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.
10//
11//===----------------------------------------------------------------------===//
12
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/ErrorHandling.h"
21#include "llvm/Support/raw_ostream.h"
22using namespace llvm;
23
24static cl::opt<bool> EnableAddPhiTranslation(
25 "gvn-add-phi-translation", cl::init(Val: false), cl::Hidden,
26 cl::desc("Enable phi-translation of add instructions"));
27
28static bool canPHITrans(Instruction *Inst) {
29 if (isa<PHINode>(Val: Inst) || isa<GetElementPtrInst>(Val: Inst) || isa<CastInst>(Val: Inst))
30 return true;
31
32 if (Inst->getOpcode() == Instruction::Add &&
33 isa<ConstantInt>(Val: Inst->getOperand(i: 1)))
34 return true;
35
36 return false;
37}
38
39#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
40LLVM_DUMP_METHOD void PHITransAddr::dump() const {
41 if (!Addr) {
42 dbgs() << "PHITransAddr: null\n";
43 return;
44 }
45 dbgs() << "PHITransAddr: " << *Addr << "\n";
46 for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
47 dbgs() << " Input #" << i << " is " << *InstInputs[i] << "\n";
48}
49#endif
50
51static bool verifySubExpr(Value *Expr,
52 SmallVectorImpl<Instruction *> &InstInputs) {
53 // If this is a non-instruction value, there is nothing to do.
54 Instruction *I = dyn_cast<Instruction>(Val: Expr);
55 if (!I) return true;
56
57 // If it's an instruction, it is either in Tmp or its operands recursively
58 // are.
59 if (auto Entry = find(Range&: InstInputs, Val: I); Entry != InstInputs.end()) {
60 InstInputs.erase(CI: Entry);
61 return true;
62 }
63
64 // If it isn't in the InstInputs list it is a subexpr incorporated into the
65 // address. Validate that it is phi translatable.
66 if (!canPHITrans(Inst: I)) {
67 errs() << "Instruction in PHITransAddr is not phi-translatable:\n";
68 errs() << *I << '\n';
69 llvm_unreachable("Either something is missing from InstInputs or "
70 "canPHITrans is wrong.");
71 }
72
73 // Validate the operands of the instruction.
74 return all_of(Range: I->operands(),
75 P: [&](Value *Op) { return verifySubExpr(Expr: Op, InstInputs); });
76}
77
78/// verify - Check internal consistency of this data structure. If the
79/// structure is valid, it returns true. If invalid, it prints errors and
80/// returns false.
81bool PHITransAddr::verify() const {
82 if (!Addr) return true;
83
84 SmallVector<Instruction*, 8> Tmp(InstInputs.begin(), InstInputs.end());
85
86 if (!verifySubExpr(Expr: Addr, InstInputs&: Tmp))
87 return false;
88
89 if (!Tmp.empty()) {
90 errs() << "PHITransAddr contains extra instructions:\n";
91 for (unsigned i = 0, e = InstInputs.size(); i != e; ++i)
92 errs() << " InstInput #" << i << " is " << *InstInputs[i] << "\n";
93 llvm_unreachable("This is unexpected.");
94 }
95
96 // a-ok.
97 return true;
98}
99
100/// isPotentiallyPHITranslatable - If this needs PHI translation, return true
101/// if we have some hope of doing it. This should be used as a filter to
102/// avoid calling PHITranslateValue in hopeless situations.
103bool PHITransAddr::isPotentiallyPHITranslatable() const {
104 // If the input value is not an instruction, or if it is not defined in CurBB,
105 // then we don't need to phi translate it.
106 Instruction *Inst = dyn_cast<Instruction>(Val: Addr);
107 return !Inst || canPHITrans(Inst);
108}
109
110static void RemoveInstInputs(Value *V,
111 SmallVectorImpl<Instruction*> &InstInputs) {
112 Instruction *I = dyn_cast<Instruction>(Val: V);
113 if (!I) return;
114
115 // If the instruction is in the InstInputs list, remove it.
116 if (auto Entry = find(Range&: InstInputs, Val: I); Entry != InstInputs.end()) {
117 InstInputs.erase(CI: Entry);
118 return;
119 }
120
121 assert(!isa<PHINode>(I) && "Error, removing something that isn't an input");
122
123 // Otherwise, it must have instruction inputs itself. Zap them recursively.
124 for (Value *Op : I->operands())
125 if (Instruction *OpInst = dyn_cast<Instruction>(Val: Op))
126 RemoveInstInputs(V: OpInst, InstInputs);
127}
128
129Value *PHITransAddr::translateSubExpr(Value *V, BasicBlock *CurBB,
130 BasicBlock *PredBB,
131 const DominatorTree *DT) {
132 // If this is a non-instruction value, it can't require PHI translation.
133 Instruction *Inst = dyn_cast<Instruction>(Val: V);
134 if (!Inst) return V;
135
136 // Determine whether 'Inst' is an input to our PHI translatable expression.
137 bool isInput = is_contained(Range&: InstInputs, Element: Inst);
138
139 // Handle inputs instructions if needed.
140 if (isInput) {
141 if (Inst->getParent() != CurBB) {
142 // If it is an input defined in a different block, then it remains an
143 // input.
144 return Inst;
145 }
146
147 // If 'Inst' is defined in this block and is an input that needs to be phi
148 // translated, we need to incorporate the value into the expression or fail.
149
150 // In either case, the instruction itself isn't an input any longer.
151 InstInputs.erase(CI: find(Range&: InstInputs, Val: Inst));
152
153 // If this is a PHI, go ahead and translate it.
154 if (PHINode *PN = dyn_cast<PHINode>(Val: Inst))
155 return addAsInput(V: PN->getIncomingValueForBlock(BB: PredBB));
156
157 // If this is a non-phi value, and it is analyzable, we can incorporate it
158 // into the expression by making all instruction operands be inputs.
159 if (!canPHITrans(Inst))
160 return nullptr;
161
162 // All instruction operands are now inputs (and of course, they may also be
163 // defined in this block, so they may need to be phi translated themselves.
164 for (Value *Op : Inst->operands())
165 addAsInput(V: Op);
166 }
167
168 // Ok, it must be an intermediate result (either because it started that way
169 // or because we just incorporated it into the expression). See if its
170 // operands need to be phi translated, and if so, reconstruct it.
171
172 if (CastInst *Cast = dyn_cast<CastInst>(Val: Inst)) {
173 Value *PHIIn = translateSubExpr(V: Cast->getOperand(i_nocapture: 0), CurBB, PredBB, DT);
174 if (!PHIIn) return nullptr;
175 if (PHIIn == Cast->getOperand(i_nocapture: 0))
176 return Cast;
177
178 // Find an available version of this cast.
179
180 // Try to simplify cast first.
181 if (Value *V = simplifyCastInst(CastOpc: Cast->getOpcode(), Op: PHIIn, Ty: Cast->getType(),
182 Q: {DL, TLI, DT, AC})) {
183 RemoveInstInputs(V: PHIIn, InstInputs);
184 return addAsInput(V);
185 }
186
187 // Otherwise we have to see if a casted version of the incoming pointer
188 // is available. If so, we can use it, otherwise we have to fail.
189 for (User *U : PHIIn->users()) {
190 if (CastInst *CastI = dyn_cast<CastInst>(Val: U))
191 if (CastI->getOpcode() == Cast->getOpcode() &&
192 CastI->getType() == Cast->getType() &&
193 (!DT || DT->dominates(A: CastI->getParent(), B: PredBB)))
194 return CastI;
195 }
196 return nullptr;
197 }
198
199 // Handle getelementptr with at least one PHI translatable operand.
200 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Val: Inst)) {
201 SmallVector<Value*, 8> GEPOps;
202 bool AnyChanged = false;
203 for (Value *Op : GEP->operands()) {
204 Value *GEPOp = translateSubExpr(V: Op, CurBB, PredBB, DT);
205 if (!GEPOp) return nullptr;
206
207 AnyChanged |= GEPOp != Op;
208 GEPOps.push_back(Elt: GEPOp);
209 }
210
211 if (!AnyChanged)
212 return GEP;
213
214 // Simplify the GEP to handle 'gep x, 0' -> x etc.
215 if (Value *V = simplifyGEPInst(SrcTy: GEP->getSourceElementType(), Ptr: GEPOps[0],
216 Indices: ArrayRef<Value *>(GEPOps).slice(N: 1),
217 InBounds: GEP->isInBounds(), Q: {DL, TLI, DT, AC})) {
218 for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
219 RemoveInstInputs(V: GEPOps[i], InstInputs);
220
221 return addAsInput(V);
222 }
223
224 // Scan to see if we have this GEP available.
225 Value *APHIOp = GEPOps[0];
226 for (User *U : APHIOp->users()) {
227 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Val: U))
228 if (GEPI->getType() == GEP->getType() &&
229 GEPI->getSourceElementType() == GEP->getSourceElementType() &&
230 GEPI->getNumOperands() == GEPOps.size() &&
231 GEPI->getParent()->getParent() == CurBB->getParent() &&
232 (!DT || DT->dominates(A: GEPI->getParent(), B: PredBB))) {
233 if (std::equal(first1: GEPOps.begin(), last1: GEPOps.end(), first2: GEPI->op_begin()))
234 return GEPI;
235 }
236 }
237 return nullptr;
238 }
239
240 // Handle add with a constant RHS.
241 if (Inst->getOpcode() == Instruction::Add &&
242 isa<ConstantInt>(Val: Inst->getOperand(i: 1))) {
243 // PHI translate the LHS.
244 Constant *RHS = cast<ConstantInt>(Val: Inst->getOperand(i: 1));
245 bool isNSW = cast<BinaryOperator>(Val: Inst)->hasNoSignedWrap();
246 bool isNUW = cast<BinaryOperator>(Val: Inst)->hasNoUnsignedWrap();
247
248 Value *LHS = translateSubExpr(V: Inst->getOperand(i: 0), CurBB, PredBB, DT);
249 if (!LHS) return nullptr;
250
251 // If the PHI translated LHS is an add of a constant, fold the immediates.
252 if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(Val: LHS))
253 if (BOp->getOpcode() == Instruction::Add)
254 if (ConstantInt *CI = dyn_cast<ConstantInt>(Val: BOp->getOperand(i_nocapture: 1))) {
255 LHS = BOp->getOperand(i_nocapture: 0);
256 RHS = ConstantExpr::getAdd(C1: RHS, C2: CI);
257 isNSW = isNUW = false;
258
259 // If the old 'LHS' was an input, add the new 'LHS' as an input.
260 if (is_contained(Range&: InstInputs, Element: BOp)) {
261 RemoveInstInputs(V: BOp, InstInputs);
262 addAsInput(V: LHS);
263 }
264 }
265
266 // See if the add simplifies away.
267 if (Value *Res = simplifyAddInst(LHS, RHS, IsNSW: isNSW, IsNUW: isNUW, Q: {DL, TLI, DT, AC})) {
268 // If we simplified the operands, the LHS is no longer an input, but Res
269 // is.
270 RemoveInstInputs(V: LHS, InstInputs);
271 return addAsInput(V: Res);
272 }
273
274 // If we didn't modify the add, just return it.
275 if (LHS == Inst->getOperand(i: 0) && RHS == Inst->getOperand(i: 1))
276 return Inst;
277
278 // Otherwise, see if we have this add available somewhere.
279 for (User *U : LHS->users()) {
280 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Val: U))
281 if (BO->getOpcode() == Instruction::Add &&
282 BO->getOperand(i_nocapture: 0) == LHS && BO->getOperand(i_nocapture: 1) == RHS &&
283 BO->getParent()->getParent() == CurBB->getParent() &&
284 (!DT || DT->dominates(A: BO->getParent(), B: PredBB)))
285 return BO;
286 }
287
288 return nullptr;
289 }
290
291 // Otherwise, we failed.
292 return nullptr;
293}
294
295/// PHITranslateValue - PHI translate the current address up the CFG from
296/// CurBB to Pred, updating our state to reflect any needed changes. If
297/// 'MustDominate' is true, the translated value must dominate PredBB.
298Value *PHITransAddr::translateValue(BasicBlock *CurBB, BasicBlock *PredBB,
299 const DominatorTree *DT,
300 bool MustDominate) {
301 assert(DT || !MustDominate);
302 assert(verify() && "Invalid PHITransAddr!");
303 if (DT && DT->isReachableFromEntry(A: PredBB))
304 Addr = translateSubExpr(V: Addr, CurBB, PredBB, DT);
305 else
306 Addr = nullptr;
307 assert(verify() && "Invalid PHITransAddr!");
308
309 if (MustDominate)
310 // Make sure the value is live in the predecessor.
311 if (Instruction *Inst = dyn_cast_or_null<Instruction>(Val: Addr))
312 if (!DT->dominates(A: Inst->getParent(), B: PredBB))
313 Addr = nullptr;
314
315 return Addr;
316}
317
318/// PHITranslateWithInsertion - PHI translate this value into the specified
319/// predecessor block, inserting a computation of the value if it is
320/// unavailable.
321///
322/// All newly created instructions are added to the NewInsts list. This
323/// returns null on failure.
324///
325Value *
326PHITransAddr::translateWithInsertion(BasicBlock *CurBB, BasicBlock *PredBB,
327 const DominatorTree &DT,
328 SmallVectorImpl<Instruction *> &NewInsts) {
329 unsigned NISize = NewInsts.size();
330
331 // Attempt to PHI translate with insertion.
332 Addr = insertTranslatedSubExpr(InVal: Addr, CurBB, PredBB, DT, NewInsts);
333
334 // If successful, return the new value.
335 if (Addr) return Addr;
336
337 // If not, destroy any intermediate instructions inserted.
338 while (NewInsts.size() != NISize)
339 NewInsts.pop_back_val()->eraseFromParent();
340 return nullptr;
341}
342
343/// insertTranslatedSubExpr - Insert a computation of the PHI translated
344/// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
345/// block. All newly created instructions are added to the NewInsts list.
346/// This returns null on failure.
347///
348Value *PHITransAddr::insertTranslatedSubExpr(
349 Value *InVal, BasicBlock *CurBB, BasicBlock *PredBB,
350 const DominatorTree &DT, SmallVectorImpl<Instruction *> &NewInsts) {
351 // See if we have a version of this value already available and dominating
352 // PredBB. If so, there is no need to insert a new instance of it.
353 PHITransAddr Tmp(InVal, DL, AC);
354 if (Value *Addr =
355 Tmp.translateValue(CurBB, PredBB, DT: &DT, /*MustDominate=*/true))
356 return Addr;
357
358 // We don't need to PHI translate values which aren't instructions.
359 auto *Inst = dyn_cast<Instruction>(Val: InVal);
360 if (!Inst)
361 return nullptr;
362
363 // Handle cast of PHI translatable value.
364 if (CastInst *Cast = dyn_cast<CastInst>(Val: Inst)) {
365 Value *OpVal = insertTranslatedSubExpr(InVal: Cast->getOperand(i_nocapture: 0), CurBB, PredBB,
366 DT, NewInsts);
367 if (!OpVal) return nullptr;
368
369 // Otherwise insert a cast at the end of PredBB.
370 CastInst *New = CastInst::Create(Cast->getOpcode(), S: OpVal, Ty: InVal->getType(),
371 Name: InVal->getName() + ".phi.trans.insert",
372 InsertBefore: PredBB->getTerminator());
373 New->setDebugLoc(Inst->getDebugLoc());
374 NewInsts.push_back(Elt: New);
375 return New;
376 }
377
378 // Handle getelementptr with at least one PHI operand.
379 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Val: Inst)) {
380 SmallVector<Value*, 8> GEPOps;
381 BasicBlock *CurBB = GEP->getParent();
382 for (Value *Op : GEP->operands()) {
383 Value *OpVal = insertTranslatedSubExpr(InVal: Op, CurBB, PredBB, DT, NewInsts);
384 if (!OpVal) return nullptr;
385 GEPOps.push_back(Elt: OpVal);
386 }
387
388 GetElementPtrInst *Result = GetElementPtrInst::Create(
389 PointeeType: GEP->getSourceElementType(), Ptr: GEPOps[0], IdxList: ArrayRef(GEPOps).slice(N: 1),
390 NameStr: InVal->getName() + ".phi.trans.insert", InsertBefore: PredBB->getTerminator());
391 Result->setDebugLoc(Inst->getDebugLoc());
392 Result->setIsInBounds(GEP->isInBounds());
393 NewInsts.push_back(Elt: Result);
394 return Result;
395 }
396
397 // Handle add with a constant RHS.
398 if (EnableAddPhiTranslation && Inst->getOpcode() == Instruction::Add &&
399 isa<ConstantInt>(Val: Inst->getOperand(i: 1))) {
400
401 // FIXME: This code works, but it is unclear that we actually want to insert
402 // a big chain of computation in order to make a value available in a block.
403 // This needs to be evaluated carefully to consider its cost trade offs.
404
405 // PHI translate the LHS.
406 Value *OpVal = insertTranslatedSubExpr(InVal: Inst->getOperand(i: 0), CurBB, PredBB,
407 DT, NewInsts);
408 if (OpVal == nullptr)
409 return nullptr;
410
411 BinaryOperator *Res = BinaryOperator::CreateAdd(V1: OpVal, V2: Inst->getOperand(i: 1),
412 Name: InVal->getName()+".phi.trans.insert",
413 I: PredBB->getTerminator());
414 Res->setHasNoSignedWrap(cast<BinaryOperator>(Val: Inst)->hasNoSignedWrap());
415 Res->setHasNoUnsignedWrap(cast<BinaryOperator>(Val: Inst)->hasNoUnsignedWrap());
416 NewInsts.push_back(Elt: Res);
417 return Res;
418 }
419
420 return nullptr;
421}
422

source code of llvm/lib/Analysis/PHITransAddr.cpp