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(Instruction &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);
109 RegisterOpt<InstCombiner> X("instcombine", "Combine redundant instructions");
113 // Make sure that this instruction has a constant on the right hand side if it
114 // has any constant arguments. If not, fix it an return true.
116 static bool SimplifyBinOp(BinaryOperator &I) {
117 if (isa<Constant>(I.getOperand(0)) && !isa<Constant>(I.getOperand(1)))
118 return !I.swapOperands();
122 // dyn_castNegInst - Given a 'sub' instruction, return the RHS of the
123 // instruction if the LHS is a constant zero (which is the 'negate' form).
125 static inline Value *dyn_castNegInst(Value *V) {
126 return BinaryOperator::isNeg(V) ?
127 BinaryOperator::getNegArgument(cast<BinaryOperator>(V)) : 0;
130 static inline Value *dyn_castNotInst(Value *V) {
131 return BinaryOperator::isNot(V) ?
132 BinaryOperator::getNotArgument(cast<BinaryOperator>(V)) : 0;
136 // Log2 - Calculate the log base 2 for the specified value if it is exactly a
138 static unsigned Log2(uint64_t Val) {
139 assert(Val > 1 && "Values 0 and 1 should be handled elsewhere!");
142 if (Val & 1) return 0; // Multiple bits set?
149 static inline Value *dyn_castFoldableMul(Value *V) {
150 if (V->use_size() == 1 && V->getType()->isInteger())
151 if (Instruction *I = dyn_cast<Instruction>(V))
152 if (I->getOpcode() == Instruction::Mul)
153 if (isa<Constant>(I->getOperand(1)))
154 return I->getOperand(0);
159 Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
160 bool Changed = SimplifyBinOp(I);
161 Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
163 // Eliminate 'add int %X, 0'
164 if (RHS == Constant::getNullValue(I.getType()))
165 return ReplaceInstUsesWith(I, LHS);
168 if (Value *V = dyn_castNegInst(LHS))
169 return BinaryOperator::create(Instruction::Sub, RHS, V);
172 if (Value *V = dyn_castNegInst(RHS))
173 return BinaryOperator::create(Instruction::Sub, LHS, V);
175 // Simplify add instructions with a constant RHS...
176 if (Constant *Op2 = dyn_cast<Constant>(RHS)) {
177 if (BinaryOperator *ILHS = dyn_cast<BinaryOperator>(LHS)) {
178 if (ILHS->getOpcode() == Instruction::Add &&
179 isa<Constant>(ILHS->getOperand(1))) {
181 // %Y = add int %X, 1
182 // %Z = add int %Y, 1
184 // %Z = add int %X, 2
186 if (Constant *Val = *Op2 + *cast<Constant>(ILHS->getOperand(1))) {
187 I.setOperand(0, ILHS->getOperand(0));
188 I.setOperand(1, Val);
195 // X*C + X --> X * (C+1)
196 if (dyn_castFoldableMul(LHS) == RHS) {
197 Constant *CP1 = *cast<Constant>(cast<Instruction>(LHS)->getOperand(1)) +
198 *ConstantInt::get(I.getType(), 1);
199 assert(CP1 && "Couldn't constant fold C + 1?");
200 return BinaryOperator::create(Instruction::Mul, RHS, CP1);
203 // X + X*C --> X * (C+1)
204 if (dyn_castFoldableMul(RHS) == LHS) {
205 Constant *CP1 = *cast<Constant>(cast<Instruction>(RHS)->getOperand(1)) +
206 *ConstantInt::get(I.getType(), 1);
207 assert(CP1 && "Couldn't constant fold C + 1?");
208 return BinaryOperator::create(Instruction::Mul, LHS, CP1);
211 return Changed ? &I : 0;
214 Instruction *InstCombiner::visitSub(BinaryOperator &I) {
215 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
217 if (Op0 == Op1) // sub X, X -> 0
218 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
220 // If this is a subtract instruction with a constant RHS, convert it to an add
221 // instruction of a negative constant
223 if (Constant *Op2 = dyn_cast<Constant>(Op1))
224 if (Constant *RHS = *Constant::getNullValue(I.getType()) - *Op2) // 0 - RHS
225 return BinaryOperator::create(Instruction::Add, Op0, RHS, I.getName());
227 // If this is a 'B = x-(-A)', change to B = x+A...
228 if (Value *V = dyn_castNegInst(Op1))
229 return BinaryOperator::create(Instruction::Add, Op0, V);
231 // Replace (-1 - A) with (~A)...
232 if (ConstantInt *C = dyn_cast<ConstantInt>(Op0))
233 if (C->isAllOnesValue())
234 return BinaryOperator::createNot(Op1);
236 if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1))
237 if (Op1I->use_size() == 1) {
238 // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression
239 // is not used by anyone else...
241 if (Op1I->getOpcode() == Instruction::Sub) {
242 // Swap the two operands of the subexpr...
243 Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
244 Op1I->setOperand(0, IIOp1);
245 Op1I->setOperand(1, IIOp0);
247 // Create the new top level add instruction...
248 return BinaryOperator::create(Instruction::Add, Op0, Op1);
251 // Replace (A - (A & B)) with (A & ~B) if this is the only use of (A&B)...
253 if (Op1I->getOpcode() == Instruction::And &&
254 (Op1I->getOperand(0) == Op0 || Op1I->getOperand(1) == Op0)) {
255 Value *OtherOp = Op1I->getOperand(Op1I->getOperand(0) == Op0);
257 Instruction *NewNot = BinaryOperator::createNot(OtherOp, "B.not", &I);
258 return BinaryOperator::create(Instruction::And, Op0, NewNot);
261 // X - X*C --> X * (1-C)
262 if (dyn_castFoldableMul(Op1I) == Op0) {
263 Constant *CP1 = *ConstantInt::get(I.getType(), 1) -
264 *cast<Constant>(cast<Instruction>(Op1)->getOperand(1));
265 assert(CP1 && "Couldn't constant fold 1-C?");
266 return BinaryOperator::create(Instruction::Mul, Op0, CP1);
270 // X*C - X --> X * (C-1)
271 if (dyn_castFoldableMul(Op0) == Op1) {
272 Constant *CP1 = *cast<Constant>(cast<Instruction>(Op0)->getOperand(1)) -
273 *ConstantInt::get(I.getType(), 1);
274 assert(CP1 && "Couldn't constant fold C - 1?");
275 return BinaryOperator::create(Instruction::Mul, Op1, CP1);
281 Instruction *InstCombiner::visitMul(BinaryOperator &I) {
282 bool Changed = SimplifyBinOp(I);
283 Value *Op0 = I.getOperand(0);
285 // Simplify mul instructions with a constant RHS...
286 if (Constant *Op1 = dyn_cast<Constant>(I.getOperand(1))) {
287 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
288 const Type *Ty = CI->getType();
289 uint64_t Val = Ty->isSigned() ?
290 (uint64_t)cast<ConstantSInt>(CI)->getValue() :
291 cast<ConstantUInt>(CI)->getValue();
294 return ReplaceInstUsesWith(I, Op1); // Eliminate 'mul double %X, 0'
296 return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul int %X, 1'
297 case 2: // Convert 'mul int %X, 2' to 'add int %X, %X'
298 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
301 if (uint64_t C = Log2(Val)) // Replace X*(2^C) with X << C
302 return new ShiftInst(Instruction::Shl, Op0,
303 ConstantUInt::get(Type::UByteTy, C));
305 ConstantFP *Op1F = cast<ConstantFP>(Op1);
306 if (Op1F->isNullValue())
307 return ReplaceInstUsesWith(I, Op1);
309 // "In IEEE floating point, x*1 is not equivalent to x for nans. However,
310 // ANSI says we can drop signals, so we can do this anyway." (from GCC)
311 if (Op1F->getValue() == 1.0)
312 return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul double %X, 1.0'
316 return Changed ? &I : 0;
319 Instruction *InstCombiner::visitDiv(BinaryOperator &I) {
321 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) {
322 if (RHS->equalsInt(1))
323 return ReplaceInstUsesWith(I, I.getOperand(0));
325 // Check to see if this is an unsigned division with an exact power of 2,
326 // if so, convert to a right shift.
327 if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
328 if (uint64_t Val = C->getValue()) // Don't break X / 0
329 if (uint64_t C = Log2(Val))
330 return new ShiftInst(Instruction::Shr, I.getOperand(0),
331 ConstantUInt::get(Type::UByteTy, C));
334 // 0 / X == 0, we don't need to preserve faults!
335 if (ConstantInt *LHS = dyn_cast<ConstantInt>(I.getOperand(0)))
336 if (LHS->equalsInt(0))
337 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
343 Instruction *InstCombiner::visitRem(BinaryOperator &I) {
344 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) {
345 if (RHS->equalsInt(1)) // X % 1 == 0
346 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
348 // Check to see if this is an unsigned remainder with an exact power of 2,
349 // if so, convert to a bitwise and.
350 if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
351 if (uint64_t Val = C->getValue()) // Don't break X % 0 (divide by zero)
353 return BinaryOperator::create(Instruction::And, I.getOperand(0),
354 ConstantUInt::get(I.getType(), Val-1));
357 // 0 % X == 0, we don't need to preserve faults!
358 if (ConstantInt *LHS = dyn_cast<ConstantInt>(I.getOperand(0)))
359 if (LHS->equalsInt(0))
360 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
365 // isMaxValueMinusOne - return true if this is Max-1
366 static bool isMaxValueMinusOne(const ConstantInt *C) {
367 if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C)) {
368 // Calculate -1 casted to the right type...
369 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
370 uint64_t Val = ~0ULL; // All ones
371 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
372 return CU->getValue() == Val-1;
375 const ConstantSInt *CS = cast<ConstantSInt>(C);
377 // Calculate 0111111111..11111
378 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
379 int64_t Val = INT64_MAX; // All ones
380 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
381 return CS->getValue() == Val-1;
384 // isMinValuePlusOne - return true if this is Min+1
385 static bool isMinValuePlusOne(const ConstantInt *C) {
386 if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C))
387 return CU->getValue() == 1;
389 const ConstantSInt *CS = cast<ConstantSInt>(C);
391 // Calculate 1111111111000000000000
392 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
393 int64_t Val = -1; // All ones
394 Val <<= TypeBits-1; // Shift over to the right spot
395 return CS->getValue() == Val+1;
399 Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
400 bool Changed = SimplifyBinOp(I);
401 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
403 // and X, X = X and X, 0 == 0
404 if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
405 return ReplaceInstUsesWith(I, Op1);
408 if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
409 if (RHS->isAllOnesValue())
410 return ReplaceInstUsesWith(I, Op0);
412 Value *Op0NotVal = dyn_castNotInst(Op0);
413 Value *Op1NotVal = dyn_castNotInst(Op1);
415 // (~A & ~B) == (~(A | B)) - Demorgan's Law
416 if (Op0->use_size() == 1 && Op1->use_size() == 1 && Op0NotVal && Op1NotVal) {
417 Instruction *Or = BinaryOperator::create(Instruction::Or, Op0NotVal,
418 Op1NotVal,I.getName()+".demorgan",
420 return BinaryOperator::createNot(Or);
423 if (Op0NotVal == Op1 || Op1NotVal == Op0) // A & ~A == ~A & A == 0
424 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
426 return Changed ? &I : 0;
431 Instruction *InstCombiner::visitOr(BinaryOperator &I) {
432 bool Changed = SimplifyBinOp(I);
433 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
435 // or X, X = X or X, 0 == X
436 if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
437 return ReplaceInstUsesWith(I, Op0);
440 if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
441 if (RHS->isAllOnesValue())
442 return ReplaceInstUsesWith(I, Op1);
444 if (Value *X = dyn_castNotInst(Op0)) // ~A | A == -1
446 return ReplaceInstUsesWith(I,
447 ConstantIntegral::getAllOnesValue(I.getType()));
449 if (Value *X = dyn_castNotInst(Op1)) // A | ~A == -1
451 return ReplaceInstUsesWith(I,
452 ConstantIntegral::getAllOnesValue(I.getType()));
454 return Changed ? &I : 0;
459 Instruction *InstCombiner::visitXor(BinaryOperator &I) {
460 bool Changed = SimplifyBinOp(I);
461 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
465 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
467 if (ConstantIntegral *Op1C = dyn_cast<ConstantIntegral>(Op1)) {
469 if (Op1C->isNullValue())
470 return ReplaceInstUsesWith(I, Op0);
472 // Is this a "NOT" instruction?
473 if (Op1C->isAllOnesValue()) {
474 // xor (xor X, -1), -1 = not (not X) = X
475 if (Value *X = dyn_castNotInst(Op0))
476 return ReplaceInstUsesWith(I, X);
478 // xor (setcc A, B), true = not (setcc A, B) = setncc A, B
479 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Op0))
480 if (SCI->use_size() == 1)
481 return new SetCondInst(SCI->getInverseCondition(),
482 SCI->getOperand(0), SCI->getOperand(1));
486 if (Value *X = dyn_castNotInst(Op0)) // ~A ^ A == -1
488 return ReplaceInstUsesWith(I,
489 ConstantIntegral::getAllOnesValue(I.getType()));
491 if (Value *X = dyn_castNotInst(Op1)) // A ^ ~A == -1
493 return ReplaceInstUsesWith(I,
494 ConstantIntegral::getAllOnesValue(I.getType()));
496 return Changed ? &I : 0;
499 // AddOne, SubOne - Add or subtract a constant one from an integer constant...
500 static Constant *AddOne(ConstantInt *C) {
501 Constant *Result = *C + *ConstantInt::get(C->getType(), 1);
502 assert(Result && "Constant folding integer addition failed!");
505 static Constant *SubOne(ConstantInt *C) {
506 Constant *Result = *C - *ConstantInt::get(C->getType(), 1);
507 assert(Result && "Constant folding integer addition failed!");
511 // isTrueWhenEqual - Return true if the specified setcondinst instruction is
512 // true when both operands are equal...
514 static bool isTrueWhenEqual(Instruction &I) {
515 return I.getOpcode() == Instruction::SetEQ ||
516 I.getOpcode() == Instruction::SetGE ||
517 I.getOpcode() == Instruction::SetLE;
520 Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
521 bool Changed = SimplifyBinOp(I);
522 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
523 const Type *Ty = Op0->getType();
527 return ReplaceInstUsesWith(I, ConstantBool::get(isTrueWhenEqual(I)));
529 // setcc <global*>, 0 - Global value addresses are never null!
530 if (isa<GlobalValue>(Op0) && isa<ConstantPointerNull>(Op1))
531 return ReplaceInstUsesWith(I, ConstantBool::get(!isTrueWhenEqual(I)));
533 // setcc's with boolean values can always be turned into bitwise operations
534 if (Ty == Type::BoolTy) {
535 // If this is <, >, or !=, we can change this into a simple xor instruction
536 if (!isTrueWhenEqual(I))
537 return BinaryOperator::create(Instruction::Xor, Op0, Op1, I.getName());
539 // Otherwise we need to make a temporary intermediate instruction and insert
540 // it into the instruction stream. This is what we are after:
542 // seteq bool %A, %B -> ~(A^B)
543 // setle bool %A, %B -> ~A | B
544 // setge bool %A, %B -> A | ~B
546 if (I.getOpcode() == Instruction::SetEQ) { // seteq case
547 Instruction *Xor = BinaryOperator::create(Instruction::Xor, Op0, Op1,
549 InsertNewInstBefore(Xor, I);
550 return BinaryOperator::createNot(Xor, I.getName());
553 // Handle the setXe cases...
554 assert(I.getOpcode() == Instruction::SetGE ||
555 I.getOpcode() == Instruction::SetLE);
557 if (I.getOpcode() == Instruction::SetGE)
558 std::swap(Op0, Op1); // Change setge -> setle
560 // Now we just have the SetLE case.
561 Instruction *Not = BinaryOperator::createNot(Op0, I.getName()+"tmp");
562 InsertNewInstBefore(Not, I);
563 return BinaryOperator::create(Instruction::Or, Not, Op1, I.getName());
566 // Check to see if we are doing one of many comparisons against constant
567 // integers at the end of their ranges...
569 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
570 // Check to see if we are comparing against the minimum or maximum value...
571 if (CI->isMinValue()) {
572 if (I.getOpcode() == Instruction::SetLT) // A < MIN -> FALSE
573 return ReplaceInstUsesWith(I, ConstantBool::False);
574 if (I.getOpcode() == Instruction::SetGE) // A >= MIN -> TRUE
575 return ReplaceInstUsesWith(I, ConstantBool::True);
576 if (I.getOpcode() == Instruction::SetLE) // A <= MIN -> A == MIN
577 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
578 if (I.getOpcode() == Instruction::SetGT) // A > MIN -> A != MIN
579 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
581 } else if (CI->isMaxValue()) {
582 if (I.getOpcode() == Instruction::SetGT) // A > MAX -> FALSE
583 return ReplaceInstUsesWith(I, ConstantBool::False);
584 if (I.getOpcode() == Instruction::SetLE) // A <= MAX -> TRUE
585 return ReplaceInstUsesWith(I, ConstantBool::True);
586 if (I.getOpcode() == Instruction::SetGE) // A >= MAX -> A == MAX
587 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
588 if (I.getOpcode() == Instruction::SetLT) // A < MAX -> A != MAX
589 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
591 // Comparing against a value really close to min or max?
592 } else if (isMinValuePlusOne(CI)) {
593 if (I.getOpcode() == Instruction::SetLT) // A < MIN+1 -> A == MIN
594 return BinaryOperator::create(Instruction::SetEQ, Op0,
595 SubOne(CI), I.getName());
596 if (I.getOpcode() == Instruction::SetGE) // A >= MIN-1 -> A != MIN
597 return BinaryOperator::create(Instruction::SetNE, Op0,
598 SubOne(CI), I.getName());
600 } else if (isMaxValueMinusOne(CI)) {
601 if (I.getOpcode() == Instruction::SetGT) // A > MAX-1 -> A == MAX
602 return BinaryOperator::create(Instruction::SetEQ, Op0,
603 AddOne(CI), I.getName());
604 if (I.getOpcode() == Instruction::SetLE) // A <= MAX-1 -> A != MAX
605 return BinaryOperator::create(Instruction::SetNE, Op0,
606 AddOne(CI), I.getName());
610 return Changed ? &I : 0;
615 Instruction *InstCombiner::visitShiftInst(Instruction &I) {
616 assert(I.getOperand(1)->getType() == Type::UByteTy);
617 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
619 // shl X, 0 == X and shr X, 0 == X
620 // shl 0, X == 0 and shr 0, X == 0
621 if (Op1 == Constant::getNullValue(Type::UByteTy) ||
622 Op0 == Constant::getNullValue(Op0->getType()))
623 return ReplaceInstUsesWith(I, Op0);
625 // shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr of
628 if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
629 if (I.getOpcode() == Instruction::Shr) {
630 unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
631 if (CUI->getValue() >= TypeBits && !(Op0->getType()->isSigned()))
632 return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
635 // Check to see if we are shifting left by 1. If so, turn it into an add
637 if (I.getOpcode() == Instruction::Shl && CUI->equalsInt(1))
638 // Convert 'shl int %X, 1' to 'add int %X, %X'
639 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
643 // shr int -1, X = -1 (for any arithmetic shift rights of ~0)
644 if (ConstantSInt *CSI = dyn_cast<ConstantSInt>(Op0))
645 if (I.getOpcode() == Instruction::Shr && CSI->isAllOnesValue())
646 return ReplaceInstUsesWith(I, CSI);
652 // isEliminableCastOfCast - Return true if it is valid to eliminate the CI
655 static inline bool isEliminableCastOfCast(const CastInst &CI,
656 const CastInst *CSrc) {
657 assert(CI.getOperand(0) == CSrc);
658 const Type *SrcTy = CSrc->getOperand(0)->getType();
659 const Type *MidTy = CSrc->getType();
660 const Type *DstTy = CI.getType();
662 // It is legal to eliminate the instruction if casting A->B->A if the sizes
663 // are identical and the bits don't get reinterpreted (for example
664 // int->float->int would not be allowed)
665 if (SrcTy == DstTy && SrcTy->isLosslesslyConvertableTo(MidTy))
668 // Allow free casting and conversion of sizes as long as the sign doesn't
670 if (SrcTy->isIntegral() && MidTy->isIntegral() && DstTy->isIntegral()) {
671 unsigned SrcSize = SrcTy->getPrimitiveSize();
672 unsigned MidSize = MidTy->getPrimitiveSize();
673 unsigned DstSize = DstTy->getPrimitiveSize();
675 // Cases where we are monotonically decreasing the size of the type are
676 // always ok, regardless of what sign changes are going on.
678 if (SrcSize >= MidSize && MidSize >= DstSize)
681 // Cases where the source and destination type are the same, but the middle
682 // type is bigger are noops.
684 if (SrcSize == DstSize && MidSize > SrcSize)
687 // If we are monotonically growing, things are more complex.
689 if (SrcSize <= MidSize && MidSize <= DstSize) {
690 // We have eight combinations of signedness to worry about. Here's the
692 static const int SignTable[8] = {
693 // CODE, SrcSigned, MidSigned, DstSigned, Comment
694 1, // U U U Always ok
695 1, // U U S Always ok
696 3, // U S U Ok iff SrcSize != MidSize
697 3, // U S S Ok iff SrcSize != MidSize
699 2, // S U S Ok iff MidSize == DstSize
700 1, // S S U Always ok
701 1, // S S S Always ok
704 // Choose an action based on the current entry of the signtable that this
705 // cast of cast refers to...
706 unsigned Row = SrcTy->isSigned()*4+MidTy->isSigned()*2+DstTy->isSigned();
707 switch (SignTable[Row]) {
708 case 0: return false; // Never ok
709 case 1: return true; // Always ok
710 case 2: return MidSize == DstSize; // Ok iff MidSize == DstSize
711 case 3: // Ok iff SrcSize != MidSize
712 return SrcSize != MidSize || SrcTy == Type::BoolTy;
713 default: assert(0 && "Bad entry in sign table!");
718 // Otherwise, we cannot succeed. Specifically we do not want to allow things
719 // like: short -> ushort -> uint, because this can create wrong results if
720 // the input short is negative!
726 // CastInst simplification
728 Instruction *InstCombiner::visitCastInst(CastInst &CI) {
729 // If the user is casting a value to the same type, eliminate this cast
731 if (CI.getType() == CI.getOperand(0)->getType())
732 return ReplaceInstUsesWith(CI, CI.getOperand(0));
734 // If casting the result of another cast instruction, try to eliminate this
737 if (CastInst *CSrc = dyn_cast<CastInst>(CI.getOperand(0))) {
738 if (isEliminableCastOfCast(CI, CSrc)) {
739 // This instruction now refers directly to the cast's src operand. This
740 // has a good chance of making CSrc dead.
741 CI.setOperand(0, CSrc->getOperand(0));
745 // If this is an A->B->A cast, and we are dealing with integral types, try
746 // to convert this into a logical 'and' instruction.
748 if (CSrc->getOperand(0)->getType() == CI.getType() &&
749 CI.getType()->isInteger() && CSrc->getType()->isInteger() &&
750 CI.getType()->isUnsigned() && CSrc->getType()->isUnsigned() &&
751 CSrc->getType()->getPrimitiveSize() < CI.getType()->getPrimitiveSize()){
752 assert(CSrc->getType() != Type::ULongTy &&
753 "Cannot have type bigger than ulong!");
754 unsigned AndValue = (1U << CSrc->getType()->getPrimitiveSize()*8)-1;
755 Constant *AndOp = ConstantUInt::get(CI.getType(), AndValue);
756 return BinaryOperator::create(Instruction::And, CSrc->getOperand(0),
765 // PHINode simplification
767 Instruction *InstCombiner::visitPHINode(PHINode &PN) {
768 // If the PHI node only has one incoming value, eliminate the PHI node...
769 if (PN.getNumIncomingValues() == 1)
770 return ReplaceInstUsesWith(PN, PN.getIncomingValue(0));
772 // Otherwise if all of the incoming values are the same for the PHI, replace
773 // the PHI node with the incoming value.
776 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
777 if (PN.getIncomingValue(i) != &PN) // Not the PHI node itself...
778 if (InVal && PN.getIncomingValue(i) != InVal)
779 return 0; // Not the same, bail out.
781 InVal = PN.getIncomingValue(i);
783 // The only case that could cause InVal to be null is if we have a PHI node
784 // that only has entries for itself. In this case, there is no entry into the
785 // loop, so kill the PHI.
787 if (InVal == 0) InVal = Constant::getNullValue(PN.getType());
789 // All of the incoming values are the same, replace the PHI node now.
790 return ReplaceInstUsesWith(PN, InVal);
794 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
795 // Is it 'getelementptr %P, uint 0' or 'getelementptr %P'
796 // If so, eliminate the noop.
797 if ((GEP.getNumOperands() == 2 &&
798 GEP.getOperand(1) == Constant::getNullValue(Type::LongTy)) ||
799 GEP.getNumOperands() == 1)
800 return ReplaceInstUsesWith(GEP, GEP.getOperand(0));
802 // Combine Indices - If the source pointer to this getelementptr instruction
803 // is a getelementptr instruction, combine the indices of the two
804 // getelementptr instructions into a single instruction.
806 if (GetElementPtrInst *Src = dyn_cast<GetElementPtrInst>(GEP.getOperand(0))) {
807 std::vector<Value *> Indices;
809 // Can we combine the two pointer arithmetics offsets?
810 if (Src->getNumOperands() == 2 && isa<Constant>(Src->getOperand(1)) &&
811 isa<Constant>(GEP.getOperand(1))) {
812 // Replace the index list on this GEP with the index on the getelementptr
813 Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end());
814 Indices[0] = *cast<Constant>(Src->getOperand(1)) +
815 *cast<Constant>(GEP.getOperand(1));
816 assert(Indices[0] != 0 && "Constant folding of uint's failed!?");
818 } else if (*GEP.idx_begin() == Constant::getNullValue(Type::LongTy) &&
819 Src->getNumOperands() != 1) {
820 // Otherwise we can do the fold if the first index of the GEP is a zero
821 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
822 Indices.insert(Indices.end(), GEP.idx_begin()+1, GEP.idx_end());
823 } else if (Src->getOperand(Src->getNumOperands()-1) ==
824 Constant::getNullValue(Type::LongTy)) {
825 // If the src gep ends with a constant array index, merge this get into
826 // it, even if we have a non-zero array index.
827 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end()-1);
828 Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end());
831 if (!Indices.empty())
832 return new GetElementPtrInst(Src->getOperand(0), Indices, GEP.getName());
834 } else if (GlobalValue *GV = dyn_cast<GlobalValue>(GEP.getOperand(0))) {
835 // GEP of global variable. If all of the indices for this GEP are
836 // constants, we can promote this to a constexpr instead of an instruction.
838 // Scan for nonconstants...
839 std::vector<Constant*> Indices;
840 User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end();
841 for (; I != E && isa<Constant>(*I); ++I)
842 Indices.push_back(cast<Constant>(*I));
844 if (I == E) { // If they are all constants...
846 ConstantExpr::getGetElementPtr(ConstantPointerRef::get(GV), Indices);
848 // Replace all uses of the GEP with the new constexpr...
849 return ReplaceInstUsesWith(GEP, CE);
856 Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
857 // Convert: malloc Ty, C - where C is a constant != 1 into: malloc [C x Ty], 1
858 if (AI.isArrayAllocation()) // Check C != 1
859 if (const ConstantUInt *C = dyn_cast<ConstantUInt>(AI.getArraySize())) {
860 const Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getValue());
861 AllocationInst *New = 0;
863 // Create and insert the replacement instruction...
864 if (isa<MallocInst>(AI))
865 New = new MallocInst(NewTy, 0, AI.getName(), &AI);
867 assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
868 New = new AllocaInst(NewTy, 0, AI.getName(), &AI);
871 // Scan to the end of the allocation instructions, to skip over a block of
872 // allocas if possible...
874 BasicBlock::iterator It = New;
875 while (isa<AllocationInst>(*It)) ++It;
877 // Now that I is pointing to the first non-allocation-inst in the block,
878 // insert our getelementptr instruction...
880 std::vector<Value*> Idx(2, Constant::getNullValue(Type::LongTy));
881 Value *V = new GetElementPtrInst(New, Idx, New->getName()+".sub", It);
883 // Now make everything use the getelementptr instead of the original
885 ReplaceInstUsesWith(AI, V);
893 void InstCombiner::removeFromWorkList(Instruction *I) {
894 WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),
898 bool InstCombiner::runOnFunction(Function &F) {
899 bool Changed = false;
901 WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F));
903 while (!WorkList.empty()) {
904 Instruction *I = WorkList.back(); // Get an instruction from the worklist
907 // Check to see if we can DCE or ConstantPropagate the instruction...
908 // Check to see if we can DIE the instruction...
909 if (isInstructionTriviallyDead(I)) {
910 // Add operands to the worklist...
911 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
912 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
913 WorkList.push_back(Op);
916 BasicBlock::iterator BBI = I;
917 if (dceInstruction(BBI)) {
918 removeFromWorkList(I);
923 // Instruction isn't dead, see if we can constant propagate it...
924 if (Constant *C = ConstantFoldInstruction(I)) {
925 // Add operands to the worklist...
926 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
927 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
928 WorkList.push_back(Op);
929 ReplaceInstUsesWith(*I, C);
932 BasicBlock::iterator BBI = I;
933 if (dceInstruction(BBI)) {
934 removeFromWorkList(I);
939 // Now that we have an instruction, try combining it to simplify it...
940 if (Instruction *Result = visit(*I)) {
942 // Should we replace the old instruction with a new one?
944 // Instructions can end up on the worklist more than once. Make sure
945 // we do not process an instruction that has been deleted.
946 removeFromWorkList(I);
947 ReplaceInstWithInst(I, Result);
949 BasicBlock::iterator II = I;
951 // If the instruction was modified, it's possible that it is now dead.
953 if (dceInstruction(II)) {
954 // Instructions may end up in the worklist more than once. Erase them
956 removeFromWorkList(I);
962 WorkList.push_back(Result);
963 AddUsesToWorkList(*Result);
972 Pass *createInstructionCombiningPass() {
973 return new InstCombiner();