1 //===- InstructionCombining.cpp - Combine multiple instructions -----------===//
3 // InstructionCombining - Combine instructions to form fewer, simple
4 // instructions. This pass does not modify the CFG This pass is where algebraic
5 // simplification happens.
7 // This pass combines things like:
13 // This is a simple worklist driven algorithm.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Transforms/Scalar.h"
18 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
19 #include "llvm/Transforms/Utils/Local.h"
20 #include "llvm/ConstantHandling.h"
21 #include "llvm/iMemory.h"
22 #include "llvm/iOther.h"
23 #include "llvm/iPHINode.h"
24 #include "llvm/iOperators.h"
25 #include "llvm/Pass.h"
26 #include "llvm/DerivedTypes.h"
27 #include "llvm/Support/InstIterator.h"
28 #include "llvm/Support/InstVisitor.h"
29 #include "Support/Statistic.h"
33 Statistic<> NumCombined ("instcombine", "Number of insts combined");
34 Statistic<> NumConstProp("instcombine", "Number of constant folds");
35 Statistic<> NumDeadInst ("instcombine", "Number of dead inst eliminated");
37 class InstCombiner : public FunctionPass,
38 public InstVisitor<InstCombiner, Instruction*> {
39 // Worklist of all of the instructions that need to be simplified.
40 std::vector<Instruction*> WorkList;
42 void AddUsesToWorkList(Instruction &I) {
43 // The instruction was simplified, add all users of the instruction to
44 // the work lists because they might get more simplified now...
46 for (Value::use_iterator UI = I.use_begin(), UE = I.use_end();
48 WorkList.push_back(cast<Instruction>(*UI));
51 // removeFromWorkList - remove all instances of I from the worklist.
52 void removeFromWorkList(Instruction *I);
54 virtual bool runOnFunction(Function &F);
56 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
60 // Visitation implementation - Implement instruction combining for different
61 // instruction types. The semantics are as follows:
63 // null - No change was made
64 // I - Change was made, I is still valid, I may be dead though
65 // otherwise - Change was made, replace I with returned instruction
67 Instruction *visitAdd(BinaryOperator &I);
68 Instruction *visitSub(BinaryOperator &I);
69 Instruction *visitMul(BinaryOperator &I);
70 Instruction *visitDiv(BinaryOperator &I);
71 Instruction *visitRem(BinaryOperator &I);
72 Instruction *visitAnd(BinaryOperator &I);
73 Instruction *visitOr (BinaryOperator &I);
74 Instruction *visitXor(BinaryOperator &I);
75 Instruction *visitSetCondInst(BinaryOperator &I);
76 Instruction *visitShiftInst(ShiftInst &I);
77 Instruction *visitCastInst(CastInst &CI);
78 Instruction *visitPHINode(PHINode &PN);
79 Instruction *visitGetElementPtrInst(GetElementPtrInst &GEP);
80 Instruction *visitAllocationInst(AllocationInst &AI);
82 // visitInstruction - Specify what to return for unhandled instructions...
83 Instruction *visitInstruction(Instruction &I) { return 0; }
85 // InsertNewInstBefore - insert an instruction New before instruction Old
86 // in the program. Add the new instruction to the worklist.
88 void InsertNewInstBefore(Instruction *New, Instruction &Old) {
89 assert(New && New->getParent() == 0 &&
90 "New instruction already inserted into a basic block!");
91 BasicBlock *BB = Old.getParent();
92 BB->getInstList().insert(&Old, New); // Insert inst
93 WorkList.push_back(New); // Add to worklist
96 // ReplaceInstUsesWith - This method is to be used when an instruction is
97 // found to be dead, replacable with another preexisting expression. Here
98 // we add all uses of I to the worklist, replace all uses of I with the new
99 // value, then return I, so that the inst combiner will know that I was
102 Instruction *ReplaceInstUsesWith(Instruction &I, Value *V) {
103 AddUsesToWorkList(I); // Add all modified instrs to worklist
104 I.replaceAllUsesWith(V);
108 // SimplifyCommutative - This performs a few simplifications for commutative
110 bool SimplifyCommutative(BinaryOperator &I);
114 RegisterOpt<InstCombiner> X("instcombine", "Combine redundant instructions");
117 // getComplexity: Assign a complexity or rank value to LLVM Values...
118 // 0 -> Constant, 1 -> Other, 2 -> Argument, 2 -> Unary, 3 -> OtherInst
119 static unsigned getComplexity(Value *V) {
120 if (isa<Instruction>(V)) {
121 if (BinaryOperator::isNeg(V) || BinaryOperator::isNot(V))
125 if (isa<Argument>(V)) return 2;
126 return isa<Constant>(V) ? 0 : 1;
129 // isOnlyUse - Return true if this instruction will be deleted if we stop using
131 static bool isOnlyUse(Value *V) {
132 return V->use_size() == 1 || isa<Constant>(V);
135 // SimplifyCommutative - This performs a few simplifications for commutative
138 // 1. Order operands such that they are listed from right (least complex) to
139 // left (most complex). This puts constants before unary operators before
142 // 2. Transform: (op (op V, C1), C2) ==> (op V, (op C1, C2))
143 // 3. Transform: (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2))
145 bool InstCombiner::SimplifyCommutative(BinaryOperator &I) {
146 bool Changed = false;
147 if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1)))
148 Changed = !I.swapOperands();
150 if (!I.isAssociative()) return Changed;
151 Instruction::BinaryOps Opcode = I.getOpcode();
152 if (BinaryOperator *Op = dyn_cast<BinaryOperator>(I.getOperand(0)))
153 if (Op->getOpcode() == Opcode && isa<Constant>(Op->getOperand(1))) {
154 if (isa<Constant>(I.getOperand(1))) {
155 Constant *Folded = ConstantFoldBinaryInstruction(I.getOpcode(),
156 cast<Constant>(I.getOperand(1)), cast<Constant>(Op->getOperand(1)));
157 assert(Folded && "Couldn't constant fold commutative operand?");
158 I.setOperand(0, Op->getOperand(0));
159 I.setOperand(1, Folded);
161 } else if (BinaryOperator *Op1=dyn_cast<BinaryOperator>(I.getOperand(1)))
162 if (Op1->getOpcode() == Opcode && isa<Constant>(Op1->getOperand(1)) &&
163 isOnlyUse(Op) && isOnlyUse(Op1)) {
164 Constant *C1 = cast<Constant>(Op->getOperand(1));
165 Constant *C2 = cast<Constant>(Op1->getOperand(1));
167 // Fold (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2))
168 Constant *Folded = ConstantFoldBinaryInstruction(I.getOpcode(),C1,C2);
169 assert(Folded && "Couldn't constant fold commutative operand?");
170 Instruction *New = BinaryOperator::create(Opcode, Op->getOperand(0),
173 WorkList.push_back(New);
174 I.setOperand(0, New);
175 I.setOperand(1, Folded);
182 // dyn_castNegVal - Given a 'sub' instruction, return the RHS of the instruction
183 // if the LHS is a constant zero (which is the 'negate' form).
185 static inline Value *dyn_castNegVal(Value *V) {
186 if (BinaryOperator::isNeg(V))
187 return BinaryOperator::getNegArgument(cast<BinaryOperator>(V));
189 // Constants can be considered to be negated values...
190 if (Constant *C = dyn_cast<Constant>(V)) {
191 Constant *NC = *Constant::getNullValue(V->getType()) - *C;
192 assert(NC && "Couldn't constant fold a subtract!");
198 static inline Value *dyn_castNotVal(Value *V) {
199 if (BinaryOperator::isNot(V))
200 return BinaryOperator::getNotArgument(cast<BinaryOperator>(V));
202 // Constants can be considered to be not'ed values...
203 if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(V)) {
204 Constant *NC = *ConstantIntegral::getAllOnesValue(C->getType()) ^ *C;
205 assert(NC && "Couldn't constant fold an exclusive or!");
211 // dyn_castFoldableMul - If this value is a multiply that can be folded into
212 // other computations (because it has a constant operand), return the
213 // non-constant operand of the multiply.
215 static inline Value *dyn_castFoldableMul(Value *V) {
216 if (V->use_size() == 1 && V->getType()->isInteger())
217 if (Instruction *I = dyn_cast<Instruction>(V))
218 if (I->getOpcode() == Instruction::Mul)
219 if (isa<Constant>(I->getOperand(1)))
220 return I->getOperand(0);
224 // dyn_castMaskingAnd - If this value is an And instruction masking a value with
225 // a constant, return the constant being anded with.
227 static inline Constant *dyn_castMaskingAnd(Value *V) {
228 if (Instruction *I = dyn_cast<Instruction>(V))
229 if (I->getOpcode() == Instruction::And)
230 return dyn_cast<Constant>(I->getOperand(1));
232 // If this is a constant, it acts just like we were masking with it.
233 return dyn_cast<Constant>(V);
236 // Log2 - Calculate the log base 2 for the specified value if it is exactly a
238 static unsigned Log2(uint64_t Val) {
239 assert(Val > 1 && "Values 0 and 1 should be handled elsewhere!");
242 if (Val & 1) return 0; // Multiple bits set?
249 Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
250 bool Changed = SimplifyCommutative(I);
251 Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
253 // Eliminate 'add int %X, 0'
254 if (RHS == Constant::getNullValue(I.getType()))
255 return ReplaceInstUsesWith(I, LHS);
258 if (Value *V = dyn_castNegVal(LHS))
259 return BinaryOperator::create(Instruction::Sub, RHS, V);
262 if (!isa<Constant>(RHS))
263 if (Value *V = dyn_castNegVal(RHS))
264 return BinaryOperator::create(Instruction::Sub, LHS, V);
266 // X*C + X --> X * (C+1)
267 if (dyn_castFoldableMul(LHS) == RHS) {
268 Constant *CP1 = *cast<Constant>(cast<Instruction>(LHS)->getOperand(1)) +
269 *ConstantInt::get(I.getType(), 1);
270 assert(CP1 && "Couldn't constant fold C + 1?");
271 return BinaryOperator::create(Instruction::Mul, RHS, CP1);
274 // X + X*C --> X * (C+1)
275 if (dyn_castFoldableMul(RHS) == LHS) {
276 Constant *CP1 = *cast<Constant>(cast<Instruction>(RHS)->getOperand(1)) +
277 *ConstantInt::get(I.getType(), 1);
278 assert(CP1 && "Couldn't constant fold C + 1?");
279 return BinaryOperator::create(Instruction::Mul, LHS, CP1);
282 // (A & C1)+(B & C2) -> (A & C1)|(B & C2) iff C1&C2 == 0
283 if (Constant *C1 = dyn_castMaskingAnd(LHS))
284 if (Constant *C2 = dyn_castMaskingAnd(RHS))
285 if ((*C1 & *C2)->isNullValue())
286 return BinaryOperator::create(Instruction::Or, LHS, RHS);
288 return Changed ? &I : 0;
291 Instruction *InstCombiner::visitSub(BinaryOperator &I) {
292 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
294 if (Op0 == Op1) // sub X, X -> 0
295 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
297 // If this is a 'B = x-(-A)', change to B = x+A...
298 if (Value *V = dyn_castNegVal(Op1))
299 return BinaryOperator::create(Instruction::Add, Op0, V);
301 // Replace (-1 - A) with (~A)...
302 if (ConstantInt *C = dyn_cast<ConstantInt>(Op0))
303 if (C->isAllOnesValue())
304 return BinaryOperator::createNot(Op1);
306 if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1))
307 if (Op1I->use_size() == 1) {
308 // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression
309 // is not used by anyone else...
311 if (Op1I->getOpcode() == Instruction::Sub) {
312 // Swap the two operands of the subexpr...
313 Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
314 Op1I->setOperand(0, IIOp1);
315 Op1I->setOperand(1, IIOp0);
317 // Create the new top level add instruction...
318 return BinaryOperator::create(Instruction::Add, Op0, Op1);
321 // Replace (A - (A & B)) with (A & ~B) if this is the only use of (A&B)...
323 if (Op1I->getOpcode() == Instruction::And &&
324 (Op1I->getOperand(0) == Op0 || Op1I->getOperand(1) == Op0)) {
325 Value *OtherOp = Op1I->getOperand(Op1I->getOperand(0) == Op0);
327 Instruction *NewNot = BinaryOperator::createNot(OtherOp, "B.not", &I);
328 return BinaryOperator::create(Instruction::And, Op0, NewNot);
331 // X - X*C --> X * (1-C)
332 if (dyn_castFoldableMul(Op1I) == Op0) {
333 Constant *CP1 = *ConstantInt::get(I.getType(), 1) -
334 *cast<Constant>(cast<Instruction>(Op1)->getOperand(1));
335 assert(CP1 && "Couldn't constant fold 1-C?");
336 return BinaryOperator::create(Instruction::Mul, Op0, CP1);
340 // X*C - X --> X * (C-1)
341 if (dyn_castFoldableMul(Op0) == Op1) {
342 Constant *CP1 = *cast<Constant>(cast<Instruction>(Op0)->getOperand(1)) -
343 *ConstantInt::get(I.getType(), 1);
344 assert(CP1 && "Couldn't constant fold C - 1?");
345 return BinaryOperator::create(Instruction::Mul, Op1, CP1);
351 Instruction *InstCombiner::visitMul(BinaryOperator &I) {
352 bool Changed = SimplifyCommutative(I);
353 Value *Op0 = I.getOperand(0);
355 // Simplify mul instructions with a constant RHS...
356 if (Constant *Op1 = dyn_cast<Constant>(I.getOperand(1))) {
357 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
358 const Type *Ty = CI->getType();
359 uint64_t Val = Ty->isSigned() ?
360 (uint64_t)cast<ConstantSInt>(CI)->getValue() :
361 cast<ConstantUInt>(CI)->getValue();
364 return ReplaceInstUsesWith(I, Op1); // Eliminate 'mul double %X, 0'
366 return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul int %X, 1'
367 case 2: // Convert 'mul int %X, 2' to 'add int %X, %X'
368 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
371 if (uint64_t C = Log2(Val)) // Replace X*(2^C) with X << C
372 return new ShiftInst(Instruction::Shl, Op0,
373 ConstantUInt::get(Type::UByteTy, C));
375 ConstantFP *Op1F = cast<ConstantFP>(Op1);
376 if (Op1F->isNullValue())
377 return ReplaceInstUsesWith(I, Op1);
379 // "In IEEE floating point, x*1 is not equivalent to x for nans. However,
380 // ANSI says we can drop signals, so we can do this anyway." (from GCC)
381 if (Op1F->getValue() == 1.0)
382 return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul double %X, 1.0'
386 if (Value *Op0v = dyn_castNegVal(Op0)) // -X * -Y = X*Y
387 if (Value *Op1v = dyn_castNegVal(I.getOperand(1)))
388 return BinaryOperator::create(Instruction::Mul, Op0v, Op1v);
390 return Changed ? &I : 0;
393 Instruction *InstCombiner::visitDiv(BinaryOperator &I) {
395 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) {
396 if (RHS->equalsInt(1))
397 return ReplaceInstUsesWith(I, I.getOperand(0));
399 // Check to see if this is an unsigned division with an exact power of 2,
400 // if so, convert to a right shift.
401 if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
402 if (uint64_t Val = C->getValue()) // Don't break X / 0
403 if (uint64_t C = Log2(Val))
404 return new ShiftInst(Instruction::Shr, I.getOperand(0),
405 ConstantUInt::get(Type::UByteTy, C));
408 // 0 / X == 0, we don't need to preserve faults!
409 if (ConstantInt *LHS = dyn_cast<ConstantInt>(I.getOperand(0)))
410 if (LHS->equalsInt(0))
411 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
417 Instruction *InstCombiner::visitRem(BinaryOperator &I) {
418 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) {
419 if (RHS->equalsInt(1)) // X % 1 == 0
420 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
422 // Check to see if this is an unsigned remainder with an exact power of 2,
423 // if so, convert to a bitwise and.
424 if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
425 if (uint64_t Val = C->getValue()) // Don't break X % 0 (divide by zero)
427 return BinaryOperator::create(Instruction::And, I.getOperand(0),
428 ConstantUInt::get(I.getType(), Val-1));
431 // 0 % X == 0, we don't need to preserve faults!
432 if (ConstantInt *LHS = dyn_cast<ConstantInt>(I.getOperand(0)))
433 if (LHS->equalsInt(0))
434 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
439 // isMaxValueMinusOne - return true if this is Max-1
440 static bool isMaxValueMinusOne(const ConstantInt *C) {
441 if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C)) {
442 // Calculate -1 casted to the right type...
443 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
444 uint64_t Val = ~0ULL; // All ones
445 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
446 return CU->getValue() == Val-1;
449 const ConstantSInt *CS = cast<ConstantSInt>(C);
451 // Calculate 0111111111..11111
452 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
453 int64_t Val = INT64_MAX; // All ones
454 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
455 return CS->getValue() == Val-1;
458 // isMinValuePlusOne - return true if this is Min+1
459 static bool isMinValuePlusOne(const ConstantInt *C) {
460 if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C))
461 return CU->getValue() == 1;
463 const ConstantSInt *CS = cast<ConstantSInt>(C);
465 // Calculate 1111111111000000000000
466 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
467 int64_t Val = -1; // All ones
468 Val <<= TypeBits-1; // Shift over to the right spot
469 return CS->getValue() == Val+1;
473 Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
474 bool Changed = SimplifyCommutative(I);
475 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
477 // and X, X = X and X, 0 == 0
478 if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
479 return ReplaceInstUsesWith(I, Op1);
482 if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
483 if (RHS->isAllOnesValue())
484 return ReplaceInstUsesWith(I, Op0);
486 Value *Op0NotVal = dyn_castNotVal(Op0);
487 Value *Op1NotVal = dyn_castNotVal(Op1);
489 // (~A & ~B) == (~(A | B)) - Demorgan's Law
490 if (Op0NotVal && Op1NotVal && isOnlyUse(Op0) && isOnlyUse(Op1)) {
491 Instruction *Or = BinaryOperator::create(Instruction::Or, Op0NotVal,
492 Op1NotVal,I.getName()+".demorgan",
494 WorkList.push_back(Or);
495 return BinaryOperator::createNot(Or);
498 if (Op0NotVal == Op1 || Op1NotVal == Op0) // A & ~A == ~A & A == 0
499 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
501 return Changed ? &I : 0;
506 Instruction *InstCombiner::visitOr(BinaryOperator &I) {
507 bool Changed = SimplifyCommutative(I);
508 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
510 // or X, X = X or X, 0 == X
511 if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
512 return ReplaceInstUsesWith(I, Op0);
515 if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
516 if (RHS->isAllOnesValue())
517 return ReplaceInstUsesWith(I, Op1);
519 Value *Op0NotVal = dyn_castNotVal(Op0);
520 Value *Op1NotVal = dyn_castNotVal(Op1);
522 if (Op1 == Op0NotVal) // ~A | A == -1
523 return ReplaceInstUsesWith(I,
524 ConstantIntegral::getAllOnesValue(I.getType()));
526 if (Op0 == Op1NotVal) // A | ~A == -1
527 return ReplaceInstUsesWith(I,
528 ConstantIntegral::getAllOnesValue(I.getType()));
530 // (~A | ~B) == (~(A & B)) - Demorgan's Law
531 if (Op0NotVal && Op1NotVal && isOnlyUse(Op0) && isOnlyUse(Op1)) {
532 Instruction *And = BinaryOperator::create(Instruction::And, Op0NotVal,
533 Op1NotVal,I.getName()+".demorgan",
535 WorkList.push_back(And);
536 return BinaryOperator::createNot(And);
539 return Changed ? &I : 0;
544 Instruction *InstCombiner::visitXor(BinaryOperator &I) {
545 bool Changed = SimplifyCommutative(I);
546 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
550 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
552 if (ConstantIntegral *Op1C = dyn_cast<ConstantIntegral>(Op1)) {
554 if (Op1C->isNullValue())
555 return ReplaceInstUsesWith(I, Op0);
557 // Is this a "NOT" instruction?
558 if (Op1C->isAllOnesValue()) {
559 // xor (xor X, -1), -1 = not (not X) = X
560 if (Value *X = dyn_castNotVal(Op0))
561 return ReplaceInstUsesWith(I, X);
563 // xor (setcc A, B), true = not (setcc A, B) = setncc A, B
564 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Op0))
565 if (SCI->use_size() == 1)
566 return new SetCondInst(SCI->getInverseCondition(),
567 SCI->getOperand(0), SCI->getOperand(1));
571 if (Value *X = dyn_castNotVal(Op0)) // ~A ^ A == -1
573 return ReplaceInstUsesWith(I,
574 ConstantIntegral::getAllOnesValue(I.getType()));
576 if (Value *X = dyn_castNotVal(Op1)) // A ^ ~A == -1
578 return ReplaceInstUsesWith(I,
579 ConstantIntegral::getAllOnesValue(I.getType()));
581 if (Instruction *Op1I = dyn_cast<Instruction>(Op1))
582 if (Op1I->getOpcode() == Instruction::Or)
583 if (Op1I->getOperand(0) == Op0) { // B^(B|A) == (A|B)^B
584 cast<BinaryOperator>(Op1I)->swapOperands();
587 } else if (Op1I->getOperand(1) == Op0) { // B^(A|B) == (A|B)^B
592 if (Instruction *Op0I = dyn_cast<Instruction>(Op0))
593 if (Op0I->getOpcode() == Instruction::Or && Op0I->use_size() == 1) {
594 if (Op0I->getOperand(0) == Op1) // (B|A)^B == (A|B)^B
595 cast<BinaryOperator>(Op0I)->swapOperands();
596 if (Op0I->getOperand(1) == Op1) { // (A|B)^B == A & ~B
597 Value *NotB = BinaryOperator::createNot(Op1, Op1->getName()+".not", &I);
598 WorkList.push_back(cast<Instruction>(NotB));
599 return BinaryOperator::create(Instruction::And, Op0I->getOperand(0),
604 // (A & C1)^(B & C2) -> (A & C1)|(B & C2) iff C1^C2 == 0
605 if (Constant *C1 = dyn_castMaskingAnd(Op0))
606 if (Constant *C2 = dyn_castMaskingAnd(Op1))
607 if ((*C1 & *C2)->isNullValue())
608 return BinaryOperator::create(Instruction::Or, Op0, Op1);
610 return Changed ? &I : 0;
613 // AddOne, SubOne - Add or subtract a constant one from an integer constant...
614 static Constant *AddOne(ConstantInt *C) {
615 Constant *Result = *C + *ConstantInt::get(C->getType(), 1);
616 assert(Result && "Constant folding integer addition failed!");
619 static Constant *SubOne(ConstantInt *C) {
620 Constant *Result = *C - *ConstantInt::get(C->getType(), 1);
621 assert(Result && "Constant folding integer addition failed!");
625 // isTrueWhenEqual - Return true if the specified setcondinst instruction is
626 // true when both operands are equal...
628 static bool isTrueWhenEqual(Instruction &I) {
629 return I.getOpcode() == Instruction::SetEQ ||
630 I.getOpcode() == Instruction::SetGE ||
631 I.getOpcode() == Instruction::SetLE;
634 Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
635 bool Changed = SimplifyCommutative(I);
636 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
637 const Type *Ty = Op0->getType();
641 return ReplaceInstUsesWith(I, ConstantBool::get(isTrueWhenEqual(I)));
643 // setcc <global*>, 0 - Global value addresses are never null!
644 if (isa<GlobalValue>(Op0) && isa<ConstantPointerNull>(Op1))
645 return ReplaceInstUsesWith(I, ConstantBool::get(!isTrueWhenEqual(I)));
647 // setcc's with boolean values can always be turned into bitwise operations
648 if (Ty == Type::BoolTy) {
649 // If this is <, >, or !=, we can change this into a simple xor instruction
650 if (!isTrueWhenEqual(I))
651 return BinaryOperator::create(Instruction::Xor, Op0, Op1, I.getName());
653 // Otherwise we need to make a temporary intermediate instruction and insert
654 // it into the instruction stream. This is what we are after:
656 // seteq bool %A, %B -> ~(A^B)
657 // setle bool %A, %B -> ~A | B
658 // setge bool %A, %B -> A | ~B
660 if (I.getOpcode() == Instruction::SetEQ) { // seteq case
661 Instruction *Xor = BinaryOperator::create(Instruction::Xor, Op0, Op1,
663 InsertNewInstBefore(Xor, I);
664 return BinaryOperator::createNot(Xor, I.getName());
667 // Handle the setXe cases...
668 assert(I.getOpcode() == Instruction::SetGE ||
669 I.getOpcode() == Instruction::SetLE);
671 if (I.getOpcode() == Instruction::SetGE)
672 std::swap(Op0, Op1); // Change setge -> setle
674 // Now we just have the SetLE case.
675 Instruction *Not = BinaryOperator::createNot(Op0, I.getName()+"tmp");
676 InsertNewInstBefore(Not, I);
677 return BinaryOperator::create(Instruction::Or, Not, Op1, I.getName());
680 // Check to see if we are doing one of many comparisons against constant
681 // integers at the end of their ranges...
683 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
684 // Check to see if we are comparing against the minimum or maximum value...
685 if (CI->isMinValue()) {
686 if (I.getOpcode() == Instruction::SetLT) // A < MIN -> FALSE
687 return ReplaceInstUsesWith(I, ConstantBool::False);
688 if (I.getOpcode() == Instruction::SetGE) // A >= MIN -> TRUE
689 return ReplaceInstUsesWith(I, ConstantBool::True);
690 if (I.getOpcode() == Instruction::SetLE) // A <= MIN -> A == MIN
691 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
692 if (I.getOpcode() == Instruction::SetGT) // A > MIN -> A != MIN
693 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
695 } else if (CI->isMaxValue()) {
696 if (I.getOpcode() == Instruction::SetGT) // A > MAX -> FALSE
697 return ReplaceInstUsesWith(I, ConstantBool::False);
698 if (I.getOpcode() == Instruction::SetLE) // A <= MAX -> TRUE
699 return ReplaceInstUsesWith(I, ConstantBool::True);
700 if (I.getOpcode() == Instruction::SetGE) // A >= MAX -> A == MAX
701 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
702 if (I.getOpcode() == Instruction::SetLT) // A < MAX -> A != MAX
703 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
705 // Comparing against a value really close to min or max?
706 } else if (isMinValuePlusOne(CI)) {
707 if (I.getOpcode() == Instruction::SetLT) // A < MIN+1 -> A == MIN
708 return BinaryOperator::create(Instruction::SetEQ, Op0,
709 SubOne(CI), I.getName());
710 if (I.getOpcode() == Instruction::SetGE) // A >= MIN-1 -> A != MIN
711 return BinaryOperator::create(Instruction::SetNE, Op0,
712 SubOne(CI), I.getName());
714 } else if (isMaxValueMinusOne(CI)) {
715 if (I.getOpcode() == Instruction::SetGT) // A > MAX-1 -> A == MAX
716 return BinaryOperator::create(Instruction::SetEQ, Op0,
717 AddOne(CI), I.getName());
718 if (I.getOpcode() == Instruction::SetLE) // A <= MAX-1 -> A != MAX
719 return BinaryOperator::create(Instruction::SetNE, Op0,
720 AddOne(CI), I.getName());
724 return Changed ? &I : 0;
729 Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
730 assert(I.getOperand(1)->getType() == Type::UByteTy);
731 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
733 // shl X, 0 == X and shr X, 0 == X
734 // shl 0, X == 0 and shr 0, X == 0
735 if (Op1 == Constant::getNullValue(Type::UByteTy) ||
736 Op0 == Constant::getNullValue(Op0->getType()))
737 return ReplaceInstUsesWith(I, Op0);
739 // If this is a shift of a shift, see if we can fold the two together...
740 if (ShiftInst *Op0SI = dyn_cast<ShiftInst>(Op0)) {
741 if (isa<Constant>(Op1) && isa<Constant>(Op0SI->getOperand(1))) {
742 ConstantUInt *ShiftAmt1C = cast<ConstantUInt>(Op0SI->getOperand(1));
743 unsigned ShiftAmt1 = ShiftAmt1C->getValue();
744 unsigned ShiftAmt2 = cast<ConstantUInt>(Op1)->getValue();
746 // Check for (A << c1) << c2 and (A >> c1) >> c2
747 if (I.getOpcode() == Op0SI->getOpcode()) {
748 unsigned Amt = ShiftAmt1+ShiftAmt2; // Fold into one big shift...
749 return new ShiftInst(I.getOpcode(), Op0SI->getOperand(0),
750 ConstantUInt::get(Type::UByteTy, Amt));
753 if (I.getType()->isUnsigned()) { // Check for (A << c1) >> c2 or visaversa
754 // Calculate bitmask for what gets shifted off the edge...
755 Constant *C = ConstantIntegral::getAllOnesValue(I.getType());
756 if (I.getOpcode() == Instruction::Shr)
757 C = *C >> *ShiftAmt1C;
759 C = *C << *ShiftAmt1C;
760 assert(C && "Couldn't constant fold shift expression?");
763 BinaryOperator::create(Instruction::And, Op0SI->getOperand(0),
764 C, Op0SI->getOperand(0)->getName()+".mask",&I);
765 WorkList.push_back(Mask);
767 // Figure out what flavor of shift we should use...
768 if (ShiftAmt1 == ShiftAmt2)
769 return ReplaceInstUsesWith(I, Mask); // (A << c) >> c === A & c2
770 else if (ShiftAmt1 < ShiftAmt2) {
771 return new ShiftInst(I.getOpcode(), Mask,
772 ConstantUInt::get(Type::UByteTy, ShiftAmt2-ShiftAmt1));
774 return new ShiftInst(Op0SI->getOpcode(), Mask,
775 ConstantUInt::get(Type::UByteTy, ShiftAmt1-ShiftAmt2));
781 // shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr of
784 if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
785 unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
786 if (CUI->getValue() >= TypeBits &&
787 (!Op0->getType()->isSigned() || I.getOpcode() == Instruction::Shl))
788 return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
790 // Check to see if we are shifting left by 1. If so, turn it into an add
792 if (I.getOpcode() == Instruction::Shl && CUI->equalsInt(1))
793 // Convert 'shl int %X, 1' to 'add int %X, %X'
794 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
798 // shr int -1, X = -1 (for any arithmetic shift rights of ~0)
799 if (ConstantSInt *CSI = dyn_cast<ConstantSInt>(Op0))
800 if (I.getOpcode() == Instruction::Shr && CSI->isAllOnesValue())
801 return ReplaceInstUsesWith(I, CSI);
807 // isEliminableCastOfCast - Return true if it is valid to eliminate the CI
810 static inline bool isEliminableCastOfCast(const CastInst &CI,
811 const CastInst *CSrc) {
812 assert(CI.getOperand(0) == CSrc);
813 const Type *SrcTy = CSrc->getOperand(0)->getType();
814 const Type *MidTy = CSrc->getType();
815 const Type *DstTy = CI.getType();
817 // It is legal to eliminate the instruction if casting A->B->A if the sizes
818 // are identical and the bits don't get reinterpreted (for example
819 // int->float->int would not be allowed)
820 if (SrcTy == DstTy && SrcTy->isLosslesslyConvertableTo(MidTy))
823 // Allow free casting and conversion of sizes as long as the sign doesn't
825 if (SrcTy->isIntegral() && MidTy->isIntegral() && DstTy->isIntegral()) {
826 unsigned SrcSize = SrcTy->getPrimitiveSize();
827 unsigned MidSize = MidTy->getPrimitiveSize();
828 unsigned DstSize = DstTy->getPrimitiveSize();
830 // Cases where we are monotonically decreasing the size of the type are
831 // always ok, regardless of what sign changes are going on.
833 if (SrcSize >= MidSize && MidSize >= DstSize)
836 // Cases where the source and destination type are the same, but the middle
837 // type is bigger are noops.
839 if (SrcSize == DstSize && MidSize > SrcSize)
842 // If we are monotonically growing, things are more complex.
844 if (SrcSize <= MidSize && MidSize <= DstSize) {
845 // We have eight combinations of signedness to worry about. Here's the
847 static const int SignTable[8] = {
848 // CODE, SrcSigned, MidSigned, DstSigned, Comment
849 1, // U U U Always ok
850 1, // U U S Always ok
851 3, // U S U Ok iff SrcSize != MidSize
852 3, // U S S Ok iff SrcSize != MidSize
854 2, // S U S Ok iff MidSize == DstSize
855 1, // S S U Always ok
856 1, // S S S Always ok
859 // Choose an action based on the current entry of the signtable that this
860 // cast of cast refers to...
861 unsigned Row = SrcTy->isSigned()*4+MidTy->isSigned()*2+DstTy->isSigned();
862 switch (SignTable[Row]) {
863 case 0: return false; // Never ok
864 case 1: return true; // Always ok
865 case 2: return MidSize == DstSize; // Ok iff MidSize == DstSize
866 case 3: // Ok iff SrcSize != MidSize
867 return SrcSize != MidSize || SrcTy == Type::BoolTy;
868 default: assert(0 && "Bad entry in sign table!");
873 // Otherwise, we cannot succeed. Specifically we do not want to allow things
874 // like: short -> ushort -> uint, because this can create wrong results if
875 // the input short is negative!
881 // CastInst simplification
883 Instruction *InstCombiner::visitCastInst(CastInst &CI) {
884 // If the user is casting a value to the same type, eliminate this cast
886 if (CI.getType() == CI.getOperand(0)->getType())
887 return ReplaceInstUsesWith(CI, CI.getOperand(0));
889 // If casting the result of another cast instruction, try to eliminate this
892 if (CastInst *CSrc = dyn_cast<CastInst>(CI.getOperand(0))) {
893 if (isEliminableCastOfCast(CI, CSrc)) {
894 // This instruction now refers directly to the cast's src operand. This
895 // has a good chance of making CSrc dead.
896 CI.setOperand(0, CSrc->getOperand(0));
900 // If this is an A->B->A cast, and we are dealing with integral types, try
901 // to convert this into a logical 'and' instruction.
903 if (CSrc->getOperand(0)->getType() == CI.getType() &&
904 CI.getType()->isInteger() && CSrc->getType()->isInteger() &&
905 CI.getType()->isUnsigned() && CSrc->getType()->isUnsigned() &&
906 CSrc->getType()->getPrimitiveSize() < CI.getType()->getPrimitiveSize()){
907 assert(CSrc->getType() != Type::ULongTy &&
908 "Cannot have type bigger than ulong!");
909 unsigned AndValue = (1U << CSrc->getType()->getPrimitiveSize()*8)-1;
910 Constant *AndOp = ConstantUInt::get(CI.getType(), AndValue);
911 return BinaryOperator::create(Instruction::And, CSrc->getOperand(0),
920 // PHINode simplification
922 Instruction *InstCombiner::visitPHINode(PHINode &PN) {
923 // If the PHI node only has one incoming value, eliminate the PHI node...
924 if (PN.getNumIncomingValues() == 1)
925 return ReplaceInstUsesWith(PN, PN.getIncomingValue(0));
927 // Otherwise if all of the incoming values are the same for the PHI, replace
928 // the PHI node with the incoming value.
931 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
932 if (PN.getIncomingValue(i) != &PN) // Not the PHI node itself...
933 if (InVal && PN.getIncomingValue(i) != InVal)
934 return 0; // Not the same, bail out.
936 InVal = PN.getIncomingValue(i);
938 // The only case that could cause InVal to be null is if we have a PHI node
939 // that only has entries for itself. In this case, there is no entry into the
940 // loop, so kill the PHI.
942 if (InVal == 0) InVal = Constant::getNullValue(PN.getType());
944 // All of the incoming values are the same, replace the PHI node now.
945 return ReplaceInstUsesWith(PN, InVal);
949 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
950 // Is it 'getelementptr %P, uint 0' or 'getelementptr %P'
951 // If so, eliminate the noop.
952 if ((GEP.getNumOperands() == 2 &&
953 GEP.getOperand(1) == Constant::getNullValue(Type::LongTy)) ||
954 GEP.getNumOperands() == 1)
955 return ReplaceInstUsesWith(GEP, GEP.getOperand(0));
957 // Combine Indices - If the source pointer to this getelementptr instruction
958 // is a getelementptr instruction, combine the indices of the two
959 // getelementptr instructions into a single instruction.
961 if (GetElementPtrInst *Src = dyn_cast<GetElementPtrInst>(GEP.getOperand(0))) {
962 std::vector<Value *> Indices;
964 // Can we combine the two pointer arithmetics offsets?
965 if (Src->getNumOperands() == 2 && isa<Constant>(Src->getOperand(1)) &&
966 isa<Constant>(GEP.getOperand(1))) {
967 // Replace: gep (gep %P, long C1), long C2, ...
968 // With: gep %P, long (C1+C2), ...
969 Value *Sum = *cast<Constant>(Src->getOperand(1)) +
970 *cast<Constant>(GEP.getOperand(1));
971 assert(Sum && "Constant folding of longs failed!?");
972 GEP.setOperand(0, Src->getOperand(0));
973 GEP.setOperand(1, Sum);
974 AddUsesToWorkList(*Src); // Reduce use count of Src
976 } else if (Src->getNumOperands() == 2 && Src->use_size() == 1) {
977 // Replace: gep (gep %P, long B), long A, ...
978 // With: T = long A+B; gep %P, T, ...
980 Value *Sum = BinaryOperator::create(Instruction::Add, Src->getOperand(1),
982 Src->getName()+".sum", &GEP);
983 GEP.setOperand(0, Src->getOperand(0));
984 GEP.setOperand(1, Sum);
985 WorkList.push_back(cast<Instruction>(Sum));
987 } else if (*GEP.idx_begin() == Constant::getNullValue(Type::LongTy) &&
988 Src->getNumOperands() != 1) {
989 // Otherwise we can do the fold if the first index of the GEP is a zero
990 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
991 Indices.insert(Indices.end(), GEP.idx_begin()+1, GEP.idx_end());
992 } else if (Src->getOperand(Src->getNumOperands()-1) ==
993 Constant::getNullValue(Type::LongTy)) {
994 // If the src gep ends with a constant array index, merge this get into
995 // it, even if we have a non-zero array index.
996 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end()-1);
997 Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end());
1000 if (!Indices.empty())
1001 return new GetElementPtrInst(Src->getOperand(0), Indices, GEP.getName());
1003 } else if (GlobalValue *GV = dyn_cast<GlobalValue>(GEP.getOperand(0))) {
1004 // GEP of global variable. If all of the indices for this GEP are
1005 // constants, we can promote this to a constexpr instead of an instruction.
1007 // Scan for nonconstants...
1008 std::vector<Constant*> Indices;
1009 User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end();
1010 for (; I != E && isa<Constant>(*I); ++I)
1011 Indices.push_back(cast<Constant>(*I));
1013 if (I == E) { // If they are all constants...
1015 ConstantExpr::getGetElementPtr(ConstantPointerRef::get(GV), Indices);
1017 // Replace all uses of the GEP with the new constexpr...
1018 return ReplaceInstUsesWith(GEP, CE);
1025 Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
1026 // Convert: malloc Ty, C - where C is a constant != 1 into: malloc [C x Ty], 1
1027 if (AI.isArrayAllocation()) // Check C != 1
1028 if (const ConstantUInt *C = dyn_cast<ConstantUInt>(AI.getArraySize())) {
1029 const Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getValue());
1030 AllocationInst *New = 0;
1032 // Create and insert the replacement instruction...
1033 if (isa<MallocInst>(AI))
1034 New = new MallocInst(NewTy, 0, AI.getName(), &AI);
1036 assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
1037 New = new AllocaInst(NewTy, 0, AI.getName(), &AI);
1040 // Scan to the end of the allocation instructions, to skip over a block of
1041 // allocas if possible...
1043 BasicBlock::iterator It = New;
1044 while (isa<AllocationInst>(*It)) ++It;
1046 // Now that I is pointing to the first non-allocation-inst in the block,
1047 // insert our getelementptr instruction...
1049 std::vector<Value*> Idx(2, Constant::getNullValue(Type::LongTy));
1050 Value *V = new GetElementPtrInst(New, Idx, New->getName()+".sub", It);
1052 // Now make everything use the getelementptr instead of the original
1054 ReplaceInstUsesWith(AI, V);
1062 void InstCombiner::removeFromWorkList(Instruction *I) {
1063 WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),
1067 bool InstCombiner::runOnFunction(Function &F) {
1068 bool Changed = false;
1070 WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F));
1072 while (!WorkList.empty()) {
1073 Instruction *I = WorkList.back(); // Get an instruction from the worklist
1074 WorkList.pop_back();
1076 // Check to see if we can DCE or ConstantPropagate the instruction...
1077 // Check to see if we can DIE the instruction...
1078 if (isInstructionTriviallyDead(I)) {
1079 // Add operands to the worklist...
1080 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1081 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
1082 WorkList.push_back(Op);
1085 BasicBlock::iterator BBI = I;
1086 if (dceInstruction(BBI)) {
1087 removeFromWorkList(I);
1092 // Instruction isn't dead, see if we can constant propagate it...
1093 if (Constant *C = ConstantFoldInstruction(I)) {
1094 // Add operands to the worklist...
1095 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1096 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
1097 WorkList.push_back(Op);
1098 ReplaceInstUsesWith(*I, C);
1101 BasicBlock::iterator BBI = I;
1102 if (dceInstruction(BBI)) {
1103 removeFromWorkList(I);
1108 // Now that we have an instruction, try combining it to simplify it...
1109 if (Instruction *Result = visit(*I)) {
1111 // Should we replace the old instruction with a new one?
1113 // Instructions can end up on the worklist more than once. Make sure
1114 // we do not process an instruction that has been deleted.
1115 removeFromWorkList(I);
1116 ReplaceInstWithInst(I, Result);
1118 BasicBlock::iterator II = I;
1120 // If the instruction was modified, it's possible that it is now dead.
1121 // if so, remove it.
1122 if (dceInstruction(II)) {
1123 // Instructions may end up in the worklist more than once. Erase them
1125 removeFromWorkList(I);
1131 WorkList.push_back(Result);
1132 AddUsesToWorkList(*Result);
1141 Pass *createInstructionCombiningPass() {
1142 return new InstCombiner();