1//===- InstCombineNegator.cpp -----------------------------------*- C++ -*-===//
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 sinking of negation into expression trees,
10// as long as that can be done without increasing instruction count.
11//
12//===----------------------------------------------------------------------===//
13
14#include "InstCombineInternal.h"
15#include "llvm/ADT/APInt.h"
16#include "llvm/ADT/ArrayRef.h"
17#include "llvm/ADT/DenseMap.h"
18#include "llvm/ADT/STLExtras.h"
19#include "llvm/ADT/SmallVector.h"
20#include "llvm/ADT/Statistic.h"
21#include "llvm/ADT/StringRef.h"
22#include "llvm/ADT/Twine.h"
23#include "llvm/Analysis/TargetFolder.h"
24#include "llvm/Analysis/ValueTracking.h"
25#include "llvm/IR/Constant.h"
26#include "llvm/IR/Constants.h"
27#include "llvm/IR/DebugLoc.h"
28#include "llvm/IR/IRBuilder.h"
29#include "llvm/IR/Instruction.h"
30#include "llvm/IR/Instructions.h"
31#include "llvm/IR/PatternMatch.h"
32#include "llvm/IR/Type.h"
33#include "llvm/IR/Use.h"
34#include "llvm/IR/User.h"
35#include "llvm/IR/Value.h"
36#include "llvm/Support/Casting.h"
37#include "llvm/Support/CommandLine.h"
38#include "llvm/Support/Compiler.h"
39#include "llvm/Support/DebugCounter.h"
40#include "llvm/Support/ErrorHandling.h"
41#include "llvm/Support/raw_ostream.h"
42#include "llvm/Transforms/InstCombine/InstCombiner.h"
43#include <cassert>
44#include <cstdint>
45#include <functional>
46#include <type_traits>
47#include <utility>
48
49namespace llvm {
50class DataLayout;
51class LLVMContext;
52} // namespace llvm
53
54using namespace llvm;
55
56#define DEBUG_TYPE "instcombine"
57
58STATISTIC(NegatorTotalNegationsAttempted,
59 "Negator: Number of negations attempted to be sinked");
60STATISTIC(NegatorNumTreesNegated,
61 "Negator: Number of negations successfully sinked");
62STATISTIC(NegatorMaxDepthVisited, "Negator: Maximal traversal depth ever "
63 "reached while attempting to sink negation");
64STATISTIC(NegatorTimesDepthLimitReached,
65 "Negator: How many times did the traversal depth limit was reached "
66 "during sinking");
67STATISTIC(
68 NegatorNumValuesVisited,
69 "Negator: Total number of values visited during attempts to sink negation");
70STATISTIC(NegatorNumNegationsFoundInCache,
71 "Negator: How many negations did we retrieve/reuse from cache");
72STATISTIC(NegatorMaxTotalValuesVisited,
73 "Negator: Maximal number of values ever visited while attempting to "
74 "sink negation");
75STATISTIC(NegatorNumInstructionsCreatedTotal,
76 "Negator: Number of new negated instructions created, total");
77STATISTIC(NegatorMaxInstructionsCreated,
78 "Negator: Maximal number of new instructions created during negation "
79 "attempt");
80STATISTIC(NegatorNumInstructionsNegatedSuccess,
81 "Negator: Number of new negated instructions created in successful "
82 "negation sinking attempts");
83
84DEBUG_COUNTER(NegatorCounter, "instcombine-negator",
85 "Controls Negator transformations in InstCombine pass");
86
87static cl::opt<bool>
88 NegatorEnabled("instcombine-negator-enabled", cl::init(Val: true),
89 cl::desc("Should we attempt to sink negations?"));
90
91static cl::opt<unsigned>
92 NegatorMaxDepth("instcombine-negator-max-depth",
93 cl::init(Val: NegatorDefaultMaxDepth),
94 cl::desc("What is the maximal lookup depth when trying to "
95 "check for viability of negation sinking."));
96
97Negator::Negator(LLVMContext &C, const DataLayout &DL, bool IsTrulyNegation_)
98 : Builder(C, TargetFolder(DL),
99 IRBuilderCallbackInserter([&](Instruction *I) {
100 ++NegatorNumInstructionsCreatedTotal;
101 NewInstructions.push_back(Elt: I);
102 })),
103 IsTrulyNegation(IsTrulyNegation_) {}
104
105#if LLVM_ENABLE_STATS
106Negator::~Negator() {
107 NegatorMaxTotalValuesVisited.updateMax(NumValuesVisitedInThisNegator);
108}
109#endif
110
111// Due to the InstCombine's worklist management, there are no guarantees that
112// each instruction we'll encounter has been visited by InstCombine already.
113// In particular, most importantly for us, that means we have to canonicalize
114// constants to RHS ourselves, since that is helpful sometimes.
115std::array<Value *, 2> Negator::getSortedOperandsOfBinOp(Instruction *I) {
116 assert(I->getNumOperands() == 2 && "Only for binops!");
117 std::array<Value *, 2> Ops{I->getOperand(i: 0), I->getOperand(i: 1)};
118 if (I->isCommutative() && InstCombiner::getComplexity(V: I->getOperand(i: 0)) <
119 InstCombiner::getComplexity(V: I->getOperand(i: 1)))
120 std::swap(a&: Ops[0], b&: Ops[1]);
121 return Ops;
122}
123
124// FIXME: can this be reworked into a worklist-based algorithm while preserving
125// the depth-first, early bailout traversal?
126[[nodiscard]] Value *Negator::visitImpl(Value *V, bool IsNSW, unsigned Depth) {
127 // -(undef) -> undef.
128 if (match(V, P: m_Undef()))
129 return V;
130
131 // In i1, negation can simply be ignored.
132 if (V->getType()->isIntOrIntVectorTy(BitWidth: 1))
133 return V;
134
135 Value *X;
136
137 // -(-(X)) -> X.
138 if (match(V, P: m_Neg(V: m_Value(V&: X))))
139 return X;
140
141 // Integral constants can be freely negated.
142 if (match(V, P: m_AnyIntegralConstant()))
143 return ConstantExpr::getNeg(C: cast<Constant>(Val: V),
144 /*HasNSW=*/false);
145
146 // If we have a non-instruction, then give up.
147 if (!isa<Instruction>(Val: V))
148 return nullptr;
149
150 // If we have started with a true negation (i.e. `sub 0, %y`), then if we've
151 // got instruction that does not require recursive reasoning, we can still
152 // negate it even if it has other uses, without increasing instruction count.
153 if (!V->hasOneUse() && !IsTrulyNegation)
154 return nullptr;
155
156 auto *I = cast<Instruction>(Val: V);
157 unsigned BitWidth = I->getType()->getScalarSizeInBits();
158
159 // We must preserve the insertion point and debug info that is set in the
160 // builder at the time this function is called.
161 InstCombiner::BuilderTy::InsertPointGuard Guard(Builder);
162 // And since we are trying to negate instruction I, that tells us about the
163 // insertion point and the debug info that we need to keep.
164 Builder.SetInsertPoint(I);
165
166 // In some cases we can give the answer without further recursion.
167 switch (I->getOpcode()) {
168 case Instruction::Add: {
169 std::array<Value *, 2> Ops = getSortedOperandsOfBinOp(I);
170 // `inc` is always negatible.
171 if (match(V: Ops[1], P: m_One()))
172 return Builder.CreateNot(V: Ops[0], Name: I->getName() + ".neg");
173 break;
174 }
175 case Instruction::Xor:
176 // `not` is always negatible.
177 if (match(V: I, P: m_Not(V: m_Value(V&: X))))
178 return Builder.CreateAdd(LHS: X, RHS: ConstantInt::get(Ty: X->getType(), V: 1),
179 Name: I->getName() + ".neg");
180 break;
181 case Instruction::AShr:
182 case Instruction::LShr: {
183 // Right-shift sign bit smear is negatible.
184 const APInt *Op1Val;
185 if (match(V: I->getOperand(i: 1), P: m_APInt(Res&: Op1Val)) && *Op1Val == BitWidth - 1) {
186 Value *BO = I->getOpcode() == Instruction::AShr
187 ? Builder.CreateLShr(LHS: I->getOperand(i: 0), RHS: I->getOperand(i: 1))
188 : Builder.CreateAShr(LHS: I->getOperand(i: 0), RHS: I->getOperand(i: 1));
189 if (auto *NewInstr = dyn_cast<Instruction>(Val: BO)) {
190 NewInstr->copyIRFlags(V: I);
191 NewInstr->setName(I->getName() + ".neg");
192 }
193 return BO;
194 }
195 // While we could negate exact arithmetic shift:
196 // ashr exact %x, C --> sdiv exact i8 %x, -1<<C
197 // iff C != 0 and C u< bitwidth(%x), we don't want to,
198 // because division is *THAT* much worse than a shift.
199 break;
200 }
201 case Instruction::SExt:
202 case Instruction::ZExt:
203 // `*ext` of i1 is always negatible
204 if (I->getOperand(i: 0)->getType()->isIntOrIntVectorTy(BitWidth: 1))
205 return I->getOpcode() == Instruction::SExt
206 ? Builder.CreateZExt(V: I->getOperand(i: 0), DestTy: I->getType(),
207 Name: I->getName() + ".neg")
208 : Builder.CreateSExt(V: I->getOperand(i: 0), DestTy: I->getType(),
209 Name: I->getName() + ".neg");
210 break;
211 case Instruction::Select: {
212 // If both arms of the select are constants, we don't need to recurse.
213 // Therefore, this transform is not limited by uses.
214 auto *Sel = cast<SelectInst>(Val: I);
215 Constant *TrueC, *FalseC;
216 if (match(V: Sel->getTrueValue(), P: m_ImmConstant(C&: TrueC)) &&
217 match(V: Sel->getFalseValue(), P: m_ImmConstant(C&: FalseC))) {
218 Constant *NegTrueC = ConstantExpr::getNeg(C: TrueC);
219 Constant *NegFalseC = ConstantExpr::getNeg(C: FalseC);
220 return Builder.CreateSelect(C: Sel->getCondition(), True: NegTrueC, False: NegFalseC,
221 Name: I->getName() + ".neg", /*MDFrom=*/I);
222 }
223 break;
224 }
225 case Instruction::Call:
226 if (auto *CI = dyn_cast<CmpIntrinsic>(Val: I); CI && CI->hasOneUse())
227 return Builder.CreateIntrinsic(RetTy: CI->getType(), ID: CI->getIntrinsicID(),
228 Args: {CI->getRHS(), CI->getLHS()});
229 break;
230 default:
231 break; // Other instructions require recursive reasoning.
232 }
233
234 if (I->getOpcode() == Instruction::Sub &&
235 (I->hasOneUse() || match(V: I->getOperand(i: 0), P: m_ImmConstant()))) {
236 // `sub` is always negatible.
237 // However, only do this either if the old `sub` doesn't stick around, or
238 // it was subtracting from a constant. Otherwise, this isn't profitable.
239 return Builder.CreateSub(LHS: I->getOperand(i: 1), RHS: I->getOperand(i: 0),
240 Name: I->getName() + ".neg", /* HasNUW */ false,
241 HasNSW: IsNSW && I->hasNoSignedWrap());
242 }
243
244 // Some other cases, while still don't require recursion,
245 // are restricted to the one-use case.
246 if (!V->hasOneUse())
247 return nullptr;
248
249 switch (I->getOpcode()) {
250 case Instruction::ZExt: {
251 // Negation of zext of signbit is signbit splat:
252 // 0 - (zext (i8 X u>> 7) to iN) --> sext (i8 X s>> 7) to iN
253 Value *SrcOp = I->getOperand(i: 0);
254 unsigned SrcWidth = SrcOp->getType()->getScalarSizeInBits();
255 const APInt &FullShift = APInt(SrcWidth, SrcWidth - 1);
256 if (IsTrulyNegation &&
257 match(V: SrcOp, P: m_LShr(L: m_Value(V&: X), R: m_SpecificIntAllowPoison(V: FullShift)))) {
258 Value *Ashr = Builder.CreateAShr(LHS: X, RHS: FullShift);
259 return Builder.CreateSExt(V: Ashr, DestTy: I->getType());
260 }
261 break;
262 }
263 case Instruction::And: {
264 Constant *ShAmt;
265 // sub(y,and(lshr(x,C),1)) --> add(ashr(shl(x,(BW-1)-C),BW-1),y)
266 if (match(V: I, P: m_And(L: m_OneUse(SubPattern: m_TruncOrSelf(
267 Op: m_LShr(L: m_Value(V&: X), R: m_ImmConstant(C&: ShAmt)))),
268 R: m_One()))) {
269 unsigned BW = X->getType()->getScalarSizeInBits();
270 Constant *BWMinusOne = ConstantInt::get(Ty: X->getType(), V: BW - 1);
271 Value *R = Builder.CreateShl(LHS: X, RHS: Builder.CreateSub(LHS: BWMinusOne, RHS: ShAmt));
272 R = Builder.CreateAShr(LHS: R, RHS: BWMinusOne);
273 return Builder.CreateTruncOrBitCast(V: R, DestTy: I->getType());
274 }
275 break;
276 }
277 case Instruction::SDiv:
278 // `sdiv` is negatible if divisor is not undef/INT_MIN/1.
279 // While this is normally not behind a use-check,
280 // let's consider division to be special since it's costly.
281 if (auto *Op1C = dyn_cast<Constant>(Val: I->getOperand(i: 1))) {
282 if (!Op1C->containsUndefOrPoisonElement() &&
283 Op1C->isNotMinSignedValue() && Op1C->isNotOneValue()) {
284 Value *BO =
285 Builder.CreateSDiv(LHS: I->getOperand(i: 0), RHS: ConstantExpr::getNeg(C: Op1C),
286 Name: I->getName() + ".neg");
287 if (auto *NewInstr = dyn_cast<Instruction>(Val: BO))
288 NewInstr->setIsExact(I->isExact());
289 return BO;
290 }
291 }
292 break;
293 }
294
295 // Rest of the logic is recursive, so if it's time to give up then it's time.
296 if (Depth > NegatorMaxDepth) {
297 LLVM_DEBUG(dbgs() << "Negator: reached maximal allowed traversal depth in "
298 << *V << ". Giving up.\n");
299 ++NegatorTimesDepthLimitReached;
300 return nullptr;
301 }
302
303 switch (I->getOpcode()) {
304 case Instruction::Freeze: {
305 // `freeze` is negatible if its operand is negatible.
306 Value *NegOp = negate(V: I->getOperand(i: 0), IsNSW, Depth: Depth + 1);
307 if (!NegOp) // Early return.
308 return nullptr;
309 return Builder.CreateFreeze(V: NegOp, Name: I->getName() + ".neg");
310 }
311 case Instruction::PHI: {
312 // `phi` is negatible if all the incoming values are negatible.
313 auto *PHI = cast<PHINode>(Val: I);
314 SmallVector<Value *, 4> NegatedIncomingValues(PHI->getNumOperands());
315 for (auto I : zip(t: PHI->incoming_values(), u&: NegatedIncomingValues)) {
316 if (!(std::get<1>(t&: I) =
317 negate(V: std::get<0>(t&: I), IsNSW, Depth: Depth + 1))) // Early return.
318 return nullptr;
319 }
320 // All incoming values are indeed negatible. Create negated PHI node.
321 PHINode *NegatedPHI = Builder.CreatePHI(
322 Ty: PHI->getType(), NumReservedValues: PHI->getNumOperands(), Name: PHI->getName() + ".neg");
323 for (auto I : zip(t&: NegatedIncomingValues, u: PHI->blocks()))
324 NegatedPHI->addIncoming(V: std::get<0>(t&: I), BB: std::get<1>(t&: I));
325 return NegatedPHI;
326 }
327 case Instruction::Select: {
328 if (isKnownNegation(X: I->getOperand(i: 1), Y: I->getOperand(i: 2), /*NeedNSW=*/false,
329 /*AllowPoison=*/false)) {
330 // Of one hand of select is known to be negation of another hand,
331 // just swap the hands around.
332 auto *NewSelect = cast<SelectInst>(Val: I->clone());
333 // Just swap the operands of the select.
334 NewSelect->swapValues();
335 // Don't swap prof metadata, we didn't change the branch behavior.
336 NewSelect->setName(I->getName() + ".neg");
337 Builder.Insert(I: NewSelect);
338 return NewSelect;
339 }
340 // `select` is negatible if both hands of `select` are negatible.
341 Value *NegOp1 = negate(V: I->getOperand(i: 1), IsNSW, Depth: Depth + 1);
342 if (!NegOp1) // Early return.
343 return nullptr;
344 Value *NegOp2 = negate(V: I->getOperand(i: 2), IsNSW, Depth: Depth + 1);
345 if (!NegOp2)
346 return nullptr;
347 // Do preserve the metadata!
348 return Builder.CreateSelect(C: I->getOperand(i: 0), True: NegOp1, False: NegOp2,
349 Name: I->getName() + ".neg", /*MDFrom=*/I);
350 }
351 case Instruction::ShuffleVector: {
352 // `shufflevector` is negatible if both operands are negatible.
353 auto *Shuf = cast<ShuffleVectorInst>(Val: I);
354 Value *NegOp0 = negate(V: I->getOperand(i: 0), IsNSW, Depth: Depth + 1);
355 if (!NegOp0) // Early return.
356 return nullptr;
357 Value *NegOp1 = negate(V: I->getOperand(i: 1), IsNSW, Depth: Depth + 1);
358 if (!NegOp1)
359 return nullptr;
360 return Builder.CreateShuffleVector(V1: NegOp0, V2: NegOp1, Mask: Shuf->getShuffleMask(),
361 Name: I->getName() + ".neg");
362 }
363 case Instruction::ExtractElement: {
364 // `extractelement` is negatible if source operand is negatible.
365 auto *EEI = cast<ExtractElementInst>(Val: I);
366 Value *NegVector = negate(V: EEI->getVectorOperand(), IsNSW, Depth: Depth + 1);
367 if (!NegVector) // Early return.
368 return nullptr;
369 return Builder.CreateExtractElement(Vec: NegVector, Idx: EEI->getIndexOperand(),
370 Name: I->getName() + ".neg");
371 }
372 case Instruction::InsertElement: {
373 // `insertelement` is negatible if both the source vector and
374 // element-to-be-inserted are negatible.
375 auto *IEI = cast<InsertElementInst>(Val: I);
376 Value *NegVector = negate(V: IEI->getOperand(i_nocapture: 0), IsNSW, Depth: Depth + 1);
377 if (!NegVector) // Early return.
378 return nullptr;
379 Value *NegNewElt = negate(V: IEI->getOperand(i_nocapture: 1), IsNSW, Depth: Depth + 1);
380 if (!NegNewElt) // Early return.
381 return nullptr;
382 return Builder.CreateInsertElement(Vec: NegVector, NewElt: NegNewElt, Idx: IEI->getOperand(i_nocapture: 2),
383 Name: I->getName() + ".neg");
384 }
385 case Instruction::Trunc: {
386 // `trunc` is negatible if its operand is negatible.
387 Value *NegOp = negate(V: I->getOperand(i: 0), /* IsNSW */ false, Depth: Depth + 1);
388 if (!NegOp) // Early return.
389 return nullptr;
390 return Builder.CreateTrunc(V: NegOp, DestTy: I->getType(), Name: I->getName() + ".neg");
391 }
392 case Instruction::Shl: {
393 // `shl` is negatible if the first operand is negatible.
394 IsNSW &= I->hasNoSignedWrap();
395 if (Value *NegOp0 = negate(V: I->getOperand(i: 0), IsNSW, Depth: Depth + 1))
396 return Builder.CreateShl(LHS: NegOp0, RHS: I->getOperand(i: 1), Name: I->getName() + ".neg",
397 /* HasNUW */ false, HasNSW: IsNSW);
398 // Otherwise, `shl %x, C` can be interpreted as `mul %x, 1<<C`.
399 Constant *Op1C;
400 if (!match(V: I->getOperand(i: 1), P: m_ImmConstant(C&: Op1C)) || !IsTrulyNegation)
401 return nullptr;
402 return Builder.CreateMul(
403 LHS: I->getOperand(i: 0),
404 RHS: Builder.CreateShl(LHS: Constant::getAllOnesValue(Ty: Op1C->getType()), RHS: Op1C),
405 Name: I->getName() + ".neg", /* HasNUW */ false, HasNSW: IsNSW);
406 }
407 case Instruction::Or: {
408 if (!cast<PossiblyDisjointInst>(Val: I)->isDisjoint())
409 return nullptr; // Don't know how to handle `or` in general.
410 std::array<Value *, 2> Ops = getSortedOperandsOfBinOp(I);
411 // `or`/`add` are interchangeable when operands have no common bits set.
412 // `inc` is always negatible.
413 if (match(V: Ops[1], P: m_One()))
414 return Builder.CreateNot(V: Ops[0], Name: I->getName() + ".neg");
415 // Else, just defer to Instruction::Add handling.
416 [[fallthrough]];
417 }
418 case Instruction::Add: {
419 // `add` is negatible if both of its operands are negatible.
420 SmallVector<Value *, 2> NegatedOps, NonNegatedOps;
421 for (Value *Op : I->operands()) {
422 // Can we sink the negation into this operand?
423 if (Value *NegOp = negate(V: Op, /* IsNSW */ false, Depth: Depth + 1)) {
424 NegatedOps.emplace_back(Args&: NegOp); // Successfully negated operand!
425 continue;
426 }
427 // Failed to sink negation into this operand. IFF we started from negation
428 // and we manage to sink negation into one operand, we can still do this.
429 if (!IsTrulyNegation)
430 return nullptr;
431 NonNegatedOps.emplace_back(Args&: Op); // Just record which operand that was.
432 }
433 assert((NegatedOps.size() + NonNegatedOps.size()) == 2 &&
434 "Internal consistency check failed.");
435 // Did we manage to sink negation into both of the operands?
436 if (NegatedOps.size() == 2) // Then we get to keep the `add`!
437 return Builder.CreateAdd(LHS: NegatedOps[0], RHS: NegatedOps[1],
438 Name: I->getName() + ".neg");
439 assert(IsTrulyNegation && "We should have early-exited then.");
440 // Completely failed to sink negation?
441 if (NonNegatedOps.size() == 2)
442 return nullptr;
443 // 0-(a+b) --> (-a)-b
444 return Builder.CreateSub(LHS: NegatedOps[0], RHS: NonNegatedOps[0],
445 Name: I->getName() + ".neg");
446 }
447 case Instruction::Xor: {
448 std::array<Value *, 2> Ops = getSortedOperandsOfBinOp(I);
449 // `xor` is negatible if one of its operands is invertible.
450 // FIXME: InstCombineInverter? But how to connect Inverter and Negator?
451 if (auto *C = dyn_cast<Constant>(Val: Ops[1])) {
452 if (IsTrulyNegation) {
453 Value *Xor = Builder.CreateXor(LHS: Ops[0], RHS: ConstantExpr::getNot(C));
454 return Builder.CreateAdd(LHS: Xor, RHS: ConstantInt::get(Ty: Xor->getType(), V: 1),
455 Name: I->getName() + ".neg");
456 }
457 }
458 return nullptr;
459 }
460 case Instruction::Mul: {
461 std::array<Value *, 2> Ops = getSortedOperandsOfBinOp(I);
462 // `mul` is negatible if one of its operands is negatible.
463 Value *NegatedOp, *OtherOp;
464 // First try the second operand, in case it's a constant it will be best to
465 // just invert it instead of sinking the `neg` deeper.
466 if (Value *NegOp1 = negate(V: Ops[1], /* IsNSW */ false, Depth: Depth + 1)) {
467 NegatedOp = NegOp1;
468 OtherOp = Ops[0];
469 } else if (Value *NegOp0 = negate(V: Ops[0], /* IsNSW */ false, Depth: Depth + 1)) {
470 NegatedOp = NegOp0;
471 OtherOp = Ops[1];
472 } else
473 // Can't negate either of them.
474 return nullptr;
475 return Builder.CreateMul(LHS: NegatedOp, RHS: OtherOp, Name: I->getName() + ".neg",
476 /* HasNUW */ false, HasNSW: IsNSW && I->hasNoSignedWrap());
477 }
478 default:
479 return nullptr; // Don't know, likely not negatible for free.
480 }
481
482 llvm_unreachable("Can't get here. We always return from switch.");
483}
484
485[[nodiscard]] Value *Negator::negate(Value *V, bool IsNSW, unsigned Depth) {
486 NegatorMaxDepthVisited.updateMax(V: Depth);
487 ++NegatorNumValuesVisited;
488
489#if LLVM_ENABLE_STATS
490 ++NumValuesVisitedInThisNegator;
491#endif
492
493#ifndef NDEBUG
494 // We can't ever have a Value with such an address.
495 Value *Placeholder = reinterpret_cast<Value *>(static_cast<uintptr_t>(-1));
496#endif
497
498 // Did we already try to negate this value?
499 auto NegationsCacheIterator = NegationsCache.find(Val: V);
500 if (NegationsCacheIterator != NegationsCache.end()) {
501 ++NegatorNumNegationsFoundInCache;
502 Value *NegatedV = NegationsCacheIterator->second;
503 assert(NegatedV != Placeholder && "Encountered a cycle during negation.");
504 return NegatedV;
505 }
506
507#ifndef NDEBUG
508 // We did not find a cached result for negation of V. While there,
509 // let's temporairly cache a placeholder value, with the idea that if later
510 // during negation we fetch it from cache, we'll know we're in a cycle.
511 NegationsCache[V] = Placeholder;
512#endif
513
514 // No luck. Try negating it for real.
515 Value *NegatedV = visitImpl(V, IsNSW, Depth);
516 // And cache the (real) result for the future.
517 NegationsCache[V] = NegatedV;
518
519 return NegatedV;
520}
521
522[[nodiscard]] std::optional<Negator::Result> Negator::run(Value *Root,
523 bool IsNSW) {
524 Value *Negated = negate(V: Root, IsNSW, /*Depth=*/0);
525 if (!Negated) {
526 // We must cleanup newly-inserted instructions, to avoid any potential
527 // endless combine looping.
528 for (Instruction *I : llvm::reverse(C&: NewInstructions))
529 I->eraseFromParent();
530 return std::nullopt;
531 }
532 return std::make_pair(x: ArrayRef<Instruction *>(NewInstructions), y&: Negated);
533}
534
535[[nodiscard]] Value *Negator::Negate(bool LHSIsZero, bool IsNSW, Value *Root,
536 InstCombinerImpl &IC) {
537 ++NegatorTotalNegationsAttempted;
538 LLVM_DEBUG(dbgs() << "Negator: attempting to sink negation into " << *Root
539 << "\n");
540
541 if (!NegatorEnabled || !DebugCounter::shouldExecute(CounterName: NegatorCounter))
542 return nullptr;
543
544 Negator N(Root->getContext(), IC.getDataLayout(), LHSIsZero);
545 std::optional<Result> Res = N.run(Root, IsNSW);
546 if (!Res) { // Negation failed.
547 LLVM_DEBUG(dbgs() << "Negator: failed to sink negation into " << *Root
548 << "\n");
549 return nullptr;
550 }
551
552 LLVM_DEBUG(dbgs() << "Negator: successfully sunk negation into " << *Root
553 << "\n NEW: " << *Res->second << "\n");
554 ++NegatorNumTreesNegated;
555
556 // We must temporarily unset the 'current' insertion point and DebugLoc of the
557 // InstCombine's IRBuilder so that it won't interfere with the ones we have
558 // already specified when producing negated instructions.
559 InstCombiner::BuilderTy::InsertPointGuard Guard(IC.Builder);
560 IC.Builder.ClearInsertionPoint();
561 IC.Builder.SetCurrentDebugLocation(DebugLoc());
562
563 // And finally, we must add newly-created instructions into the InstCombine's
564 // worklist (in a proper order!) so it can attempt to combine them.
565 LLVM_DEBUG(dbgs() << "Negator: Propagating " << Res->first.size()
566 << " instrs to InstCombine\n");
567 NegatorMaxInstructionsCreated.updateMax(V: Res->first.size());
568 NegatorNumInstructionsNegatedSuccess += Res->first.size();
569
570 // They are in def-use order, so nothing fancy, just insert them in order.
571 for (Instruction *I : Res->first)
572 IC.Builder.Insert(I, Name: I->getName());
573
574 // And return the new root.
575 return Res->second;
576}
577