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IR types. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202827 91177308-0d34-0410-b5e6-96231b3b80d8
1080 lines
39 KiB
C++
1080 lines
39 KiB
C++
//===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===//
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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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// This file promotes memory references to be register references. It promotes
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// alloca instructions which only have loads and stores as uses. An alloca is
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// transformed by using iterated dominator frontiers to place PHI nodes, then
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// traversing the function in depth-first order to rewrite loads and stores as
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// appropriate.
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//
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// The algorithm used here is based on:
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//
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// Sreedhar and Gao. A linear time algorithm for placing phi-nodes.
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// In Proceedings of the 22nd ACM SIGPLAN-SIGACT Symposium on Principles of
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// Programming Languages
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// POPL '95. ACM, New York, NY, 62-73.
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//
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// It has been modified to not explicitly use the DJ graph data structure and to
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// directly compute pruned SSA using per-variable liveness information.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "mem2reg"
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#include "llvm/Transforms/Utils/PromoteMemToReg.h"
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasSetTracker.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/DIBuilder.h"
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#include "llvm/DebugInfo.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.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/IR/Metadata.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include <algorithm>
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#include <queue>
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using namespace llvm;
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STATISTIC(NumLocalPromoted, "Number of alloca's promoted within one block");
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STATISTIC(NumSingleStore, "Number of alloca's promoted with a single store");
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STATISTIC(NumDeadAlloca, "Number of dead alloca's removed");
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STATISTIC(NumPHIInsert, "Number of PHI nodes inserted");
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bool llvm::isAllocaPromotable(const AllocaInst *AI) {
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// FIXME: If the memory unit is of pointer or integer type, we can permit
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// assignments to subsections of the memory unit.
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// Only allow direct and non-volatile loads and stores...
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for (Value::const_use_iterator UI = AI->use_begin(), UE = AI->use_end();
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UI != UE; ++UI) { // Loop over all of the uses of the alloca
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const User *U = *UI;
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if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
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// Note that atomic loads can be transformed; atomic semantics do
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// not have any meaning for a local alloca.
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if (LI->isVolatile())
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return false;
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} else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
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if (SI->getOperand(0) == AI)
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return false; // Don't allow a store OF the AI, only INTO the AI.
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// Note that atomic stores can be transformed; atomic semantics do
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// not have any meaning for a local alloca.
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if (SI->isVolatile())
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return false;
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} else if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U)) {
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if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
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II->getIntrinsicID() != Intrinsic::lifetime_end)
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return false;
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} else if (const BitCastInst *BCI = dyn_cast<BitCastInst>(U)) {
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if (BCI->getType() != Type::getInt8PtrTy(U->getContext()))
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return false;
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if (!onlyUsedByLifetimeMarkers(BCI))
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return false;
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} else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
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if (GEPI->getType() != Type::getInt8PtrTy(U->getContext()))
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return false;
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if (!GEPI->hasAllZeroIndices())
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return false;
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if (!onlyUsedByLifetimeMarkers(GEPI))
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return false;
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} else {
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return false;
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}
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}
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return true;
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}
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namespace {
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struct AllocaInfo {
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SmallVector<BasicBlock *, 32> DefiningBlocks;
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SmallVector<BasicBlock *, 32> UsingBlocks;
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StoreInst *OnlyStore;
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BasicBlock *OnlyBlock;
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bool OnlyUsedInOneBlock;
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Value *AllocaPointerVal;
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DbgDeclareInst *DbgDeclare;
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void clear() {
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DefiningBlocks.clear();
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UsingBlocks.clear();
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OnlyStore = 0;
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OnlyBlock = 0;
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OnlyUsedInOneBlock = true;
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AllocaPointerVal = 0;
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DbgDeclare = 0;
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}
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/// Scan the uses of the specified alloca, filling in the AllocaInfo used
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/// by the rest of the pass to reason about the uses of this alloca.
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void AnalyzeAlloca(AllocaInst *AI) {
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clear();
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// As we scan the uses of the alloca instruction, keep track of stores,
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// and decide whether all of the loads and stores to the alloca are within
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// the same basic block.
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for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
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UI != E;) {
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Instruction *User = cast<Instruction>(*UI++);
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if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
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// Remember the basic blocks which define new values for the alloca
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DefiningBlocks.push_back(SI->getParent());
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AllocaPointerVal = SI->getOperand(0);
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OnlyStore = SI;
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} else {
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LoadInst *LI = cast<LoadInst>(User);
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// Otherwise it must be a load instruction, keep track of variable
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// reads.
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UsingBlocks.push_back(LI->getParent());
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AllocaPointerVal = LI;
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}
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if (OnlyUsedInOneBlock) {
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if (OnlyBlock == 0)
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OnlyBlock = User->getParent();
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else if (OnlyBlock != User->getParent())
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OnlyUsedInOneBlock = false;
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}
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}
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DbgDeclare = FindAllocaDbgDeclare(AI);
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}
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};
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// Data package used by RenamePass()
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class RenamePassData {
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public:
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typedef std::vector<Value *> ValVector;
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RenamePassData() : BB(NULL), Pred(NULL), Values() {}
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RenamePassData(BasicBlock *B, BasicBlock *P, const ValVector &V)
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: BB(B), Pred(P), Values(V) {}
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BasicBlock *BB;
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BasicBlock *Pred;
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ValVector Values;
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void swap(RenamePassData &RHS) {
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std::swap(BB, RHS.BB);
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std::swap(Pred, RHS.Pred);
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Values.swap(RHS.Values);
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}
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};
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/// \brief This assigns and keeps a per-bb relative ordering of load/store
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/// instructions in the block that directly load or store an alloca.
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///
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/// This functionality is important because it avoids scanning large basic
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/// blocks multiple times when promoting many allocas in the same block.
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class LargeBlockInfo {
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/// \brief For each instruction that we track, keep the index of the
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/// instruction.
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///
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/// The index starts out as the number of the instruction from the start of
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/// the block.
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DenseMap<const Instruction *, unsigned> InstNumbers;
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public:
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/// This code only looks at accesses to allocas.
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static bool isInterestingInstruction(const Instruction *I) {
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return (isa<LoadInst>(I) && isa<AllocaInst>(I->getOperand(0))) ||
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(isa<StoreInst>(I) && isa<AllocaInst>(I->getOperand(1)));
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}
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/// Get or calculate the index of the specified instruction.
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unsigned getInstructionIndex(const Instruction *I) {
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assert(isInterestingInstruction(I) &&
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"Not a load/store to/from an alloca?");
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// If we already have this instruction number, return it.
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DenseMap<const Instruction *, unsigned>::iterator It = InstNumbers.find(I);
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if (It != InstNumbers.end())
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return It->second;
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// Scan the whole block to get the instruction. This accumulates
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// information for every interesting instruction in the block, in order to
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// avoid gratuitus rescans.
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const BasicBlock *BB = I->getParent();
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unsigned InstNo = 0;
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for (BasicBlock::const_iterator BBI = BB->begin(), E = BB->end(); BBI != E;
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++BBI)
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if (isInterestingInstruction(BBI))
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InstNumbers[BBI] = InstNo++;
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It = InstNumbers.find(I);
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assert(It != InstNumbers.end() && "Didn't insert instruction?");
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return It->second;
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}
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void deleteValue(const Instruction *I) { InstNumbers.erase(I); }
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void clear() { InstNumbers.clear(); }
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};
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struct PromoteMem2Reg {
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/// The alloca instructions being promoted.
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std::vector<AllocaInst *> Allocas;
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DominatorTree &DT;
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DIBuilder DIB;
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/// An AliasSetTracker object to update. If null, don't update it.
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AliasSetTracker *AST;
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/// Reverse mapping of Allocas.
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DenseMap<AllocaInst *, unsigned> AllocaLookup;
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/// \brief The PhiNodes we're adding.
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///
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/// That map is used to simplify some Phi nodes as we iterate over it, so
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/// it should have deterministic iterators. We could use a MapVector, but
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/// since we already maintain a map from BasicBlock* to a stable numbering
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/// (BBNumbers), the DenseMap is more efficient (also supports removal).
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DenseMap<std::pair<unsigned, unsigned>, PHINode *> NewPhiNodes;
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/// For each PHI node, keep track of which entry in Allocas it corresponds
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/// to.
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DenseMap<PHINode *, unsigned> PhiToAllocaMap;
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/// If we are updating an AliasSetTracker, then for each alloca that is of
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/// pointer type, we keep track of what to copyValue to the inserted PHI
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/// nodes here.
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std::vector<Value *> PointerAllocaValues;
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/// For each alloca, we keep track of the dbg.declare intrinsic that
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/// describes it, if any, so that we can convert it to a dbg.value
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/// intrinsic if the alloca gets promoted.
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SmallVector<DbgDeclareInst *, 8> AllocaDbgDeclares;
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/// The set of basic blocks the renamer has already visited.
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///
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SmallPtrSet<BasicBlock *, 16> Visited;
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/// Contains a stable numbering of basic blocks to avoid non-determinstic
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/// behavior.
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DenseMap<BasicBlock *, unsigned> BBNumbers;
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/// Maps DomTreeNodes to their level in the dominator tree.
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DenseMap<DomTreeNode *, unsigned> DomLevels;
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/// Lazily compute the number of predecessors a block has.
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DenseMap<const BasicBlock *, unsigned> BBNumPreds;
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public:
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PromoteMem2Reg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,
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AliasSetTracker *AST)
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: Allocas(Allocas.begin(), Allocas.end()), DT(DT),
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DIB(*DT.getRoot()->getParent()->getParent()), AST(AST) {}
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void run();
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private:
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void RemoveFromAllocasList(unsigned &AllocaIdx) {
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Allocas[AllocaIdx] = Allocas.back();
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Allocas.pop_back();
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--AllocaIdx;
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}
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unsigned getNumPreds(const BasicBlock *BB) {
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unsigned &NP = BBNumPreds[BB];
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if (NP == 0)
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NP = std::distance(pred_begin(BB), pred_end(BB)) + 1;
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return NP - 1;
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}
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void DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum,
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AllocaInfo &Info);
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void ComputeLiveInBlocks(AllocaInst *AI, AllocaInfo &Info,
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const SmallPtrSet<BasicBlock *, 32> &DefBlocks,
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SmallPtrSet<BasicBlock *, 32> &LiveInBlocks);
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void RenamePass(BasicBlock *BB, BasicBlock *Pred,
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RenamePassData::ValVector &IncVals,
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std::vector<RenamePassData> &Worklist);
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bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version);
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};
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} // end of anonymous namespace
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static void removeLifetimeIntrinsicUsers(AllocaInst *AI) {
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// Knowing that this alloca is promotable, we know that it's safe to kill all
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// instructions except for load and store.
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for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end();
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UI != UE;) {
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Instruction *I = cast<Instruction>(*UI);
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++UI;
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if (isa<LoadInst>(I) || isa<StoreInst>(I))
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continue;
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if (!I->getType()->isVoidTy()) {
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// The only users of this bitcast/GEP instruction are lifetime intrinsics.
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// Follow the use/def chain to erase them now instead of leaving it for
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// dead code elimination later.
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for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
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UI != UE;) {
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Instruction *Inst = cast<Instruction>(*UI);
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++UI;
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Inst->eraseFromParent();
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}
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}
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I->eraseFromParent();
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}
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}
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/// \brief Rewrite as many loads as possible given a single store.
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///
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/// When there is only a single store, we can use the domtree to trivially
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/// replace all of the dominated loads with the stored value. Do so, and return
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/// true if this has successfully promoted the alloca entirely. If this returns
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/// false there were some loads which were not dominated by the single store
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/// and thus must be phi-ed with undef. We fall back to the standard alloca
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/// promotion algorithm in that case.
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static bool rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info,
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LargeBlockInfo &LBI,
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DominatorTree &DT,
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AliasSetTracker *AST) {
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StoreInst *OnlyStore = Info.OnlyStore;
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bool StoringGlobalVal = !isa<Instruction>(OnlyStore->getOperand(0));
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BasicBlock *StoreBB = OnlyStore->getParent();
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int StoreIndex = -1;
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// Clear out UsingBlocks. We will reconstruct it here if needed.
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Info.UsingBlocks.clear();
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for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E;) {
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Instruction *UserInst = cast<Instruction>(*UI++);
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if (!isa<LoadInst>(UserInst)) {
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assert(UserInst == OnlyStore && "Should only have load/stores");
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continue;
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}
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LoadInst *LI = cast<LoadInst>(UserInst);
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// Okay, if we have a load from the alloca, we want to replace it with the
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// only value stored to the alloca. We can do this if the value is
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// dominated by the store. If not, we use the rest of the mem2reg machinery
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// to insert the phi nodes as needed.
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if (!StoringGlobalVal) { // Non-instructions are always dominated.
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if (LI->getParent() == StoreBB) {
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// If we have a use that is in the same block as the store, compare the
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// indices of the two instructions to see which one came first. If the
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// load came before the store, we can't handle it.
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if (StoreIndex == -1)
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StoreIndex = LBI.getInstructionIndex(OnlyStore);
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if (unsigned(StoreIndex) > LBI.getInstructionIndex(LI)) {
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// Can't handle this load, bail out.
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Info.UsingBlocks.push_back(StoreBB);
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continue;
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}
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} else if (LI->getParent() != StoreBB &&
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!DT.dominates(StoreBB, LI->getParent())) {
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// If the load and store are in different blocks, use BB dominance to
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// check their relationships. If the store doesn't dom the use, bail
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// out.
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Info.UsingBlocks.push_back(LI->getParent());
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continue;
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}
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}
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// Otherwise, we *can* safely rewrite this load.
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Value *ReplVal = OnlyStore->getOperand(0);
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// If the replacement value is the load, this must occur in unreachable
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// code.
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if (ReplVal == LI)
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ReplVal = UndefValue::get(LI->getType());
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LI->replaceAllUsesWith(ReplVal);
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if (AST && LI->getType()->isPointerTy())
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AST->deleteValue(LI);
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LI->eraseFromParent();
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LBI.deleteValue(LI);
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}
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// Finally, after the scan, check to see if the store is all that is left.
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if (!Info.UsingBlocks.empty())
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return false; // If not, we'll have to fall back for the remainder.
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// Record debuginfo for the store and remove the declaration's
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// debuginfo.
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if (DbgDeclareInst *DDI = Info.DbgDeclare) {
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DIBuilder DIB(*AI->getParent()->getParent()->getParent());
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ConvertDebugDeclareToDebugValue(DDI, Info.OnlyStore, DIB);
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DDI->eraseFromParent();
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LBI.deleteValue(DDI);
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}
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// Remove the (now dead) store and alloca.
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Info.OnlyStore->eraseFromParent();
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LBI.deleteValue(Info.OnlyStore);
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if (AST)
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AST->deleteValue(AI);
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AI->eraseFromParent();
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LBI.deleteValue(AI);
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return true;
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}
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/// Many allocas are only used within a single basic block. If this is the
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/// case, avoid traversing the CFG and inserting a lot of potentially useless
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/// PHI nodes by just performing a single linear pass over the basic block
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/// using the Alloca.
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///
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/// If we cannot promote this alloca (because it is read before it is written),
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/// return true. This is necessary in cases where, due to control flow, the
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/// alloca is potentially undefined on some control flow paths. e.g. code like
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/// this is potentially correct:
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///
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/// for (...) { if (c) { A = undef; undef = B; } }
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///
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/// ... so long as A is not used before undef is set.
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static void promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info,
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LargeBlockInfo &LBI,
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AliasSetTracker *AST) {
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// The trickiest case to handle is when we have large blocks. Because of this,
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// this code is optimized assuming that large blocks happen. This does not
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// significantly pessimize the small block case. This uses LargeBlockInfo to
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// make it efficient to get the index of various operations in the block.
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// Walk the use-def list of the alloca, getting the locations of all stores.
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typedef SmallVector<std::pair<unsigned, StoreInst *>, 64> StoresByIndexTy;
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StoresByIndexTy StoresByIndex;
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for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E;
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++UI)
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if (StoreInst *SI = dyn_cast<StoreInst>(*UI))
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StoresByIndex.push_back(std::make_pair(LBI.getInstructionIndex(SI), SI));
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// Sort the stores by their index, making it efficient to do a lookup with a
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// binary search.
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std::sort(StoresByIndex.begin(), StoresByIndex.end(), less_first());
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// Walk all of the loads from this alloca, replacing them with the nearest
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// store above them, if any.
|
|
for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end(); UI != E;) {
|
|
LoadInst *LI = dyn_cast<LoadInst>(*UI++);
|
|
if (!LI)
|
|
continue;
|
|
|
|
unsigned LoadIdx = LBI.getInstructionIndex(LI);
|
|
|
|
// Find the nearest store that has a lower index than this load.
|
|
StoresByIndexTy::iterator I =
|
|
std::lower_bound(StoresByIndex.begin(), StoresByIndex.end(),
|
|
std::make_pair(LoadIdx, static_cast<StoreInst *>(0)),
|
|
less_first());
|
|
|
|
if (I == StoresByIndex.begin())
|
|
// If there is no store before this load, the load takes the undef value.
|
|
LI->replaceAllUsesWith(UndefValue::get(LI->getType()));
|
|
else
|
|
// Otherwise, there was a store before this load, the load takes its value.
|
|
LI->replaceAllUsesWith(std::prev(I)->second->getOperand(0));
|
|
|
|
if (AST && LI->getType()->isPointerTy())
|
|
AST->deleteValue(LI);
|
|
LI->eraseFromParent();
|
|
LBI.deleteValue(LI);
|
|
}
|
|
|
|
// Remove the (now dead) stores and alloca.
|
|
while (!AI->use_empty()) {
|
|
StoreInst *SI = cast<StoreInst>(AI->use_back());
|
|
// Record debuginfo for the store before removing it.
|
|
if (DbgDeclareInst *DDI = Info.DbgDeclare) {
|
|
DIBuilder DIB(*AI->getParent()->getParent()->getParent());
|
|
ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
|
|
}
|
|
SI->eraseFromParent();
|
|
LBI.deleteValue(SI);
|
|
}
|
|
|
|
if (AST)
|
|
AST->deleteValue(AI);
|
|
AI->eraseFromParent();
|
|
LBI.deleteValue(AI);
|
|
|
|
// The alloca's debuginfo can be removed as well.
|
|
if (DbgDeclareInst *DDI = Info.DbgDeclare) {
|
|
DDI->eraseFromParent();
|
|
LBI.deleteValue(DDI);
|
|
}
|
|
|
|
++NumLocalPromoted;
|
|
}
|
|
|
|
void PromoteMem2Reg::run() {
|
|
Function &F = *DT.getRoot()->getParent();
|
|
|
|
if (AST)
|
|
PointerAllocaValues.resize(Allocas.size());
|
|
AllocaDbgDeclares.resize(Allocas.size());
|
|
|
|
AllocaInfo Info;
|
|
LargeBlockInfo LBI;
|
|
|
|
for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
|
|
AllocaInst *AI = Allocas[AllocaNum];
|
|
|
|
assert(isAllocaPromotable(AI) && "Cannot promote non-promotable alloca!");
|
|
assert(AI->getParent()->getParent() == &F &&
|
|
"All allocas should be in the same function, which is same as DF!");
|
|
|
|
removeLifetimeIntrinsicUsers(AI);
|
|
|
|
if (AI->use_empty()) {
|
|
// If there are no uses of the alloca, just delete it now.
|
|
if (AST)
|
|
AST->deleteValue(AI);
|
|
AI->eraseFromParent();
|
|
|
|
// Remove the alloca from the Allocas list, since it has been processed
|
|
RemoveFromAllocasList(AllocaNum);
|
|
++NumDeadAlloca;
|
|
continue;
|
|
}
|
|
|
|
// Calculate the set of read and write-locations for each alloca. This is
|
|
// analogous to finding the 'uses' and 'definitions' of each variable.
|
|
Info.AnalyzeAlloca(AI);
|
|
|
|
// If there is only a single store to this value, replace any loads of
|
|
// it that are directly dominated by the definition with the value stored.
|
|
if (Info.DefiningBlocks.size() == 1) {
|
|
if (rewriteSingleStoreAlloca(AI, Info, LBI, DT, AST)) {
|
|
// The alloca has been processed, move on.
|
|
RemoveFromAllocasList(AllocaNum);
|
|
++NumSingleStore;
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// If the alloca is only read and written in one basic block, just perform a
|
|
// linear sweep over the block to eliminate it.
|
|
if (Info.OnlyUsedInOneBlock) {
|
|
promoteSingleBlockAlloca(AI, Info, LBI, AST);
|
|
|
|
// The alloca has been processed, move on.
|
|
RemoveFromAllocasList(AllocaNum);
|
|
continue;
|
|
}
|
|
|
|
// If we haven't computed dominator tree levels, do so now.
|
|
if (DomLevels.empty()) {
|
|
SmallVector<DomTreeNode *, 32> Worklist;
|
|
|
|
DomTreeNode *Root = DT.getRootNode();
|
|
DomLevels[Root] = 0;
|
|
Worklist.push_back(Root);
|
|
|
|
while (!Worklist.empty()) {
|
|
DomTreeNode *Node = Worklist.pop_back_val();
|
|
unsigned ChildLevel = DomLevels[Node] + 1;
|
|
for (DomTreeNode::iterator CI = Node->begin(), CE = Node->end();
|
|
CI != CE; ++CI) {
|
|
DomLevels[*CI] = ChildLevel;
|
|
Worklist.push_back(*CI);
|
|
}
|
|
}
|
|
}
|
|
|
|
// If we haven't computed a numbering for the BB's in the function, do so
|
|
// now.
|
|
if (BBNumbers.empty()) {
|
|
unsigned ID = 0;
|
|
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
|
|
BBNumbers[I] = ID++;
|
|
}
|
|
|
|
// If we have an AST to keep updated, remember some pointer value that is
|
|
// stored into the alloca.
|
|
if (AST)
|
|
PointerAllocaValues[AllocaNum] = Info.AllocaPointerVal;
|
|
|
|
// Remember the dbg.declare intrinsic describing this alloca, if any.
|
|
if (Info.DbgDeclare)
|
|
AllocaDbgDeclares[AllocaNum] = Info.DbgDeclare;
|
|
|
|
// Keep the reverse mapping of the 'Allocas' array for the rename pass.
|
|
AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
|
|
|
|
// At this point, we're committed to promoting the alloca using IDF's, and
|
|
// the standard SSA construction algorithm. Determine which blocks need PHI
|
|
// nodes and see if we can optimize out some work by avoiding insertion of
|
|
// dead phi nodes.
|
|
DetermineInsertionPoint(AI, AllocaNum, Info);
|
|
}
|
|
|
|
if (Allocas.empty())
|
|
return; // All of the allocas must have been trivial!
|
|
|
|
LBI.clear();
|
|
|
|
// Set the incoming values for the basic block to be null values for all of
|
|
// the alloca's. We do this in case there is a load of a value that has not
|
|
// been stored yet. In this case, it will get this null value.
|
|
//
|
|
RenamePassData::ValVector Values(Allocas.size());
|
|
for (unsigned i = 0, e = Allocas.size(); i != e; ++i)
|
|
Values[i] = UndefValue::get(Allocas[i]->getAllocatedType());
|
|
|
|
// Walks all basic blocks in the function performing the SSA rename algorithm
|
|
// and inserting the phi nodes we marked as necessary
|
|
//
|
|
std::vector<RenamePassData> RenamePassWorkList;
|
|
RenamePassWorkList.push_back(RenamePassData(F.begin(), 0, Values));
|
|
do {
|
|
RenamePassData RPD;
|
|
RPD.swap(RenamePassWorkList.back());
|
|
RenamePassWorkList.pop_back();
|
|
// RenamePass may add new worklist entries.
|
|
RenamePass(RPD.BB, RPD.Pred, RPD.Values, RenamePassWorkList);
|
|
} while (!RenamePassWorkList.empty());
|
|
|
|
// The renamer uses the Visited set to avoid infinite loops. Clear it now.
|
|
Visited.clear();
|
|
|
|
// Remove the allocas themselves from the function.
|
|
for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
|
|
Instruction *A = Allocas[i];
|
|
|
|
// If there are any uses of the alloca instructions left, they must be in
|
|
// unreachable basic blocks that were not processed by walking the dominator
|
|
// tree. Just delete the users now.
|
|
if (!A->use_empty())
|
|
A->replaceAllUsesWith(UndefValue::get(A->getType()));
|
|
if (AST)
|
|
AST->deleteValue(A);
|
|
A->eraseFromParent();
|
|
}
|
|
|
|
// Remove alloca's dbg.declare instrinsics from the function.
|
|
for (unsigned i = 0, e = AllocaDbgDeclares.size(); i != e; ++i)
|
|
if (DbgDeclareInst *DDI = AllocaDbgDeclares[i])
|
|
DDI->eraseFromParent();
|
|
|
|
// Loop over all of the PHI nodes and see if there are any that we can get
|
|
// rid of because they merge all of the same incoming values. This can
|
|
// happen due to undef values coming into the PHI nodes. This process is
|
|
// iterative, because eliminating one PHI node can cause others to be removed.
|
|
bool EliminatedAPHI = true;
|
|
while (EliminatedAPHI) {
|
|
EliminatedAPHI = false;
|
|
|
|
// Iterating over NewPhiNodes is deterministic, so it is safe to try to
|
|
// simplify and RAUW them as we go. If it was not, we could add uses to
|
|
// the values we replace with in a non-deterministic order, thus creating
|
|
// non-deterministic def->use chains.
|
|
for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator
|
|
I = NewPhiNodes.begin(),
|
|
E = NewPhiNodes.end();
|
|
I != E;) {
|
|
PHINode *PN = I->second;
|
|
|
|
// If this PHI node merges one value and/or undefs, get the value.
|
|
if (Value *V = SimplifyInstruction(PN, 0, 0, &DT)) {
|
|
if (AST && PN->getType()->isPointerTy())
|
|
AST->deleteValue(PN);
|
|
PN->replaceAllUsesWith(V);
|
|
PN->eraseFromParent();
|
|
NewPhiNodes.erase(I++);
|
|
EliminatedAPHI = true;
|
|
continue;
|
|
}
|
|
++I;
|
|
}
|
|
}
|
|
|
|
// At this point, the renamer has added entries to PHI nodes for all reachable
|
|
// code. Unfortunately, there may be unreachable blocks which the renamer
|
|
// hasn't traversed. If this is the case, the PHI nodes may not
|
|
// have incoming values for all predecessors. Loop over all PHI nodes we have
|
|
// created, inserting undef values if they are missing any incoming values.
|
|
//
|
|
for (DenseMap<std::pair<unsigned, unsigned>, PHINode *>::iterator
|
|
I = NewPhiNodes.begin(),
|
|
E = NewPhiNodes.end();
|
|
I != E; ++I) {
|
|
// We want to do this once per basic block. As such, only process a block
|
|
// when we find the PHI that is the first entry in the block.
|
|
PHINode *SomePHI = I->second;
|
|
BasicBlock *BB = SomePHI->getParent();
|
|
if (&BB->front() != SomePHI)
|
|
continue;
|
|
|
|
// Only do work here if there the PHI nodes are missing incoming values. We
|
|
// know that all PHI nodes that were inserted in a block will have the same
|
|
// number of incoming values, so we can just check any of them.
|
|
if (SomePHI->getNumIncomingValues() == getNumPreds(BB))
|
|
continue;
|
|
|
|
// Get the preds for BB.
|
|
SmallVector<BasicBlock *, 16> Preds(pred_begin(BB), pred_end(BB));
|
|
|
|
// Ok, now we know that all of the PHI nodes are missing entries for some
|
|
// basic blocks. Start by sorting the incoming predecessors for efficient
|
|
// access.
|
|
std::sort(Preds.begin(), Preds.end());
|
|
|
|
// Now we loop through all BB's which have entries in SomePHI and remove
|
|
// them from the Preds list.
|
|
for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
|
|
// Do a log(n) search of the Preds list for the entry we want.
|
|
SmallVectorImpl<BasicBlock *>::iterator EntIt = std::lower_bound(
|
|
Preds.begin(), Preds.end(), SomePHI->getIncomingBlock(i));
|
|
assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i) &&
|
|
"PHI node has entry for a block which is not a predecessor!");
|
|
|
|
// Remove the entry
|
|
Preds.erase(EntIt);
|
|
}
|
|
|
|
// At this point, the blocks left in the preds list must have dummy
|
|
// entries inserted into every PHI nodes for the block. Update all the phi
|
|
// nodes in this block that we are inserting (there could be phis before
|
|
// mem2reg runs).
|
|
unsigned NumBadPreds = SomePHI->getNumIncomingValues();
|
|
BasicBlock::iterator BBI = BB->begin();
|
|
while ((SomePHI = dyn_cast<PHINode>(BBI++)) &&
|
|
SomePHI->getNumIncomingValues() == NumBadPreds) {
|
|
Value *UndefVal = UndefValue::get(SomePHI->getType());
|
|
for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred)
|
|
SomePHI->addIncoming(UndefVal, Preds[pred]);
|
|
}
|
|
}
|
|
|
|
NewPhiNodes.clear();
|
|
}
|
|
|
|
/// \brief Determine which blocks the value is live in.
|
|
///
|
|
/// These are blocks which lead to uses. Knowing this allows us to avoid
|
|
/// inserting PHI nodes into blocks which don't lead to uses (thus, the
|
|
/// inserted phi nodes would be dead).
|
|
void PromoteMem2Reg::ComputeLiveInBlocks(
|
|
AllocaInst *AI, AllocaInfo &Info,
|
|
const SmallPtrSet<BasicBlock *, 32> &DefBlocks,
|
|
SmallPtrSet<BasicBlock *, 32> &LiveInBlocks) {
|
|
|
|
// To determine liveness, we must iterate through the predecessors of blocks
|
|
// where the def is live. Blocks are added to the worklist if we need to
|
|
// check their predecessors. Start with all the using blocks.
|
|
SmallVector<BasicBlock *, 64> LiveInBlockWorklist(Info.UsingBlocks.begin(),
|
|
Info.UsingBlocks.end());
|
|
|
|
// If any of the using blocks is also a definition block, check to see if the
|
|
// definition occurs before or after the use. If it happens before the use,
|
|
// the value isn't really live-in.
|
|
for (unsigned i = 0, e = LiveInBlockWorklist.size(); i != e; ++i) {
|
|
BasicBlock *BB = LiveInBlockWorklist[i];
|
|
if (!DefBlocks.count(BB))
|
|
continue;
|
|
|
|
// Okay, this is a block that both uses and defines the value. If the first
|
|
// reference to the alloca is a def (store), then we know it isn't live-in.
|
|
for (BasicBlock::iterator I = BB->begin();; ++I) {
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
|
|
if (SI->getOperand(1) != AI)
|
|
continue;
|
|
|
|
// We found a store to the alloca before a load. The alloca is not
|
|
// actually live-in here.
|
|
LiveInBlockWorklist[i] = LiveInBlockWorklist.back();
|
|
LiveInBlockWorklist.pop_back();
|
|
--i, --e;
|
|
break;
|
|
}
|
|
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
|
|
if (LI->getOperand(0) != AI)
|
|
continue;
|
|
|
|
// Okay, we found a load before a store to the alloca. It is actually
|
|
// live into this block.
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Now that we have a set of blocks where the phi is live-in, recursively add
|
|
// their predecessors until we find the full region the value is live.
|
|
while (!LiveInBlockWorklist.empty()) {
|
|
BasicBlock *BB = LiveInBlockWorklist.pop_back_val();
|
|
|
|
// The block really is live in here, insert it into the set. If already in
|
|
// the set, then it has already been processed.
|
|
if (!LiveInBlocks.insert(BB))
|
|
continue;
|
|
|
|
// Since the value is live into BB, it is either defined in a predecessor or
|
|
// live into it to. Add the preds to the worklist unless they are a
|
|
// defining block.
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
|
|
BasicBlock *P = *PI;
|
|
|
|
// The value is not live into a predecessor if it defines the value.
|
|
if (DefBlocks.count(P))
|
|
continue;
|
|
|
|
// Otherwise it is, add to the worklist.
|
|
LiveInBlockWorklist.push_back(P);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// At this point, we're committed to promoting the alloca using IDF's, and the
|
|
/// standard SSA construction algorithm. Determine which blocks need phi nodes
|
|
/// and see if we can optimize out some work by avoiding insertion of dead phi
|
|
/// nodes.
|
|
void PromoteMem2Reg::DetermineInsertionPoint(AllocaInst *AI, unsigned AllocaNum,
|
|
AllocaInfo &Info) {
|
|
// Unique the set of defining blocks for efficient lookup.
|
|
SmallPtrSet<BasicBlock *, 32> DefBlocks;
|
|
DefBlocks.insert(Info.DefiningBlocks.begin(), Info.DefiningBlocks.end());
|
|
|
|
// Determine which blocks the value is live in. These are blocks which lead
|
|
// to uses.
|
|
SmallPtrSet<BasicBlock *, 32> LiveInBlocks;
|
|
ComputeLiveInBlocks(AI, Info, DefBlocks, LiveInBlocks);
|
|
|
|
// Use a priority queue keyed on dominator tree level so that inserted nodes
|
|
// are handled from the bottom of the dominator tree upwards.
|
|
typedef std::pair<DomTreeNode *, unsigned> DomTreeNodePair;
|
|
typedef std::priority_queue<DomTreeNodePair, SmallVector<DomTreeNodePair, 32>,
|
|
less_second> IDFPriorityQueue;
|
|
IDFPriorityQueue PQ;
|
|
|
|
for (SmallPtrSet<BasicBlock *, 32>::const_iterator I = DefBlocks.begin(),
|
|
E = DefBlocks.end();
|
|
I != E; ++I) {
|
|
if (DomTreeNode *Node = DT.getNode(*I))
|
|
PQ.push(std::make_pair(Node, DomLevels[Node]));
|
|
}
|
|
|
|
SmallVector<std::pair<unsigned, BasicBlock *>, 32> DFBlocks;
|
|
SmallPtrSet<DomTreeNode *, 32> Visited;
|
|
SmallVector<DomTreeNode *, 32> Worklist;
|
|
while (!PQ.empty()) {
|
|
DomTreeNodePair RootPair = PQ.top();
|
|
PQ.pop();
|
|
DomTreeNode *Root = RootPair.first;
|
|
unsigned RootLevel = RootPair.second;
|
|
|
|
// Walk all dominator tree children of Root, inspecting their CFG edges with
|
|
// targets elsewhere on the dominator tree. Only targets whose level is at
|
|
// most Root's level are added to the iterated dominance frontier of the
|
|
// definition set.
|
|
|
|
Worklist.clear();
|
|
Worklist.push_back(Root);
|
|
|
|
while (!Worklist.empty()) {
|
|
DomTreeNode *Node = Worklist.pop_back_val();
|
|
BasicBlock *BB = Node->getBlock();
|
|
|
|
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE;
|
|
++SI) {
|
|
DomTreeNode *SuccNode = DT.getNode(*SI);
|
|
|
|
// Quickly skip all CFG edges that are also dominator tree edges instead
|
|
// of catching them below.
|
|
if (SuccNode->getIDom() == Node)
|
|
continue;
|
|
|
|
unsigned SuccLevel = DomLevels[SuccNode];
|
|
if (SuccLevel > RootLevel)
|
|
continue;
|
|
|
|
if (!Visited.insert(SuccNode))
|
|
continue;
|
|
|
|
BasicBlock *SuccBB = SuccNode->getBlock();
|
|
if (!LiveInBlocks.count(SuccBB))
|
|
continue;
|
|
|
|
DFBlocks.push_back(std::make_pair(BBNumbers[SuccBB], SuccBB));
|
|
if (!DefBlocks.count(SuccBB))
|
|
PQ.push(std::make_pair(SuccNode, SuccLevel));
|
|
}
|
|
|
|
for (DomTreeNode::iterator CI = Node->begin(), CE = Node->end(); CI != CE;
|
|
++CI) {
|
|
if (!Visited.count(*CI))
|
|
Worklist.push_back(*CI);
|
|
}
|
|
}
|
|
}
|
|
|
|
if (DFBlocks.size() > 1)
|
|
std::sort(DFBlocks.begin(), DFBlocks.end());
|
|
|
|
unsigned CurrentVersion = 0;
|
|
for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i)
|
|
QueuePhiNode(DFBlocks[i].second, AllocaNum, CurrentVersion);
|
|
}
|
|
|
|
/// \brief Queue a phi-node to be added to a basic-block for a specific Alloca.
|
|
///
|
|
/// Returns true if there wasn't already a phi-node for that variable
|
|
bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
|
|
unsigned &Version) {
|
|
// Look up the basic-block in question.
|
|
PHINode *&PN = NewPhiNodes[std::make_pair(BBNumbers[BB], AllocaNo)];
|
|
|
|
// If the BB already has a phi node added for the i'th alloca then we're done!
|
|
if (PN)
|
|
return false;
|
|
|
|
// Create a PhiNode using the dereferenced type... and add the phi-node to the
|
|
// BasicBlock.
|
|
PN = PHINode::Create(Allocas[AllocaNo]->getAllocatedType(), getNumPreds(BB),
|
|
Allocas[AllocaNo]->getName() + "." + Twine(Version++),
|
|
BB->begin());
|
|
++NumPHIInsert;
|
|
PhiToAllocaMap[PN] = AllocaNo;
|
|
|
|
if (AST && PN->getType()->isPointerTy())
|
|
AST->copyValue(PointerAllocaValues[AllocaNo], PN);
|
|
|
|
return true;
|
|
}
|
|
|
|
/// \brief Recursively traverse the CFG of the function, renaming loads and
|
|
/// stores to the allocas which we are promoting.
|
|
///
|
|
/// IncomingVals indicates what value each Alloca contains on exit from the
|
|
/// predecessor block Pred.
|
|
void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
|
|
RenamePassData::ValVector &IncomingVals,
|
|
std::vector<RenamePassData> &Worklist) {
|
|
NextIteration:
|
|
// If we are inserting any phi nodes into this BB, they will already be in the
|
|
// block.
|
|
if (PHINode *APN = dyn_cast<PHINode>(BB->begin())) {
|
|
// If we have PHI nodes to update, compute the number of edges from Pred to
|
|
// BB.
|
|
if (PhiToAllocaMap.count(APN)) {
|
|
// We want to be able to distinguish between PHI nodes being inserted by
|
|
// this invocation of mem2reg from those phi nodes that already existed in
|
|
// the IR before mem2reg was run. We determine that APN is being inserted
|
|
// because it is missing incoming edges. All other PHI nodes being
|
|
// inserted by this pass of mem2reg will have the same number of incoming
|
|
// operands so far. Remember this count.
|
|
unsigned NewPHINumOperands = APN->getNumOperands();
|
|
|
|
unsigned NumEdges = std::count(succ_begin(Pred), succ_end(Pred), BB);
|
|
assert(NumEdges && "Must be at least one edge from Pred to BB!");
|
|
|
|
// Add entries for all the phis.
|
|
BasicBlock::iterator PNI = BB->begin();
|
|
do {
|
|
unsigned AllocaNo = PhiToAllocaMap[APN];
|
|
|
|
// Add N incoming values to the PHI node.
|
|
for (unsigned i = 0; i != NumEdges; ++i)
|
|
APN->addIncoming(IncomingVals[AllocaNo], Pred);
|
|
|
|
// The currently active variable for this block is now the PHI.
|
|
IncomingVals[AllocaNo] = APN;
|
|
|
|
// Get the next phi node.
|
|
++PNI;
|
|
APN = dyn_cast<PHINode>(PNI);
|
|
if (APN == 0)
|
|
break;
|
|
|
|
// Verify that it is missing entries. If not, it is not being inserted
|
|
// by this mem2reg invocation so we want to ignore it.
|
|
} while (APN->getNumOperands() == NewPHINumOperands);
|
|
}
|
|
}
|
|
|
|
// Don't revisit blocks.
|
|
if (!Visited.insert(BB))
|
|
return;
|
|
|
|
for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II);) {
|
|
Instruction *I = II++; // get the instruction, increment iterator
|
|
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
|
|
AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand());
|
|
if (!Src)
|
|
continue;
|
|
|
|
DenseMap<AllocaInst *, unsigned>::iterator AI = AllocaLookup.find(Src);
|
|
if (AI == AllocaLookup.end())
|
|
continue;
|
|
|
|
Value *V = IncomingVals[AI->second];
|
|
|
|
// Anything using the load now uses the current value.
|
|
LI->replaceAllUsesWith(V);
|
|
if (AST && LI->getType()->isPointerTy())
|
|
AST->deleteValue(LI);
|
|
BB->getInstList().erase(LI);
|
|
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
|
|
// Delete this instruction and mark the name as the current holder of the
|
|
// value
|
|
AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand());
|
|
if (!Dest)
|
|
continue;
|
|
|
|
DenseMap<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
|
|
if (ai == AllocaLookup.end())
|
|
continue;
|
|
|
|
// what value were we writing?
|
|
IncomingVals[ai->second] = SI->getOperand(0);
|
|
// Record debuginfo for the store before removing it.
|
|
if (DbgDeclareInst *DDI = AllocaDbgDeclares[ai->second])
|
|
ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
|
|
BB->getInstList().erase(SI);
|
|
}
|
|
}
|
|
|
|
// 'Recurse' to our successors.
|
|
succ_iterator I = succ_begin(BB), E = succ_end(BB);
|
|
if (I == E)
|
|
return;
|
|
|
|
// Keep track of the successors so we don't visit the same successor twice
|
|
SmallPtrSet<BasicBlock *, 8> VisitedSuccs;
|
|
|
|
// Handle the first successor without using the worklist.
|
|
VisitedSuccs.insert(*I);
|
|
Pred = BB;
|
|
BB = *I;
|
|
++I;
|
|
|
|
for (; I != E; ++I)
|
|
if (VisitedSuccs.insert(*I))
|
|
Worklist.push_back(RenamePassData(*I, Pred, IncomingVals));
|
|
|
|
goto NextIteration;
|
|
}
|
|
|
|
void llvm::PromoteMemToReg(ArrayRef<AllocaInst *> Allocas, DominatorTree &DT,
|
|
AliasSetTracker *AST) {
|
|
// If there is nothing to do, bail out...
|
|
if (Allocas.empty())
|
|
return;
|
|
|
|
PromoteMem2Reg(Allocas, DT, AST).run();
|
|
}
|