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[llvm-core.git] / lib / Analysis / PHITransAddr.cpp
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1 //===- PHITransAddr.cpp - PHI Translation for Addresses -------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the PHITransAddr class.
11 //===----------------------------------------------------------------------===//
13 #include "llvm/Analysis/PHITransAddr.h"
14 #include "llvm/Analysis/InstructionSimplify.h"
15 #include "llvm/Analysis/ValueTracking.h"
16 #include "llvm/Config/llvm-config.h"
17 #include "llvm/IR/Constants.h"
18 #include "llvm/IR/Dominators.h"
19 #include "llvm/IR/Instructions.h"
20 #include "llvm/Support/Debug.h"
21 #include "llvm/Support/ErrorHandling.h"
22 #include "llvm/Support/raw_ostream.h"
23 using namespace llvm;
25 static bool CanPHITrans(Instruction *Inst) {
26 if (isa<PHINode>(Inst) ||
27 isa<GetElementPtrInst>(Inst))
28 return true;
30 if (isa<CastInst>(Inst) &&
31 isSafeToSpeculativelyExecute(Inst))
32 return true;
34 if (Inst->getOpcode() == Instruction::Add &&
35 isa<ConstantInt>(Inst->getOperand(1)))
36 return true;
38 // cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
39 // if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
40 // cerr << "OP:\t\t\t\t" << *PtrInst->getOperand(0);
41 return false;
44 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
45 LLVM_DUMP_METHOD void PHITransAddr::dump() const {
46 if (!Addr) {
47 dbgs() << "PHITransAddr: null\n";
48 return;
50 dbgs() << "PHITransAddr: " << *Addr << "\n";
51 for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
52 dbgs() << " Input #" << i << " is " << *InstInputs[i] << "\n";
54 #endif
57 static bool VerifySubExpr(Value *Expr,
58 SmallVectorImpl<Instruction*> &InstInputs) {
59 // If this is a non-instruction value, there is nothing to do.
60 Instruction *I = dyn_cast<Instruction>(Expr);
61 if (!I) return true;
63 // If it's an instruction, it is either in Tmp or its operands recursively
64 // are.
65 SmallVectorImpl<Instruction *>::iterator Entry = find(InstInputs, I);
66 if (Entry != InstInputs.end()) {
67 InstInputs.erase(Entry);
68 return true;
71 // If it isn't in the InstInputs list it is a subexpr incorporated into the
72 // address. Sanity check that it is phi translatable.
73 if (!CanPHITrans(I)) {
74 errs() << "Instruction in PHITransAddr is not phi-translatable:\n";
75 errs() << *I << '\n';
76 llvm_unreachable("Either something is missing from InstInputs or "
77 "CanPHITrans is wrong.");
80 // Validate the operands of the instruction.
81 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
82 if (!VerifySubExpr(I->getOperand(i), InstInputs))
83 return false;
85 return true;
88 /// Verify - Check internal consistency of this data structure. If the
89 /// structure is valid, it returns true. If invalid, it prints errors and
90 /// returns false.
91 bool PHITransAddr::Verify() const {
92 if (!Addr) return true;
94 SmallVector<Instruction*, 8> Tmp(InstInputs.begin(), InstInputs.end());
96 if (!VerifySubExpr(Addr, Tmp))
97 return false;
99 if (!Tmp.empty()) {
100 errs() << "PHITransAddr contains extra instructions:\n";
101 for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
102 errs() << " InstInput #" << i << " is " << *InstInputs[i] << "\n";
103 llvm_unreachable("This is unexpected.");
106 // a-ok.
107 return true;
111 /// IsPotentiallyPHITranslatable - If this needs PHI translation, return true
112 /// if we have some hope of doing it. This should be used as a filter to
113 /// avoid calling PHITranslateValue in hopeless situations.
114 bool PHITransAddr::IsPotentiallyPHITranslatable() const {
115 // If the input value is not an instruction, or if it is not defined in CurBB,
116 // then we don't need to phi translate it.
117 Instruction *Inst = dyn_cast<Instruction>(Addr);
118 return !Inst || CanPHITrans(Inst);
122 static void RemoveInstInputs(Value *V,
123 SmallVectorImpl<Instruction*> &InstInputs) {
124 Instruction *I = dyn_cast<Instruction>(V);
125 if (!I) return;
127 // If the instruction is in the InstInputs list, remove it.
128 SmallVectorImpl<Instruction *>::iterator Entry = find(InstInputs, I);
129 if (Entry != InstInputs.end()) {
130 InstInputs.erase(Entry);
131 return;
134 assert(!isa<PHINode>(I) && "Error, removing something that isn't an input");
136 // Otherwise, it must have instruction inputs itself. Zap them recursively.
137 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
138 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
139 RemoveInstInputs(Op, InstInputs);
143 Value *PHITransAddr::PHITranslateSubExpr(Value *V, BasicBlock *CurBB,
144 BasicBlock *PredBB,
145 const DominatorTree *DT) {
146 // If this is a non-instruction value, it can't require PHI translation.
147 Instruction *Inst = dyn_cast<Instruction>(V);
148 if (!Inst) return V;
150 // Determine whether 'Inst' is an input to our PHI translatable expression.
151 bool isInput = is_contained(InstInputs, Inst);
153 // Handle inputs instructions if needed.
154 if (isInput) {
155 if (Inst->getParent() != CurBB) {
156 // If it is an input defined in a different block, then it remains an
157 // input.
158 return Inst;
161 // If 'Inst' is defined in this block and is an input that needs to be phi
162 // translated, we need to incorporate the value into the expression or fail.
164 // In either case, the instruction itself isn't an input any longer.
165 InstInputs.erase(find(InstInputs, Inst));
167 // If this is a PHI, go ahead and translate it.
168 if (PHINode *PN = dyn_cast<PHINode>(Inst))
169 return AddAsInput(PN->getIncomingValueForBlock(PredBB));
171 // If this is a non-phi value, and it is analyzable, we can incorporate it
172 // into the expression by making all instruction operands be inputs.
173 if (!CanPHITrans(Inst))
174 return nullptr;
176 // All instruction operands are now inputs (and of course, they may also be
177 // defined in this block, so they may need to be phi translated themselves.
178 for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
179 if (Instruction *Op = dyn_cast<Instruction>(Inst->getOperand(i)))
180 InstInputs.push_back(Op);
183 // Ok, it must be an intermediate result (either because it started that way
184 // or because we just incorporated it into the expression). See if its
185 // operands need to be phi translated, and if so, reconstruct it.
187 if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
188 if (!isSafeToSpeculativelyExecute(Cast)) return nullptr;
189 Value *PHIIn = PHITranslateSubExpr(Cast->getOperand(0), CurBB, PredBB, DT);
190 if (!PHIIn) return nullptr;
191 if (PHIIn == Cast->getOperand(0))
192 return Cast;
194 // Find an available version of this cast.
196 // Constants are trivial to find.
197 if (Constant *C = dyn_cast<Constant>(PHIIn))
198 return AddAsInput(ConstantExpr::getCast(Cast->getOpcode(),
199 C, Cast->getType()));
201 // Otherwise we have to see if a casted version of the incoming pointer
202 // is available. If so, we can use it, otherwise we have to fail.
203 for (User *U : PHIIn->users()) {
204 if (CastInst *CastI = dyn_cast<CastInst>(U))
205 if (CastI->getOpcode() == Cast->getOpcode() &&
206 CastI->getType() == Cast->getType() &&
207 (!DT || DT->dominates(CastI->getParent(), PredBB)))
208 return CastI;
210 return nullptr;
213 // Handle getelementptr with at least one PHI translatable operand.
214 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
215 SmallVector<Value*, 8> GEPOps;
216 bool AnyChanged = false;
217 for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
218 Value *GEPOp = PHITranslateSubExpr(GEP->getOperand(i), CurBB, PredBB, DT);
219 if (!GEPOp) return nullptr;
221 AnyChanged |= GEPOp != GEP->getOperand(i);
222 GEPOps.push_back(GEPOp);
225 if (!AnyChanged)
226 return GEP;
228 // Simplify the GEP to handle 'gep x, 0' -> x etc.
229 if (Value *V = SimplifyGEPInst(GEP->getSourceElementType(),
230 GEPOps, {DL, TLI, DT, AC})) {
231 for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
232 RemoveInstInputs(GEPOps[i], InstInputs);
234 return AddAsInput(V);
237 // Scan to see if we have this GEP available.
238 Value *APHIOp = GEPOps[0];
239 for (User *U : APHIOp->users()) {
240 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U))
241 if (GEPI->getType() == GEP->getType() &&
242 GEPI->getNumOperands() == GEPOps.size() &&
243 GEPI->getParent()->getParent() == CurBB->getParent() &&
244 (!DT || DT->dominates(GEPI->getParent(), PredBB))) {
245 if (std::equal(GEPOps.begin(), GEPOps.end(), GEPI->op_begin()))
246 return GEPI;
249 return nullptr;
252 // Handle add with a constant RHS.
253 if (Inst->getOpcode() == Instruction::Add &&
254 isa<ConstantInt>(Inst->getOperand(1))) {
255 // PHI translate the LHS.
256 Constant *RHS = cast<ConstantInt>(Inst->getOperand(1));
257 bool isNSW = cast<BinaryOperator>(Inst)->hasNoSignedWrap();
258 bool isNUW = cast<BinaryOperator>(Inst)->hasNoUnsignedWrap();
260 Value *LHS = PHITranslateSubExpr(Inst->getOperand(0), CurBB, PredBB, DT);
261 if (!LHS) return nullptr;
263 // If the PHI translated LHS is an add of a constant, fold the immediates.
264 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(LHS))
265 if (BOp->getOpcode() == Instruction::Add)
266 if (ConstantInt *CI = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
267 LHS = BOp->getOperand(0);
268 RHS = ConstantExpr::getAdd(RHS, CI);
269 isNSW = isNUW = false;
271 // If the old 'LHS' was an input, add the new 'LHS' as an input.
272 if (is_contained(InstInputs, BOp)) {
273 RemoveInstInputs(BOp, InstInputs);
274 AddAsInput(LHS);
278 // See if the add simplifies away.
279 if (Value *Res = SimplifyAddInst(LHS, RHS, isNSW, isNUW, {DL, TLI, DT, AC})) {
280 // If we simplified the operands, the LHS is no longer an input, but Res
281 // is.
282 RemoveInstInputs(LHS, InstInputs);
283 return AddAsInput(Res);
286 // If we didn't modify the add, just return it.
287 if (LHS == Inst->getOperand(0) && RHS == Inst->getOperand(1))
288 return Inst;
290 // Otherwise, see if we have this add available somewhere.
291 for (User *U : LHS->users()) {
292 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U))
293 if (BO->getOpcode() == Instruction::Add &&
294 BO->getOperand(0) == LHS && BO->getOperand(1) == RHS &&
295 BO->getParent()->getParent() == CurBB->getParent() &&
296 (!DT || DT->dominates(BO->getParent(), PredBB)))
297 return BO;
300 return nullptr;
303 // Otherwise, we failed.
304 return nullptr;
308 /// PHITranslateValue - PHI translate the current address up the CFG from
309 /// CurBB to Pred, updating our state to reflect any needed changes. If
310 /// 'MustDominate' is true, the translated value must dominate
311 /// PredBB. This returns true on failure and sets Addr to null.
312 bool PHITransAddr::PHITranslateValue(BasicBlock *CurBB, BasicBlock *PredBB,
313 const DominatorTree *DT,
314 bool MustDominate) {
315 assert(DT || !MustDominate);
316 assert(Verify() && "Invalid PHITransAddr!");
317 if (DT && DT->isReachableFromEntry(PredBB))
318 Addr =
319 PHITranslateSubExpr(Addr, CurBB, PredBB, MustDominate ? DT : nullptr);
320 else
321 Addr = nullptr;
322 assert(Verify() && "Invalid PHITransAddr!");
324 if (MustDominate)
325 // Make sure the value is live in the predecessor.
326 if (Instruction *Inst = dyn_cast_or_null<Instruction>(Addr))
327 if (!DT->dominates(Inst->getParent(), PredBB))
328 Addr = nullptr;
330 return Addr == nullptr;
333 /// PHITranslateWithInsertion - PHI translate this value into the specified
334 /// predecessor block, inserting a computation of the value if it is
335 /// unavailable.
337 /// All newly created instructions are added to the NewInsts list. This
338 /// returns null on failure.
340 Value *PHITransAddr::
341 PHITranslateWithInsertion(BasicBlock *CurBB, BasicBlock *PredBB,
342 const DominatorTree &DT,
343 SmallVectorImpl<Instruction*> &NewInsts) {
344 unsigned NISize = NewInsts.size();
346 // Attempt to PHI translate with insertion.
347 Addr = InsertPHITranslatedSubExpr(Addr, CurBB, PredBB, DT, NewInsts);
349 // If successful, return the new value.
350 if (Addr) return Addr;
352 // If not, destroy any intermediate instructions inserted.
353 while (NewInsts.size() != NISize)
354 NewInsts.pop_back_val()->eraseFromParent();
355 return nullptr;
359 /// InsertPHITranslatedPointer - Insert a computation of the PHI translated
360 /// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
361 /// block. All newly created instructions are added to the NewInsts list.
362 /// This returns null on failure.
364 Value *PHITransAddr::
365 InsertPHITranslatedSubExpr(Value *InVal, BasicBlock *CurBB,
366 BasicBlock *PredBB, const DominatorTree &DT,
367 SmallVectorImpl<Instruction*> &NewInsts) {
368 // See if we have a version of this value already available and dominating
369 // PredBB. If so, there is no need to insert a new instance of it.
370 PHITransAddr Tmp(InVal, DL, AC);
371 if (!Tmp.PHITranslateValue(CurBB, PredBB, &DT, /*MustDominate=*/true))
372 return Tmp.getAddr();
374 // We don't need to PHI translate values which aren't instructions.
375 auto *Inst = dyn_cast<Instruction>(InVal);
376 if (!Inst)
377 return nullptr;
379 // Handle cast of PHI translatable value.
380 if (CastInst *Cast = dyn_cast<CastInst>(Inst)) {
381 if (!isSafeToSpeculativelyExecute(Cast)) return nullptr;
382 Value *OpVal = InsertPHITranslatedSubExpr(Cast->getOperand(0),
383 CurBB, PredBB, DT, NewInsts);
384 if (!OpVal) return nullptr;
386 // Otherwise insert a cast at the end of PredBB.
387 CastInst *New = CastInst::Create(Cast->getOpcode(), OpVal, InVal->getType(),
388 InVal->getName() + ".phi.trans.insert",
389 PredBB->getTerminator());
390 New->setDebugLoc(Inst->getDebugLoc());
391 NewInsts.push_back(New);
392 return New;
395 // Handle getelementptr with at least one PHI operand.
396 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
397 SmallVector<Value*, 8> GEPOps;
398 BasicBlock *CurBB = GEP->getParent();
399 for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
400 Value *OpVal = InsertPHITranslatedSubExpr(GEP->getOperand(i),
401 CurBB, PredBB, DT, NewInsts);
402 if (!OpVal) return nullptr;
403 GEPOps.push_back(OpVal);
406 GetElementPtrInst *Result = GetElementPtrInst::Create(
407 GEP->getSourceElementType(), GEPOps[0], makeArrayRef(GEPOps).slice(1),
408 InVal->getName() + ".phi.trans.insert", PredBB->getTerminator());
409 Result->setDebugLoc(Inst->getDebugLoc());
410 Result->setIsInBounds(GEP->isInBounds());
411 NewInsts.push_back(Result);
412 return Result;
415 #if 0
416 // FIXME: This code works, but it is unclear that we actually want to insert
417 // a big chain of computation in order to make a value available in a block.
418 // This needs to be evaluated carefully to consider its cost trade offs.
420 // Handle add with a constant RHS.
421 if (Inst->getOpcode() == Instruction::Add &&
422 isa<ConstantInt>(Inst->getOperand(1))) {
423 // PHI translate the LHS.
424 Value *OpVal = InsertPHITranslatedSubExpr(Inst->getOperand(0),
425 CurBB, PredBB, DT, NewInsts);
426 if (OpVal == 0) return 0;
428 BinaryOperator *Res = BinaryOperator::CreateAdd(OpVal, Inst->getOperand(1),
429 InVal->getName()+".phi.trans.insert",
430 PredBB->getTerminator());
431 Res->setHasNoSignedWrap(cast<BinaryOperator>(Inst)->hasNoSignedWrap());
432 Res->setHasNoUnsignedWrap(cast<BinaryOperator>(Inst)->hasNoUnsignedWrap());
433 NewInsts.push_back(Res);
434 return Res;
436 #endif
438 return nullptr;