1//===- InstCombineShifts.cpp ----------------------------------------------===//
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 visitShl, visitLShr, and visitAShr functions.
10//
11//===----------------------------------------------------------------------===//
12
13#include "InstCombineInternal.h"
14#include "llvm/Analysis/InstructionSimplify.h"
15#include "llvm/IR/IntrinsicInst.h"
16#include "llvm/IR/PatternMatch.h"
17#include "llvm/Transforms/InstCombine/InstCombiner.h"
18using namespace llvm;
19using namespace PatternMatch;
20
21#define DEBUG_TYPE "instcombine"
22
23bool canTryToConstantAddTwoShiftAmounts(Value *Sh0, Value *ShAmt0, Value *Sh1,
24 Value *ShAmt1) {
25 // We have two shift amounts from two different shifts. The types of those
26 // shift amounts may not match. If that's the case let's bailout now..
27 if (ShAmt0->getType() != ShAmt1->getType())
28 return false;
29
30 // As input, we have the following pattern:
31 // Sh0 (Sh1 X, Q), K
32 // We want to rewrite that as:
33 // Sh x, (Q+K) iff (Q+K) u< bitwidth(x)
34 // While we know that originally (Q+K) would not overflow
35 // (because 2 * (N-1) u<= iN -1), we have looked past extensions of
36 // shift amounts. so it may now overflow in smaller bitwidth.
37 // To ensure that does not happen, we need to ensure that the total maximal
38 // shift amount is still representable in that smaller bit width.
39 unsigned MaximalPossibleTotalShiftAmount =
40 (Sh0->getType()->getScalarSizeInBits() - 1) +
41 (Sh1->getType()->getScalarSizeInBits() - 1);
42 APInt MaximalRepresentableShiftAmount =
43 APInt::getAllOnes(numBits: ShAmt0->getType()->getScalarSizeInBits());
44 return MaximalRepresentableShiftAmount.uge(RHS: MaximalPossibleTotalShiftAmount);
45}
46
47// Given pattern:
48// (x shiftopcode Q) shiftopcode K
49// we should rewrite it as
50// x shiftopcode (Q+K) iff (Q+K) u< bitwidth(x) and
51//
52// This is valid for any shift, but they must be identical, and we must be
53// careful in case we have (zext(Q)+zext(K)) and look past extensions,
54// (Q+K) must not overflow or else (Q+K) u< bitwidth(x) is bogus.
55//
56// AnalyzeForSignBitExtraction indicates that we will only analyze whether this
57// pattern has any 2 right-shifts that sum to 1 less than original bit width.
58Value *InstCombinerImpl::reassociateShiftAmtsOfTwoSameDirectionShifts(
59 BinaryOperator *Sh0, const SimplifyQuery &SQ,
60 bool AnalyzeForSignBitExtraction) {
61 // Look for a shift of some instruction, ignore zext of shift amount if any.
62 Instruction *Sh0Op0;
63 Value *ShAmt0;
64 if (!match(V: Sh0,
65 P: m_Shift(L: m_Instruction(I&: Sh0Op0), R: m_ZExtOrSelf(Op: m_Value(V&: ShAmt0)))))
66 return nullptr;
67
68 // If there is a truncation between the two shifts, we must make note of it
69 // and look through it. The truncation imposes additional constraints on the
70 // transform.
71 Instruction *Sh1;
72 Value *Trunc = nullptr;
73 match(V: Sh0Op0,
74 P: m_CombineOr(L: m_CombineAnd(L: m_Trunc(Op: m_Instruction(I&: Sh1)), R: m_Value(V&: Trunc)),
75 R: m_Instruction(I&: Sh1)));
76
77 // Inner shift: (x shiftopcode ShAmt1)
78 // Like with other shift, ignore zext of shift amount if any.
79 Value *X, *ShAmt1;
80 if (!match(V: Sh1, P: m_Shift(L: m_Value(V&: X), R: m_ZExtOrSelf(Op: m_Value(V&: ShAmt1)))))
81 return nullptr;
82
83 // Verify that it would be safe to try to add those two shift amounts.
84 if (!canTryToConstantAddTwoShiftAmounts(Sh0, ShAmt0, Sh1, ShAmt1))
85 return nullptr;
86
87 // We are only looking for signbit extraction if we have two right shifts.
88 bool HadTwoRightShifts = match(V: Sh0, P: m_Shr(L: m_Value(), R: m_Value())) &&
89 match(V: Sh1, P: m_Shr(L: m_Value(), R: m_Value()));
90 // ... and if it's not two right-shifts, we know the answer already.
91 if (AnalyzeForSignBitExtraction && !HadTwoRightShifts)
92 return nullptr;
93
94 // The shift opcodes must be identical, unless we are just checking whether
95 // this pattern can be interpreted as a sign-bit-extraction.
96 Instruction::BinaryOps ShiftOpcode = Sh0->getOpcode();
97 bool IdenticalShOpcodes = Sh0->getOpcode() == Sh1->getOpcode();
98 if (!IdenticalShOpcodes && !AnalyzeForSignBitExtraction)
99 return nullptr;
100
101 // If we saw truncation, we'll need to produce extra instruction,
102 // and for that one of the operands of the shift must be one-use,
103 // unless of course we don't actually plan to produce any instructions here.
104 if (Trunc && !AnalyzeForSignBitExtraction &&
105 !match(V: Sh0, P: m_c_BinOp(L: m_OneUse(SubPattern: m_Value()), R: m_Value())))
106 return nullptr;
107
108 // Can we fold (ShAmt0+ShAmt1) ?
109 auto *NewShAmt = dyn_cast_or_null<Constant>(
110 Val: simplifyAddInst(LHS: ShAmt0, RHS: ShAmt1, /*isNSW=*/IsNSW: false, /*isNUW=*/IsNUW: false,
111 Q: SQ.getWithInstruction(I: Sh0)));
112 if (!NewShAmt)
113 return nullptr; // Did not simplify.
114 unsigned NewShAmtBitWidth = NewShAmt->getType()->getScalarSizeInBits();
115 unsigned XBitWidth = X->getType()->getScalarSizeInBits();
116 // Is the new shift amount smaller than the bit width of inner/new shift?
117 if (!match(V: NewShAmt, P: m_SpecificInt_ICMP(Predicate: ICmpInst::Predicate::ICMP_ULT,
118 Threshold: APInt(NewShAmtBitWidth, XBitWidth))))
119 return nullptr; // FIXME: could perform constant-folding.
120
121 // If there was a truncation, and we have a right-shift, we can only fold if
122 // we are left with the original sign bit. Likewise, if we were just checking
123 // that this is a sighbit extraction, this is the place to check it.
124 // FIXME: zero shift amount is also legal here, but we can't *easily* check
125 // more than one predicate so it's not really worth it.
126 if (HadTwoRightShifts && (Trunc || AnalyzeForSignBitExtraction)) {
127 // If it's not a sign bit extraction, then we're done.
128 if (!match(V: NewShAmt,
129 P: m_SpecificInt_ICMP(Predicate: ICmpInst::Predicate::ICMP_EQ,
130 Threshold: APInt(NewShAmtBitWidth, XBitWidth - 1))))
131 return nullptr;
132 // If it is, and that was the question, return the base value.
133 if (AnalyzeForSignBitExtraction)
134 return X;
135 }
136
137 assert(IdenticalShOpcodes && "Should not get here with different shifts.");
138
139 if (NewShAmt->getType() != X->getType()) {
140 NewShAmt = ConstantFoldCastOperand(Opcode: Instruction::ZExt, C: NewShAmt,
141 DestTy: X->getType(), DL: SQ.DL);
142 if (!NewShAmt)
143 return nullptr;
144 }
145
146 // All good, we can do this fold.
147 BinaryOperator *NewShift = BinaryOperator::Create(Op: ShiftOpcode, S1: X, S2: NewShAmt);
148
149 // The flags can only be propagated if there wasn't a trunc.
150 if (!Trunc) {
151 // If the pattern did not involve trunc, and both of the original shifts
152 // had the same flag set, preserve the flag.
153 if (ShiftOpcode == Instruction::BinaryOps::Shl) {
154 NewShift->setHasNoUnsignedWrap(Sh0->hasNoUnsignedWrap() &&
155 Sh1->hasNoUnsignedWrap());
156 NewShift->setHasNoSignedWrap(Sh0->hasNoSignedWrap() &&
157 Sh1->hasNoSignedWrap());
158 } else {
159 NewShift->setIsExact(Sh0->isExact() && Sh1->isExact());
160 }
161 }
162
163 Instruction *Ret = NewShift;
164 if (Trunc) {
165 Builder.Insert(I: NewShift);
166 Ret = CastInst::Create(Instruction::Trunc, S: NewShift, Ty: Sh0->getType());
167 }
168
169 return Ret;
170}
171
172// If we have some pattern that leaves only some low bits set, and then performs
173// left-shift of those bits, if none of the bits that are left after the final
174// shift are modified by the mask, we can omit the mask.
175//
176// There are many variants to this pattern:
177// a) (x & ((1 << MaskShAmt) - 1)) << ShiftShAmt
178// b) (x & (~(-1 << MaskShAmt))) << ShiftShAmt
179// c) (x & (-1 l>> MaskShAmt)) << ShiftShAmt
180// d) (x & ((-1 << MaskShAmt) l>> MaskShAmt)) << ShiftShAmt
181// e) ((x << MaskShAmt) l>> MaskShAmt) << ShiftShAmt
182// f) ((x << MaskShAmt) a>> MaskShAmt) << ShiftShAmt
183// All these patterns can be simplified to just:
184// x << ShiftShAmt
185// iff:
186// a,b) (MaskShAmt+ShiftShAmt) u>= bitwidth(x)
187// c,d,e,f) (ShiftShAmt-MaskShAmt) s>= 0 (i.e. ShiftShAmt u>= MaskShAmt)
188static Instruction *
189dropRedundantMaskingOfLeftShiftInput(BinaryOperator *OuterShift,
190 const SimplifyQuery &Q,
191 InstCombiner::BuilderTy &Builder) {
192 assert(OuterShift->getOpcode() == Instruction::BinaryOps::Shl &&
193 "The input must be 'shl'!");
194
195 Value *Masked, *ShiftShAmt;
196 match(V: OuterShift,
197 P: m_Shift(L: m_Value(V&: Masked), R: m_ZExtOrSelf(Op: m_Value(V&: ShiftShAmt))));
198
199 // *If* there is a truncation between an outer shift and a possibly-mask,
200 // then said truncation *must* be one-use, else we can't perform the fold.
201 Value *Trunc;
202 if (match(V: Masked, P: m_CombineAnd(L: m_Trunc(Op: m_Value(V&: Masked)), R: m_Value(V&: Trunc))) &&
203 !Trunc->hasOneUse())
204 return nullptr;
205
206 Type *NarrowestTy = OuterShift->getType();
207 Type *WidestTy = Masked->getType();
208 bool HadTrunc = WidestTy != NarrowestTy;
209
210 // The mask must be computed in a type twice as wide to ensure
211 // that no bits are lost if the sum-of-shifts is wider than the base type.
212 Type *ExtendedTy = WidestTy->getExtendedType();
213
214 Value *MaskShAmt;
215
216 // ((1 << MaskShAmt) - 1)
217 auto MaskA = m_Add(L: m_Shl(L: m_One(), R: m_Value(V&: MaskShAmt)), R: m_AllOnes());
218 // (~(-1 << maskNbits))
219 auto MaskB = m_Not(V: m_Shl(L: m_AllOnes(), R: m_Value(V&: MaskShAmt)));
220 // (-1 l>> MaskShAmt)
221 auto MaskC = m_LShr(L: m_AllOnes(), R: m_Value(V&: MaskShAmt));
222 // ((-1 << MaskShAmt) l>> MaskShAmt)
223 auto MaskD =
224 m_LShr(L: m_Shl(L: m_AllOnes(), R: m_Value(V&: MaskShAmt)), R: m_Deferred(V: MaskShAmt));
225
226 Value *X;
227 Constant *NewMask;
228
229 if (match(V: Masked, P: m_c_And(L: m_CombineOr(L: MaskA, R: MaskB), R: m_Value(V&: X)))) {
230 // Peek through an optional zext of the shift amount.
231 match(V: MaskShAmt, P: m_ZExtOrSelf(Op: m_Value(V&: MaskShAmt)));
232
233 // Verify that it would be safe to try to add those two shift amounts.
234 if (!canTryToConstantAddTwoShiftAmounts(Sh0: OuterShift, ShAmt0: ShiftShAmt, Sh1: Masked,
235 ShAmt1: MaskShAmt))
236 return nullptr;
237
238 // Can we simplify (MaskShAmt+ShiftShAmt) ?
239 auto *SumOfShAmts = dyn_cast_or_null<Constant>(Val: simplifyAddInst(
240 LHS: MaskShAmt, RHS: ShiftShAmt, /*IsNSW=*/false, /*IsNUW=*/false, Q));
241 if (!SumOfShAmts)
242 return nullptr; // Did not simplify.
243 // In this pattern SumOfShAmts correlates with the number of low bits
244 // that shall remain in the root value (OuterShift).
245
246 // An extend of an undef value becomes zero because the high bits are never
247 // completely unknown. Replace the `undef` shift amounts with final
248 // shift bitwidth to ensure that the value remains undef when creating the
249 // subsequent shift op.
250 SumOfShAmts = Constant::replaceUndefsWith(
251 C: SumOfShAmts, Replacement: ConstantInt::get(Ty: SumOfShAmts->getType()->getScalarType(),
252 V: ExtendedTy->getScalarSizeInBits()));
253 auto *ExtendedSumOfShAmts = ConstantFoldCastOperand(
254 Opcode: Instruction::ZExt, C: SumOfShAmts, DestTy: ExtendedTy, DL: Q.DL);
255 if (!ExtendedSumOfShAmts)
256 return nullptr;
257
258 // And compute the mask as usual: ~(-1 << (SumOfShAmts))
259 auto *ExtendedAllOnes = ConstantExpr::getAllOnesValue(Ty: ExtendedTy);
260 Constant *ExtendedInvertedMask = ConstantFoldBinaryOpOperands(
261 Opcode: Instruction::Shl, LHS: ExtendedAllOnes, RHS: ExtendedSumOfShAmts, DL: Q.DL);
262 if (!ExtendedInvertedMask)
263 return nullptr;
264
265 NewMask = ConstantExpr::getNot(C: ExtendedInvertedMask);
266 } else if (match(V: Masked, P: m_c_And(L: m_CombineOr(L: MaskC, R: MaskD), R: m_Value(V&: X))) ||
267 match(V: Masked, P: m_Shr(L: m_Shl(L: m_Value(V&: X), R: m_Value(V&: MaskShAmt)),
268 R: m_Deferred(V: MaskShAmt)))) {
269 // Peek through an optional zext of the shift amount.
270 match(V: MaskShAmt, P: m_ZExtOrSelf(Op: m_Value(V&: MaskShAmt)));
271
272 // Verify that it would be safe to try to add those two shift amounts.
273 if (!canTryToConstantAddTwoShiftAmounts(Sh0: OuterShift, ShAmt0: ShiftShAmt, Sh1: Masked,
274 ShAmt1: MaskShAmt))
275 return nullptr;
276
277 // Can we simplify (ShiftShAmt-MaskShAmt) ?
278 auto *ShAmtsDiff = dyn_cast_or_null<Constant>(Val: simplifySubInst(
279 LHS: ShiftShAmt, RHS: MaskShAmt, /*IsNSW=*/false, /*IsNUW=*/false, Q));
280 if (!ShAmtsDiff)
281 return nullptr; // Did not simplify.
282 // In this pattern ShAmtsDiff correlates with the number of high bits that
283 // shall be unset in the root value (OuterShift).
284
285 // An extend of an undef value becomes zero because the high bits are never
286 // completely unknown. Replace the `undef` shift amounts with negated
287 // bitwidth of innermost shift to ensure that the value remains undef when
288 // creating the subsequent shift op.
289 unsigned WidestTyBitWidth = WidestTy->getScalarSizeInBits();
290 ShAmtsDiff = Constant::replaceUndefsWith(
291 C: ShAmtsDiff, Replacement: ConstantInt::get(Ty: ShAmtsDiff->getType()->getScalarType(),
292 V: -WidestTyBitWidth));
293 auto *ExtendedNumHighBitsToClear = ConstantFoldCastOperand(
294 Opcode: Instruction::ZExt,
295 C: ConstantExpr::getSub(C1: ConstantInt::get(Ty: ShAmtsDiff->getType(),
296 V: WidestTyBitWidth,
297 /*isSigned=*/IsSigned: false),
298 C2: ShAmtsDiff),
299 DestTy: ExtendedTy, DL: Q.DL);
300 if (!ExtendedNumHighBitsToClear)
301 return nullptr;
302
303 // And compute the mask as usual: (-1 l>> (NumHighBitsToClear))
304 auto *ExtendedAllOnes = ConstantExpr::getAllOnesValue(Ty: ExtendedTy);
305 NewMask = ConstantFoldBinaryOpOperands(Opcode: Instruction::LShr, LHS: ExtendedAllOnes,
306 RHS: ExtendedNumHighBitsToClear, DL: Q.DL);
307 if (!NewMask)
308 return nullptr;
309 } else
310 return nullptr; // Don't know anything about this pattern.
311
312 NewMask = ConstantExpr::getTrunc(C: NewMask, Ty: NarrowestTy);
313
314 // Does this mask has any unset bits? If not then we can just not apply it.
315 bool NeedMask = !match(V: NewMask, P: m_AllOnes());
316
317 // If we need to apply a mask, there are several more restrictions we have.
318 if (NeedMask) {
319 // The old masking instruction must go away.
320 if (!Masked->hasOneUse())
321 return nullptr;
322 // The original "masking" instruction must not have been`ashr`.
323 if (match(V: Masked, P: m_AShr(L: m_Value(), R: m_Value())))
324 return nullptr;
325 }
326
327 // If we need to apply truncation, let's do it first, since we can.
328 // We have already ensured that the old truncation will go away.
329 if (HadTrunc)
330 X = Builder.CreateTrunc(V: X, DestTy: NarrowestTy);
331
332 // No 'NUW'/'NSW'! We no longer know that we won't shift-out non-0 bits.
333 // We didn't change the Type of this outermost shift, so we can just do it.
334 auto *NewShift = BinaryOperator::Create(Op: OuterShift->getOpcode(), S1: X,
335 S2: OuterShift->getOperand(i_nocapture: 1));
336 if (!NeedMask)
337 return NewShift;
338
339 Builder.Insert(I: NewShift);
340 return BinaryOperator::Create(Op: Instruction::And, S1: NewShift, S2: NewMask);
341}
342
343/// If we have a shift-by-constant of a bin op (bitwise logic op or add/sub w/
344/// shl) that itself has a shift-by-constant operand with identical opcode, we
345/// may be able to convert that into 2 independent shifts followed by the logic
346/// op. This eliminates a use of an intermediate value (reduces dependency
347/// chain).
348static Instruction *foldShiftOfShiftedBinOp(BinaryOperator &I,
349 InstCombiner::BuilderTy &Builder) {
350 assert(I.isShift() && "Expected a shift as input");
351 auto *BinInst = dyn_cast<BinaryOperator>(Val: I.getOperand(i_nocapture: 0));
352 if (!BinInst ||
353 (!BinInst->isBitwiseLogicOp() &&
354 BinInst->getOpcode() != Instruction::Add &&
355 BinInst->getOpcode() != Instruction::Sub) ||
356 !BinInst->hasOneUse())
357 return nullptr;
358
359 Constant *C0, *C1;
360 if (!match(V: I.getOperand(i_nocapture: 1), P: m_Constant(C&: C1)))
361 return nullptr;
362
363 Instruction::BinaryOps ShiftOpcode = I.getOpcode();
364 // Transform for add/sub only works with shl.
365 if ((BinInst->getOpcode() == Instruction::Add ||
366 BinInst->getOpcode() == Instruction::Sub) &&
367 ShiftOpcode != Instruction::Shl)
368 return nullptr;
369
370 Type *Ty = I.getType();
371
372 // Find a matching shift by constant. The fold is not valid if the sum
373 // of the shift values equals or exceeds bitwidth.
374 Value *X, *Y;
375 auto matchFirstShift = [&](Value *V, Value *W) {
376 unsigned Size = Ty->getScalarSizeInBits();
377 APInt Threshold(Size, Size);
378 return match(V, P: m_BinOp(Opcode: ShiftOpcode, L: m_Value(V&: X), R: m_Constant(C&: C0))) &&
379 (V->hasOneUse() || match(V: W, P: m_ImmConstant())) &&
380 match(V: ConstantExpr::getAdd(C1: C0, C2: C1),
381 P: m_SpecificInt_ICMP(Predicate: ICmpInst::ICMP_ULT, Threshold));
382 };
383
384 // Logic ops and Add are commutative, so check each operand for a match. Sub
385 // is not so we cannot reoder if we match operand(1) and need to keep the
386 // operands in their original positions.
387 bool FirstShiftIsOp1 = false;
388 if (matchFirstShift(BinInst->getOperand(i_nocapture: 0), BinInst->getOperand(i_nocapture: 1)))
389 Y = BinInst->getOperand(i_nocapture: 1);
390 else if (matchFirstShift(BinInst->getOperand(i_nocapture: 1), BinInst->getOperand(i_nocapture: 0))) {
391 Y = BinInst->getOperand(i_nocapture: 0);
392 FirstShiftIsOp1 = BinInst->getOpcode() == Instruction::Sub;
393 } else
394 return nullptr;
395
396 // shift (binop (shift X, C0), Y), C1 -> binop (shift X, C0+C1), (shift Y, C1)
397 Constant *ShiftSumC = ConstantExpr::getAdd(C1: C0, C2: C1);
398 Value *NewShift1 = Builder.CreateBinOp(Opc: ShiftOpcode, LHS: X, RHS: ShiftSumC);
399 Value *NewShift2 = Builder.CreateBinOp(Opc: ShiftOpcode, LHS: Y, RHS: C1);
400 Value *Op1 = FirstShiftIsOp1 ? NewShift2 : NewShift1;
401 Value *Op2 = FirstShiftIsOp1 ? NewShift1 : NewShift2;
402 return BinaryOperator::Create(Op: BinInst->getOpcode(), S1: Op1, S2: Op2);
403}
404
405Instruction *InstCombinerImpl::commonShiftTransforms(BinaryOperator &I) {
406 if (Instruction *Phi = foldBinopWithPhiOperands(BO&: I))
407 return Phi;
408
409 Value *Op0 = I.getOperand(i_nocapture: 0), *Op1 = I.getOperand(i_nocapture: 1);
410 assert(Op0->getType() == Op1->getType());
411 Type *Ty = I.getType();
412
413 // If the shift amount is a one-use `sext`, we can demote it to `zext`.
414 Value *Y;
415 if (match(V: Op1, P: m_OneUse(SubPattern: m_SExt(Op: m_Value(V&: Y))))) {
416 Value *NewExt = Builder.CreateZExt(V: Y, DestTy: Ty, Name: Op1->getName());
417 return BinaryOperator::Create(Op: I.getOpcode(), S1: Op0, S2: NewExt);
418 }
419
420 // See if we can fold away this shift.
421 if (SimplifyDemandedInstructionBits(Inst&: I))
422 return &I;
423
424 // Try to fold constant and into select arguments.
425 if (isa<Constant>(Val: Op0))
426 if (SelectInst *SI = dyn_cast<SelectInst>(Val: Op1))
427 if (Instruction *R = FoldOpIntoSelect(Op&: I, SI))
428 return R;
429
430 if (Constant *CUI = dyn_cast<Constant>(Val: Op1))
431 if (Instruction *Res = FoldShiftByConstant(Op0, Op1: CUI, I))
432 return Res;
433
434 if (auto *NewShift = cast_or_null<Instruction>(
435 Val: reassociateShiftAmtsOfTwoSameDirectionShifts(Sh0: &I, SQ)))
436 return NewShift;
437
438 // Pre-shift a constant shifted by a variable amount with constant offset:
439 // C shift (A add nuw C1) --> (C shift C1) shift A
440 Value *A;
441 Constant *C, *C1;
442 if (match(V: Op0, P: m_Constant(C)) &&
443 match(V: Op1, P: m_NUWAddLike(L: m_Value(V&: A), R: m_Constant(C&: C1)))) {
444 Value *NewC = Builder.CreateBinOp(Opc: I.getOpcode(), LHS: C, RHS: C1);
445 BinaryOperator *NewShiftOp = BinaryOperator::Create(Op: I.getOpcode(), S1: NewC, S2: A);
446 if (I.getOpcode() == Instruction::Shl) {
447 NewShiftOp->setHasNoSignedWrap(I.hasNoSignedWrap());
448 NewShiftOp->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
449 } else {
450 NewShiftOp->setIsExact(I.isExact());
451 }
452 return NewShiftOp;
453 }
454
455 unsigned BitWidth = Ty->getScalarSizeInBits();
456
457 const APInt *AC, *AddC;
458 // Try to pre-shift a constant shifted by a variable amount added with a
459 // negative number:
460 // C << (X - AddC) --> (C >> AddC) << X
461 // and
462 // C >> (X - AddC) --> (C << AddC) >> X
463 if (match(V: Op0, P: m_APInt(Res&: AC)) && match(V: Op1, P: m_Add(L: m_Value(V&: A), R: m_APInt(Res&: AddC))) &&
464 AddC->isNegative() && (-*AddC).ult(RHS: BitWidth)) {
465 assert(!AC->isZero() && "Expected simplify of shifted zero");
466 unsigned PosOffset = (-*AddC).getZExtValue();
467
468 auto isSuitableForPreShift = [PosOffset, &I, AC]() {
469 switch (I.getOpcode()) {
470 default:
471 return false;
472 case Instruction::Shl:
473 return (I.hasNoSignedWrap() || I.hasNoUnsignedWrap()) &&
474 AC->eq(RHS: AC->lshr(shiftAmt: PosOffset).shl(shiftAmt: PosOffset));
475 case Instruction::LShr:
476 return I.isExact() && AC->eq(RHS: AC->shl(shiftAmt: PosOffset).lshr(shiftAmt: PosOffset));
477 case Instruction::AShr:
478 return I.isExact() && AC->eq(RHS: AC->shl(shiftAmt: PosOffset).ashr(ShiftAmt: PosOffset));
479 }
480 };
481 if (isSuitableForPreShift()) {
482 Constant *NewC = ConstantInt::get(Ty, V: I.getOpcode() == Instruction::Shl
483 ? AC->lshr(shiftAmt: PosOffset)
484 : AC->shl(shiftAmt: PosOffset));
485 BinaryOperator *NewShiftOp =
486 BinaryOperator::Create(Op: I.getOpcode(), S1: NewC, S2: A);
487 if (I.getOpcode() == Instruction::Shl) {
488 NewShiftOp->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
489 } else {
490 NewShiftOp->setIsExact();
491 }
492 return NewShiftOp;
493 }
494 }
495
496 // X shift (A srem C) -> X shift (A and (C - 1)) iff C is a power of 2.
497 // Because shifts by negative values (which could occur if A were negative)
498 // are undefined.
499 if (Op1->hasOneUse() && match(V: Op1, P: m_SRem(L: m_Value(V&: A), R: m_Constant(C))) &&
500 match(V: C, P: m_Power2())) {
501 // FIXME: Should this get moved into SimplifyDemandedBits by saying we don't
502 // demand the sign bit (and many others) here??
503 Constant *Mask = ConstantExpr::getSub(C1: C, C2: ConstantInt::get(Ty, V: 1));
504 Value *Rem = Builder.CreateAnd(LHS: A, RHS: Mask, Name: Op1->getName());
505 return replaceOperand(I, OpNum: 1, V: Rem);
506 }
507
508 if (Instruction *Logic = foldShiftOfShiftedBinOp(I, Builder))
509 return Logic;
510
511 if (match(V: Op1, P: m_Or(L: m_Value(), R: m_SpecificInt(V: BitWidth - 1))))
512 return replaceOperand(I, OpNum: 1, V: ConstantInt::get(Ty, V: BitWidth - 1));
513
514 return nullptr;
515}
516
517/// Return true if we can simplify two logical (either left or right) shifts
518/// that have constant shift amounts: OuterShift (InnerShift X, C1), C2.
519static bool canEvaluateShiftedShift(unsigned OuterShAmt, bool IsOuterShl,
520 Instruction *InnerShift,
521 InstCombinerImpl &IC, Instruction *CxtI) {
522 assert(InnerShift->isLogicalShift() && "Unexpected instruction type");
523
524 // We need constant scalar or constant splat shifts.
525 const APInt *InnerShiftConst;
526 if (!match(V: InnerShift->getOperand(i: 1), P: m_APInt(Res&: InnerShiftConst)))
527 return false;
528
529 // Two logical shifts in the same direction:
530 // shl (shl X, C1), C2 --> shl X, C1 + C2
531 // lshr (lshr X, C1), C2 --> lshr X, C1 + C2
532 bool IsInnerShl = InnerShift->getOpcode() == Instruction::Shl;
533 if (IsInnerShl == IsOuterShl)
534 return true;
535
536 // Equal shift amounts in opposite directions become bitwise 'and':
537 // lshr (shl X, C), C --> and X, C'
538 // shl (lshr X, C), C --> and X, C'
539 if (*InnerShiftConst == OuterShAmt)
540 return true;
541
542 // If the 2nd shift is bigger than the 1st, we can fold:
543 // lshr (shl X, C1), C2 --> and (shl X, C1 - C2), C3
544 // shl (lshr X, C1), C2 --> and (lshr X, C1 - C2), C3
545 // but it isn't profitable unless we know the and'd out bits are already zero.
546 // Also, check that the inner shift is valid (less than the type width) or
547 // we'll crash trying to produce the bit mask for the 'and'.
548 unsigned TypeWidth = InnerShift->getType()->getScalarSizeInBits();
549 if (InnerShiftConst->ugt(RHS: OuterShAmt) && InnerShiftConst->ult(RHS: TypeWidth)) {
550 unsigned InnerShAmt = InnerShiftConst->getZExtValue();
551 unsigned MaskShift =
552 IsInnerShl ? TypeWidth - InnerShAmt : InnerShAmt - OuterShAmt;
553 APInt Mask = APInt::getLowBitsSet(numBits: TypeWidth, loBitsSet: OuterShAmt) << MaskShift;
554 if (IC.MaskedValueIsZero(V: InnerShift->getOperand(i: 0), Mask, Depth: 0, CxtI))
555 return true;
556 }
557
558 return false;
559}
560
561/// See if we can compute the specified value, but shifted logically to the left
562/// or right by some number of bits. This should return true if the expression
563/// can be computed for the same cost as the current expression tree. This is
564/// used to eliminate extraneous shifting from things like:
565/// %C = shl i128 %A, 64
566/// %D = shl i128 %B, 96
567/// %E = or i128 %C, %D
568/// %F = lshr i128 %E, 64
569/// where the client will ask if E can be computed shifted right by 64-bits. If
570/// this succeeds, getShiftedValue() will be called to produce the value.
571static bool canEvaluateShifted(Value *V, unsigned NumBits, bool IsLeftShift,
572 InstCombinerImpl &IC, Instruction *CxtI) {
573 // We can always evaluate immediate constants.
574 if (match(V, P: m_ImmConstant()))
575 return true;
576
577 Instruction *I = dyn_cast<Instruction>(Val: V);
578 if (!I) return false;
579
580 // We can't mutate something that has multiple uses: doing so would
581 // require duplicating the instruction in general, which isn't profitable.
582 if (!I->hasOneUse()) return false;
583
584 switch (I->getOpcode()) {
585 default: return false;
586 case Instruction::And:
587 case Instruction::Or:
588 case Instruction::Xor:
589 // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
590 return canEvaluateShifted(V: I->getOperand(i: 0), NumBits, IsLeftShift, IC, CxtI: I) &&
591 canEvaluateShifted(V: I->getOperand(i: 1), NumBits, IsLeftShift, IC, CxtI: I);
592
593 case Instruction::Shl:
594 case Instruction::LShr:
595 return canEvaluateShiftedShift(OuterShAmt: NumBits, IsOuterShl: IsLeftShift, InnerShift: I, IC, CxtI);
596
597 case Instruction::Select: {
598 SelectInst *SI = cast<SelectInst>(Val: I);
599 Value *TrueVal = SI->getTrueValue();
600 Value *FalseVal = SI->getFalseValue();
601 return canEvaluateShifted(V: TrueVal, NumBits, IsLeftShift, IC, CxtI: SI) &&
602 canEvaluateShifted(V: FalseVal, NumBits, IsLeftShift, IC, CxtI: SI);
603 }
604 case Instruction::PHI: {
605 // We can change a phi if we can change all operands. Note that we never
606 // get into trouble with cyclic PHIs here because we only consider
607 // instructions with a single use.
608 PHINode *PN = cast<PHINode>(Val: I);
609 for (Value *IncValue : PN->incoming_values())
610 if (!canEvaluateShifted(V: IncValue, NumBits, IsLeftShift, IC, CxtI: PN))
611 return false;
612 return true;
613 }
614 case Instruction::Mul: {
615 const APInt *MulConst;
616 // We can fold (shr (mul X, -(1 << C)), C) -> (and (neg X), C`)
617 return !IsLeftShift && match(V: I->getOperand(i: 1), P: m_APInt(Res&: MulConst)) &&
618 MulConst->isNegatedPowerOf2() && MulConst->countr_zero() == NumBits;
619 }
620 }
621}
622
623/// Fold OuterShift (InnerShift X, C1), C2.
624/// See canEvaluateShiftedShift() for the constraints on these instructions.
625static Value *foldShiftedShift(BinaryOperator *InnerShift, unsigned OuterShAmt,
626 bool IsOuterShl,
627 InstCombiner::BuilderTy &Builder) {
628 bool IsInnerShl = InnerShift->getOpcode() == Instruction::Shl;
629 Type *ShType = InnerShift->getType();
630 unsigned TypeWidth = ShType->getScalarSizeInBits();
631
632 // We only accept shifts-by-a-constant in canEvaluateShifted().
633 const APInt *C1;
634 match(V: InnerShift->getOperand(i_nocapture: 1), P: m_APInt(Res&: C1));
635 unsigned InnerShAmt = C1->getZExtValue();
636
637 // Change the shift amount and clear the appropriate IR flags.
638 auto NewInnerShift = [&](unsigned ShAmt) {
639 InnerShift->setOperand(i_nocapture: 1, Val_nocapture: ConstantInt::get(Ty: ShType, V: ShAmt));
640 if (IsInnerShl) {
641 InnerShift->setHasNoUnsignedWrap(false);
642 InnerShift->setHasNoSignedWrap(false);
643 } else {
644 InnerShift->setIsExact(false);
645 }
646 return InnerShift;
647 };
648
649 // Two logical shifts in the same direction:
650 // shl (shl X, C1), C2 --> shl X, C1 + C2
651 // lshr (lshr X, C1), C2 --> lshr X, C1 + C2
652 if (IsInnerShl == IsOuterShl) {
653 // If this is an oversized composite shift, then unsigned shifts get 0.
654 if (InnerShAmt + OuterShAmt >= TypeWidth)
655 return Constant::getNullValue(Ty: ShType);
656
657 return NewInnerShift(InnerShAmt + OuterShAmt);
658 }
659
660 // Equal shift amounts in opposite directions become bitwise 'and':
661 // lshr (shl X, C), C --> and X, C'
662 // shl (lshr X, C), C --> and X, C'
663 if (InnerShAmt == OuterShAmt) {
664 APInt Mask = IsInnerShl
665 ? APInt::getLowBitsSet(numBits: TypeWidth, loBitsSet: TypeWidth - OuterShAmt)
666 : APInt::getHighBitsSet(numBits: TypeWidth, hiBitsSet: TypeWidth - OuterShAmt);
667 Value *And = Builder.CreateAnd(LHS: InnerShift->getOperand(i_nocapture: 0),
668 RHS: ConstantInt::get(Ty: ShType, V: Mask));
669 if (auto *AndI = dyn_cast<Instruction>(Val: And)) {
670 AndI->moveBefore(MovePos: InnerShift);
671 AndI->takeName(V: InnerShift);
672 }
673 return And;
674 }
675
676 assert(InnerShAmt > OuterShAmt &&
677 "Unexpected opposite direction logical shift pair");
678
679 // In general, we would need an 'and' for this transform, but
680 // canEvaluateShiftedShift() guarantees that the masked-off bits are not used.
681 // lshr (shl X, C1), C2 --> shl X, C1 - C2
682 // shl (lshr X, C1), C2 --> lshr X, C1 - C2
683 return NewInnerShift(InnerShAmt - OuterShAmt);
684}
685
686/// When canEvaluateShifted() returns true for an expression, this function
687/// inserts the new computation that produces the shifted value.
688static Value *getShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
689 InstCombinerImpl &IC, const DataLayout &DL) {
690 // We can always evaluate constants shifted.
691 if (Constant *C = dyn_cast<Constant>(Val: V)) {
692 if (isLeftShift)
693 return IC.Builder.CreateShl(LHS: C, RHS: NumBits);
694 else
695 return IC.Builder.CreateLShr(LHS: C, RHS: NumBits);
696 }
697
698 Instruction *I = cast<Instruction>(Val: V);
699 IC.addToWorklist(I);
700
701 switch (I->getOpcode()) {
702 default: llvm_unreachable("Inconsistency with CanEvaluateShifted");
703 case Instruction::And:
704 case Instruction::Or:
705 case Instruction::Xor:
706 // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
707 I->setOperand(
708 i: 0, Val: getShiftedValue(V: I->getOperand(i: 0), NumBits, isLeftShift, IC, DL));
709 I->setOperand(
710 i: 1, Val: getShiftedValue(V: I->getOperand(i: 1), NumBits, isLeftShift, IC, DL));
711 return I;
712
713 case Instruction::Shl:
714 case Instruction::LShr:
715 return foldShiftedShift(InnerShift: cast<BinaryOperator>(Val: I), OuterShAmt: NumBits, IsOuterShl: isLeftShift,
716 Builder&: IC.Builder);
717
718 case Instruction::Select:
719 I->setOperand(
720 i: 1, Val: getShiftedValue(V: I->getOperand(i: 1), NumBits, isLeftShift, IC, DL));
721 I->setOperand(
722 i: 2, Val: getShiftedValue(V: I->getOperand(i: 2), NumBits, isLeftShift, IC, DL));
723 return I;
724 case Instruction::PHI: {
725 // We can change a phi if we can change all operands. Note that we never
726 // get into trouble with cyclic PHIs here because we only consider
727 // instructions with a single use.
728 PHINode *PN = cast<PHINode>(Val: I);
729 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
730 PN->setIncomingValue(i, V: getShiftedValue(V: PN->getIncomingValue(i), NumBits,
731 isLeftShift, IC, DL));
732 return PN;
733 }
734 case Instruction::Mul: {
735 assert(!isLeftShift && "Unexpected shift direction!");
736 auto *Neg = BinaryOperator::CreateNeg(Op: I->getOperand(i: 0));
737 IC.InsertNewInstWith(New: Neg, Old: I->getIterator());
738 unsigned TypeWidth = I->getType()->getScalarSizeInBits();
739 APInt Mask = APInt::getLowBitsSet(numBits: TypeWidth, loBitsSet: TypeWidth - NumBits);
740 auto *And = BinaryOperator::CreateAnd(V1: Neg,
741 V2: ConstantInt::get(Ty: I->getType(), V: Mask));
742 And->takeName(V: I);
743 return IC.InsertNewInstWith(New: And, Old: I->getIterator());
744 }
745 }
746}
747
748// If this is a bitwise operator or add with a constant RHS we might be able
749// to pull it through a shift.
750static bool canShiftBinOpWithConstantRHS(BinaryOperator &Shift,
751 BinaryOperator *BO) {
752 switch (BO->getOpcode()) {
753 default:
754 return false; // Do not perform transform!
755 case Instruction::Add:
756 return Shift.getOpcode() == Instruction::Shl;
757 case Instruction::Or:
758 case Instruction::And:
759 return true;
760 case Instruction::Xor:
761 // Do not change a 'not' of logical shift because that would create a normal
762 // 'xor'. The 'not' is likely better for analysis, SCEV, and codegen.
763 return !(Shift.isLogicalShift() && match(V: BO, P: m_Not(V: m_Value())));
764 }
765}
766
767Instruction *InstCombinerImpl::FoldShiftByConstant(Value *Op0, Constant *C1,
768 BinaryOperator &I) {
769 // (C2 << X) << C1 --> (C2 << C1) << X
770 // (C2 >> X) >> C1 --> (C2 >> C1) >> X
771 Constant *C2;
772 Value *X;
773 bool IsLeftShift = I.getOpcode() == Instruction::Shl;
774 if (match(V: Op0, P: m_BinOp(Opcode: I.getOpcode(), L: m_ImmConstant(C&: C2), R: m_Value(V&: X)))) {
775 Instruction *R = BinaryOperator::Create(
776 Op: I.getOpcode(), S1: Builder.CreateBinOp(Opc: I.getOpcode(), LHS: C2, RHS: C1), S2: X);
777 BinaryOperator *BO0 = cast<BinaryOperator>(Val: Op0);
778 if (IsLeftShift) {
779 R->setHasNoUnsignedWrap(I.hasNoUnsignedWrap() &&
780 BO0->hasNoUnsignedWrap());
781 R->setHasNoSignedWrap(I.hasNoSignedWrap() && BO0->hasNoSignedWrap());
782 } else
783 R->setIsExact(I.isExact() && BO0->isExact());
784 return R;
785 }
786
787 Type *Ty = I.getType();
788 unsigned TypeBits = Ty->getScalarSizeInBits();
789
790 // (X / +DivC) >> (Width - 1) --> ext (X <= -DivC)
791 // (X / -DivC) >> (Width - 1) --> ext (X >= +DivC)
792 const APInt *DivC;
793 if (!IsLeftShift && match(V: C1, P: m_SpecificIntAllowPoison(V: TypeBits - 1)) &&
794 match(V: Op0, P: m_SDiv(L: m_Value(V&: X), R: m_APInt(Res&: DivC))) && !DivC->isZero() &&
795 !DivC->isMinSignedValue()) {
796 Constant *NegDivC = ConstantInt::get(Ty, V: -(*DivC));
797 ICmpInst::Predicate Pred =
798 DivC->isNegative() ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_SLE;
799 Value *Cmp = Builder.CreateICmp(P: Pred, LHS: X, RHS: NegDivC);
800 auto ExtOpcode = (I.getOpcode() == Instruction::AShr) ? Instruction::SExt
801 : Instruction::ZExt;
802 return CastInst::Create(ExtOpcode, S: Cmp, Ty);
803 }
804
805 const APInt *Op1C;
806 if (!match(V: C1, P: m_APInt(Res&: Op1C)))
807 return nullptr;
808
809 assert(!Op1C->uge(TypeBits) &&
810 "Shift over the type width should have been removed already");
811
812 // See if we can propagate this shift into the input, this covers the trivial
813 // cast of lshr(shl(x,c1),c2) as well as other more complex cases.
814 if (I.getOpcode() != Instruction::AShr &&
815 canEvaluateShifted(V: Op0, NumBits: Op1C->getZExtValue(), IsLeftShift, IC&: *this, CxtI: &I)) {
816 LLVM_DEBUG(
817 dbgs() << "ICE: GetShiftedValue propagating shift through expression"
818 " to eliminate shift:\n IN: "
819 << *Op0 << "\n SH: " << I << "\n");
820
821 return replaceInstUsesWith(
822 I, V: getShiftedValue(V: Op0, NumBits: Op1C->getZExtValue(), isLeftShift: IsLeftShift, IC&: *this, DL));
823 }
824
825 if (Instruction *FoldedShift = foldBinOpIntoSelectOrPhi(I))
826 return FoldedShift;
827
828 if (!Op0->hasOneUse())
829 return nullptr;
830
831 if (auto *Op0BO = dyn_cast<BinaryOperator>(Val: Op0)) {
832 // If the operand is a bitwise operator with a constant RHS, and the
833 // shift is the only use, we can pull it out of the shift.
834 const APInt *Op0C;
835 if (match(V: Op0BO->getOperand(i_nocapture: 1), P: m_APInt(Res&: Op0C))) {
836 if (canShiftBinOpWithConstantRHS(Shift&: I, BO: Op0BO)) {
837 Value *NewRHS =
838 Builder.CreateBinOp(Opc: I.getOpcode(), LHS: Op0BO->getOperand(i_nocapture: 1), RHS: C1);
839
840 Value *NewShift =
841 Builder.CreateBinOp(Opc: I.getOpcode(), LHS: Op0BO->getOperand(i_nocapture: 0), RHS: C1);
842 NewShift->takeName(V: Op0BO);
843
844 return BinaryOperator::Create(Op: Op0BO->getOpcode(), S1: NewShift, S2: NewRHS);
845 }
846 }
847 }
848
849 // If we have a select that conditionally executes some binary operator,
850 // see if we can pull it the select and operator through the shift.
851 //
852 // For example, turning:
853 // shl (select C, (add X, C1), X), C2
854 // Into:
855 // Y = shl X, C2
856 // select C, (add Y, C1 << C2), Y
857 Value *Cond;
858 BinaryOperator *TBO;
859 Value *FalseVal;
860 if (match(V: Op0, P: m_Select(C: m_Value(V&: Cond), L: m_OneUse(SubPattern: m_BinOp(I&: TBO)),
861 R: m_Value(V&: FalseVal)))) {
862 const APInt *C;
863 if (!isa<Constant>(Val: FalseVal) && TBO->getOperand(i_nocapture: 0) == FalseVal &&
864 match(V: TBO->getOperand(i_nocapture: 1), P: m_APInt(Res&: C)) &&
865 canShiftBinOpWithConstantRHS(Shift&: I, BO: TBO)) {
866 Value *NewRHS =
867 Builder.CreateBinOp(Opc: I.getOpcode(), LHS: TBO->getOperand(i_nocapture: 1), RHS: C1);
868
869 Value *NewShift = Builder.CreateBinOp(Opc: I.getOpcode(), LHS: FalseVal, RHS: C1);
870 Value *NewOp = Builder.CreateBinOp(Opc: TBO->getOpcode(), LHS: NewShift, RHS: NewRHS);
871 return SelectInst::Create(C: Cond, S1: NewOp, S2: NewShift);
872 }
873 }
874
875 BinaryOperator *FBO;
876 Value *TrueVal;
877 if (match(V: Op0, P: m_Select(C: m_Value(V&: Cond), L: m_Value(V&: TrueVal),
878 R: m_OneUse(SubPattern: m_BinOp(I&: FBO))))) {
879 const APInt *C;
880 if (!isa<Constant>(Val: TrueVal) && FBO->getOperand(i_nocapture: 0) == TrueVal &&
881 match(V: FBO->getOperand(i_nocapture: 1), P: m_APInt(Res&: C)) &&
882 canShiftBinOpWithConstantRHS(Shift&: I, BO: FBO)) {
883 Value *NewRHS =
884 Builder.CreateBinOp(Opc: I.getOpcode(), LHS: FBO->getOperand(i_nocapture: 1), RHS: C1);
885
886 Value *NewShift = Builder.CreateBinOp(Opc: I.getOpcode(), LHS: TrueVal, RHS: C1);
887 Value *NewOp = Builder.CreateBinOp(Opc: FBO->getOpcode(), LHS: NewShift, RHS: NewRHS);
888 return SelectInst::Create(C: Cond, S1: NewShift, S2: NewOp);
889 }
890 }
891
892 return nullptr;
893}
894
895// Tries to perform
896// (lshr (add (zext X), (zext Y)), K)
897// -> (icmp ult (add X, Y), X)
898// where
899// - The add's operands are zexts from a K-bits integer to a bigger type.
900// - The add is only used by the shr, or by iK (or narrower) truncates.
901// - The lshr type has more than 2 bits (other types are boolean math).
902// - K > 1
903// note that
904// - The resulting add cannot have nuw/nsw, else on overflow we get a
905// poison value and the transform isn't legal anymore.
906Instruction *InstCombinerImpl::foldLShrOverflowBit(BinaryOperator &I) {
907 assert(I.getOpcode() == Instruction::LShr);
908
909 Value *Add = I.getOperand(i_nocapture: 0);
910 Value *ShiftAmt = I.getOperand(i_nocapture: 1);
911 Type *Ty = I.getType();
912
913 if (Ty->getScalarSizeInBits() < 3)
914 return nullptr;
915
916 const APInt *ShAmtAPInt = nullptr;
917 Value *X = nullptr, *Y = nullptr;
918 if (!match(V: ShiftAmt, P: m_APInt(Res&: ShAmtAPInt)) ||
919 !match(V: Add,
920 P: m_Add(L: m_OneUse(SubPattern: m_ZExt(Op: m_Value(V&: X))), R: m_OneUse(SubPattern: m_ZExt(Op: m_Value(V&: Y))))))
921 return nullptr;
922
923 const unsigned ShAmt = ShAmtAPInt->getZExtValue();
924 if (ShAmt == 1)
925 return nullptr;
926
927 // X/Y are zexts from `ShAmt`-sized ints.
928 if (X->getType()->getScalarSizeInBits() != ShAmt ||
929 Y->getType()->getScalarSizeInBits() != ShAmt)
930 return nullptr;
931
932 // Make sure that `Add` is only used by `I` and `ShAmt`-truncates.
933 if (!Add->hasOneUse()) {
934 for (User *U : Add->users()) {
935 if (U == &I)
936 continue;
937
938 TruncInst *Trunc = dyn_cast<TruncInst>(Val: U);
939 if (!Trunc || Trunc->getType()->getScalarSizeInBits() > ShAmt)
940 return nullptr;
941 }
942 }
943
944 // Insert at Add so that the newly created `NarrowAdd` will dominate it's
945 // users (i.e. `Add`'s users).
946 Instruction *AddInst = cast<Instruction>(Val: Add);
947 Builder.SetInsertPoint(AddInst);
948
949 Value *NarrowAdd = Builder.CreateAdd(LHS: X, RHS: Y, Name: "add.narrowed");
950 Value *Overflow =
951 Builder.CreateICmpULT(LHS: NarrowAdd, RHS: X, Name: "add.narrowed.overflow");
952
953 // Replace the uses of the original add with a zext of the
954 // NarrowAdd's result. Note that all users at this stage are known to
955 // be ShAmt-sized truncs, or the lshr itself.
956 if (!Add->hasOneUse()) {
957 replaceInstUsesWith(I&: *AddInst, V: Builder.CreateZExt(V: NarrowAdd, DestTy: Ty));
958 eraseInstFromFunction(I&: *AddInst);
959 }
960
961 // Replace the LShr with a zext of the overflow check.
962 return new ZExtInst(Overflow, Ty);
963}
964
965// Try to set nuw/nsw flags on shl or exact flag on lshr/ashr using knownbits.
966static bool setShiftFlags(BinaryOperator &I, const SimplifyQuery &Q) {
967 assert(I.isShift() && "Expected a shift as input");
968 // We already have all the flags.
969 if (I.getOpcode() == Instruction::Shl) {
970 if (I.hasNoUnsignedWrap() && I.hasNoSignedWrap())
971 return false;
972 } else {
973 if (I.isExact())
974 return false;
975
976 // shr (shl X, Y), Y
977 if (match(V: I.getOperand(i_nocapture: 0), P: m_Shl(L: m_Value(), R: m_Specific(V: I.getOperand(i_nocapture: 1))))) {
978 I.setIsExact();
979 return true;
980 }
981 }
982
983 // Compute what we know about shift count.
984 KnownBits KnownCnt = computeKnownBits(V: I.getOperand(i_nocapture: 1), /* Depth */ 0, Q);
985 unsigned BitWidth = KnownCnt.getBitWidth();
986 // Since shift produces a poison value if RHS is equal to or larger than the
987 // bit width, we can safely assume that RHS is less than the bit width.
988 uint64_t MaxCnt = KnownCnt.getMaxValue().getLimitedValue(Limit: BitWidth - 1);
989
990 KnownBits KnownAmt = computeKnownBits(V: I.getOperand(i_nocapture: 0), /* Depth */ 0, Q);
991 bool Changed = false;
992
993 if (I.getOpcode() == Instruction::Shl) {
994 // If we have as many leading zeros than maximum shift cnt we have nuw.
995 if (!I.hasNoUnsignedWrap() && MaxCnt <= KnownAmt.countMinLeadingZeros()) {
996 I.setHasNoUnsignedWrap();
997 Changed = true;
998 }
999 // If we have more sign bits than maximum shift cnt we have nsw.
1000 if (!I.hasNoSignedWrap()) {
1001 if (MaxCnt < KnownAmt.countMinSignBits() ||
1002 MaxCnt < ComputeNumSignBits(Op: I.getOperand(i_nocapture: 0), DL: Q.DL, /*Depth*/ 0, AC: Q.AC,
1003 CxtI: Q.CxtI, DT: Q.DT)) {
1004 I.setHasNoSignedWrap();
1005 Changed = true;
1006 }
1007 }
1008 return Changed;
1009 }
1010
1011 // If we have at least as many trailing zeros as maximum count then we have
1012 // exact.
1013 Changed = MaxCnt <= KnownAmt.countMinTrailingZeros();
1014 I.setIsExact(Changed);
1015
1016 return Changed;
1017}
1018
1019Instruction *InstCombinerImpl::visitShl(BinaryOperator &I) {
1020 const SimplifyQuery Q = SQ.getWithInstruction(I: &I);
1021
1022 if (Value *V = simplifyShlInst(Op0: I.getOperand(i_nocapture: 0), Op1: I.getOperand(i_nocapture: 1),
1023 IsNSW: I.hasNoSignedWrap(), IsNUW: I.hasNoUnsignedWrap(), Q))
1024 return replaceInstUsesWith(I, V);
1025
1026 if (Instruction *X = foldVectorBinop(Inst&: I))
1027 return X;
1028
1029 if (Instruction *V = commonShiftTransforms(I))
1030 return V;
1031
1032 if (Instruction *V = dropRedundantMaskingOfLeftShiftInput(OuterShift: &I, Q, Builder))
1033 return V;
1034
1035 Value *Op0 = I.getOperand(i_nocapture: 0), *Op1 = I.getOperand(i_nocapture: 1);
1036 Type *Ty = I.getType();
1037 unsigned BitWidth = Ty->getScalarSizeInBits();
1038
1039 const APInt *C;
1040 if (match(V: Op1, P: m_APInt(Res&: C))) {
1041 unsigned ShAmtC = C->getZExtValue();
1042
1043 // shl (zext X), C --> zext (shl X, C)
1044 // This is only valid if X would have zeros shifted out.
1045 Value *X;
1046 if (match(V: Op0, P: m_OneUse(SubPattern: m_ZExt(Op: m_Value(V&: X))))) {
1047 unsigned SrcWidth = X->getType()->getScalarSizeInBits();
1048 if (ShAmtC < SrcWidth &&
1049 MaskedValueIsZero(V: X, Mask: APInt::getHighBitsSet(numBits: SrcWidth, hiBitsSet: ShAmtC), Depth: 0, CxtI: &I))
1050 return new ZExtInst(Builder.CreateShl(LHS: X, RHS: ShAmtC), Ty);
1051 }
1052
1053 // (X >> C) << C --> X & (-1 << C)
1054 if (match(V: Op0, P: m_Shr(L: m_Value(V&: X), R: m_Specific(V: Op1)))) {
1055 APInt Mask(APInt::getHighBitsSet(numBits: BitWidth, hiBitsSet: BitWidth - ShAmtC));
1056 return BinaryOperator::CreateAnd(V1: X, V2: ConstantInt::get(Ty, V: Mask));
1057 }
1058
1059 const APInt *C1;
1060 if (match(V: Op0, P: m_Exact(SubPattern: m_Shr(L: m_Value(V&: X), R: m_APInt(Res&: C1)))) &&
1061 C1->ult(RHS: BitWidth)) {
1062 unsigned ShrAmt = C1->getZExtValue();
1063 if (ShrAmt < ShAmtC) {
1064 // If C1 < C: (X >>?,exact C1) << C --> X << (C - C1)
1065 Constant *ShiftDiff = ConstantInt::get(Ty, V: ShAmtC - ShrAmt);
1066 auto *NewShl = BinaryOperator::CreateShl(V1: X, V2: ShiftDiff);
1067 NewShl->setHasNoUnsignedWrap(
1068 I.hasNoUnsignedWrap() ||
1069 (ShrAmt &&
1070 cast<Instruction>(Val: Op0)->getOpcode() == Instruction::LShr &&
1071 I.hasNoSignedWrap()));
1072 NewShl->setHasNoSignedWrap(I.hasNoSignedWrap());
1073 return NewShl;
1074 }
1075 if (ShrAmt > ShAmtC) {
1076 // If C1 > C: (X >>?exact C1) << C --> X >>?exact (C1 - C)
1077 Constant *ShiftDiff = ConstantInt::get(Ty, V: ShrAmt - ShAmtC);
1078 auto *NewShr = BinaryOperator::Create(
1079 Op: cast<BinaryOperator>(Val: Op0)->getOpcode(), S1: X, S2: ShiftDiff);
1080 NewShr->setIsExact(true);
1081 return NewShr;
1082 }
1083 }
1084
1085 if (match(V: Op0, P: m_OneUse(SubPattern: m_Shr(L: m_Value(V&: X), R: m_APInt(Res&: C1)))) &&
1086 C1->ult(RHS: BitWidth)) {
1087 unsigned ShrAmt = C1->getZExtValue();
1088 if (ShrAmt < ShAmtC) {
1089 // If C1 < C: (X >>? C1) << C --> (X << (C - C1)) & (-1 << C)
1090 Constant *ShiftDiff = ConstantInt::get(Ty, V: ShAmtC - ShrAmt);
1091 auto *NewShl = BinaryOperator::CreateShl(V1: X, V2: ShiftDiff);
1092 NewShl->setHasNoUnsignedWrap(
1093 I.hasNoUnsignedWrap() ||
1094 (ShrAmt &&
1095 cast<Instruction>(Val: Op0)->getOpcode() == Instruction::LShr &&
1096 I.hasNoSignedWrap()));
1097 NewShl->setHasNoSignedWrap(I.hasNoSignedWrap());
1098 Builder.Insert(I: NewShl);
1099 APInt Mask(APInt::getHighBitsSet(numBits: BitWidth, hiBitsSet: BitWidth - ShAmtC));
1100 return BinaryOperator::CreateAnd(V1: NewShl, V2: ConstantInt::get(Ty, V: Mask));
1101 }
1102 if (ShrAmt > ShAmtC) {
1103 // If C1 > C: (X >>? C1) << C --> (X >>? (C1 - C)) & (-1 << C)
1104 Constant *ShiftDiff = ConstantInt::get(Ty, V: ShrAmt - ShAmtC);
1105 auto *OldShr = cast<BinaryOperator>(Val: Op0);
1106 auto *NewShr =
1107 BinaryOperator::Create(Op: OldShr->getOpcode(), S1: X, S2: ShiftDiff);
1108 NewShr->setIsExact(OldShr->isExact());
1109 Builder.Insert(I: NewShr);
1110 APInt Mask(APInt::getHighBitsSet(numBits: BitWidth, hiBitsSet: BitWidth - ShAmtC));
1111 return BinaryOperator::CreateAnd(V1: NewShr, V2: ConstantInt::get(Ty, V: Mask));
1112 }
1113 }
1114
1115 // Similar to above, but look through an intermediate trunc instruction.
1116 BinaryOperator *Shr;
1117 if (match(V: Op0, P: m_OneUse(SubPattern: m_Trunc(Op: m_OneUse(SubPattern: m_BinOp(I&: Shr))))) &&
1118 match(V: Shr, P: m_Shr(L: m_Value(V&: X), R: m_APInt(Res&: C1)))) {
1119 // The larger shift direction survives through the transform.
1120 unsigned ShrAmtC = C1->getZExtValue();
1121 unsigned ShDiff = ShrAmtC > ShAmtC ? ShrAmtC - ShAmtC : ShAmtC - ShrAmtC;
1122 Constant *ShiftDiffC = ConstantInt::get(Ty: X->getType(), V: ShDiff);
1123 auto ShiftOpc = ShrAmtC > ShAmtC ? Shr->getOpcode() : Instruction::Shl;
1124
1125 // If C1 > C:
1126 // (trunc (X >> C1)) << C --> (trunc (X >> (C1 - C))) && (-1 << C)
1127 // If C > C1:
1128 // (trunc (X >> C1)) << C --> (trunc (X << (C - C1))) && (-1 << C)
1129 Value *NewShift = Builder.CreateBinOp(Opc: ShiftOpc, LHS: X, RHS: ShiftDiffC, Name: "sh.diff");
1130 Value *Trunc = Builder.CreateTrunc(V: NewShift, DestTy: Ty, Name: "tr.sh.diff");
1131 APInt Mask(APInt::getHighBitsSet(numBits: BitWidth, hiBitsSet: BitWidth - ShAmtC));
1132 return BinaryOperator::CreateAnd(V1: Trunc, V2: ConstantInt::get(Ty, V: Mask));
1133 }
1134
1135 // If we have an opposite shift by the same amount, we may be able to
1136 // reorder binops and shifts to eliminate math/logic.
1137 auto isSuitableBinOpcode = [](Instruction::BinaryOps BinOpcode) {
1138 switch (BinOpcode) {
1139 default:
1140 return false;
1141 case Instruction::Add:
1142 case Instruction::And:
1143 case Instruction::Or:
1144 case Instruction::Xor:
1145 case Instruction::Sub:
1146 // NOTE: Sub is not commutable and the tranforms below may not be valid
1147 // when the shift-right is operand 1 (RHS) of the sub.
1148 return true;
1149 }
1150 };
1151 BinaryOperator *Op0BO;
1152 if (match(V: Op0, P: m_OneUse(SubPattern: m_BinOp(I&: Op0BO))) &&
1153 isSuitableBinOpcode(Op0BO->getOpcode())) {
1154 // Commute so shift-right is on LHS of the binop.
1155 // (Y bop (X >> C)) << C -> ((X >> C) bop Y) << C
1156 // (Y bop ((X >> C) & CC)) << C -> (((X >> C) & CC) bop Y) << C
1157 Value *Shr = Op0BO->getOperand(i_nocapture: 0);
1158 Value *Y = Op0BO->getOperand(i_nocapture: 1);
1159 Value *X;
1160 const APInt *CC;
1161 if (Op0BO->isCommutative() && Y->hasOneUse() &&
1162 (match(V: Y, P: m_Shr(L: m_Value(), R: m_Specific(V: Op1))) ||
1163 match(V: Y, P: m_And(L: m_OneUse(SubPattern: m_Shr(L: m_Value(), R: m_Specific(V: Op1))),
1164 R: m_APInt(Res&: CC)))))
1165 std::swap(a&: Shr, b&: Y);
1166
1167 // ((X >> C) bop Y) << C -> (X bop (Y << C)) & (~0 << C)
1168 if (match(V: Shr, P: m_OneUse(SubPattern: m_Shr(L: m_Value(V&: X), R: m_Specific(V: Op1))))) {
1169 // Y << C
1170 Value *YS = Builder.CreateShl(LHS: Y, RHS: Op1, Name: Op0BO->getName());
1171 // (X bop (Y << C))
1172 Value *B =
1173 Builder.CreateBinOp(Opc: Op0BO->getOpcode(), LHS: X, RHS: YS, Name: Shr->getName());
1174 unsigned Op1Val = C->getLimitedValue(Limit: BitWidth);
1175 APInt Bits = APInt::getHighBitsSet(numBits: BitWidth, hiBitsSet: BitWidth - Op1Val);
1176 Constant *Mask = ConstantInt::get(Ty, V: Bits);
1177 return BinaryOperator::CreateAnd(V1: B, V2: Mask);
1178 }
1179
1180 // (((X >> C) & CC) bop Y) << C -> (X & (CC << C)) bop (Y << C)
1181 if (match(V: Shr,
1182 P: m_OneUse(SubPattern: m_And(L: m_OneUse(SubPattern: m_Shr(L: m_Value(V&: X), R: m_Specific(V: Op1))),
1183 R: m_APInt(Res&: CC))))) {
1184 // Y << C
1185 Value *YS = Builder.CreateShl(LHS: Y, RHS: Op1, Name: Op0BO->getName());
1186 // X & (CC << C)
1187 Value *M = Builder.CreateAnd(LHS: X, RHS: ConstantInt::get(Ty, V: CC->shl(ShiftAmt: *C)),
1188 Name: X->getName() + ".mask");
1189 auto *NewOp = BinaryOperator::Create(Op: Op0BO->getOpcode(), S1: M, S2: YS);
1190 if (auto *Disjoint = dyn_cast<PossiblyDisjointInst>(Val: Op0BO);
1191 Disjoint && Disjoint->isDisjoint())
1192 cast<PossiblyDisjointInst>(Val: NewOp)->setIsDisjoint(true);
1193 return NewOp;
1194 }
1195 }
1196
1197 // (C1 - X) << C --> (C1 << C) - (X << C)
1198 if (match(V: Op0, P: m_OneUse(SubPattern: m_Sub(L: m_APInt(Res&: C1), R: m_Value(V&: X))))) {
1199 Constant *NewLHS = ConstantInt::get(Ty, V: C1->shl(ShiftAmt: *C));
1200 Value *NewShift = Builder.CreateShl(LHS: X, RHS: Op1);
1201 return BinaryOperator::CreateSub(V1: NewLHS, V2: NewShift);
1202 }
1203 }
1204
1205 if (setShiftFlags(I, Q))
1206 return &I;
1207
1208 // Transform (x >> y) << y to x & (-1 << y)
1209 // Valid for any type of right-shift.
1210 Value *X;
1211 if (match(V: Op0, P: m_OneUse(SubPattern: m_Shr(L: m_Value(V&: X), R: m_Specific(V: Op1))))) {
1212 Constant *AllOnes = ConstantInt::getAllOnesValue(Ty);
1213 Value *Mask = Builder.CreateShl(LHS: AllOnes, RHS: Op1);
1214 return BinaryOperator::CreateAnd(V1: Mask, V2: X);
1215 }
1216
1217 // Transform (-1 >> y) << y to -1 << y
1218 if (match(V: Op0, P: m_LShr(L: m_AllOnes(), R: m_Specific(V: Op1)))) {
1219 Constant *AllOnes = ConstantInt::getAllOnesValue(Ty);
1220 return BinaryOperator::CreateShl(V1: AllOnes, V2: Op1);
1221 }
1222
1223 Constant *C1;
1224 if (match(V: Op1, P: m_ImmConstant(C&: C1))) {
1225 Constant *C2;
1226 Value *X;
1227 // (X * C2) << C1 --> X * (C2 << C1)
1228 if (match(V: Op0, P: m_Mul(L: m_Value(V&: X), R: m_ImmConstant(C&: C2))))
1229 return BinaryOperator::CreateMul(V1: X, V2: Builder.CreateShl(LHS: C2, RHS: C1));
1230
1231 // shl (zext i1 X), C1 --> select (X, 1 << C1, 0)
1232 if (match(V: Op0, P: m_ZExt(Op: m_Value(V&: X))) && X->getType()->isIntOrIntVectorTy(BitWidth: 1)) {
1233 auto *NewC = Builder.CreateShl(LHS: ConstantInt::get(Ty, V: 1), RHS: C1);
1234 return SelectInst::Create(C: X, S1: NewC, S2: ConstantInt::getNullValue(Ty));
1235 }
1236 }
1237
1238 if (match(V: Op0, P: m_One())) {
1239 // (1 << (C - x)) -> ((1 << C) >> x) if C is bitwidth - 1
1240 if (match(V: Op1, P: m_Sub(L: m_SpecificInt(V: BitWidth - 1), R: m_Value(V&: X))))
1241 return BinaryOperator::CreateLShr(
1242 V1: ConstantInt::get(Ty, V: APInt::getSignMask(BitWidth)), V2: X);
1243
1244 // Canonicalize "extract lowest set bit" using cttz to and-with-negate:
1245 // 1 << (cttz X) --> -X & X
1246 if (match(V: Op1,
1247 P: m_OneUse(SubPattern: m_Intrinsic<Intrinsic::cttz>(Op0: m_Value(V&: X), Op1: m_Value())))) {
1248 Value *NegX = Builder.CreateNeg(V: X, Name: "neg");
1249 return BinaryOperator::CreateAnd(V1: NegX, V2: X);
1250 }
1251 }
1252
1253 return nullptr;
1254}
1255
1256Instruction *InstCombinerImpl::visitLShr(BinaryOperator &I) {
1257 if (Value *V = simplifyLShrInst(Op0: I.getOperand(i_nocapture: 0), Op1: I.getOperand(i_nocapture: 1), IsExact: I.isExact(),
1258 Q: SQ.getWithInstruction(I: &I)))
1259 return replaceInstUsesWith(I, V);
1260
1261 if (Instruction *X = foldVectorBinop(Inst&: I))
1262 return X;
1263
1264 if (Instruction *R = commonShiftTransforms(I))
1265 return R;
1266
1267 Value *Op0 = I.getOperand(i_nocapture: 0), *Op1 = I.getOperand(i_nocapture: 1);
1268 Type *Ty = I.getType();
1269 Value *X;
1270 const APInt *C;
1271 unsigned BitWidth = Ty->getScalarSizeInBits();
1272
1273 // (iN (~X) u>> (N - 1)) --> zext (X > -1)
1274 if (match(V: Op0, P: m_OneUse(SubPattern: m_Not(V: m_Value(V&: X)))) &&
1275 match(V: Op1, P: m_SpecificIntAllowPoison(V: BitWidth - 1)))
1276 return new ZExtInst(Builder.CreateIsNotNeg(Arg: X, Name: "isnotneg"), Ty);
1277
1278 // ((X << nuw Z) sub nuw Y) >>u exact Z --> X sub nuw (Y >>u exact Z)
1279 Value *Y;
1280 if (I.isExact() &&
1281 match(V: Op0, P: m_OneUse(SubPattern: m_NUWSub(L: m_NUWShl(L: m_Value(V&: X), R: m_Specific(V: Op1)),
1282 R: m_Value(V&: Y))))) {
1283 Value *NewLshr = Builder.CreateLShr(LHS: Y, RHS: Op1, Name: "", /*isExact=*/true);
1284 auto *NewSub = BinaryOperator::CreateNUWSub(V1: X, V2: NewLshr);
1285 NewSub->setHasNoSignedWrap(
1286 cast<OverflowingBinaryOperator>(Val: Op0)->hasNoSignedWrap());
1287 return NewSub;
1288 }
1289
1290 // Fold (X + Y) / 2 --> (X & Y) iff (X u<= 1) && (Y u<= 1)
1291 if (match(V: Op0, P: m_Add(L: m_Value(V&: X), R: m_Value(V&: Y))) && match(V: Op1, P: m_One()) &&
1292 computeKnownBits(V: X, /*Depth=*/0, CxtI: &I).countMaxActiveBits() <= 1 &&
1293 computeKnownBits(V: Y, /*Depth=*/0, CxtI: &I).countMaxActiveBits() <= 1)
1294 return BinaryOperator::CreateAnd(V1: X, V2: Y);
1295
1296 // (sub nuw X, (Y << nuw Z)) >>u exact Z --> (X >>u exact Z) sub nuw Y
1297 if (I.isExact() &&
1298 match(V: Op0, P: m_OneUse(SubPattern: m_NUWSub(L: m_Value(V&: X),
1299 R: m_NUWShl(L: m_Value(V&: Y), R: m_Specific(V: Op1)))))) {
1300 Value *NewLshr = Builder.CreateLShr(LHS: X, RHS: Op1, Name: "", /*isExact=*/true);
1301 auto *NewSub = BinaryOperator::CreateNUWSub(V1: NewLshr, V2: Y);
1302 NewSub->setHasNoSignedWrap(
1303 cast<OverflowingBinaryOperator>(Val: Op0)->hasNoSignedWrap());
1304 return NewSub;
1305 }
1306
1307 auto isSuitableBinOpcode = [](Instruction::BinaryOps BinOpcode) {
1308 switch (BinOpcode) {
1309 default:
1310 return false;
1311 case Instruction::Add:
1312 case Instruction::And:
1313 case Instruction::Or:
1314 case Instruction::Xor:
1315 // Sub is handled separately.
1316 return true;
1317 }
1318 };
1319
1320 // If both the binop and the shift are nuw, then:
1321 // ((X << nuw Z) binop nuw Y) >>u Z --> X binop nuw (Y >>u Z)
1322 if (match(V: Op0, P: m_OneUse(SubPattern: m_c_BinOp(L: m_NUWShl(L: m_Value(V&: X), R: m_Specific(V: Op1)),
1323 R: m_Value(V&: Y))))) {
1324 BinaryOperator *Op0OB = cast<BinaryOperator>(Val: Op0);
1325 if (isSuitableBinOpcode(Op0OB->getOpcode())) {
1326 if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(Val: Op0);
1327 !OBO || OBO->hasNoUnsignedWrap()) {
1328 Value *NewLshr = Builder.CreateLShr(
1329 LHS: Y, RHS: Op1, Name: "", isExact: I.isExact() && Op0OB->getOpcode() != Instruction::And);
1330 auto *NewBinOp = BinaryOperator::Create(Op: Op0OB->getOpcode(), S1: NewLshr, S2: X);
1331 if (OBO) {
1332 NewBinOp->setHasNoUnsignedWrap(true);
1333 NewBinOp->setHasNoSignedWrap(OBO->hasNoSignedWrap());
1334 } else if (auto *Disjoint = dyn_cast<PossiblyDisjointInst>(Val: Op0)) {
1335 cast<PossiblyDisjointInst>(Val: NewBinOp)->setIsDisjoint(
1336 Disjoint->isDisjoint());
1337 }
1338 return NewBinOp;
1339 }
1340 }
1341 }
1342
1343 if (match(V: Op1, P: m_APInt(Res&: C))) {
1344 unsigned ShAmtC = C->getZExtValue();
1345 auto *II = dyn_cast<IntrinsicInst>(Val: Op0);
1346 if (II && isPowerOf2_32(Value: BitWidth) && Log2_32(Value: BitWidth) == ShAmtC &&
1347 (II->getIntrinsicID() == Intrinsic::ctlz ||
1348 II->getIntrinsicID() == Intrinsic::cttz ||
1349 II->getIntrinsicID() == Intrinsic::ctpop)) {
1350 // ctlz.i32(x)>>5 --> zext(x == 0)
1351 // cttz.i32(x)>>5 --> zext(x == 0)
1352 // ctpop.i32(x)>>5 --> zext(x == -1)
1353 bool IsPop = II->getIntrinsicID() == Intrinsic::ctpop;
1354 Constant *RHS = ConstantInt::getSigned(Ty, V: IsPop ? -1 : 0);
1355 Value *Cmp = Builder.CreateICmpEQ(LHS: II->getArgOperand(i: 0), RHS);
1356 return new ZExtInst(Cmp, Ty);
1357 }
1358
1359 const APInt *C1;
1360 if (match(V: Op0, P: m_Shl(L: m_Value(V&: X), R: m_APInt(Res&: C1))) && C1->ult(RHS: BitWidth)) {
1361 if (C1->ult(RHS: ShAmtC)) {
1362 unsigned ShlAmtC = C1->getZExtValue();
1363 Constant *ShiftDiff = ConstantInt::get(Ty, V: ShAmtC - ShlAmtC);
1364 if (cast<BinaryOperator>(Val: Op0)->hasNoUnsignedWrap()) {
1365 // (X <<nuw C1) >>u C --> X >>u (C - C1)
1366 auto *NewLShr = BinaryOperator::CreateLShr(V1: X, V2: ShiftDiff);
1367 NewLShr->setIsExact(I.isExact());
1368 return NewLShr;
1369 }
1370 if (Op0->hasOneUse()) {
1371 // (X << C1) >>u C --> (X >>u (C - C1)) & (-1 >> C)
1372 Value *NewLShr = Builder.CreateLShr(LHS: X, RHS: ShiftDiff, Name: "", isExact: I.isExact());
1373 APInt Mask(APInt::getLowBitsSet(numBits: BitWidth, loBitsSet: BitWidth - ShAmtC));
1374 return BinaryOperator::CreateAnd(V1: NewLShr, V2: ConstantInt::get(Ty, V: Mask));
1375 }
1376 } else if (C1->ugt(RHS: ShAmtC)) {
1377 unsigned ShlAmtC = C1->getZExtValue();
1378 Constant *ShiftDiff = ConstantInt::get(Ty, V: ShlAmtC - ShAmtC);
1379 if (cast<BinaryOperator>(Val: Op0)->hasNoUnsignedWrap()) {
1380 // (X <<nuw C1) >>u C --> X <<nuw/nsw (C1 - C)
1381 auto *NewShl = BinaryOperator::CreateShl(V1: X, V2: ShiftDiff);
1382 NewShl->setHasNoUnsignedWrap(true);
1383 NewShl->setHasNoSignedWrap(ShAmtC > 0);
1384 return NewShl;
1385 }
1386 if (Op0->hasOneUse()) {
1387 // (X << C1) >>u C --> X << (C1 - C) & (-1 >> C)
1388 Value *NewShl = Builder.CreateShl(LHS: X, RHS: ShiftDiff);
1389 APInt Mask(APInt::getLowBitsSet(numBits: BitWidth, loBitsSet: BitWidth - ShAmtC));
1390 return BinaryOperator::CreateAnd(V1: NewShl, V2: ConstantInt::get(Ty, V: Mask));
1391 }
1392 } else {
1393 assert(*C1 == ShAmtC);
1394 // (X << C) >>u C --> X & (-1 >>u C)
1395 APInt Mask(APInt::getLowBitsSet(numBits: BitWidth, loBitsSet: BitWidth - ShAmtC));
1396 return BinaryOperator::CreateAnd(V1: X, V2: ConstantInt::get(Ty, V: Mask));
1397 }
1398 }
1399
1400 // ((X << C) + Y) >>u C --> (X + (Y >>u C)) & (-1 >>u C)
1401 // TODO: Consolidate with the more general transform that starts from shl
1402 // (the shifts are in the opposite order).
1403 if (match(V: Op0,
1404 P: m_OneUse(SubPattern: m_c_Add(L: m_OneUse(SubPattern: m_Shl(L: m_Value(V&: X), R: m_Specific(V: Op1))),
1405 R: m_Value(V&: Y))))) {
1406 Value *NewLshr = Builder.CreateLShr(LHS: Y, RHS: Op1);
1407 Value *NewAdd = Builder.CreateAdd(LHS: NewLshr, RHS: X);
1408 unsigned Op1Val = C->getLimitedValue(Limit: BitWidth);
1409 APInt Bits = APInt::getLowBitsSet(numBits: BitWidth, loBitsSet: BitWidth - Op1Val);
1410 Constant *Mask = ConstantInt::get(Ty, V: Bits);
1411 return BinaryOperator::CreateAnd(V1: NewAdd, V2: Mask);
1412 }
1413
1414 if (match(V: Op0, P: m_OneUse(SubPattern: m_ZExt(Op: m_Value(V&: X)))) &&
1415 (!Ty->isIntegerTy() || shouldChangeType(From: Ty, To: X->getType()))) {
1416 assert(ShAmtC < X->getType()->getScalarSizeInBits() &&
1417 "Big shift not simplified to zero?");
1418 // lshr (zext iM X to iN), C --> zext (lshr X, C) to iN
1419 Value *NewLShr = Builder.CreateLShr(LHS: X, RHS: ShAmtC);
1420 return new ZExtInst(NewLShr, Ty);
1421 }
1422
1423 if (match(V: Op0, P: m_SExt(Op: m_Value(V&: X)))) {
1424 unsigned SrcTyBitWidth = X->getType()->getScalarSizeInBits();
1425 // lshr (sext i1 X to iN), C --> select (X, -1 >> C, 0)
1426 if (SrcTyBitWidth == 1) {
1427 auto *NewC = ConstantInt::get(
1428 Ty, V: APInt::getLowBitsSet(numBits: BitWidth, loBitsSet: BitWidth - ShAmtC));
1429 return SelectInst::Create(C: X, S1: NewC, S2: ConstantInt::getNullValue(Ty));
1430 }
1431
1432 if ((!Ty->isIntegerTy() || shouldChangeType(From: Ty, To: X->getType())) &&
1433 Op0->hasOneUse()) {
1434 // Are we moving the sign bit to the low bit and widening with high
1435 // zeros? lshr (sext iM X to iN), N-1 --> zext (lshr X, M-1) to iN
1436 if (ShAmtC == BitWidth - 1) {
1437 Value *NewLShr = Builder.CreateLShr(LHS: X, RHS: SrcTyBitWidth - 1);
1438 return new ZExtInst(NewLShr, Ty);
1439 }
1440
1441 // lshr (sext iM X to iN), N-M --> zext (ashr X, min(N-M, M-1)) to iN
1442 if (ShAmtC == BitWidth - SrcTyBitWidth) {
1443 // The new shift amount can't be more than the narrow source type.
1444 unsigned NewShAmt = std::min(a: ShAmtC, b: SrcTyBitWidth - 1);
1445 Value *AShr = Builder.CreateAShr(LHS: X, RHS: NewShAmt);
1446 return new ZExtInst(AShr, Ty);
1447 }
1448 }
1449 }
1450
1451 if (ShAmtC == BitWidth - 1) {
1452 // lshr i32 or(X,-X), 31 --> zext (X != 0)
1453 if (match(V: Op0, P: m_OneUse(SubPattern: m_c_Or(L: m_Neg(V: m_Value(V&: X)), R: m_Deferred(V: X)))))
1454 return new ZExtInst(Builder.CreateIsNotNull(Arg: X), Ty);
1455
1456 // lshr i32 (X -nsw Y), 31 --> zext (X < Y)
1457 if (match(V: Op0, P: m_OneUse(SubPattern: m_NSWSub(L: m_Value(V&: X), R: m_Value(V&: Y)))))
1458 return new ZExtInst(Builder.CreateICmpSLT(LHS: X, RHS: Y), Ty);
1459
1460 // Check if a number is negative and odd:
1461 // lshr i32 (srem X, 2), 31 --> and (X >> 31), X
1462 if (match(V: Op0, P: m_OneUse(SubPattern: m_SRem(L: m_Value(V&: X), R: m_SpecificInt(V: 2))))) {
1463 Value *Signbit = Builder.CreateLShr(LHS: X, RHS: ShAmtC);
1464 return BinaryOperator::CreateAnd(V1: Signbit, V2: X);
1465 }
1466 }
1467
1468 Instruction *TruncSrc;
1469 if (match(V: Op0, P: m_OneUse(SubPattern: m_Trunc(Op: m_Instruction(I&: TruncSrc)))) &&
1470 match(V: TruncSrc, P: m_LShr(L: m_Value(V&: X), R: m_APInt(Res&: C1)))) {
1471 unsigned SrcWidth = X->getType()->getScalarSizeInBits();
1472 unsigned AmtSum = ShAmtC + C1->getZExtValue();
1473
1474 // If the combined shift fits in the source width:
1475 // (trunc (X >>u C1)) >>u C --> and (trunc (X >>u (C1 + C)), MaskC
1476 //
1477 // If the first shift covers the number of bits truncated, then the
1478 // mask instruction is eliminated (and so the use check is relaxed).
1479 if (AmtSum < SrcWidth &&
1480 (TruncSrc->hasOneUse() || C1->uge(RHS: SrcWidth - BitWidth))) {
1481 Value *SumShift = Builder.CreateLShr(LHS: X, RHS: AmtSum, Name: "sum.shift");
1482 Value *Trunc = Builder.CreateTrunc(V: SumShift, DestTy: Ty, Name: I.getName());
1483
1484 // If the first shift does not cover the number of bits truncated, then
1485 // we require a mask to get rid of high bits in the result.
1486 APInt MaskC = APInt::getAllOnes(numBits: BitWidth).lshr(shiftAmt: ShAmtC);
1487 return BinaryOperator::CreateAnd(V1: Trunc, V2: ConstantInt::get(Ty, V: MaskC));
1488 }
1489 }
1490
1491 const APInt *MulC;
1492 if (match(V: Op0, P: m_NUWMul(L: m_Value(V&: X), R: m_APInt(Res&: MulC)))) {
1493 if (BitWidth > 2 && (*MulC - 1).isPowerOf2() &&
1494 MulC->logBase2() == ShAmtC) {
1495 // Look for a "splat" mul pattern - it replicates bits across each half
1496 // of a value, so a right shift simplifies back to just X:
1497 // lshr i[2N] (mul nuw X, (2^N)+1), N --> X
1498 if (ShAmtC * 2 == BitWidth)
1499 return replaceInstUsesWith(I, V: X);
1500
1501 // lshr (mul nuw (X, 2^N + 1)), N -> add nuw (X, lshr(X, N))
1502 if (Op0->hasOneUse()) {
1503 auto *NewAdd = BinaryOperator::CreateNUWAdd(
1504 V1: X, V2: Builder.CreateLShr(LHS: X, RHS: ConstantInt::get(Ty, V: ShAmtC), Name: "",
1505 isExact: I.isExact()));
1506 NewAdd->setHasNoSignedWrap(
1507 cast<OverflowingBinaryOperator>(Val: Op0)->hasNoSignedWrap());
1508 return NewAdd;
1509 }
1510 }
1511
1512 // The one-use check is not strictly necessary, but codegen may not be
1513 // able to invert the transform and perf may suffer with an extra mul
1514 // instruction.
1515 if (Op0->hasOneUse()) {
1516 APInt NewMulC = MulC->lshr(shiftAmt: ShAmtC);
1517 // if c is divisible by (1 << ShAmtC):
1518 // lshr (mul nuw x, MulC), ShAmtC -> mul nuw nsw x, (MulC >> ShAmtC)
1519 if (MulC->eq(RHS: NewMulC.shl(shiftAmt: ShAmtC))) {
1520 auto *NewMul =
1521 BinaryOperator::CreateNUWMul(V1: X, V2: ConstantInt::get(Ty, V: NewMulC));
1522 assert(ShAmtC != 0 &&
1523 "lshr X, 0 should be handled by simplifyLShrInst.");
1524 NewMul->setHasNoSignedWrap(true);
1525 return NewMul;
1526 }
1527 }
1528 }
1529
1530 // lshr (mul nsw (X, 2^N + 1)), N -> add nsw (X, lshr(X, N))
1531 if (match(V: Op0, P: m_OneUse(SubPattern: m_NSWMul(L: m_Value(V&: X), R: m_APInt(Res&: MulC))))) {
1532 if (BitWidth > 2 && (*MulC - 1).isPowerOf2() &&
1533 MulC->logBase2() == ShAmtC) {
1534 return BinaryOperator::CreateNSWAdd(
1535 V1: X, V2: Builder.CreateLShr(LHS: X, RHS: ConstantInt::get(Ty, V: ShAmtC), Name: "",
1536 isExact: I.isExact()));
1537 }
1538 }
1539
1540 // Try to narrow bswap.
1541 // In the case where the shift amount equals the bitwidth difference, the
1542 // shift is eliminated.
1543 if (match(V: Op0, P: m_OneUse(SubPattern: m_Intrinsic<Intrinsic::bswap>(
1544 Op0: m_OneUse(SubPattern: m_ZExt(Op: m_Value(V&: X))))))) {
1545 unsigned SrcWidth = X->getType()->getScalarSizeInBits();
1546 unsigned WidthDiff = BitWidth - SrcWidth;
1547 if (SrcWidth % 16 == 0) {
1548 Value *NarrowSwap = Builder.CreateUnaryIntrinsic(ID: Intrinsic::bswap, V: X);
1549 if (ShAmtC >= WidthDiff) {
1550 // (bswap (zext X)) >> C --> zext (bswap X >> C')
1551 Value *NewShift = Builder.CreateLShr(LHS: NarrowSwap, RHS: ShAmtC - WidthDiff);
1552 return new ZExtInst(NewShift, Ty);
1553 } else {
1554 // (bswap (zext X)) >> C --> (zext (bswap X)) << C'
1555 Value *NewZExt = Builder.CreateZExt(V: NarrowSwap, DestTy: Ty);
1556 Constant *ShiftDiff = ConstantInt::get(Ty, V: WidthDiff - ShAmtC);
1557 return BinaryOperator::CreateShl(V1: NewZExt, V2: ShiftDiff);
1558 }
1559 }
1560 }
1561
1562 // Reduce add-carry of bools to logic:
1563 // ((zext BoolX) + (zext BoolY)) >> 1 --> zext (BoolX && BoolY)
1564 Value *BoolX, *BoolY;
1565 if (ShAmtC == 1 && match(V: Op0, P: m_Add(L: m_Value(V&: X), R: m_Value(V&: Y))) &&
1566 match(V: X, P: m_ZExt(Op: m_Value(V&: BoolX))) && match(V: Y, P: m_ZExt(Op: m_Value(V&: BoolY))) &&
1567 BoolX->getType()->isIntOrIntVectorTy(BitWidth: 1) &&
1568 BoolY->getType()->isIntOrIntVectorTy(BitWidth: 1) &&
1569 (X->hasOneUse() || Y->hasOneUse() || Op0->hasOneUse())) {
1570 Value *And = Builder.CreateAnd(LHS: BoolX, RHS: BoolY);
1571 return new ZExtInst(And, Ty);
1572 }
1573 }
1574
1575 const SimplifyQuery Q = SQ.getWithInstruction(I: &I);
1576 if (setShiftFlags(I, Q))
1577 return &I;
1578
1579 // Transform (x << y) >> y to x & (-1 >> y)
1580 if (match(V: Op0, P: m_OneUse(SubPattern: m_Shl(L: m_Value(V&: X), R: m_Specific(V: Op1))))) {
1581 Constant *AllOnes = ConstantInt::getAllOnesValue(Ty);
1582 Value *Mask = Builder.CreateLShr(LHS: AllOnes, RHS: Op1);
1583 return BinaryOperator::CreateAnd(V1: Mask, V2: X);
1584 }
1585
1586 // Transform (-1 << y) >> y to -1 >> y
1587 if (match(V: Op0, P: m_Shl(L: m_AllOnes(), R: m_Specific(V: Op1)))) {
1588 Constant *AllOnes = ConstantInt::getAllOnesValue(Ty);
1589 return BinaryOperator::CreateLShr(V1: AllOnes, V2: Op1);
1590 }
1591
1592 if (Instruction *Overflow = foldLShrOverflowBit(I))
1593 return Overflow;
1594
1595 return nullptr;
1596}
1597
1598Instruction *
1599InstCombinerImpl::foldVariableSignZeroExtensionOfVariableHighBitExtract(
1600 BinaryOperator &OldAShr) {
1601 assert(OldAShr.getOpcode() == Instruction::AShr &&
1602 "Must be called with arithmetic right-shift instruction only.");
1603
1604 // Check that constant C is a splat of the element-wise bitwidth of V.
1605 auto BitWidthSplat = [](Constant *C, Value *V) {
1606 return match(
1607 V: C, P: m_SpecificInt_ICMP(Predicate: ICmpInst::Predicate::ICMP_EQ,
1608 Threshold: APInt(C->getType()->getScalarSizeInBits(),
1609 V->getType()->getScalarSizeInBits())));
1610 };
1611
1612 // It should look like variable-length sign-extension on the outside:
1613 // (Val << (bitwidth(Val)-Nbits)) a>> (bitwidth(Val)-Nbits)
1614 Value *NBits;
1615 Instruction *MaybeTrunc;
1616 Constant *C1, *C2;
1617 if (!match(V: &OldAShr,
1618 P: m_AShr(L: m_Shl(L: m_Instruction(I&: MaybeTrunc),
1619 R: m_ZExtOrSelf(Op: m_Sub(L: m_Constant(C&: C1),
1620 R: m_ZExtOrSelf(Op: m_Value(V&: NBits))))),
1621 R: m_ZExtOrSelf(Op: m_Sub(L: m_Constant(C&: C2),
1622 R: m_ZExtOrSelf(Op: m_Deferred(V: NBits)))))) ||
1623 !BitWidthSplat(C1, &OldAShr) || !BitWidthSplat(C2, &OldAShr))
1624 return nullptr;
1625
1626 // There may or may not be a truncation after outer two shifts.
1627 Instruction *HighBitExtract;
1628 match(V: MaybeTrunc, P: m_TruncOrSelf(Op: m_Instruction(I&: HighBitExtract)));
1629 bool HadTrunc = MaybeTrunc != HighBitExtract;
1630
1631 // And finally, the innermost part of the pattern must be a right-shift.
1632 Value *X, *NumLowBitsToSkip;
1633 if (!match(V: HighBitExtract, P: m_Shr(L: m_Value(V&: X), R: m_Value(V&: NumLowBitsToSkip))))
1634 return nullptr;
1635
1636 // Said right-shift must extract high NBits bits - C0 must be it's bitwidth.
1637 Constant *C0;
1638 if (!match(V: NumLowBitsToSkip,
1639 P: m_ZExtOrSelf(
1640 Op: m_Sub(L: m_Constant(C&: C0), R: m_ZExtOrSelf(Op: m_Specific(V: NBits))))) ||
1641 !BitWidthSplat(C0, HighBitExtract))
1642 return nullptr;
1643
1644 // Since the NBits is identical for all shifts, if the outermost and
1645 // innermost shifts are identical, then outermost shifts are redundant.
1646 // If we had truncation, do keep it though.
1647 if (HighBitExtract->getOpcode() == OldAShr.getOpcode())
1648 return replaceInstUsesWith(I&: OldAShr, V: MaybeTrunc);
1649
1650 // Else, if there was a truncation, then we need to ensure that one
1651 // instruction will go away.
1652 if (HadTrunc && !match(V: &OldAShr, P: m_c_BinOp(L: m_OneUse(SubPattern: m_Value()), R: m_Value())))
1653 return nullptr;
1654
1655 // Finally, bypass two innermost shifts, and perform the outermost shift on
1656 // the operands of the innermost shift.
1657 Instruction *NewAShr =
1658 BinaryOperator::Create(Op: OldAShr.getOpcode(), S1: X, S2: NumLowBitsToSkip);
1659 NewAShr->copyIRFlags(V: HighBitExtract); // We can preserve 'exact'-ness.
1660 if (!HadTrunc)
1661 return NewAShr;
1662
1663 Builder.Insert(I: NewAShr);
1664 return TruncInst::CreateTruncOrBitCast(S: NewAShr, Ty: OldAShr.getType());
1665}
1666
1667Instruction *InstCombinerImpl::visitAShr(BinaryOperator &I) {
1668 if (Value *V = simplifyAShrInst(Op0: I.getOperand(i_nocapture: 0), Op1: I.getOperand(i_nocapture: 1), IsExact: I.isExact(),
1669 Q: SQ.getWithInstruction(I: &I)))
1670 return replaceInstUsesWith(I, V);
1671
1672 if (Instruction *X = foldVectorBinop(Inst&: I))
1673 return X;
1674
1675 if (Instruction *R = commonShiftTransforms(I))
1676 return R;
1677
1678 Value *Op0 = I.getOperand(i_nocapture: 0), *Op1 = I.getOperand(i_nocapture: 1);
1679 Type *Ty = I.getType();
1680 unsigned BitWidth = Ty->getScalarSizeInBits();
1681 const APInt *ShAmtAPInt;
1682 if (match(V: Op1, P: m_APInt(Res&: ShAmtAPInt)) && ShAmtAPInt->ult(RHS: BitWidth)) {
1683 unsigned ShAmt = ShAmtAPInt->getZExtValue();
1684
1685 // If the shift amount equals the difference in width of the destination
1686 // and source scalar types:
1687 // ashr (shl (zext X), C), C --> sext X
1688 Value *X;
1689 if (match(V: Op0, P: m_Shl(L: m_ZExt(Op: m_Value(V&: X)), R: m_Specific(V: Op1))) &&
1690 ShAmt == BitWidth - X->getType()->getScalarSizeInBits())
1691 return new SExtInst(X, Ty);
1692
1693 // We can't handle (X << C1) >>s C2. It shifts arbitrary bits in. However,
1694 // we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits.
1695 const APInt *ShOp1;
1696 if (match(V: Op0, P: m_NSWShl(L: m_Value(V&: X), R: m_APInt(Res&: ShOp1))) &&
1697 ShOp1->ult(RHS: BitWidth)) {
1698 unsigned ShlAmt = ShOp1->getZExtValue();
1699 if (ShlAmt < ShAmt) {
1700 // (X <<nsw C1) >>s C2 --> X >>s (C2 - C1)
1701 Constant *ShiftDiff = ConstantInt::get(Ty, V: ShAmt - ShlAmt);
1702 auto *NewAShr = BinaryOperator::CreateAShr(V1: X, V2: ShiftDiff);
1703 NewAShr->setIsExact(I.isExact());
1704 return NewAShr;
1705 }
1706 if (ShlAmt > ShAmt) {
1707 // (X <<nsw C1) >>s C2 --> X <<nsw (C1 - C2)
1708 Constant *ShiftDiff = ConstantInt::get(Ty, V: ShlAmt - ShAmt);
1709 auto *NewShl = BinaryOperator::Create(Op: Instruction::Shl, S1: X, S2: ShiftDiff);
1710 NewShl->setHasNoSignedWrap(true);
1711 return NewShl;
1712 }
1713 }
1714
1715 if (match(V: Op0, P: m_AShr(L: m_Value(V&: X), R: m_APInt(Res&: ShOp1))) &&
1716 ShOp1->ult(RHS: BitWidth)) {
1717 unsigned AmtSum = ShAmt + ShOp1->getZExtValue();
1718 // Oversized arithmetic shifts replicate the sign bit.
1719 AmtSum = std::min(a: AmtSum, b: BitWidth - 1);
1720 // (X >>s C1) >>s C2 --> X >>s (C1 + C2)
1721 return BinaryOperator::CreateAShr(V1: X, V2: ConstantInt::get(Ty, V: AmtSum));
1722 }
1723
1724 if (match(V: Op0, P: m_OneUse(SubPattern: m_SExt(Op: m_Value(V&: X)))) &&
1725 (Ty->isVectorTy() || shouldChangeType(From: Ty, To: X->getType()))) {
1726 // ashr (sext X), C --> sext (ashr X, C')
1727 Type *SrcTy = X->getType();
1728 ShAmt = std::min(a: ShAmt, b: SrcTy->getScalarSizeInBits() - 1);
1729 Value *NewSh = Builder.CreateAShr(LHS: X, RHS: ConstantInt::get(Ty: SrcTy, V: ShAmt));
1730 return new SExtInst(NewSh, Ty);
1731 }
1732
1733 if (ShAmt == BitWidth - 1) {
1734 // ashr i32 or(X,-X), 31 --> sext (X != 0)
1735 if (match(V: Op0, P: m_OneUse(SubPattern: m_c_Or(L: m_Neg(V: m_Value(V&: X)), R: m_Deferred(V: X)))))
1736 return new SExtInst(Builder.CreateIsNotNull(Arg: X), Ty);
1737
1738 // ashr i32 (X -nsw Y), 31 --> sext (X < Y)
1739 Value *Y;
1740 if (match(V: Op0, P: m_OneUse(SubPattern: m_NSWSub(L: m_Value(V&: X), R: m_Value(V&: Y)))))
1741 return new SExtInst(Builder.CreateICmpSLT(LHS: X, RHS: Y), Ty);
1742 }
1743
1744 const APInt *MulC;
1745 if (match(V: Op0, P: m_OneUse(SubPattern: m_NSWMul(L: m_Value(V&: X), R: m_APInt(Res&: MulC)))) &&
1746 (BitWidth > 2 && (*MulC - 1).isPowerOf2() &&
1747 MulC->logBase2() == ShAmt &&
1748 (ShAmt < BitWidth - 1))) /* Minus 1 for the sign bit */ {
1749
1750 // ashr (mul nsw (X, 2^N + 1)), N -> add nsw (X, ashr(X, N))
1751 auto *NewAdd = BinaryOperator::CreateNSWAdd(
1752 V1: X,
1753 V2: Builder.CreateAShr(LHS: X, RHS: ConstantInt::get(Ty, V: ShAmt), Name: "", isExact: I.isExact()));
1754 NewAdd->setHasNoUnsignedWrap(
1755 cast<OverflowingBinaryOperator>(Val: Op0)->hasNoUnsignedWrap());
1756 return NewAdd;
1757 }
1758 }
1759
1760 const SimplifyQuery Q = SQ.getWithInstruction(I: &I);
1761 if (setShiftFlags(I, Q))
1762 return &I;
1763
1764 // Prefer `-(x & 1)` over `(x << (bitwidth(x)-1)) a>> (bitwidth(x)-1)`
1765 // as the pattern to splat the lowest bit.
1766 // FIXME: iff X is already masked, we don't need the one-use check.
1767 Value *X;
1768 if (match(V: Op1, P: m_SpecificIntAllowPoison(V: BitWidth - 1)) &&
1769 match(V: Op0, P: m_OneUse(SubPattern: m_Shl(L: m_Value(V&: X),
1770 R: m_SpecificIntAllowPoison(V: BitWidth - 1))))) {
1771 Constant *Mask = ConstantInt::get(Ty, V: 1);
1772 // Retain the knowledge about the ignored lanes.
1773 Mask = Constant::mergeUndefsWith(
1774 C: Constant::mergeUndefsWith(C: Mask, Other: cast<Constant>(Val: Op1)),
1775 Other: cast<Constant>(Val: cast<Instruction>(Val: Op0)->getOperand(i: 1)));
1776 X = Builder.CreateAnd(LHS: X, RHS: Mask);
1777 return BinaryOperator::CreateNeg(Op: X);
1778 }
1779
1780 if (Instruction *R = foldVariableSignZeroExtensionOfVariableHighBitExtract(OldAShr&: I))
1781 return R;
1782
1783 // See if we can turn a signed shr into an unsigned shr.
1784 if (MaskedValueIsZero(V: Op0, Mask: APInt::getSignMask(BitWidth), Depth: 0, CxtI: &I)) {
1785 Instruction *Lshr = BinaryOperator::CreateLShr(V1: Op0, V2: Op1);
1786 Lshr->setIsExact(I.isExact());
1787 return Lshr;
1788 }
1789
1790 // ashr (xor %x, -1), %y --> xor (ashr %x, %y), -1
1791 if (match(V: Op0, P: m_OneUse(SubPattern: m_Not(V: m_Value(V&: X))))) {
1792 // Note that we must drop 'exact'-ness of the shift!
1793 // Note that we can't keep undef's in -1 vector constant!
1794 auto *NewAShr = Builder.CreateAShr(LHS: X, RHS: Op1, Name: Op0->getName() + ".not");
1795 return BinaryOperator::CreateNot(Op: NewAShr);
1796 }
1797
1798 return nullptr;
1799}
1800