1 //===- InstCombineShifts.cpp ----------------------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the visitShl, visitLShr, and visitAShr functions.
12 //===----------------------------------------------------------------------===//
14 #include "InstCombine.h"
15 #include "llvm/IntrinsicInst.h"
16 #include "llvm/Analysis/ConstantFolding.h"
17 #include "llvm/Analysis/InstructionSimplify.h"
18 #include "llvm/Support/PatternMatch.h"
20 using namespace PatternMatch;
22 Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
23 assert(I.getOperand(1)->getType() == I.getOperand(0)->getType());
24 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
26 // See if we can fold away this shift.
27 if (SimplifyDemandedInstructionBits(I))
30 // Try to fold constant and into select arguments.
31 if (isa<Constant>(Op0))
32 if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
33 if (Instruction *R = FoldOpIntoSelect(I, SI))
36 if (ConstantInt *CUI = dyn_cast<ConstantInt>(Op1))
37 if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I))
40 // X shift (A srem B) -> X shift (A and B-1) iff B is a power of 2.
41 // Because shifts by negative values (which could occur if A were negative)
43 Value *A; const APInt *B;
44 if (Op1->hasOneUse() && match(Op1, m_SRem(m_Value(A), m_Power2(B)))) {
45 // FIXME: Should this get moved into SimplifyDemandedBits by saying we don't
46 // demand the sign bit (and many others) here??
47 Value *Rem = Builder->CreateAnd(A, ConstantInt::get(I.getType(), *B-1),
56 /// CanEvaluateShifted - See if we can compute the specified value, but shifted
57 /// logically to the left or right by some number of bits. This should return
58 /// true if the expression can be computed for the same cost as the current
59 /// expression tree. This is used to eliminate extraneous shifting from things
61 /// %C = shl i128 %A, 64
62 /// %D = shl i128 %B, 96
63 /// %E = or i128 %C, %D
64 /// %F = lshr i128 %E, 64
65 /// where the client will ask if E can be computed shifted right by 64-bits. If
66 /// this succeeds, the GetShiftedValue function will be called to produce the
68 static bool CanEvaluateShifted(Value *V, unsigned NumBits, bool isLeftShift,
70 // We can always evaluate constants shifted.
74 Instruction *I = dyn_cast<Instruction>(V);
77 // If this is the opposite shift, we can directly reuse the input of the shift
78 // if the needed bits are already zero in the input. This allows us to reuse
79 // the value which means that we don't care if the shift has multiple uses.
80 // TODO: Handle opposite shift by exact value.
82 if ((isLeftShift && match(I, m_LShr(m_Value(), m_ConstantInt(CI)))) ||
83 (!isLeftShift && match(I, m_Shl(m_Value(), m_ConstantInt(CI))))) {
84 if (CI->getZExtValue() == NumBits) {
85 // TODO: Check that the input bits are already zero with MaskedValueIsZero
87 // If this is a truncate of a logical shr, we can truncate it to a smaller
88 // lshr iff we know that the bits we would otherwise be shifting in are
90 uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
91 uint32_t BitWidth = Ty->getScalarSizeInBits();
92 if (MaskedValueIsZero(I->getOperand(0),
93 APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
94 CI->getLimitedValue(BitWidth) < BitWidth) {
95 return CanEvaluateTruncated(I->getOperand(0), Ty);
102 // We can't mutate something that has multiple uses: doing so would
103 // require duplicating the instruction in general, which isn't profitable.
104 if (!I->hasOneUse()) return false;
106 switch (I->getOpcode()) {
107 default: return false;
108 case Instruction::And:
109 case Instruction::Or:
110 case Instruction::Xor:
111 // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
112 return CanEvaluateShifted(I->getOperand(0), NumBits, isLeftShift, IC) &&
113 CanEvaluateShifted(I->getOperand(1), NumBits, isLeftShift, IC);
115 case Instruction::Shl: {
116 // We can often fold the shift into shifts-by-a-constant.
117 CI = dyn_cast<ConstantInt>(I->getOperand(1));
118 if (CI == 0) return false;
120 // We can always fold shl(c1)+shl(c2) -> shl(c1+c2).
121 if (isLeftShift) return true;
123 // We can always turn shl(c)+shr(c) -> and(c2).
124 if (CI->getValue() == NumBits) return true;
126 unsigned TypeWidth = I->getType()->getScalarSizeInBits();
128 // We can turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but it isn't
129 // profitable unless we know the and'd out bits are already zero.
130 if (CI->getZExtValue() > NumBits) {
131 unsigned LowBits = TypeWidth - CI->getZExtValue();
132 if (MaskedValueIsZero(I->getOperand(0),
133 APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits))
139 case Instruction::LShr: {
140 // We can often fold the shift into shifts-by-a-constant.
141 CI = dyn_cast<ConstantInt>(I->getOperand(1));
142 if (CI == 0) return false;
144 // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2).
145 if (!isLeftShift) return true;
147 // We can always turn lshr(c)+shl(c) -> and(c2).
148 if (CI->getValue() == NumBits) return true;
150 unsigned TypeWidth = I->getType()->getScalarSizeInBits();
152 // We can always turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but it isn't
153 // profitable unless we know the and'd out bits are already zero.
154 if (CI->getZExtValue() > NumBits) {
155 unsigned LowBits = CI->getZExtValue() - NumBits;
156 if (MaskedValueIsZero(I->getOperand(0),
157 APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits))
163 case Instruction::Select: {
164 SelectInst *SI = cast<SelectInst>(I);
165 return CanEvaluateShifted(SI->getTrueValue(), NumBits, isLeftShift, IC) &&
166 CanEvaluateShifted(SI->getFalseValue(), NumBits, isLeftShift, IC);
168 case Instruction::PHI: {
169 // We can change a phi if we can change all operands. Note that we never
170 // get into trouble with cyclic PHIs here because we only consider
171 // instructions with a single use.
172 PHINode *PN = cast<PHINode>(I);
173 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
174 if (!CanEvaluateShifted(PN->getIncomingValue(i), NumBits, isLeftShift,IC))
181 /// GetShiftedValue - When CanEvaluateShifted returned true for an expression,
182 /// this value inserts the new computation that produces the shifted value.
183 static Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
185 // We can always evaluate constants shifted.
186 if (Constant *C = dyn_cast<Constant>(V)) {
188 V = IC.Builder->CreateShl(C, NumBits);
190 V = IC.Builder->CreateLShr(C, NumBits);
191 // If we got a constantexpr back, try to simplify it with TD info.
192 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
193 V = ConstantFoldConstantExpression(CE, IC.getTargetData());
197 Instruction *I = cast<Instruction>(V);
200 switch (I->getOpcode()) {
201 default: assert(0 && "Inconsistency with CanEvaluateShifted");
202 case Instruction::And:
203 case Instruction::Or:
204 case Instruction::Xor:
205 // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
206 I->setOperand(0, GetShiftedValue(I->getOperand(0), NumBits,isLeftShift,IC));
207 I->setOperand(1, GetShiftedValue(I->getOperand(1), NumBits,isLeftShift,IC));
210 case Instruction::Shl: {
211 unsigned TypeWidth = I->getType()->getScalarSizeInBits();
213 // We only accept shifts-by-a-constant in CanEvaluateShifted.
214 ConstantInt *CI = cast<ConstantInt>(I->getOperand(1));
216 // We can always fold shl(c1)+shl(c2) -> shl(c1+c2).
218 // If this is oversized composite shift, then unsigned shifts get 0.
219 unsigned NewShAmt = NumBits+CI->getZExtValue();
220 if (NewShAmt >= TypeWidth)
221 return Constant::getNullValue(I->getType());
223 I->setOperand(1, ConstantInt::get(I->getType(), NewShAmt));
227 // We turn shl(c)+lshr(c) -> and(c2) if the input doesn't already have
229 if (CI->getValue() == NumBits) {
230 APInt Mask(APInt::getLowBitsSet(TypeWidth, TypeWidth - NumBits));
231 V = IC.Builder->CreateAnd(I->getOperand(0),
232 ConstantInt::get(I->getContext(), Mask));
233 if (Instruction *VI = dyn_cast<Instruction>(V)) {
240 // We turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but only when we know that
241 // the and won't be needed.
242 assert(CI->getZExtValue() > NumBits);
243 I->setOperand(1, ConstantInt::get(I->getType(),
244 CI->getZExtValue() - NumBits));
247 case Instruction::LShr: {
248 unsigned TypeWidth = I->getType()->getScalarSizeInBits();
249 // We only accept shifts-by-a-constant in CanEvaluateShifted.
250 ConstantInt *CI = cast<ConstantInt>(I->getOperand(1));
252 // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2).
254 // If this is oversized composite shift, then unsigned shifts get 0.
255 unsigned NewShAmt = NumBits+CI->getZExtValue();
256 if (NewShAmt >= TypeWidth)
257 return Constant::getNullValue(I->getType());
259 I->setOperand(1, ConstantInt::get(I->getType(), NewShAmt));
263 // We turn lshr(c)+shl(c) -> and(c2) if the input doesn't already have
265 if (CI->getValue() == NumBits) {
266 APInt Mask(APInt::getHighBitsSet(TypeWidth, TypeWidth - NumBits));
267 V = IC.Builder->CreateAnd(I->getOperand(0),
268 ConstantInt::get(I->getContext(), Mask));
269 if (Instruction *VI = dyn_cast<Instruction>(V)) {
276 // We turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but only when we know that
277 // the and won't be needed.
278 assert(CI->getZExtValue() > NumBits);
279 I->setOperand(1, ConstantInt::get(I->getType(),
280 CI->getZExtValue() - NumBits));
284 case Instruction::Select:
285 I->setOperand(1, GetShiftedValue(I->getOperand(1), NumBits,isLeftShift,IC));
286 I->setOperand(2, GetShiftedValue(I->getOperand(2), NumBits,isLeftShift,IC));
288 case Instruction::PHI: {
289 // We can change a phi if we can change all operands. Note that we never
290 // get into trouble with cyclic PHIs here because we only consider
291 // instructions with a single use.
292 PHINode *PN = cast<PHINode>(I);
293 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
294 PN->setIncomingValue(i, GetShiftedValue(PN->getIncomingValue(i),
295 NumBits, isLeftShift, IC));
303 Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
305 bool isLeftShift = I.getOpcode() == Instruction::Shl;
308 // See if we can propagate this shift into the input, this covers the trivial
309 // cast of lshr(shl(x,c1),c2) as well as other more complex cases.
310 if (I.getOpcode() != Instruction::AShr &&
311 CanEvaluateShifted(Op0, Op1->getZExtValue(), isLeftShift, *this)) {
312 DEBUG(dbgs() << "ICE: GetShiftedValue propagating shift through expression"
313 " to eliminate shift:\n IN: " << *Op0 << "\n SH: " << I <<"\n");
315 return ReplaceInstUsesWith(I,
316 GetShiftedValue(Op0, Op1->getZExtValue(), isLeftShift, *this));
320 // See if we can simplify any instructions used by the instruction whose sole
321 // purpose is to compute bits we don't care about.
322 uint32_t TypeBits = Op0->getType()->getScalarSizeInBits();
324 // shl i32 X, 32 = 0 and srl i8 Y, 9 = 0, ... just don't eliminate
327 if (Op1->uge(TypeBits)) {
328 if (I.getOpcode() != Instruction::AShr)
329 return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
330 // ashr i32 X, 32 --> ashr i32 X, 31
331 I.setOperand(1, ConstantInt::get(I.getType(), TypeBits-1));
335 // ((X*C1) << C2) == (X * (C1 << C2))
336 if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0))
337 if (BO->getOpcode() == Instruction::Mul && isLeftShift)
338 if (Constant *BOOp = dyn_cast<Constant>(BO->getOperand(1)))
339 return BinaryOperator::CreateMul(BO->getOperand(0),
340 ConstantExpr::getShl(BOOp, Op1));
342 // Try to fold constant and into select arguments.
343 if (SelectInst *SI = dyn_cast<SelectInst>(Op0))
344 if (Instruction *R = FoldOpIntoSelect(I, SI))
346 if (isa<PHINode>(Op0))
347 if (Instruction *NV = FoldOpIntoPhi(I))
350 // Fold shift2(trunc(shift1(x,c1)), c2) -> trunc(shift2(shift1(x,c1),c2))
351 if (TruncInst *TI = dyn_cast<TruncInst>(Op0)) {
352 Instruction *TrOp = dyn_cast<Instruction>(TI->getOperand(0));
353 // If 'shift2' is an ashr, we would have to get the sign bit into a funny
354 // place. Don't try to do this transformation in this case. Also, we
355 // require that the input operand is a shift-by-constant so that we have
356 // confidence that the shifts will get folded together. We could do this
357 // xform in more cases, but it is unlikely to be profitable.
358 if (TrOp && I.isLogicalShift() && TrOp->isShift() &&
359 isa<ConstantInt>(TrOp->getOperand(1))) {
360 // Okay, we'll do this xform. Make the shift of shift.
361 Constant *ShAmt = ConstantExpr::getZExt(Op1, TrOp->getType());
362 // (shift2 (shift1 & 0x00FF), c2)
363 Value *NSh = Builder->CreateBinOp(I.getOpcode(), TrOp, ShAmt,I.getName());
365 // For logical shifts, the truncation has the effect of making the high
366 // part of the register be zeros. Emulate this by inserting an AND to
367 // clear the top bits as needed. This 'and' will usually be zapped by
368 // other xforms later if dead.
369 unsigned SrcSize = TrOp->getType()->getScalarSizeInBits();
370 unsigned DstSize = TI->getType()->getScalarSizeInBits();
371 APInt MaskV(APInt::getLowBitsSet(SrcSize, DstSize));
373 // The mask we constructed says what the trunc would do if occurring
374 // between the shifts. We want to know the effect *after* the second
375 // shift. We know that it is a logical shift by a constant, so adjust the
376 // mask as appropriate.
377 if (I.getOpcode() == Instruction::Shl)
378 MaskV <<= Op1->getZExtValue();
380 assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift");
381 MaskV = MaskV.lshr(Op1->getZExtValue());
385 Value *And = Builder->CreateAnd(NSh,
386 ConstantInt::get(I.getContext(), MaskV),
389 // Return the value truncated to the interesting size.
390 return new TruncInst(And, I.getType());
394 if (Op0->hasOneUse()) {
395 if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) {
396 // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
399 switch (Op0BO->getOpcode()) {
401 case Instruction::Add:
402 case Instruction::And:
403 case Instruction::Or:
404 case Instruction::Xor: {
405 // These operators commute.
406 // Turn (Y + (X >> C)) << C -> (X + (Y << C)) & (~0 << C)
407 if (isLeftShift && Op0BO->getOperand(1)->hasOneUse() &&
408 match(Op0BO->getOperand(1), m_Shr(m_Value(V1),
410 Value *YS = // (Y << C)
411 Builder->CreateShl(Op0BO->getOperand(0), Op1, Op0BO->getName());
413 Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), YS, V1,
414 Op0BO->getOperand(1)->getName());
415 uint32_t Op1Val = Op1->getLimitedValue(TypeBits);
416 return BinaryOperator::CreateAnd(X, ConstantInt::get(I.getContext(),
417 APInt::getHighBitsSet(TypeBits, TypeBits-Op1Val)));
420 // Turn (Y + ((X >> C) & CC)) << C -> ((X & (CC << C)) + (Y << C))
421 Value *Op0BOOp1 = Op0BO->getOperand(1);
422 if (isLeftShift && Op0BOOp1->hasOneUse() &&
424 m_And(m_Shr(m_Value(V1), m_Specific(Op1)),
425 m_ConstantInt(CC))) &&
426 cast<BinaryOperator>(Op0BOOp1)->getOperand(0)->hasOneUse()) {
427 Value *YS = // (Y << C)
428 Builder->CreateShl(Op0BO->getOperand(0), Op1,
431 Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
432 V1->getName()+".mask");
433 return BinaryOperator::Create(Op0BO->getOpcode(), YS, XM);
438 case Instruction::Sub: {
439 // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
440 if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
441 match(Op0BO->getOperand(0), m_Shr(m_Value(V1),
443 Value *YS = // (Y << C)
444 Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
446 Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), V1, YS,
447 Op0BO->getOperand(0)->getName());
448 uint32_t Op1Val = Op1->getLimitedValue(TypeBits);
449 return BinaryOperator::CreateAnd(X, ConstantInt::get(I.getContext(),
450 APInt::getHighBitsSet(TypeBits, TypeBits-Op1Val)));
453 // Turn (((X >> C)&CC) + Y) << C -> (X + (Y << C)) & (CC << C)
454 if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
455 match(Op0BO->getOperand(0),
456 m_And(m_Shr(m_Value(V1), m_Value(V2)),
457 m_ConstantInt(CC))) && V2 == Op1 &&
458 cast<BinaryOperator>(Op0BO->getOperand(0))
459 ->getOperand(0)->hasOneUse()) {
460 Value *YS = // (Y << C)
461 Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
463 Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
464 V1->getName()+".mask");
466 return BinaryOperator::Create(Op0BO->getOpcode(), XM, YS);
474 // If the operand is an bitwise operator with a constant RHS, and the
475 // shift is the only use, we can pull it out of the shift.
476 if (ConstantInt *Op0C = dyn_cast<ConstantInt>(Op0BO->getOperand(1))) {
477 bool isValid = true; // Valid only for And, Or, Xor
478 bool highBitSet = false; // Transform if high bit of constant set?
480 switch (Op0BO->getOpcode()) {
481 default: isValid = false; break; // Do not perform transform!
482 case Instruction::Add:
483 isValid = isLeftShift;
485 case Instruction::Or:
486 case Instruction::Xor:
489 case Instruction::And:
494 // If this is a signed shift right, and the high bit is modified
495 // by the logical operation, do not perform the transformation.
496 // The highBitSet boolean indicates the value of the high bit of
497 // the constant which would cause it to be modified for this
500 if (isValid && I.getOpcode() == Instruction::AShr)
501 isValid = Op0C->getValue()[TypeBits-1] == highBitSet;
504 Constant *NewRHS = ConstantExpr::get(I.getOpcode(), Op0C, Op1);
507 Builder->CreateBinOp(I.getOpcode(), Op0BO->getOperand(0), Op1);
508 NewShift->takeName(Op0BO);
510 return BinaryOperator::Create(Op0BO->getOpcode(), NewShift,
517 // Find out if this is a shift of a shift by a constant.
518 BinaryOperator *ShiftOp = dyn_cast<BinaryOperator>(Op0);
519 if (ShiftOp && !ShiftOp->isShift())
522 if (ShiftOp && isa<ConstantInt>(ShiftOp->getOperand(1))) {
523 ConstantInt *ShiftAmt1C = cast<ConstantInt>(ShiftOp->getOperand(1));
524 uint32_t ShiftAmt1 = ShiftAmt1C->getLimitedValue(TypeBits);
525 uint32_t ShiftAmt2 = Op1->getLimitedValue(TypeBits);
526 assert(ShiftAmt2 != 0 && "Should have been simplified earlier");
527 if (ShiftAmt1 == 0) return 0; // Will be simplified in the future.
528 Value *X = ShiftOp->getOperand(0);
530 uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift.
532 IntegerType *Ty = cast<IntegerType>(I.getType());
534 // Check for (X << c1) << c2 and (X >> c1) >> c2
535 if (I.getOpcode() == ShiftOp->getOpcode()) {
536 // If this is oversized composite shift, then unsigned shifts get 0, ashr
538 if (AmtSum >= TypeBits) {
539 if (I.getOpcode() != Instruction::AShr)
540 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
541 AmtSum = TypeBits-1; // Saturate to 31 for i32 ashr.
544 return BinaryOperator::Create(I.getOpcode(), X,
545 ConstantInt::get(Ty, AmtSum));
548 if (ShiftAmt1 == ShiftAmt2) {
549 // If we have ((X >>? C) << C), turn this into X & (-1 << C).
550 if (I.getOpcode() == Instruction::Shl &&
551 ShiftOp->getOpcode() != Instruction::Shl) {
552 APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt1));
553 return BinaryOperator::CreateAnd(X,
554 ConstantInt::get(I.getContext(),Mask));
556 // If we have ((X << C) >>u C), turn this into X & (-1 >>u C).
557 if (I.getOpcode() == Instruction::LShr &&
558 ShiftOp->getOpcode() == Instruction::Shl) {
559 APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt1));
560 return BinaryOperator::CreateAnd(X,
561 ConstantInt::get(I.getContext(), Mask));
563 } else if (ShiftAmt1 < ShiftAmt2) {
564 uint32_t ShiftDiff = ShiftAmt2-ShiftAmt1;
566 // (X >>? C1) << C2 --> X << (C2-C1) & (-1 << C2)
567 if (I.getOpcode() == Instruction::Shl &&
568 ShiftOp->getOpcode() != Instruction::Shl) {
569 assert(ShiftOp->getOpcode() == Instruction::LShr ||
570 ShiftOp->getOpcode() == Instruction::AShr);
571 Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff));
573 APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
574 return BinaryOperator::CreateAnd(Shift,
575 ConstantInt::get(I.getContext(),Mask));
578 // (X << C1) >>u C2 --> X >>u (C2-C1) & (-1 >> C2)
579 if (I.getOpcode() == Instruction::LShr &&
580 ShiftOp->getOpcode() == Instruction::Shl) {
581 assert(ShiftOp->getOpcode() == Instruction::Shl);
582 Value *Shift = Builder->CreateLShr(X, ConstantInt::get(Ty, ShiftDiff));
584 APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
585 return BinaryOperator::CreateAnd(Shift,
586 ConstantInt::get(I.getContext(),Mask));
589 // We can't handle (X << C1) >>s C2, it shifts arbitrary bits in.
591 assert(ShiftAmt2 < ShiftAmt1);
592 uint32_t ShiftDiff = ShiftAmt1-ShiftAmt2;
594 // (X >>? C1) << C2 --> X >>? (C1-C2) & (-1 << C2)
595 if (I.getOpcode() == Instruction::Shl &&
596 ShiftOp->getOpcode() != Instruction::Shl) {
597 Value *Shift = Builder->CreateBinOp(ShiftOp->getOpcode(), X,
598 ConstantInt::get(Ty, ShiftDiff));
600 APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
601 return BinaryOperator::CreateAnd(Shift,
602 ConstantInt::get(I.getContext(),Mask));
605 // (X << C1) >>u C2 --> X << (C1-C2) & (-1 >> C2)
606 if (I.getOpcode() == Instruction::LShr &&
607 ShiftOp->getOpcode() == Instruction::Shl) {
608 Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff));
610 APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
611 return BinaryOperator::CreateAnd(Shift,
612 ConstantInt::get(I.getContext(),Mask));
615 // We can't handle (X << C1) >>a C2, it shifts arbitrary bits in.
621 Instruction *InstCombiner::visitShl(BinaryOperator &I) {
622 if (Value *V = SimplifyShlInst(I.getOperand(0), I.getOperand(1),
623 I.hasNoSignedWrap(), I.hasNoUnsignedWrap(),
625 return ReplaceInstUsesWith(I, V);
627 if (Instruction *V = commonShiftTransforms(I))
630 if (ConstantInt *Op1C = dyn_cast<ConstantInt>(I.getOperand(1))) {
631 unsigned ShAmt = Op1C->getZExtValue();
633 // If the shifted-out value is known-zero, then this is a NUW shift.
634 if (!I.hasNoUnsignedWrap() &&
635 MaskedValueIsZero(I.getOperand(0),
636 APInt::getHighBitsSet(Op1C->getBitWidth(), ShAmt))) {
637 I.setHasNoUnsignedWrap();
641 // If the shifted out value is all signbits, this is a NSW shift.
642 if (!I.hasNoSignedWrap() &&
643 ComputeNumSignBits(I.getOperand(0)) > ShAmt) {
644 I.setHasNoSignedWrap();
649 // (C1 << A) << C2 -> (C1 << C2) << A
652 if (match(I.getOperand(0), m_OneUse(m_Shl(m_Constant(C1), m_Value(A)))) &&
653 match(I.getOperand(1), m_Constant(C2)))
654 return BinaryOperator::CreateShl(ConstantExpr::getShl(C1, C2), A);
659 Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
660 if (Value *V = SimplifyLShrInst(I.getOperand(0), I.getOperand(1),
662 return ReplaceInstUsesWith(I, V);
664 if (Instruction *R = commonShiftTransforms(I))
667 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
669 if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
670 unsigned ShAmt = Op1C->getZExtValue();
672 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0)) {
673 unsigned BitWidth = Op0->getType()->getScalarSizeInBits();
674 // ctlz.i32(x)>>5 --> zext(x == 0)
675 // cttz.i32(x)>>5 --> zext(x == 0)
676 // ctpop.i32(x)>>5 --> zext(x == -1)
677 if ((II->getIntrinsicID() == Intrinsic::ctlz ||
678 II->getIntrinsicID() == Intrinsic::cttz ||
679 II->getIntrinsicID() == Intrinsic::ctpop) &&
680 isPowerOf2_32(BitWidth) && Log2_32(BitWidth) == ShAmt) {
681 bool isCtPop = II->getIntrinsicID() == Intrinsic::ctpop;
682 Constant *RHS = ConstantInt::getSigned(Op0->getType(), isCtPop ? -1:0);
683 Value *Cmp = Builder->CreateICmpEQ(II->getArgOperand(0), RHS);
684 return new ZExtInst(Cmp, II->getType());
688 // If the shifted-out value is known-zero, then this is an exact shift.
690 MaskedValueIsZero(Op0,APInt::getLowBitsSet(Op1C->getBitWidth(),ShAmt))){
699 Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
700 if (Value *V = SimplifyAShrInst(I.getOperand(0), I.getOperand(1),
702 return ReplaceInstUsesWith(I, V);
704 if (Instruction *R = commonShiftTransforms(I))
707 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
709 if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
710 unsigned ShAmt = Op1C->getZExtValue();
712 // If the input is a SHL by the same constant (ashr (shl X, C), C), then we
713 // have a sign-extend idiom.
715 if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1)))) {
716 // If the left shift is just shifting out partial signbits, delete the
718 if (cast<OverflowingBinaryOperator>(Op0)->hasNoSignedWrap())
719 return ReplaceInstUsesWith(I, X);
721 // If the input is an extension from the shifted amount value, e.g.
722 // %x = zext i8 %A to i32
723 // %y = shl i32 %x, 24
725 // then turn this into "z = sext i8 A to i32".
726 if (ZExtInst *ZI = dyn_cast<ZExtInst>(X)) {
727 uint32_t SrcBits = ZI->getOperand(0)->getType()->getScalarSizeInBits();
728 uint32_t DestBits = ZI->getType()->getScalarSizeInBits();
729 if (Op1C->getZExtValue() == DestBits-SrcBits)
730 return new SExtInst(ZI->getOperand(0), ZI->getType());
734 // If the shifted-out value is known-zero, then this is an exact shift.
736 MaskedValueIsZero(Op0,APInt::getLowBitsSet(Op1C->getBitWidth(),ShAmt))){
742 // See if we can turn a signed shr into an unsigned shr.
743 if (MaskedValueIsZero(Op0,
744 APInt::getSignBit(I.getType()->getScalarSizeInBits())))
745 return BinaryOperator::CreateLShr(Op0, Op1);
747 // Arithmetic shifting an all-sign-bit value is a no-op.
748 unsigned NumSignBits = ComputeNumSignBits(Op0);
749 if (NumSignBits == Op0->getType()->getScalarSizeInBits())
750 return ReplaceInstUsesWith(I, Op0);