440 lines
16 KiB
C++
440 lines
16 KiB
C++
//===- PHITransAddr.cpp - PHI Translation for Addresses -------------------===//
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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 implements the PHITransAddr class.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/PHITransAddr.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/IR/Constants.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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static bool CanPHITrans(Instruction *Inst) {
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if (isa<PHINode>(Inst) ||
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isa<GetElementPtrInst>(Inst))
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return true;
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if (isa<CastInst>(Inst) &&
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isSafeToSpeculativelyExecute(Inst))
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return true;
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if (Inst->getOpcode() == Instruction::Add &&
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isa<ConstantInt>(Inst->getOperand(1)))
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return true;
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// cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
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// if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
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// cerr << "OP:\t\t\t\t" << *PtrInst->getOperand(0);
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return false;
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}
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#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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LLVM_DUMP_METHOD void PHITransAddr::dump() const {
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if (!Addr) {
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dbgs() << "PHITransAddr: null\n";
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return;
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}
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dbgs() << "PHITransAddr: " << *Addr << "\n";
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for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
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dbgs() << " Input #" << i << " is " << *InstInputs[i] << "\n";
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}
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#endif
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static bool VerifySubExpr(Value *Expr,
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SmallVectorImpl<Instruction*> &InstInputs) {
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// If this is a non-instruction value, there is nothing to do.
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Instruction *I = dyn_cast<Instruction>(Expr);
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if (!I) return true;
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// If it's an instruction, it is either in Tmp or its operands recursively
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// are.
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SmallVectorImpl<Instruction *>::iterator Entry = find(InstInputs, I);
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if (Entry != InstInputs.end()) {
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InstInputs.erase(Entry);
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return true;
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}
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// If it isn't in the InstInputs list it is a subexpr incorporated into the
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// address. Sanity check that it is phi translatable.
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if (!CanPHITrans(I)) {
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errs() << "Instruction in PHITransAddr is not phi-translatable:\n";
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errs() << *I << '\n';
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llvm_unreachable("Either something is missing from InstInputs or "
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"CanPHITrans is wrong.");
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}
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// Validate the operands of the instruction.
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
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if (!VerifySubExpr(I->getOperand(i), InstInputs))
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return false;
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return true;
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}
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/// Verify - Check internal consistency of this data structure. If the
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/// structure is valid, it returns true. If invalid, it prints errors and
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/// returns false.
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bool PHITransAddr::Verify() const {
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if (!Addr) return true;
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SmallVector<Instruction*, 8> Tmp(InstInputs.begin(), InstInputs.end());
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if (!VerifySubExpr(Addr, Tmp))
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return false;
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if (!Tmp.empty()) {
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errs() << "PHITransAddr contains extra instructions:\n";
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for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
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errs() << " InstInput #" << i << " is " << *InstInputs[i] << "\n";
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llvm_unreachable("This is unexpected.");
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}
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// a-ok.
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return true;
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}
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/// IsPotentiallyPHITranslatable - If this needs PHI translation, return true
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/// if we have some hope of doing it. This should be used as a filter to
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/// avoid calling PHITranslateValue in hopeless situations.
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bool PHITransAddr::IsPotentiallyPHITranslatable() const {
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// If the input value is not an instruction, or if it is not defined in CurBB,
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// then we don't need to phi translate it.
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Instruction *Inst = dyn_cast<Instruction>(Addr);
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return !Inst || CanPHITrans(Inst);
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}
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static void RemoveInstInputs(Value *V,
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SmallVectorImpl<Instruction*> &InstInputs) {
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Instruction *I = dyn_cast<Instruction>(V);
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if (!I) return;
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// If the instruction is in the InstInputs list, remove it.
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SmallVectorImpl<Instruction *>::iterator Entry = find(InstInputs, I);
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if (Entry != InstInputs.end()) {
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InstInputs.erase(Entry);
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return;
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}
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assert(!isa<PHINode>(I) && "Error, removing something that isn't an input");
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// Otherwise, it must have instruction inputs itself. Zap them recursively.
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for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
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if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
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RemoveInstInputs(Op, InstInputs);
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}
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}
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Value *PHITransAddr::PHITranslateSubExpr(Value *V, BasicBlock *CurBB,
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BasicBlock *PredBB,
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const DominatorTree *DT) {
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// If this is a non-instruction value, it can't require PHI translation.
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Instruction *Inst = dyn_cast<Instruction>(V);
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if (!Inst) return V;
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// Determine whether 'Inst' is an input to our PHI translatable expression.
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bool isInput = is_contained(InstInputs, Inst);
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// Handle inputs instructions if needed.
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if (isInput) {
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if (Inst->getParent() != CurBB) {
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// If it is an input defined in a different block, then it remains an
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// input.
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return Inst;
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}
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// If 'Inst' is defined in this block and is an input that needs to be phi
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// translated, we need to incorporate the value into the expression or fail.
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// In either case, the instruction itself isn't an input any longer.
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InstInputs.erase(find(InstInputs, Inst));
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// If this is a PHI, go ahead and translate it.
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if (PHINode *PN = dyn_cast<PHINode>(Inst))
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return AddAsInput(PN->getIncomingValueForBlock(PredBB));
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// If this is a non-phi value, and it is analyzable, we can incorporate it
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// into the expression by making all instruction operands be inputs.
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if (!CanPHITrans(Inst))
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return nullptr;
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// All instruction operands are now inputs (and of course, they may also be
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// defined in this block, so they may need to be phi translated themselves.
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for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
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if (Instruction *Op = dyn_cast<Instruction>(Inst->getOperand(i)))
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InstInputs.push_back(Op);
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}
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// Ok, it must be an intermediate result (either because it started that way
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// or because we just incorporated it into the expression). See if its
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// operands need to be phi translated, and if so, reconstruct it.
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if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
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if (!isSafeToSpeculativelyExecute(Cast)) return nullptr;
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Value *PHIIn = PHITranslateSubExpr(Cast->getOperand(0), CurBB, PredBB, DT);
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if (!PHIIn) return nullptr;
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if (PHIIn == Cast->getOperand(0))
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return Cast;
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// Find an available version of this cast.
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// Constants are trivial to find.
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if (Constant *C = dyn_cast<Constant>(PHIIn))
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return AddAsInput(ConstantExpr::getCast(Cast->getOpcode(),
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C, Cast->getType()));
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// Otherwise we have to see if a casted version of the incoming pointer
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// is available. If so, we can use it, otherwise we have to fail.
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for (User *U : PHIIn->users()) {
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if (CastInst *CastI = dyn_cast<CastInst>(U))
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if (CastI->getOpcode() == Cast->getOpcode() &&
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CastI->getType() == Cast->getType() &&
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(!DT || DT->dominates(CastI->getParent(), PredBB)))
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return CastI;
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}
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return nullptr;
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}
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// Handle getelementptr with at least one PHI translatable operand.
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if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
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SmallVector<Value*, 8> GEPOps;
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bool AnyChanged = false;
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for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
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Value *GEPOp = PHITranslateSubExpr(GEP->getOperand(i), CurBB, PredBB, DT);
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if (!GEPOp) return nullptr;
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AnyChanged |= GEPOp != GEP->getOperand(i);
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GEPOps.push_back(GEPOp);
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}
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if (!AnyChanged)
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return GEP;
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// Simplify the GEP to handle 'gep x, 0' -> x etc.
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if (Value *V = SimplifyGEPInst(GEP->getSourceElementType(),
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GEPOps, {DL, TLI, DT, AC})) {
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for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
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RemoveInstInputs(GEPOps[i], InstInputs);
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return AddAsInput(V);
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}
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// Scan to see if we have this GEP available.
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Value *APHIOp = GEPOps[0];
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for (User *U : APHIOp->users()) {
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if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U))
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if (GEPI->getType() == GEP->getType() &&
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GEPI->getNumOperands() == GEPOps.size() &&
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GEPI->getParent()->getParent() == CurBB->getParent() &&
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(!DT || DT->dominates(GEPI->getParent(), PredBB))) {
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if (std::equal(GEPOps.begin(), GEPOps.end(), GEPI->op_begin()))
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return GEPI;
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}
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}
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return nullptr;
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}
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// Handle add with a constant RHS.
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if (Inst->getOpcode() == Instruction::Add &&
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isa<ConstantInt>(Inst->getOperand(1))) {
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// PHI translate the LHS.
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Constant *RHS = cast<ConstantInt>(Inst->getOperand(1));
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bool isNSW = cast<BinaryOperator>(Inst)->hasNoSignedWrap();
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bool isNUW = cast<BinaryOperator>(Inst)->hasNoUnsignedWrap();
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Value *LHS = PHITranslateSubExpr(Inst->getOperand(0), CurBB, PredBB, DT);
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if (!LHS) return nullptr;
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// If the PHI translated LHS is an add of a constant, fold the immediates.
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if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(LHS))
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if (BOp->getOpcode() == Instruction::Add)
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if (ConstantInt *CI = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
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LHS = BOp->getOperand(0);
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RHS = ConstantExpr::getAdd(RHS, CI);
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isNSW = isNUW = false;
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// If the old 'LHS' was an input, add the new 'LHS' as an input.
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if (is_contained(InstInputs, BOp)) {
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RemoveInstInputs(BOp, InstInputs);
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AddAsInput(LHS);
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}
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}
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// See if the add simplifies away.
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if (Value *Res = SimplifyAddInst(LHS, RHS, isNSW, isNUW, {DL, TLI, DT, AC})) {
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// If we simplified the operands, the LHS is no longer an input, but Res
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// is.
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RemoveInstInputs(LHS, InstInputs);
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return AddAsInput(Res);
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}
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// If we didn't modify the add, just return it.
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if (LHS == Inst->getOperand(0) && RHS == Inst->getOperand(1))
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return Inst;
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// Otherwise, see if we have this add available somewhere.
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for (User *U : LHS->users()) {
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if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U))
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if (BO->getOpcode() == Instruction::Add &&
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BO->getOperand(0) == LHS && BO->getOperand(1) == RHS &&
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BO->getParent()->getParent() == CurBB->getParent() &&
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(!DT || DT->dominates(BO->getParent(), PredBB)))
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return BO;
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}
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return nullptr;
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}
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// Otherwise, we failed.
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return nullptr;
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}
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/// PHITranslateValue - PHI translate the current address up the CFG from
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/// CurBB to Pred, updating our state to reflect any needed changes. If
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/// 'MustDominate' is true, the translated value must dominate
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/// PredBB. This returns true on failure and sets Addr to null.
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bool PHITransAddr::PHITranslateValue(BasicBlock *CurBB, BasicBlock *PredBB,
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const DominatorTree *DT,
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bool MustDominate) {
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assert(DT || !MustDominate);
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assert(Verify() && "Invalid PHITransAddr!");
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if (DT && DT->isReachableFromEntry(PredBB))
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Addr =
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PHITranslateSubExpr(Addr, CurBB, PredBB, MustDominate ? DT : nullptr);
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else
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Addr = nullptr;
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assert(Verify() && "Invalid PHITransAddr!");
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if (MustDominate)
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// Make sure the value is live in the predecessor.
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if (Instruction *Inst = dyn_cast_or_null<Instruction>(Addr))
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if (!DT->dominates(Inst->getParent(), PredBB))
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Addr = nullptr;
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return Addr == nullptr;
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}
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/// PHITranslateWithInsertion - PHI translate this value into the specified
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/// predecessor block, inserting a computation of the value if it is
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/// unavailable.
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///
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/// All newly created instructions are added to the NewInsts list. This
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/// returns null on failure.
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///
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Value *PHITransAddr::
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PHITranslateWithInsertion(BasicBlock *CurBB, BasicBlock *PredBB,
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const DominatorTree &DT,
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SmallVectorImpl<Instruction*> &NewInsts) {
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unsigned NISize = NewInsts.size();
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// Attempt to PHI translate with insertion.
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Addr = InsertPHITranslatedSubExpr(Addr, CurBB, PredBB, DT, NewInsts);
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// If successful, return the new value.
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if (Addr) return Addr;
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// If not, destroy any intermediate instructions inserted.
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while (NewInsts.size() != NISize)
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NewInsts.pop_back_val()->eraseFromParent();
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return nullptr;
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}
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/// InsertPHITranslatedPointer - Insert a computation of the PHI translated
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/// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
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/// block. All newly created instructions are added to the NewInsts list.
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/// This returns null on failure.
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///
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Value *PHITransAddr::
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InsertPHITranslatedSubExpr(Value *InVal, BasicBlock *CurBB,
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BasicBlock *PredBB, const DominatorTree &DT,
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SmallVectorImpl<Instruction*> &NewInsts) {
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// See if we have a version of this value already available and dominating
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// PredBB. If so, there is no need to insert a new instance of it.
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PHITransAddr Tmp(InVal, DL, AC);
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if (!Tmp.PHITranslateValue(CurBB, PredBB, &DT, /*MustDominate=*/true))
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return Tmp.getAddr();
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// We don't need to PHI translate values which aren't instructions.
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auto *Inst = dyn_cast<Instruction>(InVal);
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if (!Inst)
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return nullptr;
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// Handle cast of PHI translatable value.
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if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
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if (!isSafeToSpeculativelyExecute(Cast)) return nullptr;
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Value *OpVal = InsertPHITranslatedSubExpr(Cast->getOperand(0),
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CurBB, PredBB, DT, NewInsts);
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if (!OpVal) return nullptr;
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// Otherwise insert a cast at the end of PredBB.
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CastInst *New = CastInst::Create(Cast->getOpcode(), OpVal, InVal->getType(),
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InVal->getName() + ".phi.trans.insert",
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PredBB->getTerminator());
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New->setDebugLoc(Inst->getDebugLoc());
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NewInsts.push_back(New);
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return New;
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}
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// Handle getelementptr with at least one PHI operand.
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if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
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SmallVector<Value*, 8> GEPOps;
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BasicBlock *CurBB = GEP->getParent();
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for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
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Value *OpVal = InsertPHITranslatedSubExpr(GEP->getOperand(i),
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CurBB, PredBB, DT, NewInsts);
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if (!OpVal) return nullptr;
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GEPOps.push_back(OpVal);
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}
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GetElementPtrInst *Result = GetElementPtrInst::Create(
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GEP->getSourceElementType(), GEPOps[0], makeArrayRef(GEPOps).slice(1),
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InVal->getName() + ".phi.trans.insert", PredBB->getTerminator());
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Result->setDebugLoc(Inst->getDebugLoc());
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Result->setIsInBounds(GEP->isInBounds());
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NewInsts.push_back(Result);
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return Result;
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}
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#if 0
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// FIXME: This code works, but it is unclear that we actually want to insert
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// a big chain of computation in order to make a value available in a block.
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// This needs to be evaluated carefully to consider its cost trade offs.
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// Handle add with a constant RHS.
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if (Inst->getOpcode() == Instruction::Add &&
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isa<ConstantInt>(Inst->getOperand(1))) {
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// PHI translate the LHS.
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Value *OpVal = InsertPHITranslatedSubExpr(Inst->getOperand(0),
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CurBB, PredBB, DT, NewInsts);
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if (OpVal == 0) return 0;
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BinaryOperator *Res = BinaryOperator::CreateAdd(OpVal, Inst->getOperand(1),
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InVal->getName()+".phi.trans.insert",
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PredBB->getTerminator());
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Res->setHasNoSignedWrap(cast<BinaryOperator>(Inst)->hasNoSignedWrap());
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Res->setHasNoUnsignedWrap(cast<BinaryOperator>(Inst)->hasNoUnsignedWrap());
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NewInsts.push_back(Res);
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return Res;
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}
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#endif
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return nullptr;
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}
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