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/Instructions.h"
21 #include "llvm/Pass.h"
22 #include "llvm/Constants.h"
23 #include "llvm/ConstantHandling.h"
24 #include "llvm/DerivedTypes.h"
25 #include "llvm/Support/InstIterator.h"
26 #include "llvm/Support/InstVisitor.h"
27 #include "Support/Statistic.h"
31 Statistic<> NumCombined ("instcombine", "Number of insts combined");
32 Statistic<> NumConstProp("instcombine", "Number of constant folds");
33 Statistic<> NumDeadInst ("instcombine", "Number of dead inst eliminated");
35 class InstCombiner : public FunctionPass,
36 public InstVisitor<InstCombiner, Instruction*> {
37 // Worklist of all of the instructions that need to be simplified.
38 std::vector<Instruction*> WorkList;
40 void AddUsesToWorkList(Instruction &I) {
41 // The instruction was simplified, add all users of the instruction to
42 // the work lists because they might get more simplified now...
44 for (Value::use_iterator UI = I.use_begin(), UE = I.use_end();
46 WorkList.push_back(cast<Instruction>(*UI));
49 // removeFromWorkList - remove all instances of I from the worklist.
50 void removeFromWorkList(Instruction *I);
52 virtual bool runOnFunction(Function &F);
54 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
58 // Visitation implementation - Implement instruction combining for different
59 // instruction types. The semantics are as follows:
61 // null - No change was made
62 // I - Change was made, I is still valid, I may be dead though
63 // otherwise - Change was made, replace I with returned instruction
65 Instruction *visitAdd(BinaryOperator &I);
66 Instruction *visitSub(BinaryOperator &I);
67 Instruction *visitMul(BinaryOperator &I);
68 Instruction *visitDiv(BinaryOperator &I);
69 Instruction *visitRem(BinaryOperator &I);
70 Instruction *visitAnd(BinaryOperator &I);
71 Instruction *visitOr (BinaryOperator &I);
72 Instruction *visitXor(BinaryOperator &I);
73 Instruction *visitSetCondInst(BinaryOperator &I);
74 Instruction *visitShiftInst(ShiftInst &I);
75 Instruction *visitCastInst(CastInst &CI);
76 Instruction *visitPHINode(PHINode &PN);
77 Instruction *visitGetElementPtrInst(GetElementPtrInst &GEP);
78 Instruction *visitAllocationInst(AllocationInst &AI);
80 // visitInstruction - Specify what to return for unhandled instructions...
81 Instruction *visitInstruction(Instruction &I) { return 0; }
83 // InsertNewInstBefore - insert an instruction New before instruction Old
84 // in the program. Add the new instruction to the worklist.
86 void InsertNewInstBefore(Instruction *New, Instruction &Old) {
87 assert(New && New->getParent() == 0 &&
88 "New instruction already inserted into a basic block!");
89 BasicBlock *BB = Old.getParent();
90 BB->getInstList().insert(&Old, New); // Insert inst
91 WorkList.push_back(New); // Add to worklist
94 // ReplaceInstUsesWith - This method is to be used when an instruction is
95 // found to be dead, replacable with another preexisting expression. Here
96 // we add all uses of I to the worklist, replace all uses of I with the new
97 // value, then return I, so that the inst combiner will know that I was
100 Instruction *ReplaceInstUsesWith(Instruction &I, Value *V) {
101 AddUsesToWorkList(I); // Add all modified instrs to worklist
102 I.replaceAllUsesWith(V);
106 // SimplifyCommutative - This performs a few simplifications for commutative
108 bool SimplifyCommutative(BinaryOperator &I);
112 RegisterOpt<InstCombiner> X("instcombine", "Combine redundant instructions");
115 // getComplexity: Assign a complexity or rank value to LLVM Values...
116 // 0 -> Constant, 1 -> Other, 2 -> Argument, 2 -> Unary, 3 -> OtherInst
117 static unsigned getComplexity(Value *V) {
118 if (isa<Instruction>(V)) {
119 if (BinaryOperator::isNeg(V) || BinaryOperator::isNot(V))
123 if (isa<Argument>(V)) return 2;
124 return isa<Constant>(V) ? 0 : 1;
127 // isOnlyUse - Return true if this instruction will be deleted if we stop using
129 static bool isOnlyUse(Value *V) {
130 return V->use_size() == 1 || isa<Constant>(V);
133 // SimplifyCommutative - This performs a few simplifications for commutative
136 // 1. Order operands such that they are listed from right (least complex) to
137 // left (most complex). This puts constants before unary operators before
140 // 2. Transform: (op (op V, C1), C2) ==> (op V, (op C1, C2))
141 // 3. Transform: (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2))
143 bool InstCombiner::SimplifyCommutative(BinaryOperator &I) {
144 bool Changed = false;
145 if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1)))
146 Changed = !I.swapOperands();
148 if (!I.isAssociative()) return Changed;
149 Instruction::BinaryOps Opcode = I.getOpcode();
150 if (BinaryOperator *Op = dyn_cast<BinaryOperator>(I.getOperand(0)))
151 if (Op->getOpcode() == Opcode && isa<Constant>(Op->getOperand(1))) {
152 if (isa<Constant>(I.getOperand(1))) {
153 Constant *Folded = ConstantExpr::get(I.getOpcode(),
154 cast<Constant>(I.getOperand(1)),
155 cast<Constant>(Op->getOperand(1)));
156 I.setOperand(0, Op->getOperand(0));
157 I.setOperand(1, Folded);
159 } else if (BinaryOperator *Op1=dyn_cast<BinaryOperator>(I.getOperand(1)))
160 if (Op1->getOpcode() == Opcode && isa<Constant>(Op1->getOperand(1)) &&
161 isOnlyUse(Op) && isOnlyUse(Op1)) {
162 Constant *C1 = cast<Constant>(Op->getOperand(1));
163 Constant *C2 = cast<Constant>(Op1->getOperand(1));
165 // Fold (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2))
166 Constant *Folded = ConstantExpr::get(I.getOpcode(), C1, C2);
167 Instruction *New = BinaryOperator::create(Opcode, Op->getOperand(0),
170 WorkList.push_back(New);
171 I.setOperand(0, New);
172 I.setOperand(1, Folded);
179 // dyn_castNegVal - Given a 'sub' instruction, return the RHS of the instruction
180 // if the LHS is a constant zero (which is the 'negate' form).
182 static inline Value *dyn_castNegVal(Value *V) {
183 if (BinaryOperator::isNeg(V))
184 return BinaryOperator::getNegArgument(cast<BinaryOperator>(V));
186 // Constants can be considered to be negated values if they can be folded...
187 if (Constant *C = dyn_cast<Constant>(V))
188 return ConstantExpr::get(Instruction::Sub,
189 Constant::getNullValue(V->getType()), C);
193 static inline Value *dyn_castNotVal(Value *V) {
194 if (BinaryOperator::isNot(V))
195 return BinaryOperator::getNotArgument(cast<BinaryOperator>(V));
197 // Constants can be considered to be not'ed values...
198 if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(V))
199 return ConstantExpr::get(Instruction::Xor,
200 ConstantIntegral::getAllOnesValue(C->getType()),C);
204 // dyn_castFoldableMul - If this value is a multiply that can be folded into
205 // other computations (because it has a constant operand), return the
206 // non-constant operand of the multiply.
208 static inline Value *dyn_castFoldableMul(Value *V) {
209 if (V->use_size() == 1 && V->getType()->isInteger())
210 if (Instruction *I = dyn_cast<Instruction>(V))
211 if (I->getOpcode() == Instruction::Mul)
212 if (isa<Constant>(I->getOperand(1)))
213 return I->getOperand(0);
217 // dyn_castMaskingAnd - If this value is an And instruction masking a value with
218 // a constant, return the constant being anded with.
220 static inline Constant *dyn_castMaskingAnd(Value *V) {
221 if (Instruction *I = dyn_cast<Instruction>(V))
222 if (I->getOpcode() == Instruction::And)
223 return dyn_cast<Constant>(I->getOperand(1));
225 // If this is a constant, it acts just like we were masking with it.
226 return dyn_cast<Constant>(V);
229 // Log2 - Calculate the log base 2 for the specified value if it is exactly a
231 static unsigned Log2(uint64_t Val) {
232 assert(Val > 1 && "Values 0 and 1 should be handled elsewhere!");
235 if (Val & 1) return 0; // Multiple bits set?
242 Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
243 bool Changed = SimplifyCommutative(I);
244 Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
246 // Eliminate 'add int %X, 0'
247 if (RHS == Constant::getNullValue(I.getType()))
248 return ReplaceInstUsesWith(I, LHS);
251 if (Value *V = dyn_castNegVal(LHS))
252 return BinaryOperator::create(Instruction::Sub, RHS, V);
255 if (!isa<Constant>(RHS))
256 if (Value *V = dyn_castNegVal(RHS))
257 return BinaryOperator::create(Instruction::Sub, LHS, V);
259 // X*C + X --> X * (C+1)
260 if (dyn_castFoldableMul(LHS) == RHS) {
262 ConstantExpr::get(Instruction::Add,
263 cast<Constant>(cast<Instruction>(LHS)->getOperand(1)),
264 ConstantInt::get(I.getType(), 1));
265 return BinaryOperator::create(Instruction::Mul, RHS, CP1);
268 // X + X*C --> X * (C+1)
269 if (dyn_castFoldableMul(RHS) == LHS) {
271 ConstantExpr::get(Instruction::Add,
272 cast<Constant>(cast<Instruction>(RHS)->getOperand(1)),
273 ConstantInt::get(I.getType(), 1));
274 return BinaryOperator::create(Instruction::Mul, LHS, CP1);
277 // (A & C1)+(B & C2) -> (A & C1)|(B & C2) iff C1&C2 == 0
278 if (Constant *C1 = dyn_castMaskingAnd(LHS))
279 if (Constant *C2 = dyn_castMaskingAnd(RHS))
280 if (ConstantExpr::get(Instruction::And, C1, C2)->isNullValue())
281 return BinaryOperator::create(Instruction::Or, LHS, RHS);
283 return Changed ? &I : 0;
286 Instruction *InstCombiner::visitSub(BinaryOperator &I) {
287 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
289 if (Op0 == Op1) // sub X, X -> 0
290 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
292 // If this is a 'B = x-(-A)', change to B = x+A...
293 if (Value *V = dyn_castNegVal(Op1))
294 return BinaryOperator::create(Instruction::Add, Op0, V);
296 // Replace (-1 - A) with (~A)...
297 if (ConstantInt *C = dyn_cast<ConstantInt>(Op0))
298 if (C->isAllOnesValue())
299 return BinaryOperator::createNot(Op1);
301 if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1))
302 if (Op1I->use_size() == 1) {
303 // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression
304 // is not used by anyone else...
306 if (Op1I->getOpcode() == Instruction::Sub) {
307 // Swap the two operands of the subexpr...
308 Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
309 Op1I->setOperand(0, IIOp1);
310 Op1I->setOperand(1, IIOp0);
312 // Create the new top level add instruction...
313 return BinaryOperator::create(Instruction::Add, Op0, Op1);
316 // Replace (A - (A & B)) with (A & ~B) if this is the only use of (A&B)...
318 if (Op1I->getOpcode() == Instruction::And &&
319 (Op1I->getOperand(0) == Op0 || Op1I->getOperand(1) == Op0)) {
320 Value *OtherOp = Op1I->getOperand(Op1I->getOperand(0) == Op0);
322 Instruction *NewNot = BinaryOperator::createNot(OtherOp, "B.not", &I);
323 return BinaryOperator::create(Instruction::And, Op0, NewNot);
326 // X - X*C --> X * (1-C)
327 if (dyn_castFoldableMul(Op1I) == Op0) {
329 ConstantExpr::get(Instruction::Sub,
330 ConstantInt::get(I.getType(), 1),
331 cast<Constant>(cast<Instruction>(Op1)->getOperand(1)));
332 assert(CP1 && "Couldn't constant fold 1-C?");
333 return BinaryOperator::create(Instruction::Mul, Op0, CP1);
337 // X*C - X --> X * (C-1)
338 if (dyn_castFoldableMul(Op0) == Op1) {
340 ConstantExpr::get(Instruction::Sub,
341 cast<Constant>(cast<Instruction>(Op0)->getOperand(1)),
342 ConstantInt::get(I.getType(), 1));
343 assert(CP1 && "Couldn't constant fold C - 1?");
344 return BinaryOperator::create(Instruction::Mul, Op1, CP1);
350 Instruction *InstCombiner::visitMul(BinaryOperator &I) {
351 bool Changed = SimplifyCommutative(I);
352 Value *Op0 = I.getOperand(0);
354 // Simplify mul instructions with a constant RHS...
355 if (Constant *Op1 = dyn_cast<Constant>(I.getOperand(1))) {
356 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
357 const Type *Ty = CI->getType();
358 uint64_t Val = Ty->isSigned() ?
359 (uint64_t)cast<ConstantSInt>(CI)->getValue() :
360 cast<ConstantUInt>(CI)->getValue();
363 return ReplaceInstUsesWith(I, Op1); // Eliminate 'mul double %X, 0'
365 return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul int %X, 1'
366 case 2: // Convert 'mul int %X, 2' to 'add int %X, %X'
367 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
370 if (uint64_t C = Log2(Val)) // Replace X*(2^C) with X << C
371 return new ShiftInst(Instruction::Shl, Op0,
372 ConstantUInt::get(Type::UByteTy, C));
374 ConstantFP *Op1F = cast<ConstantFP>(Op1);
375 if (Op1F->isNullValue())
376 return ReplaceInstUsesWith(I, Op1);
378 // "In IEEE floating point, x*1 is not equivalent to x for nans. However,
379 // ANSI says we can drop signals, so we can do this anyway." (from GCC)
380 if (Op1F->getValue() == 1.0)
381 return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul double %X, 1.0'
385 if (Value *Op0v = dyn_castNegVal(Op0)) // -X * -Y = X*Y
386 if (Value *Op1v = dyn_castNegVal(I.getOperand(1)))
387 return BinaryOperator::create(Instruction::Mul, Op0v, Op1v);
389 return Changed ? &I : 0;
392 Instruction *InstCombiner::visitDiv(BinaryOperator &I) {
394 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) {
395 if (RHS->equalsInt(1))
396 return ReplaceInstUsesWith(I, I.getOperand(0));
398 // Check to see if this is an unsigned division with an exact power of 2,
399 // if so, convert to a right shift.
400 if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
401 if (uint64_t Val = C->getValue()) // Don't break X / 0
402 if (uint64_t C = Log2(Val))
403 return new ShiftInst(Instruction::Shr, I.getOperand(0),
404 ConstantUInt::get(Type::UByteTy, C));
407 // 0 / X == 0, we don't need to preserve faults!
408 if (ConstantInt *LHS = dyn_cast<ConstantInt>(I.getOperand(0)))
409 if (LHS->equalsInt(0))
410 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
416 Instruction *InstCombiner::visitRem(BinaryOperator &I) {
417 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) {
418 if (RHS->equalsInt(1)) // X % 1 == 0
419 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
421 // Check to see if this is an unsigned remainder with an exact power of 2,
422 // if so, convert to a bitwise and.
423 if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
424 if (uint64_t Val = C->getValue()) // Don't break X % 0 (divide by zero)
426 return BinaryOperator::create(Instruction::And, I.getOperand(0),
427 ConstantUInt::get(I.getType(), Val-1));
430 // 0 % X == 0, we don't need to preserve faults!
431 if (ConstantInt *LHS = dyn_cast<ConstantInt>(I.getOperand(0)))
432 if (LHS->equalsInt(0))
433 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
438 // isMaxValueMinusOne - return true if this is Max-1
439 static bool isMaxValueMinusOne(const ConstantInt *C) {
440 if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C)) {
441 // Calculate -1 casted to the right type...
442 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
443 uint64_t Val = ~0ULL; // All ones
444 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
445 return CU->getValue() == Val-1;
448 const ConstantSInt *CS = cast<ConstantSInt>(C);
450 // Calculate 0111111111..11111
451 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
452 int64_t Val = INT64_MAX; // All ones
453 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
454 return CS->getValue() == Val-1;
457 // isMinValuePlusOne - return true if this is Min+1
458 static bool isMinValuePlusOne(const ConstantInt *C) {
459 if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C))
460 return CU->getValue() == 1;
462 const ConstantSInt *CS = cast<ConstantSInt>(C);
464 // Calculate 1111111111000000000000
465 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
466 int64_t Val = -1; // All ones
467 Val <<= TypeBits-1; // Shift over to the right spot
468 return CS->getValue() == Val+1;
472 Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
473 bool Changed = SimplifyCommutative(I);
474 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
476 // and X, X = X and X, 0 == 0
477 if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
478 return ReplaceInstUsesWith(I, Op1);
481 if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
482 if (RHS->isAllOnesValue())
483 return ReplaceInstUsesWith(I, Op0);
485 Value *Op0NotVal = dyn_castNotVal(Op0);
486 Value *Op1NotVal = dyn_castNotVal(Op1);
488 // (~A & ~B) == (~(A | B)) - Demorgan's Law
489 if (Op0NotVal && Op1NotVal && isOnlyUse(Op0) && isOnlyUse(Op1)) {
490 Instruction *Or = BinaryOperator::create(Instruction::Or, Op0NotVal,
491 Op1NotVal,I.getName()+".demorgan",
493 WorkList.push_back(Or);
494 return BinaryOperator::createNot(Or);
497 if (Op0NotVal == Op1 || Op1NotVal == Op0) // A & ~A == ~A & A == 0
498 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
500 return Changed ? &I : 0;
505 Instruction *InstCombiner::visitOr(BinaryOperator &I) {
506 bool Changed = SimplifyCommutative(I);
507 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
509 // or X, X = X or X, 0 == X
510 if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
511 return ReplaceInstUsesWith(I, Op0);
514 if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
515 if (RHS->isAllOnesValue())
516 return ReplaceInstUsesWith(I, Op1);
518 Value *Op0NotVal = dyn_castNotVal(Op0);
519 Value *Op1NotVal = dyn_castNotVal(Op1);
521 if (Op1 == Op0NotVal) // ~A | A == -1
522 return ReplaceInstUsesWith(I,
523 ConstantIntegral::getAllOnesValue(I.getType()));
525 if (Op0 == Op1NotVal) // A | ~A == -1
526 return ReplaceInstUsesWith(I,
527 ConstantIntegral::getAllOnesValue(I.getType()));
529 // (~A | ~B) == (~(A & B)) - Demorgan's Law
530 if (Op0NotVal && Op1NotVal && isOnlyUse(Op0) && isOnlyUse(Op1)) {
531 Instruction *And = BinaryOperator::create(Instruction::And, Op0NotVal,
532 Op1NotVal,I.getName()+".demorgan",
534 WorkList.push_back(And);
535 return BinaryOperator::createNot(And);
538 return Changed ? &I : 0;
543 Instruction *InstCombiner::visitXor(BinaryOperator &I) {
544 bool Changed = SimplifyCommutative(I);
545 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
549 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
551 if (ConstantIntegral *Op1C = dyn_cast<ConstantIntegral>(Op1)) {
553 if (Op1C->isNullValue())
554 return ReplaceInstUsesWith(I, Op0);
556 // Is this a "NOT" instruction?
557 if (Op1C->isAllOnesValue()) {
558 // xor (xor X, -1), -1 = not (not X) = X
559 if (Value *X = dyn_castNotVal(Op0))
560 return ReplaceInstUsesWith(I, X);
562 // xor (setcc A, B), true = not (setcc A, B) = setncc A, B
563 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Op0))
564 if (SCI->use_size() == 1)
565 return new SetCondInst(SCI->getInverseCondition(),
566 SCI->getOperand(0), SCI->getOperand(1));
570 if (Value *X = dyn_castNotVal(Op0)) // ~A ^ A == -1
572 return ReplaceInstUsesWith(I,
573 ConstantIntegral::getAllOnesValue(I.getType()));
575 if (Value *X = dyn_castNotVal(Op1)) // A ^ ~A == -1
577 return ReplaceInstUsesWith(I,
578 ConstantIntegral::getAllOnesValue(I.getType()));
580 if (Instruction *Op1I = dyn_cast<Instruction>(Op1))
581 if (Op1I->getOpcode() == Instruction::Or)
582 if (Op1I->getOperand(0) == Op0) { // B^(B|A) == (A|B)^B
583 cast<BinaryOperator>(Op1I)->swapOperands();
586 } else if (Op1I->getOperand(1) == Op0) { // B^(A|B) == (A|B)^B
591 if (Instruction *Op0I = dyn_cast<Instruction>(Op0))
592 if (Op0I->getOpcode() == Instruction::Or && Op0I->use_size() == 1) {
593 if (Op0I->getOperand(0) == Op1) // (B|A)^B == (A|B)^B
594 cast<BinaryOperator>(Op0I)->swapOperands();
595 if (Op0I->getOperand(1) == Op1) { // (A|B)^B == A & ~B
596 Value *NotB = BinaryOperator::createNot(Op1, Op1->getName()+".not", &I);
597 WorkList.push_back(cast<Instruction>(NotB));
598 return BinaryOperator::create(Instruction::And, Op0I->getOperand(0),
603 // (A & C1)^(B & C2) -> (A & C1)|(B & C2) iff C1^C2 == 0
604 if (Constant *C1 = dyn_castMaskingAnd(Op0))
605 if (Constant *C2 = dyn_castMaskingAnd(Op1))
606 if (ConstantExpr::get(Instruction::And, C1, C2)->isNullValue())
607 return BinaryOperator::create(Instruction::Or, Op0, Op1);
609 return Changed ? &I : 0;
612 // AddOne, SubOne - Add or subtract a constant one from an integer constant...
613 static Constant *AddOne(ConstantInt *C) {
614 Constant *Result = ConstantExpr::get(Instruction::Add, C,
615 ConstantInt::get(C->getType(), 1));
616 assert(Result && "Constant folding integer addition failed!");
619 static Constant *SubOne(ConstantInt *C) {
620 Constant *Result = ConstantExpr::get(Instruction::Sub, C,
621 ConstantInt::get(C->getType(), 1));
622 assert(Result && "Constant folding integer addition failed!");
626 // isTrueWhenEqual - Return true if the specified setcondinst instruction is
627 // true when both operands are equal...
629 static bool isTrueWhenEqual(Instruction &I) {
630 return I.getOpcode() == Instruction::SetEQ ||
631 I.getOpcode() == Instruction::SetGE ||
632 I.getOpcode() == Instruction::SetLE;
635 Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
636 bool Changed = SimplifyCommutative(I);
637 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
638 const Type *Ty = Op0->getType();
642 return ReplaceInstUsesWith(I, ConstantBool::get(isTrueWhenEqual(I)));
644 // setcc <global*>, 0 - Global value addresses are never null!
645 if (isa<GlobalValue>(Op0) && isa<ConstantPointerNull>(Op1))
646 return ReplaceInstUsesWith(I, ConstantBool::get(!isTrueWhenEqual(I)));
648 // setcc's with boolean values can always be turned into bitwise operations
649 if (Ty == Type::BoolTy) {
650 // If this is <, >, or !=, we can change this into a simple xor instruction
651 if (!isTrueWhenEqual(I))
652 return BinaryOperator::create(Instruction::Xor, Op0, Op1, I.getName());
654 // Otherwise we need to make a temporary intermediate instruction and insert
655 // it into the instruction stream. This is what we are after:
657 // seteq bool %A, %B -> ~(A^B)
658 // setle bool %A, %B -> ~A | B
659 // setge bool %A, %B -> A | ~B
661 if (I.getOpcode() == Instruction::SetEQ) { // seteq case
662 Instruction *Xor = BinaryOperator::create(Instruction::Xor, Op0, Op1,
664 InsertNewInstBefore(Xor, I);
665 return BinaryOperator::createNot(Xor, I.getName());
668 // Handle the setXe cases...
669 assert(I.getOpcode() == Instruction::SetGE ||
670 I.getOpcode() == Instruction::SetLE);
672 if (I.getOpcode() == Instruction::SetGE)
673 std::swap(Op0, Op1); // Change setge -> setle
675 // Now we just have the SetLE case.
676 Instruction *Not = BinaryOperator::createNot(Op0, I.getName()+"tmp");
677 InsertNewInstBefore(Not, I);
678 return BinaryOperator::create(Instruction::Or, Not, Op1, I.getName());
681 // Check to see if we are doing one of many comparisons against constant
682 // integers at the end of their ranges...
684 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
685 if (CI->isNullValue() && I.getOpcode() == Instruction::SetNE)
686 return new CastInst(Op0, Type::BoolTy, I.getName());
688 // Check to see if we are comparing against the minimum or maximum value...
689 if (CI->isMinValue()) {
690 if (I.getOpcode() == Instruction::SetLT) // A < MIN -> FALSE
691 return ReplaceInstUsesWith(I, ConstantBool::False);
692 if (I.getOpcode() == Instruction::SetGE) // A >= MIN -> TRUE
693 return ReplaceInstUsesWith(I, ConstantBool::True);
694 if (I.getOpcode() == Instruction::SetLE) // A <= MIN -> A == MIN
695 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
696 if (I.getOpcode() == Instruction::SetGT) // A > MIN -> A != MIN
697 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
699 } else if (CI->isMaxValue()) {
700 if (I.getOpcode() == Instruction::SetGT) // A > MAX -> FALSE
701 return ReplaceInstUsesWith(I, ConstantBool::False);
702 if (I.getOpcode() == Instruction::SetLE) // A <= MAX -> TRUE
703 return ReplaceInstUsesWith(I, ConstantBool::True);
704 if (I.getOpcode() == Instruction::SetGE) // A >= MAX -> A == MAX
705 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
706 if (I.getOpcode() == Instruction::SetLT) // A < MAX -> A != MAX
707 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
709 // Comparing against a value really close to min or max?
710 } else if (isMinValuePlusOne(CI)) {
711 if (I.getOpcode() == Instruction::SetLT) // A < MIN+1 -> A == MIN
712 return BinaryOperator::create(Instruction::SetEQ, Op0,
713 SubOne(CI), I.getName());
714 if (I.getOpcode() == Instruction::SetGE) // A >= MIN-1 -> A != MIN
715 return BinaryOperator::create(Instruction::SetNE, Op0,
716 SubOne(CI), I.getName());
718 } else if (isMaxValueMinusOne(CI)) {
719 if (I.getOpcode() == Instruction::SetGT) // A > MAX-1 -> A == MAX
720 return BinaryOperator::create(Instruction::SetEQ, Op0,
721 AddOne(CI), I.getName());
722 if (I.getOpcode() == Instruction::SetLE) // A <= MAX-1 -> A != MAX
723 return BinaryOperator::create(Instruction::SetNE, Op0,
724 AddOne(CI), I.getName());
728 return Changed ? &I : 0;
733 Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
734 assert(I.getOperand(1)->getType() == Type::UByteTy);
735 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
737 // shl X, 0 == X and shr X, 0 == X
738 // shl 0, X == 0 and shr 0, X == 0
739 if (Op1 == Constant::getNullValue(Type::UByteTy) ||
740 Op0 == Constant::getNullValue(Op0->getType()))
741 return ReplaceInstUsesWith(I, Op0);
743 // If this is a shift of a shift, see if we can fold the two together...
744 if (ShiftInst *Op0SI = dyn_cast<ShiftInst>(Op0)) {
745 if (isa<Constant>(Op1) && isa<Constant>(Op0SI->getOperand(1))) {
746 ConstantUInt *ShiftAmt1C = cast<ConstantUInt>(Op0SI->getOperand(1));
747 unsigned ShiftAmt1 = ShiftAmt1C->getValue();
748 unsigned ShiftAmt2 = cast<ConstantUInt>(Op1)->getValue();
750 // Check for (A << c1) << c2 and (A >> c1) >> c2
751 if (I.getOpcode() == Op0SI->getOpcode()) {
752 unsigned Amt = ShiftAmt1+ShiftAmt2; // Fold into one big shift...
753 return new ShiftInst(I.getOpcode(), Op0SI->getOperand(0),
754 ConstantUInt::get(Type::UByteTy, Amt));
757 if (I.getType()->isUnsigned()) { // Check for (A << c1) >> c2 or visaversa
758 // Calculate bitmask for what gets shifted off the edge...
759 Constant *C = ConstantIntegral::getAllOnesValue(I.getType());
760 if (I.getOpcode() == Instruction::Shr)
761 C = ConstantExpr::getShift(Instruction::Shr, C, ShiftAmt1C);
763 C = ConstantExpr::getShift(Instruction::Shl, C, ShiftAmt1C);
766 BinaryOperator::create(Instruction::And, Op0SI->getOperand(0),
767 C, Op0SI->getOperand(0)->getName()+".mask",&I);
768 WorkList.push_back(Mask);
770 // Figure out what flavor of shift we should use...
771 if (ShiftAmt1 == ShiftAmt2)
772 return ReplaceInstUsesWith(I, Mask); // (A << c) >> c === A & c2
773 else if (ShiftAmt1 < ShiftAmt2) {
774 return new ShiftInst(I.getOpcode(), Mask,
775 ConstantUInt::get(Type::UByteTy, ShiftAmt2-ShiftAmt1));
777 return new ShiftInst(Op0SI->getOpcode(), Mask,
778 ConstantUInt::get(Type::UByteTy, ShiftAmt1-ShiftAmt2));
784 // shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr of
787 if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
788 unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
789 if (CUI->getValue() >= TypeBits &&
790 (!Op0->getType()->isSigned() || I.getOpcode() == Instruction::Shl))
791 return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
793 // Check to see if we are shifting left by 1. If so, turn it into an add
795 if (I.getOpcode() == Instruction::Shl && CUI->equalsInt(1))
796 // Convert 'shl int %X, 1' to 'add int %X, %X'
797 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
801 // shr int -1, X = -1 (for any arithmetic shift rights of ~0)
802 if (ConstantSInt *CSI = dyn_cast<ConstantSInt>(Op0))
803 if (I.getOpcode() == Instruction::Shr && CSI->isAllOnesValue())
804 return ReplaceInstUsesWith(I, CSI);
810 // isEliminableCastOfCast - Return true if it is valid to eliminate the CI
813 static inline bool isEliminableCastOfCast(const CastInst &CI,
814 const CastInst *CSrc) {
815 assert(CI.getOperand(0) == CSrc);
816 const Type *SrcTy = CSrc->getOperand(0)->getType();
817 const Type *MidTy = CSrc->getType();
818 const Type *DstTy = CI.getType();
820 // It is legal to eliminate the instruction if casting A->B->A if the sizes
821 // are identical and the bits don't get reinterpreted (for example
822 // int->float->int would not be allowed)
823 if (SrcTy == DstTy && SrcTy->isLosslesslyConvertibleTo(MidTy))
826 // Allow free casting and conversion of sizes as long as the sign doesn't
828 if (SrcTy->isIntegral() && MidTy->isIntegral() && DstTy->isIntegral()) {
829 unsigned SrcSize = SrcTy->getPrimitiveSize();
830 unsigned MidSize = MidTy->getPrimitiveSize();
831 unsigned DstSize = DstTy->getPrimitiveSize();
833 // Cases where we are monotonically decreasing the size of the type are
834 // always ok, regardless of what sign changes are going on.
836 if (SrcSize >= MidSize && MidSize >= DstSize)
839 // Cases where the source and destination type are the same, but the middle
840 // type is bigger are noops.
842 if (SrcSize == DstSize && MidSize > SrcSize)
845 // If we are monotonically growing, things are more complex.
847 if (SrcSize <= MidSize && MidSize <= DstSize) {
848 // We have eight combinations of signedness to worry about. Here's the
850 static const int SignTable[8] = {
851 // CODE, SrcSigned, MidSigned, DstSigned, Comment
852 1, // U U U Always ok
853 1, // U U S Always ok
854 3, // U S U Ok iff SrcSize != MidSize
855 3, // U S S Ok iff SrcSize != MidSize
857 2, // S U S Ok iff MidSize == DstSize
858 1, // S S U Always ok
859 1, // S S S Always ok
862 // Choose an action based on the current entry of the signtable that this
863 // cast of cast refers to...
864 unsigned Row = SrcTy->isSigned()*4+MidTy->isSigned()*2+DstTy->isSigned();
865 switch (SignTable[Row]) {
866 case 0: return false; // Never ok
867 case 1: return true; // Always ok
868 case 2: return MidSize == DstSize; // Ok iff MidSize == DstSize
869 case 3: // Ok iff SrcSize != MidSize
870 return SrcSize != MidSize || SrcTy == Type::BoolTy;
871 default: assert(0 && "Bad entry in sign table!");
876 // Otherwise, we cannot succeed. Specifically we do not want to allow things
877 // like: short -> ushort -> uint, because this can create wrong results if
878 // the input short is negative!
884 // CastInst simplification
886 Instruction *InstCombiner::visitCastInst(CastInst &CI) {
887 // If the user is casting a value to the same type, eliminate this cast
889 if (CI.getType() == CI.getOperand(0)->getType())
890 return ReplaceInstUsesWith(CI, CI.getOperand(0));
892 // If casting the result of another cast instruction, try to eliminate this
895 if (CastInst *CSrc = dyn_cast<CastInst>(CI.getOperand(0))) {
896 if (isEliminableCastOfCast(CI, CSrc)) {
897 // This instruction now refers directly to the cast's src operand. This
898 // has a good chance of making CSrc dead.
899 CI.setOperand(0, CSrc->getOperand(0));
903 // If this is an A->B->A cast, and we are dealing with integral types, try
904 // to convert this into a logical 'and' instruction.
906 if (CSrc->getOperand(0)->getType() == CI.getType() &&
907 CI.getType()->isInteger() && CSrc->getType()->isInteger() &&
908 CI.getType()->isUnsigned() && CSrc->getType()->isUnsigned() &&
909 CSrc->getType()->getPrimitiveSize() < CI.getType()->getPrimitiveSize()){
910 assert(CSrc->getType() != Type::ULongTy &&
911 "Cannot have type bigger than ulong!");
912 uint64_t AndValue = (1ULL << CSrc->getType()->getPrimitiveSize()*8)-1;
913 Constant *AndOp = ConstantUInt::get(CI.getType(), AndValue);
914 return BinaryOperator::create(Instruction::And, CSrc->getOperand(0),
923 // PHINode simplification
925 Instruction *InstCombiner::visitPHINode(PHINode &PN) {
926 // If the PHI node only has one incoming value, eliminate the PHI node...
927 if (PN.getNumIncomingValues() == 1)
928 return ReplaceInstUsesWith(PN, PN.getIncomingValue(0));
930 // Otherwise if all of the incoming values are the same for the PHI, replace
931 // the PHI node with the incoming value.
934 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
935 if (PN.getIncomingValue(i) != &PN) // Not the PHI node itself...
936 if (InVal && PN.getIncomingValue(i) != InVal)
937 return 0; // Not the same, bail out.
939 InVal = PN.getIncomingValue(i);
941 // The only case that could cause InVal to be null is if we have a PHI node
942 // that only has entries for itself. In this case, there is no entry into the
943 // loop, so kill the PHI.
945 if (InVal == 0) InVal = Constant::getNullValue(PN.getType());
947 // All of the incoming values are the same, replace the PHI node now.
948 return ReplaceInstUsesWith(PN, InVal);
952 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
953 // Is it 'getelementptr %P, long 0' or 'getelementptr %P'
954 // If so, eliminate the noop.
955 if ((GEP.getNumOperands() == 2 &&
956 GEP.getOperand(1) == Constant::getNullValue(Type::LongTy)) ||
957 GEP.getNumOperands() == 1)
958 return ReplaceInstUsesWith(GEP, GEP.getOperand(0));
960 // Combine Indices - If the source pointer to this getelementptr instruction
961 // is a getelementptr instruction, combine the indices of the two
962 // getelementptr instructions into a single instruction.
964 if (GetElementPtrInst *Src = dyn_cast<GetElementPtrInst>(GEP.getOperand(0))) {
965 std::vector<Value *> Indices;
967 // Can we combine the two pointer arithmetics offsets?
968 if (Src->getNumOperands() == 2 && isa<Constant>(Src->getOperand(1)) &&
969 isa<Constant>(GEP.getOperand(1))) {
970 // Replace: gep (gep %P, long C1), long C2, ...
971 // With: gep %P, long (C1+C2), ...
972 Value *Sum = ConstantExpr::get(Instruction::Add,
973 cast<Constant>(Src->getOperand(1)),
974 cast<Constant>(GEP.getOperand(1)));
975 assert(Sum && "Constant folding of longs failed!?");
976 GEP.setOperand(0, Src->getOperand(0));
977 GEP.setOperand(1, Sum);
978 AddUsesToWorkList(*Src); // Reduce use count of Src
980 } else if (Src->getNumOperands() == 2) {
981 // Replace: gep (gep %P, long B), long A, ...
982 // With: T = long A+B; gep %P, T, ...
984 Value *Sum = BinaryOperator::create(Instruction::Add, Src->getOperand(1),
986 Src->getName()+".sum", &GEP);
987 GEP.setOperand(0, Src->getOperand(0));
988 GEP.setOperand(1, Sum);
989 WorkList.push_back(cast<Instruction>(Sum));
991 } else if (*GEP.idx_begin() == Constant::getNullValue(Type::LongTy) &&
992 Src->getNumOperands() != 1) {
993 // Otherwise we can do the fold if the first index of the GEP is a zero
994 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
995 Indices.insert(Indices.end(), GEP.idx_begin()+1, GEP.idx_end());
996 } else if (Src->getOperand(Src->getNumOperands()-1) ==
997 Constant::getNullValue(Type::LongTy)) {
998 // If the src gep ends with a constant array index, merge this get into
999 // it, even if we have a non-zero array index.
1000 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end()-1);
1001 Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end());
1004 if (!Indices.empty())
1005 return new GetElementPtrInst(Src->getOperand(0), Indices, GEP.getName());
1007 } else if (GlobalValue *GV = dyn_cast<GlobalValue>(GEP.getOperand(0))) {
1008 // GEP of global variable. If all of the indices for this GEP are
1009 // constants, we can promote this to a constexpr instead of an instruction.
1011 // Scan for nonconstants...
1012 std::vector<Constant*> Indices;
1013 User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end();
1014 for (; I != E && isa<Constant>(*I); ++I)
1015 Indices.push_back(cast<Constant>(*I));
1017 if (I == E) { // If they are all constants...
1019 ConstantExpr::getGetElementPtr(ConstantPointerRef::get(GV), Indices);
1021 // Replace all uses of the GEP with the new constexpr...
1022 return ReplaceInstUsesWith(GEP, CE);
1029 Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
1030 // Convert: malloc Ty, C - where C is a constant != 1 into: malloc [C x Ty], 1
1031 if (AI.isArrayAllocation()) // Check C != 1
1032 if (const ConstantUInt *C = dyn_cast<ConstantUInt>(AI.getArraySize())) {
1033 const Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getValue());
1034 AllocationInst *New = 0;
1036 // Create and insert the replacement instruction...
1037 if (isa<MallocInst>(AI))
1038 New = new MallocInst(NewTy, 0, AI.getName(), &AI);
1040 assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
1041 New = new AllocaInst(NewTy, 0, AI.getName(), &AI);
1044 // Scan to the end of the allocation instructions, to skip over a block of
1045 // allocas if possible...
1047 BasicBlock::iterator It = New;
1048 while (isa<AllocationInst>(*It)) ++It;
1050 // Now that I is pointing to the first non-allocation-inst in the block,
1051 // insert our getelementptr instruction...
1053 std::vector<Value*> Idx(2, Constant::getNullValue(Type::LongTy));
1054 Value *V = new GetElementPtrInst(New, Idx, New->getName()+".sub", It);
1056 // Now make everything use the getelementptr instead of the original
1058 ReplaceInstUsesWith(AI, V);
1066 void InstCombiner::removeFromWorkList(Instruction *I) {
1067 WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),
1071 bool InstCombiner::runOnFunction(Function &F) {
1072 bool Changed = false;
1074 WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F));
1076 while (!WorkList.empty()) {
1077 Instruction *I = WorkList.back(); // Get an instruction from the worklist
1078 WorkList.pop_back();
1080 // Check to see if we can DCE or ConstantPropagate the instruction...
1081 // Check to see if we can DIE the instruction...
1082 if (isInstructionTriviallyDead(I)) {
1083 // Add operands to the worklist...
1084 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1085 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
1086 WorkList.push_back(Op);
1089 BasicBlock::iterator BBI = I;
1090 if (dceInstruction(BBI)) {
1091 removeFromWorkList(I);
1096 // Instruction isn't dead, see if we can constant propagate it...
1097 if (Constant *C = ConstantFoldInstruction(I)) {
1098 // Add operands to the worklist...
1099 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1100 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
1101 WorkList.push_back(Op);
1102 ReplaceInstUsesWith(*I, C);
1105 BasicBlock::iterator BBI = I;
1106 if (dceInstruction(BBI)) {
1107 removeFromWorkList(I);
1112 // Now that we have an instruction, try combining it to simplify it...
1113 if (Instruction *Result = visit(*I)) {
1115 // Should we replace the old instruction with a new one?
1117 // Instructions can end up on the worklist more than once. Make sure
1118 // we do not process an instruction that has been deleted.
1119 removeFromWorkList(I);
1120 ReplaceInstWithInst(I, Result);
1122 BasicBlock::iterator II = I;
1124 // If the instruction was modified, it's possible that it is now dead.
1125 // if so, remove it.
1126 if (dceInstruction(II)) {
1127 // Instructions may end up in the worklist more than once. Erase them
1129 removeFromWorkList(I);
1135 WorkList.push_back(Result);
1136 AddUsesToWorkList(*Result);
1145 Pass *createInstructionCombiningPass() {
1146 return new InstCombiner();