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 Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
150 bool Changed = SimplifyBinOp(I);
151 Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
153 // Eliminate 'add int %X, 0'
154 if (RHS == Constant::getNullValue(I.getType()))
155 return ReplaceInstUsesWith(I, LHS);
158 if (Value *V = dyn_castNegInst(LHS))
159 return BinaryOperator::create(Instruction::Sub, RHS, V);
162 if (Value *V = dyn_castNegInst(RHS))
163 return BinaryOperator::create(Instruction::Sub, LHS, V);
165 // Simplify add instructions with a constant RHS...
166 if (Constant *Op2 = dyn_cast<Constant>(RHS)) {
167 if (BinaryOperator *ILHS = dyn_cast<BinaryOperator>(LHS)) {
168 if (ILHS->getOpcode() == Instruction::Add &&
169 isa<Constant>(ILHS->getOperand(1))) {
171 // %Y = add int %X, 1
172 // %Z = add int %Y, 1
174 // %Z = add int %X, 2
176 if (Constant *Val = *Op2 + *cast<Constant>(ILHS->getOperand(1))) {
177 I.setOperand(0, ILHS->getOperand(0));
178 I.setOperand(1, Val);
185 return Changed ? &I : 0;
188 Instruction *InstCombiner::visitSub(BinaryOperator &I) {
189 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
191 if (Op0 == Op1) // sub X, X -> 0
192 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
194 // If this is a subtract instruction with a constant RHS, convert it to an add
195 // instruction of a negative constant
197 if (Constant *Op2 = dyn_cast<Constant>(Op1))
198 if (Constant *RHS = *Constant::getNullValue(I.getType()) - *Op2) // 0 - RHS
199 return BinaryOperator::create(Instruction::Add, Op0, RHS, I.getName());
201 // If this is a 'B = x-(-A)', change to B = x+A...
202 if (Value *V = dyn_castNegInst(Op1))
203 return BinaryOperator::create(Instruction::Add, Op0, V);
205 // Replace (-1 - A) with (~A)...
206 if (ConstantInt *C = dyn_cast<ConstantInt>(Op0))
207 if (C->isAllOnesValue())
208 return BinaryOperator::createNot(Op1);
210 if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1))
211 if (Op1I->use_size() == 1) {
212 // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression
213 // is not used by anyone else...
215 if (Op1I->getOpcode() == Instruction::Sub) {
216 // Swap the two operands of the subexpr...
217 Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
218 Op1I->setOperand(0, IIOp1);
219 Op1I->setOperand(1, IIOp0);
221 // Create the new top level add instruction...
222 return BinaryOperator::create(Instruction::Add, Op0, Op1);
225 // Replace (A - (A & B)) with (A & ~B) if this is the only use of (A&B)...
227 if (Op1I->getOpcode() == Instruction::And &&
228 (Op1I->getOperand(0) == Op0 || Op1I->getOperand(1) == Op0)) {
229 Value *OtherOp = Op1I->getOperand(Op1I->getOperand(0) == Op0);
231 Instruction *NewNot = BinaryOperator::createNot(OtherOp, "B.not", &I);
232 return BinaryOperator::create(Instruction::And, Op0, NewNot);
239 Instruction *InstCombiner::visitMul(BinaryOperator &I) {
240 bool Changed = SimplifyBinOp(I);
241 Value *Op0 = I.getOperand(0);
243 // Simplify mul instructions with a constant RHS...
244 if (Constant *Op1 = dyn_cast<Constant>(I.getOperand(1))) {
245 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
246 const Type *Ty = CI->getType();
247 uint64_t Val = Ty->isSigned() ?
248 (uint64_t)cast<ConstantSInt>(CI)->getValue() :
249 cast<ConstantUInt>(CI)->getValue();
252 return ReplaceInstUsesWith(I, Op1); // Eliminate 'mul double %X, 0'
254 return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul int %X, 1'
255 case 2: // Convert 'mul int %X, 2' to 'add int %X, %X'
256 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
259 if (uint64_t C = Log2(Val)) // Replace X*(2^C) with X << C
260 return new ShiftInst(Instruction::Shl, Op0,
261 ConstantUInt::get(Type::UByteTy, C));
263 ConstantFP *Op1F = cast<ConstantFP>(Op1);
264 if (Op1F->isNullValue())
265 return ReplaceInstUsesWith(I, Op1);
267 // "In IEEE floating point, x*1 is not equivalent to x for nans. However,
268 // ANSI says we can drop signals, so we can do this anyway." (from GCC)
269 if (Op1F->getValue() == 1.0)
270 return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul double %X, 1.0'
274 return Changed ? &I : 0;
277 Instruction *InstCombiner::visitDiv(BinaryOperator &I) {
279 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) {
280 if (RHS->equalsInt(1))
281 return ReplaceInstUsesWith(I, I.getOperand(0));
283 // Check to see if this is an unsigned division with an exact power of 2,
284 // if so, convert to a right shift.
285 if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
286 if (uint64_t Val = C->getValue()) // Don't break X / 0
287 if (uint64_t C = Log2(Val))
288 return new ShiftInst(Instruction::Shr, I.getOperand(0),
289 ConstantUInt::get(Type::UByteTy, C));
292 // 0 / X == 0, we don't need to preserve faults!
293 if (ConstantInt *LHS = dyn_cast<ConstantInt>(I.getOperand(0)))
294 if (LHS->equalsInt(0))
295 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
301 Instruction *InstCombiner::visitRem(BinaryOperator &I) {
302 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) {
303 if (RHS->equalsInt(1)) // X % 1 == 0
304 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
306 // Check to see if this is an unsigned remainder with an exact power of 2,
307 // if so, convert to a bitwise and.
308 if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
309 if (uint64_t Val = C->getValue()) // Don't break X % 0 (divide by zero)
311 return BinaryOperator::create(Instruction::And, I.getOperand(0),
312 ConstantUInt::get(I.getType(), Val-1));
315 // 0 % X == 0, we don't need to preserve faults!
316 if (ConstantInt *LHS = dyn_cast<ConstantInt>(I.getOperand(0)))
317 if (LHS->equalsInt(0))
318 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
323 // isMaxValueMinusOne - return true if this is Max-1
324 static bool isMaxValueMinusOne(const ConstantInt *C) {
325 if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C)) {
326 // Calculate -1 casted to the right type...
327 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
328 uint64_t Val = ~0ULL; // All ones
329 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
330 return CU->getValue() == Val-1;
333 const ConstantSInt *CS = cast<ConstantSInt>(C);
335 // Calculate 0111111111..11111
336 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
337 int64_t Val = INT64_MAX; // All ones
338 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
339 return CS->getValue() == Val-1;
342 // isMinValuePlusOne - return true if this is Min+1
343 static bool isMinValuePlusOne(const ConstantInt *C) {
344 if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C))
345 return CU->getValue() == 1;
347 const ConstantSInt *CS = cast<ConstantSInt>(C);
349 // Calculate 1111111111000000000000
350 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
351 int64_t Val = -1; // All ones
352 Val <<= TypeBits-1; // Shift over to the right spot
353 return CS->getValue() == Val+1;
357 Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
358 bool Changed = SimplifyBinOp(I);
359 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
361 // and X, X = X and X, 0 == 0
362 if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
363 return ReplaceInstUsesWith(I, Op1);
366 if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
367 if (RHS->isAllOnesValue())
368 return ReplaceInstUsesWith(I, Op0);
370 Value *Op0NotVal = dyn_castNotInst(Op0);
371 Value *Op1NotVal = dyn_castNotInst(Op1);
373 // (~A & ~B) == (~(A | B)) - Demorgan's Law
374 if (Op0->use_size() == 1 && Op1->use_size() == 1 && Op0NotVal && Op1NotVal) {
375 Instruction *Or = BinaryOperator::create(Instruction::Or, Op0NotVal,
376 Op1NotVal,I.getName()+".demorgan",
378 return BinaryOperator::createNot(Or);
381 if (Op0NotVal == Op1 || Op1NotVal == Op0) // A & ~A == ~A & A == 0
382 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
384 return Changed ? &I : 0;
389 Instruction *InstCombiner::visitOr(BinaryOperator &I) {
390 bool Changed = SimplifyBinOp(I);
391 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
393 // or X, X = X or X, 0 == X
394 if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
395 return ReplaceInstUsesWith(I, Op0);
398 if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
399 if (RHS->isAllOnesValue())
400 return ReplaceInstUsesWith(I, Op1);
402 if (Value *X = dyn_castNotInst(Op0)) // ~A | A == -1
404 return ReplaceInstUsesWith(I,
405 ConstantIntegral::getAllOnesValue(I.getType()));
407 if (Value *X = dyn_castNotInst(Op1)) // A | ~A == -1
409 return ReplaceInstUsesWith(I,
410 ConstantIntegral::getAllOnesValue(I.getType()));
412 return Changed ? &I : 0;
417 Instruction *InstCombiner::visitXor(BinaryOperator &I) {
418 bool Changed = SimplifyBinOp(I);
419 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
423 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
425 if (ConstantIntegral *Op1C = dyn_cast<ConstantIntegral>(Op1)) {
427 if (Op1C->isNullValue())
428 return ReplaceInstUsesWith(I, Op0);
430 // Is this a "NOT" instruction?
431 if (Op1C->isAllOnesValue()) {
432 // xor (xor X, -1), -1 = not (not X) = X
433 if (Value *X = dyn_castNotInst(Op0))
434 return ReplaceInstUsesWith(I, X);
436 // xor (setcc A, B), true = not (setcc A, B) = setncc A, B
437 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Op0))
438 if (SCI->use_size() == 1)
439 return new SetCondInst(SCI->getInverseCondition(),
440 SCI->getOperand(0), SCI->getOperand(1));
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;
457 // AddOne, SubOne - Add or subtract a constant one from an integer constant...
458 static Constant *AddOne(ConstantInt *C) {
459 Constant *Result = *C + *ConstantInt::get(C->getType(), 1);
460 assert(Result && "Constant folding integer addition failed!");
463 static Constant *SubOne(ConstantInt *C) {
464 Constant *Result = *C - *ConstantInt::get(C->getType(), 1);
465 assert(Result && "Constant folding integer addition failed!");
469 // isTrueWhenEqual - Return true if the specified setcondinst instruction is
470 // true when both operands are equal...
472 static bool isTrueWhenEqual(Instruction &I) {
473 return I.getOpcode() == Instruction::SetEQ ||
474 I.getOpcode() == Instruction::SetGE ||
475 I.getOpcode() == Instruction::SetLE;
478 Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
479 bool Changed = SimplifyBinOp(I);
480 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
481 const Type *Ty = Op0->getType();
485 return ReplaceInstUsesWith(I, ConstantBool::get(isTrueWhenEqual(I)));
487 // setcc <global*>, 0 - Global value addresses are never null!
488 if (isa<GlobalValue>(Op0) && isa<ConstantPointerNull>(Op1))
489 return ReplaceInstUsesWith(I, ConstantBool::get(!isTrueWhenEqual(I)));
491 // setcc's with boolean values can always be turned into bitwise operations
492 if (Ty == Type::BoolTy) {
493 // If this is <, >, or !=, we can change this into a simple xor instruction
494 if (!isTrueWhenEqual(I))
495 return BinaryOperator::create(Instruction::Xor, Op0, Op1, I.getName());
497 // Otherwise we need to make a temporary intermediate instruction and insert
498 // it into the instruction stream. This is what we are after:
500 // seteq bool %A, %B -> ~(A^B)
501 // setle bool %A, %B -> ~A | B
502 // setge bool %A, %B -> A | ~B
504 if (I.getOpcode() == Instruction::SetEQ) { // seteq case
505 Instruction *Xor = BinaryOperator::create(Instruction::Xor, Op0, Op1,
507 InsertNewInstBefore(Xor, I);
508 return BinaryOperator::createNot(Xor, I.getName());
511 // Handle the setXe cases...
512 assert(I.getOpcode() == Instruction::SetGE ||
513 I.getOpcode() == Instruction::SetLE);
515 if (I.getOpcode() == Instruction::SetGE)
516 std::swap(Op0, Op1); // Change setge -> setle
518 // Now we just have the SetLE case.
519 Instruction *Not = BinaryOperator::createNot(Op0, I.getName()+"tmp");
520 InsertNewInstBefore(Not, I);
521 return BinaryOperator::create(Instruction::Or, Not, Op1, I.getName());
524 // Check to see if we are doing one of many comparisons against constant
525 // integers at the end of their ranges...
527 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
528 // Check to see if we are comparing against the minimum or maximum value...
529 if (CI->isMinValue()) {
530 if (I.getOpcode() == Instruction::SetLT) // A < MIN -> FALSE
531 return ReplaceInstUsesWith(I, ConstantBool::False);
532 if (I.getOpcode() == Instruction::SetGE) // A >= MIN -> TRUE
533 return ReplaceInstUsesWith(I, ConstantBool::True);
534 if (I.getOpcode() == Instruction::SetLE) // A <= MIN -> A == MIN
535 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
536 if (I.getOpcode() == Instruction::SetGT) // A > MIN -> A != MIN
537 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
539 } else if (CI->isMaxValue()) {
540 if (I.getOpcode() == Instruction::SetGT) // A > MAX -> FALSE
541 return ReplaceInstUsesWith(I, ConstantBool::False);
542 if (I.getOpcode() == Instruction::SetLE) // A <= MAX -> TRUE
543 return ReplaceInstUsesWith(I, ConstantBool::True);
544 if (I.getOpcode() == Instruction::SetGE) // A >= MAX -> A == MAX
545 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
546 if (I.getOpcode() == Instruction::SetLT) // A < MAX -> A != MAX
547 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
549 // Comparing against a value really close to min or max?
550 } else if (isMinValuePlusOne(CI)) {
551 if (I.getOpcode() == Instruction::SetLT) // A < MIN+1 -> A == MIN
552 return BinaryOperator::create(Instruction::SetEQ, Op0,
553 SubOne(CI), I.getName());
554 if (I.getOpcode() == Instruction::SetGE) // A >= MIN-1 -> A != MIN
555 return BinaryOperator::create(Instruction::SetNE, Op0,
556 SubOne(CI), I.getName());
558 } else if (isMaxValueMinusOne(CI)) {
559 if (I.getOpcode() == Instruction::SetGT) // A > MAX-1 -> A == MAX
560 return BinaryOperator::create(Instruction::SetEQ, Op0,
561 AddOne(CI), I.getName());
562 if (I.getOpcode() == Instruction::SetLE) // A <= MAX-1 -> A != MAX
563 return BinaryOperator::create(Instruction::SetNE, Op0,
564 AddOne(CI), I.getName());
568 return Changed ? &I : 0;
573 Instruction *InstCombiner::visitShiftInst(Instruction &I) {
574 assert(I.getOperand(1)->getType() == Type::UByteTy);
575 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
577 // shl X, 0 == X and shr X, 0 == X
578 // shl 0, X == 0 and shr 0, X == 0
579 if (Op1 == Constant::getNullValue(Type::UByteTy) ||
580 Op0 == Constant::getNullValue(Op0->getType()))
581 return ReplaceInstUsesWith(I, Op0);
583 // shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr of
586 if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
587 if (I.getOpcode() == Instruction::Shr) {
588 unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
589 if (CUI->getValue() >= TypeBits && !(Op0->getType()->isSigned()))
590 return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
593 // Check to see if we are shifting left by 1. If so, turn it into an add
595 if (I.getOpcode() == Instruction::Shl && CUI->equalsInt(1))
596 // Convert 'shl int %X, 1' to 'add int %X, %X'
597 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
601 // shr int -1, X = -1 (for any arithmetic shift rights of ~0)
602 if (ConstantSInt *CSI = dyn_cast<ConstantSInt>(Op0))
603 if (I.getOpcode() == Instruction::Shr && CSI->isAllOnesValue())
604 return ReplaceInstUsesWith(I, CSI);
610 // isEliminableCastOfCast - Return true if it is valid to eliminate the CI
613 static inline bool isEliminableCastOfCast(const CastInst &CI,
614 const CastInst *CSrc) {
615 assert(CI.getOperand(0) == CSrc);
616 const Type *SrcTy = CSrc->getOperand(0)->getType();
617 const Type *MidTy = CSrc->getType();
618 const Type *DstTy = CI.getType();
620 // It is legal to eliminate the instruction if casting A->B->A if the sizes
621 // are identical and the bits don't get reinterpreted (for example
622 // int->float->int would not be allowed)
623 if (SrcTy == DstTy && SrcTy->isLosslesslyConvertableTo(MidTy))
626 // Allow free casting and conversion of sizes as long as the sign doesn't
628 if (SrcTy->isIntegral() && MidTy->isIntegral() && DstTy->isIntegral()) {
629 unsigned SrcSize = SrcTy->getPrimitiveSize();
630 unsigned MidSize = MidTy->getPrimitiveSize();
631 unsigned DstSize = DstTy->getPrimitiveSize();
633 // Cases where we are monotonically decreasing the size of the type are
634 // always ok, regardless of what sign changes are going on.
636 if (SrcSize >= MidSize && MidSize >= DstSize)
639 // Cases where the source and destination type are the same, but the middle
640 // type is bigger are noops.
642 if (SrcSize == DstSize && MidSize > SrcSize)
645 // If we are monotonically growing, things are more complex.
647 if (SrcSize <= MidSize && MidSize <= DstSize) {
648 // We have eight combinations of signedness to worry about. Here's the
650 static const int SignTable[8] = {
651 // CODE, SrcSigned, MidSigned, DstSigned, Comment
652 1, // U U U Always ok
653 1, // U U S Always ok
654 3, // U S U Ok iff SrcSize != MidSize
655 3, // U S S Ok iff SrcSize != MidSize
657 2, // S U S Ok iff MidSize == DstSize
658 1, // S S U Always ok
659 1, // S S S Always ok
662 // Choose an action based on the current entry of the signtable that this
663 // cast of cast refers to...
664 unsigned Row = SrcTy->isSigned()*4+MidTy->isSigned()*2+DstTy->isSigned();
665 switch (SignTable[Row]) {
666 case 0: return false; // Never ok
667 case 1: return true; // Always ok
668 case 2: return MidSize == DstSize; // Ok iff MidSize == DstSize
669 case 3: // Ok iff SrcSize != MidSize
670 return SrcSize != MidSize || SrcTy == Type::BoolTy;
671 default: assert(0 && "Bad entry in sign table!");
676 // Otherwise, we cannot succeed. Specifically we do not want to allow things
677 // like: short -> ushort -> uint, because this can create wrong results if
678 // the input short is negative!
684 // CastInst simplification
686 Instruction *InstCombiner::visitCastInst(CastInst &CI) {
687 // If the user is casting a value to the same type, eliminate this cast
689 if (CI.getType() == CI.getOperand(0)->getType())
690 return ReplaceInstUsesWith(CI, CI.getOperand(0));
692 // If casting the result of another cast instruction, try to eliminate this
695 if (CastInst *CSrc = dyn_cast<CastInst>(CI.getOperand(0))) {
696 if (isEliminableCastOfCast(CI, CSrc)) {
697 // This instruction now refers directly to the cast's src operand. This
698 // has a good chance of making CSrc dead.
699 CI.setOperand(0, CSrc->getOperand(0));
703 // If this is an A->B->A cast, and we are dealing with integral types, try
704 // to convert this into a logical 'and' instruction.
706 if (CSrc->getOperand(0)->getType() == CI.getType() &&
707 CI.getType()->isInteger() && CSrc->getType()->isInteger() &&
708 CI.getType()->isUnsigned() && CSrc->getType()->isUnsigned() &&
709 CSrc->getType()->getPrimitiveSize() < CI.getType()->getPrimitiveSize()){
710 assert(CSrc->getType() != Type::ULongTy &&
711 "Cannot have type bigger than ulong!");
712 unsigned AndValue = (1U << CSrc->getType()->getPrimitiveSize()*8)-1;
713 Constant *AndOp = ConstantUInt::get(CI.getType(), AndValue);
714 return BinaryOperator::create(Instruction::And, CSrc->getOperand(0),
723 // PHINode simplification
725 Instruction *InstCombiner::visitPHINode(PHINode &PN) {
726 // If the PHI node only has one incoming value, eliminate the PHI node...
727 if (PN.getNumIncomingValues() == 1)
728 return ReplaceInstUsesWith(PN, PN.getIncomingValue(0));
730 // Otherwise if all of the incoming values are the same for the PHI, replace
731 // the PHI node with the incoming value.
734 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
735 if (PN.getIncomingValue(i) != &PN) // Not the PHI node itself...
736 if (InVal && PN.getIncomingValue(i) != InVal)
737 return 0; // Not the same, bail out.
739 InVal = PN.getIncomingValue(i);
741 // The only case that could cause InVal to be null is if we have a PHI node
742 // that only has entries for itself. In this case, there is no entry into the
743 // loop, so kill the PHI.
745 if (InVal == 0) InVal = Constant::getNullValue(PN.getType());
747 // All of the incoming values are the same, replace the PHI node now.
748 return ReplaceInstUsesWith(PN, InVal);
752 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
753 // Is it 'getelementptr %P, uint 0' or 'getelementptr %P'
754 // If so, eliminate the noop.
755 if ((GEP.getNumOperands() == 2 &&
756 GEP.getOperand(1) == Constant::getNullValue(Type::LongTy)) ||
757 GEP.getNumOperands() == 1)
758 return ReplaceInstUsesWith(GEP, GEP.getOperand(0));
760 // Combine Indices - If the source pointer to this getelementptr instruction
761 // is a getelementptr instruction, combine the indices of the two
762 // getelementptr instructions into a single instruction.
764 if (GetElementPtrInst *Src = dyn_cast<GetElementPtrInst>(GEP.getOperand(0))) {
765 std::vector<Value *> Indices;
767 // Can we combine the two pointer arithmetics offsets?
768 if (Src->getNumOperands() == 2 && isa<Constant>(Src->getOperand(1)) &&
769 isa<Constant>(GEP.getOperand(1))) {
770 // Replace the index list on this GEP with the index on the getelementptr
771 Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end());
772 Indices[0] = *cast<Constant>(Src->getOperand(1)) +
773 *cast<Constant>(GEP.getOperand(1));
774 assert(Indices[0] != 0 && "Constant folding of uint's failed!?");
776 } else if (*GEP.idx_begin() == Constant::getNullValue(Type::LongTy) &&
777 Src->getNumOperands() != 1) {
778 // Otherwise we can do the fold if the first index of the GEP is a zero
779 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
780 Indices.insert(Indices.end(), GEP.idx_begin()+1, GEP.idx_end());
781 } else if (Src->getOperand(Src->getNumOperands()-1) ==
782 Constant::getNullValue(Type::LongTy)) {
783 // If the src gep ends with a constant array index, merge this get into
784 // it, even if we have a non-zero array index.
785 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end()-1);
786 Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end());
789 if (!Indices.empty())
790 return new GetElementPtrInst(Src->getOperand(0), Indices, GEP.getName());
792 } else if (GlobalValue *GV = dyn_cast<GlobalValue>(GEP.getOperand(0))) {
793 // GEP of global variable. If all of the indices for this GEP are
794 // constants, we can promote this to a constexpr instead of an instruction.
796 // Scan for nonconstants...
797 std::vector<Constant*> Indices;
798 User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end();
799 for (; I != E && isa<Constant>(*I); ++I)
800 Indices.push_back(cast<Constant>(*I));
802 if (I == E) { // If they are all constants...
804 ConstantExpr::getGetElementPtr(ConstantPointerRef::get(GV), Indices);
806 // Replace all uses of the GEP with the new constexpr...
807 return ReplaceInstUsesWith(GEP, CE);
814 Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
815 // Convert: malloc Ty, C - where C is a constant != 1 into: malloc [C x Ty], 1
816 if (AI.isArrayAllocation()) // Check C != 1
817 if (const ConstantUInt *C = dyn_cast<ConstantUInt>(AI.getArraySize())) {
818 const Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getValue());
819 AllocationInst *New = 0;
821 // Create and insert the replacement instruction...
822 if (isa<MallocInst>(AI))
823 New = new MallocInst(NewTy, 0, AI.getName(), &AI);
825 assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
826 New = new AllocaInst(NewTy, 0, AI.getName(), &AI);
829 // Scan to the end of the allocation instructions, to skip over a block of
830 // allocas if possible...
832 BasicBlock::iterator It = New;
833 while (isa<AllocationInst>(*It)) ++It;
835 // Now that I is pointing to the first non-allocation-inst in the block,
836 // insert our getelementptr instruction...
838 std::vector<Value*> Idx(2, Constant::getNullValue(Type::LongTy));
839 Value *V = new GetElementPtrInst(New, Idx, New->getName()+".sub", It);
841 // Now make everything use the getelementptr instead of the original
843 ReplaceInstUsesWith(AI, V);
851 void InstCombiner::removeFromWorkList(Instruction *I) {
852 WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),
856 bool InstCombiner::runOnFunction(Function &F) {
857 bool Changed = false;
859 WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F));
861 while (!WorkList.empty()) {
862 Instruction *I = WorkList.back(); // Get an instruction from the worklist
865 // Check to see if we can DCE or ConstantPropagate the instruction...
866 // Check to see if we can DIE the instruction...
867 if (isInstructionTriviallyDead(I)) {
868 // Add operands to the worklist...
869 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
870 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
871 WorkList.push_back(Op);
874 BasicBlock::iterator BBI = I;
875 if (dceInstruction(BBI)) {
876 removeFromWorkList(I);
881 // Instruction isn't dead, see if we can constant propagate it...
882 if (Constant *C = ConstantFoldInstruction(I)) {
883 // Add operands to the worklist...
884 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
885 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
886 WorkList.push_back(Op);
887 ReplaceInstUsesWith(*I, C);
890 BasicBlock::iterator BBI = I;
891 if (dceInstruction(BBI)) {
892 removeFromWorkList(I);
897 // Now that we have an instruction, try combining it to simplify it...
898 if (Instruction *Result = visit(*I)) {
900 // Should we replace the old instruction with a new one?
902 // Instructions can end up on the worklist more than once. Make sure
903 // we do not process an instruction that has been deleted.
904 removeFromWorkList(I);
905 ReplaceInstWithInst(I, Result);
907 BasicBlock::iterator II = I;
909 // If the instruction was modified, it's possible that it is now dead.
911 if (dceInstruction(II)) {
912 // Instructions may end up in the worklist more than once. Erase them
914 removeFromWorkList(I);
920 WorkList.push_back(Result);
921 AddUsesToWorkList(*Result);
930 Pass *createInstructionCombiningPass() {
931 return new InstCombiner();