MergedLoadStoreMotion::isSafeToHoist(Instruction *I) const {
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BasicBlock *Parent = I->getParent();
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
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Instruction *Instr = dyn_cast<Instruction>(I->getOperand(i));
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if (Instr && Instr->getParent() == Parent)
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return false;
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}
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return true;
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}
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///
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/// \brief Merge two equivalent loads and GEPs and hoist into diamond head
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///
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bool MergedLoadStoreMotion::hoistLoad(BasicBlock *BB, LoadInst *L0,
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LoadInst *L1) {
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// Only one definition?
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Instruction *A0 = dyn_cast<Instruction>(L0->getPointerOperand());
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Instruction *A1 = dyn_cast<Instruction>(L1->getPointerOperand());
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if (A0 && A1 && A0->isIdenticalTo(A1) && isSafeToHoist(A0) &&
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A0->hasOneUse() && (A0->getParent() == L0->getParent()) &&
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A1->hasOneUse() && (A1->getParent() == L1->getParent()) &&
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isa<GetElementPtrInst>(A0)) {
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DEBUG(dbgs() << "Hoist Instruction into BB \n"; BB->dump();
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dbgs() << "Instruction Left\n"; L0->dump(); dbgs() << "\n";
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dbgs() << "Instruction Right\n"; L1->dump(); dbgs() << "\n");
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hoistInstruction(BB, A0, A1);
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hoistInstruction(BB, L0, L1);
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return true;
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} else
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return false;
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}
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///
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/// \brief Try to hoist two loads to same address into diamond header
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///
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/// Starting from a diamond head block, iterate over the instructions in one
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/// successor block and try to match a load in the second successor.
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///
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bool MergedLoadStoreMotion::mergeLoads(BasicBlock *BB) {
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bool MergedLoads = false;
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assert(isDiamondHead(BB));
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BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
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BasicBlock *Succ0 = BI->getSuccessor(0);
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BasicBlock *Succ1 = BI->getSuccessor(1);
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// #Instructions in Succ1 for Compile Time Control
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int Size1 = Succ1->size();
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int NLoads = 0;
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for (BasicBlock::iterator BBI = Succ0->begin(), BBE = Succ0->end();
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BBI != BBE;) {
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Instruction *I = BBI;
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++BBI;
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// Only move non-simple (atomic, volatile) loads.
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LoadInst *L0 = dyn_cast<LoadInst>(I);
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if (!L0 || !L0->isSimple() || L0->isUsedOutsideOfBlock(Succ0))
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continue;
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++NLoads;
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if (NLoads * Size1 >= MagicCompileTimeControl)
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break;
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if (LoadInst *L1 = canHoistFromBlock(Succ1, L0)) {
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bool Res = hoistLoad(BB, L0, L1);
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MergedLoads |= Res;
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// Don't attempt to hoist above loads that had not been hoisted.
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if (!Res)
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break;
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}
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}
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return MergedLoads;
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}
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///
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/// \brief True when instruction is a sink barrier for a store
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/// located in Loc
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///
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/// Whenever an instruction could possibly read or modify the
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/// value being stored or protect against the store from
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/// happening it is considered a sink barrier.
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///
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bool MergedLoadStoreMotion::isStoreSinkBarrierInRange(const Instruction& Start,
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const Instruction& End,
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AliasAnalysis::Location
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Loc) {
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return AA->canInstructionRangeModRef(Start, End, Loc, AliasAnalysis::ModRef);
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}
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///
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/// \brief Check if \p BB contains a store to the same address as \p SI
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///
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/// \return The store in \p when it is safe to sink. Otherwise return Null.
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///
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StoreInst *MergedLoadStoreMotion::canSinkFromBlock(BasicBlock *BB1,
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StoreInst *Store0) {
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DEBUG(dbgs() << "can Sink? : "; Store0->dump(); dbgs() << "\n");
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BasicBlock *BB0 = Store0->getParent();
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for (BasicBlock::reverse_iterator RBI = BB1->rbegin(), RBE = BB1->rend();
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RBI != RBE; ++RBI) {
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Instruction *Inst = &*RBI;
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if (!isa<StoreInst>(Inst))
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continue;
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StoreInst *Store1 = cast<StoreInst>(Inst);
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AliasAnalysis::Location Loc0 = AA->getLocation(Store0);
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AliasAnalysis::Location Loc1 = AA->getLocation(Store1);
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if (AA->isMustAlias(Loc0, Loc1) && Store0->isSameOperationAs(Store1) &&
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!isStoreSinkBarrierInRange(*(std::next(BasicBlock::iterator(Store1))),
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BB1->back(), Loc1) &&
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!isStoreSinkBarrierInRange(*(std::next(BasicBlock::iterator(Store0))),
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BB0->back(), Loc0)) {
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return Store1;
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}
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}
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return nullptr;
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}
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///
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/// \brief Create a PHI node in BB for the operands of S0 and S1
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///
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PHINode *MergedLoadStoreMotion::getPHIOperand(BasicBlock *BB, StoreInst *S0,
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StoreInst *S1) {
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// Create a phi if the values mismatch.
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PHINode *NewPN = 0;
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Value *Opd1 = S0->getValueOperand();
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Value *Opd2 = S1->getValueOperand();
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if (Opd1 != Opd2) {
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NewPN = PHINode::Create(Opd1->getType(), 2, Opd2->getName() + ".sink",
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BB->begin());
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NewPN->addIncoming(Opd1, S0->getParent());
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NewPN->addIncoming(Opd2, S1->getParent());
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if (NewPN->getType()->getScalarType()->isPointerTy()) {
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// Notify AA of the new value.
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AA->copyValue(Opd1, NewPN);
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AA->copyValue(Opd2, NewPN);
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// AA needs to be informed when a PHI-use of the pointer value is added
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for (unsigned I = 0, E = NewPN->getNumIncomingValues(); I != E; ++I) {
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unsigned J = PHINode::getOperandNumForIncomingValue(I);
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AA->addEscapingUse(NewPN->getOperandUse(J));
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}
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if (MD)
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MD->invalidateCachedPointerInfo(NewPN);
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}
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}
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return NewPN;
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}
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///
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/// \brief Merge two stores to same address and sink into \p BB
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///
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/// Also sinks GEP instruction computing the store address
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///
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bool MergedLoadStoreMotion::sinkStore(BasicBlock *BB, StoreInst *S0,
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StoreInst *S1) {
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// Only one definition?
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Instruction *A0 = dyn_cast<Instruction>(S0->getPointerOperand());
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|
Instruction *A1 = dyn_cast<Instruction>(S1->getPointerOperand());
|
|
if (A0 && A1 && A0->isIdenticalTo(A1) && A0->hasOneUse() &&
|
|
(A0->getParent() == S0->getParent()) && A1->hasOneUse() &&
|
|
(A1->getParent() == S1->getParent()) && isa<GetElementPtrInst>(A0)) {
|
|
DEBUG(dbgs() << "Sink Instruction into BB \n"; BB->dump();
|
|
dbgs() << "Instruction Left\n"; S0->dump(); dbgs() << "\n";
|
|
dbgs() << "Instruction Right\n"; S1->dump(); dbgs() << "\n");
|
|
// Hoist the instruction.
|
|
BasicBlock::iterator InsertPt = BB->getFirstInsertionPt();
|
|
// Intersect optional metadata.
|
|
S0->intersectOptionalDataWith(S1);
|
|
S0->dropUnknownMetadata();
|
|
|
|
// Create the new store to be inserted at the join point.
|
|
StoreInst *SNew = (StoreInst *)(S0->clone());
|
|
Instruction *ANew = A0->clone();
|
|
AA->copyValue(S0, SNew);
|
|
SNew->insertBefore(InsertPt);
|
|
ANew->insertBefore(SNew);
|
|
|
|
assert(S0->getParent() == A0->getParent());
|
|
assert(S1->getParent() == A1->getParent());
|
|
|
|
PHINode *NewPN = getPHIOperand(BB, S0, S1);
|
|
// New PHI operand? Use it.
|
|
if (NewPN)
|
|
SNew->setOperand(0, NewPN);
|
|
removeInstruction(S0);
|
|
removeInstruction(S1);
|
|
A0->replaceAllUsesWith(ANew);
|
|
removeInstruction(A0);
|
|
A1->replaceAllUsesWith(ANew);
|
|
removeInstruction(A1);
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
///
|
|
/// \brief True when two stores are equivalent and can sink into the footer
|
|
///
|
|
/// Starting from a diamond tail block, iterate over the instructions in one
|
|
/// predecessor block and try to match a store in the second predecessor.
|
|
///
|
|
bool MergedLoadStoreMotion::mergeStores(BasicBlock *T) {
|
|
|
|
bool MergedStores = false;
|
|
assert(T && "Footer of a diamond cannot be empty");
|
|
|
|
pred_iterator PI = pred_begin(T), E = pred_end(T);
|
|
assert(PI != E);
|
|
BasicBlock *Pred0 = *PI;
|
|
++PI;
|
|
BasicBlock *Pred1 = *PI;
|
|
++PI;
|
|
// tail block of a diamond/hammock?
|
|
if (Pred0 == Pred1)
|
|
return false; // No.
|
|
if (PI != E)
|
|
return false; // No. More than 2 predecessors.
|
|
|
|
// #Instructions in Succ1 for Compile Time Control
|
|
int Size1 = Pred1->size();
|
|
int NStores = 0;
|
|
|
|
for (BasicBlock::reverse_iterator RBI = Pred0->rbegin(), RBE = Pred0->rend();
|
|
RBI != RBE;) {
|
|
|
|
Instruction *I = &*RBI;
|
|
++RBI;
|
|
|
|
// Sink move non-simple (atomic, volatile) stores
|
|
if (!isa<StoreInst>(I))
|
|
continue;
|
|
StoreInst *S0 = (StoreInst *)I;
|
|
if (!S0->isSimple())
|
|
continue;
|
|
|
|
++NStores;
|
|
if (NStores * Size1 >= MagicCompileTimeControl)
|
|
break;
|
|
if (StoreInst *S1 = canSinkFromBlock(Pred1, S0)) {
|
|
bool Res = sinkStore(T, S0, S1);
|
|
MergedStores |= Res;
|
|
// Don't attempt to sink below stores that had to stick around
|
|
// But after removal of a store and some of its feeding
|
|
// instruction search again from the beginning since the iterator
|
|
// is likely stale at this point.
|
|
if (!Res)
|
|
break;
|
|
else {
|
|
RBI = Pred0->rbegin();
|
|
RBE = Pred0->rend();
|
|
DEBUG(dbgs() << "Search again\n"; Instruction *I = &*RBI; I->dump());
|
|
}
|
|
}
|
|
}
|
|
return MergedStores;
|
|
}
|
|
///
|
|
/// \brief Run the transformation for each function
|
|
///
|
|
bool MergedLoadStoreMotion::runOnFunction(Function &F) {
|
|
MD = &getAnalysis<MemoryDependenceAnalysis>();
|
|
AA = &getAnalysis<AliasAnalysis>();
|
|
|
|
bool Changed = false;
|
|
DEBUG(dbgs() << "Instruction Merger\n");
|
|
|
|
// Merge unconditional branches, allowing PRE to catch more
|
|
// optimization opportunities.
|
|
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE;) {
|
|
BasicBlock *BB = FI++;
|
|
|
|
// Hoist equivalent loads and sink stores
|
|
// outside diamonds when possible
|
|
if (isDiamondHead(BB)) {
|
|
Changed |= mergeLoads(BB);
|
|
Changed |= mergeStores(getDiamondTail(BB));
|
|
}
|
|
}
|
|
return Changed;
|
|
}
|