1 //===- InstructionCombining.cpp - Combine multiple instructions -----------===//
3 // InstructionCombining - Combine instructions to form fewer, simple
4 // instructions. This pass does not modify the CFG This pass is where algebraic
5 // simplification happens.
7 // This pass combines things like:
13 // This is a simple worklist driven algorithm.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Transforms/Scalar.h"
18 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
19 #include "llvm/Transforms/Utils/Local.h"
20 #include "llvm/ConstantHandling.h"
21 #include "llvm/iMemory.h"
22 #include "llvm/iOther.h"
23 #include "llvm/iPHINode.h"
24 #include "llvm/iOperators.h"
25 #include "llvm/Pass.h"
26 #include "llvm/DerivedTypes.h"
27 #include "llvm/Support/InstIterator.h"
28 #include "llvm/Support/InstVisitor.h"
29 #include "Support/Statistic.h"
33 Statistic<> NumCombined ("instcombine", "Number of insts combined");
34 Statistic<> NumConstProp("instcombine", "Number of constant folds");
35 Statistic<> NumDeadInst ("instcombine", "Number of dead inst eliminated");
37 class InstCombiner : public FunctionPass,
38 public InstVisitor<InstCombiner, Instruction*> {
39 // Worklist of all of the instructions that need to be simplified.
40 std::vector<Instruction*> WorkList;
42 void AddUsesToWorkList(Instruction &I) {
43 // The instruction was simplified, add all users of the instruction to
44 // the work lists because they might get more simplified now...
46 for (Value::use_iterator UI = I.use_begin(), UE = I.use_end();
48 WorkList.push_back(cast<Instruction>(*UI));
51 // removeFromWorkList - remove all instances of I from the worklist.
52 void removeFromWorkList(Instruction *I);
54 virtual bool runOnFunction(Function &F);
56 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
60 // Visitation implementation - Implement instruction combining for different
61 // instruction types. The semantics are as follows:
63 // null - No change was made
64 // I - Change was made, I is still valid, I may be dead though
65 // otherwise - Change was made, replace I with returned instruction
67 Instruction *visitAdd(BinaryOperator &I);
68 Instruction *visitSub(BinaryOperator &I);
69 Instruction *visitMul(BinaryOperator &I);
70 Instruction *visitDiv(BinaryOperator &I);
71 Instruction *visitRem(BinaryOperator &I);
72 Instruction *visitAnd(BinaryOperator &I);
73 Instruction *visitOr (BinaryOperator &I);
74 Instruction *visitXor(BinaryOperator &I);
75 Instruction *visitSetCondInst(BinaryOperator &I);
76 Instruction *visitShiftInst(ShiftInst &I);
77 Instruction *visitCastInst(CastInst &CI);
78 Instruction *visitPHINode(PHINode &PN);
79 Instruction *visitGetElementPtrInst(GetElementPtrInst &GEP);
80 Instruction *visitAllocationInst(AllocationInst &AI);
82 // visitInstruction - Specify what to return for unhandled instructions...
83 Instruction *visitInstruction(Instruction &I) { return 0; }
85 // InsertNewInstBefore - insert an instruction New before instruction Old
86 // in the program. Add the new instruction to the worklist.
88 void InsertNewInstBefore(Instruction *New, Instruction &Old) {
89 assert(New && New->getParent() == 0 &&
90 "New instruction already inserted into a basic block!");
91 BasicBlock *BB = Old.getParent();
92 BB->getInstList().insert(&Old, New); // Insert inst
93 WorkList.push_back(New); // Add to worklist
96 // ReplaceInstUsesWith - This method is to be used when an instruction is
97 // found to be dead, replacable with another preexisting expression. Here
98 // we add all uses of I to the worklist, replace all uses of I with the new
99 // value, then return I, so that the inst combiner will know that I was
102 Instruction *ReplaceInstUsesWith(Instruction &I, Value *V) {
103 AddUsesToWorkList(I); // Add all modified instrs to worklist
104 I.replaceAllUsesWith(V);
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()));
498 if (Instruction *Op1I = dyn_cast<Instruction>(Op1))
499 if (Op1I->getOpcode() == Instruction::Or)
500 if (Op1I->getOperand(0) == Op0) { // B^(B|A) == (A|B)^B
501 cast<BinaryOperator>(Op1I)->swapOperands();
504 } else if (Op1I->getOperand(1) == Op0) { // B^(A|B) == (A|B)^B
509 if (Instruction *Op0I = dyn_cast<Instruction>(Op0))
510 if (Op0I->getOpcode() == Instruction::Or && Op0I->use_size() == 1) {
511 if (Op0I->getOperand(0) == Op1) // (B|A)^B == (A|B)^B
512 cast<BinaryOperator>(Op0I)->swapOperands();
513 if (Op0I->getOperand(1) == Op1) { // (A|B)^B == ~B & A
514 Value *NotB = BinaryOperator::createNot(Op1, Op1->getName()+".not", &I);
515 WorkList.push_back(cast<Instruction>(NotB));
516 return BinaryOperator::create(Instruction::And, NotB,
517 Op0I->getOperand(0));
521 return Changed ? &I : 0;
524 // AddOne, SubOne - Add or subtract a constant one from an integer constant...
525 static Constant *AddOne(ConstantInt *C) {
526 Constant *Result = *C + *ConstantInt::get(C->getType(), 1);
527 assert(Result && "Constant folding integer addition failed!");
530 static Constant *SubOne(ConstantInt *C) {
531 Constant *Result = *C - *ConstantInt::get(C->getType(), 1);
532 assert(Result && "Constant folding integer addition failed!");
536 // isTrueWhenEqual - Return true if the specified setcondinst instruction is
537 // true when both operands are equal...
539 static bool isTrueWhenEqual(Instruction &I) {
540 return I.getOpcode() == Instruction::SetEQ ||
541 I.getOpcode() == Instruction::SetGE ||
542 I.getOpcode() == Instruction::SetLE;
545 Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
546 bool Changed = SimplifyBinOp(I);
547 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
548 const Type *Ty = Op0->getType();
552 return ReplaceInstUsesWith(I, ConstantBool::get(isTrueWhenEqual(I)));
554 // setcc <global*>, 0 - Global value addresses are never null!
555 if (isa<GlobalValue>(Op0) && isa<ConstantPointerNull>(Op1))
556 return ReplaceInstUsesWith(I, ConstantBool::get(!isTrueWhenEqual(I)));
558 // setcc's with boolean values can always be turned into bitwise operations
559 if (Ty == Type::BoolTy) {
560 // If this is <, >, or !=, we can change this into a simple xor instruction
561 if (!isTrueWhenEqual(I))
562 return BinaryOperator::create(Instruction::Xor, Op0, Op1, I.getName());
564 // Otherwise we need to make a temporary intermediate instruction and insert
565 // it into the instruction stream. This is what we are after:
567 // seteq bool %A, %B -> ~(A^B)
568 // setle bool %A, %B -> ~A | B
569 // setge bool %A, %B -> A | ~B
571 if (I.getOpcode() == Instruction::SetEQ) { // seteq case
572 Instruction *Xor = BinaryOperator::create(Instruction::Xor, Op0, Op1,
574 InsertNewInstBefore(Xor, I);
575 return BinaryOperator::createNot(Xor, I.getName());
578 // Handle the setXe cases...
579 assert(I.getOpcode() == Instruction::SetGE ||
580 I.getOpcode() == Instruction::SetLE);
582 if (I.getOpcode() == Instruction::SetGE)
583 std::swap(Op0, Op1); // Change setge -> setle
585 // Now we just have the SetLE case.
586 Instruction *Not = BinaryOperator::createNot(Op0, I.getName()+"tmp");
587 InsertNewInstBefore(Not, I);
588 return BinaryOperator::create(Instruction::Or, Not, Op1, I.getName());
591 // Check to see if we are doing one of many comparisons against constant
592 // integers at the end of their ranges...
594 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
595 // Check to see if we are comparing against the minimum or maximum value...
596 if (CI->isMinValue()) {
597 if (I.getOpcode() == Instruction::SetLT) // A < MIN -> FALSE
598 return ReplaceInstUsesWith(I, ConstantBool::False);
599 if (I.getOpcode() == Instruction::SetGE) // A >= MIN -> TRUE
600 return ReplaceInstUsesWith(I, ConstantBool::True);
601 if (I.getOpcode() == Instruction::SetLE) // A <= MIN -> A == MIN
602 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
603 if (I.getOpcode() == Instruction::SetGT) // A > MIN -> A != MIN
604 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
606 } else if (CI->isMaxValue()) {
607 if (I.getOpcode() == Instruction::SetGT) // A > MAX -> FALSE
608 return ReplaceInstUsesWith(I, ConstantBool::False);
609 if (I.getOpcode() == Instruction::SetLE) // A <= MAX -> TRUE
610 return ReplaceInstUsesWith(I, ConstantBool::True);
611 if (I.getOpcode() == Instruction::SetGE) // A >= MAX -> A == MAX
612 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
613 if (I.getOpcode() == Instruction::SetLT) // A < MAX -> A != MAX
614 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
616 // Comparing against a value really close to min or max?
617 } else if (isMinValuePlusOne(CI)) {
618 if (I.getOpcode() == Instruction::SetLT) // A < MIN+1 -> A == MIN
619 return BinaryOperator::create(Instruction::SetEQ, Op0,
620 SubOne(CI), I.getName());
621 if (I.getOpcode() == Instruction::SetGE) // A >= MIN-1 -> A != MIN
622 return BinaryOperator::create(Instruction::SetNE, Op0,
623 SubOne(CI), I.getName());
625 } else if (isMaxValueMinusOne(CI)) {
626 if (I.getOpcode() == Instruction::SetGT) // A > MAX-1 -> A == MAX
627 return BinaryOperator::create(Instruction::SetEQ, Op0,
628 AddOne(CI), I.getName());
629 if (I.getOpcode() == Instruction::SetLE) // A <= MAX-1 -> A != MAX
630 return BinaryOperator::create(Instruction::SetNE, Op0,
631 AddOne(CI), I.getName());
635 return Changed ? &I : 0;
640 Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
641 assert(I.getOperand(1)->getType() == Type::UByteTy);
642 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
644 // shl X, 0 == X and shr X, 0 == X
645 // shl 0, X == 0 and shr 0, X == 0
646 if (Op1 == Constant::getNullValue(Type::UByteTy) ||
647 Op0 == Constant::getNullValue(Op0->getType()))
648 return ReplaceInstUsesWith(I, Op0);
650 // If this is a shift of a shift, see if we can fold the two together...
651 if (ShiftInst *Op0SI = dyn_cast<ShiftInst>(Op0)) {
652 if (isa<Constant>(Op1) && isa<Constant>(Op0SI->getOperand(1))) {
653 ConstantUInt *ShiftAmt1C = cast<ConstantUInt>(Op0SI->getOperand(1));
654 unsigned ShiftAmt1 = ShiftAmt1C->getValue();
655 unsigned ShiftAmt2 = cast<ConstantUInt>(Op1)->getValue();
657 // Check for (A << c1) << c2 and (A >> c1) >> c2
658 if (I.getOpcode() == Op0SI->getOpcode()) {
659 unsigned Amt = ShiftAmt1+ShiftAmt2; // Fold into one big shift...
660 return new ShiftInst(I.getOpcode(), Op0SI->getOperand(0),
661 ConstantUInt::get(Type::UByteTy, Amt));
664 if (I.getType()->isUnsigned()) { // Check for (A << c1) >> c2 or visaversa
665 // Calculate bitmask for what gets shifted off the edge...
666 Constant *C = ConstantIntegral::getAllOnesValue(I.getType());
667 if (I.getOpcode() == Instruction::Shr)
668 C = *C >> *ShiftAmt1C;
670 C = *C << *ShiftAmt1C;
671 assert(C && "Couldn't constant fold shift expression?");
674 BinaryOperator::create(Instruction::And, Op0SI->getOperand(0),
675 C, Op0SI->getOperand(0)->getName()+".mask",&I);
676 WorkList.push_back(Mask);
678 // Figure out what flavor of shift we should use...
679 if (ShiftAmt1 == ShiftAmt2)
680 return ReplaceInstUsesWith(I, Mask); // (A << c) >> c === A & c2
681 else if (ShiftAmt1 < ShiftAmt2) {
682 return new ShiftInst(I.getOpcode(), Mask,
683 ConstantUInt::get(Type::UByteTy, ShiftAmt2-ShiftAmt1));
685 return new ShiftInst(Op0SI->getOpcode(), Mask,
686 ConstantUInt::get(Type::UByteTy, ShiftAmt1-ShiftAmt2));
692 // shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr of
695 if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
696 unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
697 if (CUI->getValue() >= TypeBits &&
698 (!Op0->getType()->isSigned() || I.getOpcode() == Instruction::Shl))
699 return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
701 // Check to see if we are shifting left by 1. If so, turn it into an add
703 if (I.getOpcode() == Instruction::Shl && CUI->equalsInt(1))
704 // Convert 'shl int %X, 1' to 'add int %X, %X'
705 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
709 // shr int -1, X = -1 (for any arithmetic shift rights of ~0)
710 if (ConstantSInt *CSI = dyn_cast<ConstantSInt>(Op0))
711 if (I.getOpcode() == Instruction::Shr && CSI->isAllOnesValue())
712 return ReplaceInstUsesWith(I, CSI);
718 // isEliminableCastOfCast - Return true if it is valid to eliminate the CI
721 static inline bool isEliminableCastOfCast(const CastInst &CI,
722 const CastInst *CSrc) {
723 assert(CI.getOperand(0) == CSrc);
724 const Type *SrcTy = CSrc->getOperand(0)->getType();
725 const Type *MidTy = CSrc->getType();
726 const Type *DstTy = CI.getType();
728 // It is legal to eliminate the instruction if casting A->B->A if the sizes
729 // are identical and the bits don't get reinterpreted (for example
730 // int->float->int would not be allowed)
731 if (SrcTy == DstTy && SrcTy->isLosslesslyConvertableTo(MidTy))
734 // Allow free casting and conversion of sizes as long as the sign doesn't
736 if (SrcTy->isIntegral() && MidTy->isIntegral() && DstTy->isIntegral()) {
737 unsigned SrcSize = SrcTy->getPrimitiveSize();
738 unsigned MidSize = MidTy->getPrimitiveSize();
739 unsigned DstSize = DstTy->getPrimitiveSize();
741 // Cases where we are monotonically decreasing the size of the type are
742 // always ok, regardless of what sign changes are going on.
744 if (SrcSize >= MidSize && MidSize >= DstSize)
747 // Cases where the source and destination type are the same, but the middle
748 // type is bigger are noops.
750 if (SrcSize == DstSize && MidSize > SrcSize)
753 // If we are monotonically growing, things are more complex.
755 if (SrcSize <= MidSize && MidSize <= DstSize) {
756 // We have eight combinations of signedness to worry about. Here's the
758 static const int SignTable[8] = {
759 // CODE, SrcSigned, MidSigned, DstSigned, Comment
760 1, // U U U Always ok
761 1, // U U S Always ok
762 3, // U S U Ok iff SrcSize != MidSize
763 3, // U S S Ok iff SrcSize != MidSize
765 2, // S U S Ok iff MidSize == DstSize
766 1, // S S U Always ok
767 1, // S S S Always ok
770 // Choose an action based on the current entry of the signtable that this
771 // cast of cast refers to...
772 unsigned Row = SrcTy->isSigned()*4+MidTy->isSigned()*2+DstTy->isSigned();
773 switch (SignTable[Row]) {
774 case 0: return false; // Never ok
775 case 1: return true; // Always ok
776 case 2: return MidSize == DstSize; // Ok iff MidSize == DstSize
777 case 3: // Ok iff SrcSize != MidSize
778 return SrcSize != MidSize || SrcTy == Type::BoolTy;
779 default: assert(0 && "Bad entry in sign table!");
784 // Otherwise, we cannot succeed. Specifically we do not want to allow things
785 // like: short -> ushort -> uint, because this can create wrong results if
786 // the input short is negative!
792 // CastInst simplification
794 Instruction *InstCombiner::visitCastInst(CastInst &CI) {
795 // If the user is casting a value to the same type, eliminate this cast
797 if (CI.getType() == CI.getOperand(0)->getType())
798 return ReplaceInstUsesWith(CI, CI.getOperand(0));
800 // If casting the result of another cast instruction, try to eliminate this
803 if (CastInst *CSrc = dyn_cast<CastInst>(CI.getOperand(0))) {
804 if (isEliminableCastOfCast(CI, CSrc)) {
805 // This instruction now refers directly to the cast's src operand. This
806 // has a good chance of making CSrc dead.
807 CI.setOperand(0, CSrc->getOperand(0));
811 // If this is an A->B->A cast, and we are dealing with integral types, try
812 // to convert this into a logical 'and' instruction.
814 if (CSrc->getOperand(0)->getType() == CI.getType() &&
815 CI.getType()->isInteger() && CSrc->getType()->isInteger() &&
816 CI.getType()->isUnsigned() && CSrc->getType()->isUnsigned() &&
817 CSrc->getType()->getPrimitiveSize() < CI.getType()->getPrimitiveSize()){
818 assert(CSrc->getType() != Type::ULongTy &&
819 "Cannot have type bigger than ulong!");
820 unsigned AndValue = (1U << CSrc->getType()->getPrimitiveSize()*8)-1;
821 Constant *AndOp = ConstantUInt::get(CI.getType(), AndValue);
822 return BinaryOperator::create(Instruction::And, CSrc->getOperand(0),
831 // PHINode simplification
833 Instruction *InstCombiner::visitPHINode(PHINode &PN) {
834 // If the PHI node only has one incoming value, eliminate the PHI node...
835 if (PN.getNumIncomingValues() == 1)
836 return ReplaceInstUsesWith(PN, PN.getIncomingValue(0));
838 // Otherwise if all of the incoming values are the same for the PHI, replace
839 // the PHI node with the incoming value.
842 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
843 if (PN.getIncomingValue(i) != &PN) // Not the PHI node itself...
844 if (InVal && PN.getIncomingValue(i) != InVal)
845 return 0; // Not the same, bail out.
847 InVal = PN.getIncomingValue(i);
849 // The only case that could cause InVal to be null is if we have a PHI node
850 // that only has entries for itself. In this case, there is no entry into the
851 // loop, so kill the PHI.
853 if (InVal == 0) InVal = Constant::getNullValue(PN.getType());
855 // All of the incoming values are the same, replace the PHI node now.
856 return ReplaceInstUsesWith(PN, InVal);
860 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
861 // Is it 'getelementptr %P, uint 0' or 'getelementptr %P'
862 // If so, eliminate the noop.
863 if ((GEP.getNumOperands() == 2 &&
864 GEP.getOperand(1) == Constant::getNullValue(Type::LongTy)) ||
865 GEP.getNumOperands() == 1)
866 return ReplaceInstUsesWith(GEP, GEP.getOperand(0));
868 // Combine Indices - If the source pointer to this getelementptr instruction
869 // is a getelementptr instruction, combine the indices of the two
870 // getelementptr instructions into a single instruction.
872 if (GetElementPtrInst *Src = dyn_cast<GetElementPtrInst>(GEP.getOperand(0))) {
873 std::vector<Value *> Indices;
875 // Can we combine the two pointer arithmetics offsets?
876 if (Src->getNumOperands() == 2 && isa<Constant>(Src->getOperand(1)) &&
877 isa<Constant>(GEP.getOperand(1))) {
878 // Replace: gep (gep %P, long C1), long C2, ...
879 // With: gep %P, long (C1+C2), ...
880 Value *Sum = *cast<Constant>(Src->getOperand(1)) +
881 *cast<Constant>(GEP.getOperand(1));
882 assert(Sum && "Constant folding of longs failed!?");
883 GEP.setOperand(0, Src->getOperand(0));
884 GEP.setOperand(1, Sum);
885 AddUsesToWorkList(*Src); // Reduce use count of Src
887 } else if (Src->getNumOperands() == 2 && Src->use_size() == 1) {
888 // Replace: gep (gep %P, long B), long A, ...
889 // With: T = long A+B; gep %P, T, ...
891 Value *Sum = BinaryOperator::create(Instruction::Add, Src->getOperand(1),
893 Src->getName()+".sum", &GEP);
894 GEP.setOperand(0, Src->getOperand(0));
895 GEP.setOperand(1, Sum);
896 WorkList.push_back(cast<Instruction>(Sum));
898 } else if (*GEP.idx_begin() == Constant::getNullValue(Type::LongTy) &&
899 Src->getNumOperands() != 1) {
900 // Otherwise we can do the fold if the first index of the GEP is a zero
901 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
902 Indices.insert(Indices.end(), GEP.idx_begin()+1, GEP.idx_end());
903 } else if (Src->getOperand(Src->getNumOperands()-1) ==
904 Constant::getNullValue(Type::LongTy)) {
905 // If the src gep ends with a constant array index, merge this get into
906 // it, even if we have a non-zero array index.
907 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end()-1);
908 Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end());
911 if (!Indices.empty())
912 return new GetElementPtrInst(Src->getOperand(0), Indices, GEP.getName());
914 } else if (GlobalValue *GV = dyn_cast<GlobalValue>(GEP.getOperand(0))) {
915 // GEP of global variable. If all of the indices for this GEP are
916 // constants, we can promote this to a constexpr instead of an instruction.
918 // Scan for nonconstants...
919 std::vector<Constant*> Indices;
920 User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end();
921 for (; I != E && isa<Constant>(*I); ++I)
922 Indices.push_back(cast<Constant>(*I));
924 if (I == E) { // If they are all constants...
926 ConstantExpr::getGetElementPtr(ConstantPointerRef::get(GV), Indices);
928 // Replace all uses of the GEP with the new constexpr...
929 return ReplaceInstUsesWith(GEP, CE);
936 Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
937 // Convert: malloc Ty, C - where C is a constant != 1 into: malloc [C x Ty], 1
938 if (AI.isArrayAllocation()) // Check C != 1
939 if (const ConstantUInt *C = dyn_cast<ConstantUInt>(AI.getArraySize())) {
940 const Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getValue());
941 AllocationInst *New = 0;
943 // Create and insert the replacement instruction...
944 if (isa<MallocInst>(AI))
945 New = new MallocInst(NewTy, 0, AI.getName(), &AI);
947 assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
948 New = new AllocaInst(NewTy, 0, AI.getName(), &AI);
951 // Scan to the end of the allocation instructions, to skip over a block of
952 // allocas if possible...
954 BasicBlock::iterator It = New;
955 while (isa<AllocationInst>(*It)) ++It;
957 // Now that I is pointing to the first non-allocation-inst in the block,
958 // insert our getelementptr instruction...
960 std::vector<Value*> Idx(2, Constant::getNullValue(Type::LongTy));
961 Value *V = new GetElementPtrInst(New, Idx, New->getName()+".sub", It);
963 // Now make everything use the getelementptr instead of the original
965 ReplaceInstUsesWith(AI, V);
973 void InstCombiner::removeFromWorkList(Instruction *I) {
974 WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),
978 bool InstCombiner::runOnFunction(Function &F) {
979 bool Changed = false;
981 WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F));
983 while (!WorkList.empty()) {
984 Instruction *I = WorkList.back(); // Get an instruction from the worklist
987 // Check to see if we can DCE or ConstantPropagate the instruction...
988 // Check to see if we can DIE the instruction...
989 if (isInstructionTriviallyDead(I)) {
990 // Add operands to the worklist...
991 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
992 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
993 WorkList.push_back(Op);
996 BasicBlock::iterator BBI = I;
997 if (dceInstruction(BBI)) {
998 removeFromWorkList(I);
1003 // Instruction isn't dead, see if we can constant propagate it...
1004 if (Constant *C = ConstantFoldInstruction(I)) {
1005 // Add operands to the worklist...
1006 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1007 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
1008 WorkList.push_back(Op);
1009 ReplaceInstUsesWith(*I, C);
1012 BasicBlock::iterator BBI = I;
1013 if (dceInstruction(BBI)) {
1014 removeFromWorkList(I);
1019 // Now that we have an instruction, try combining it to simplify it...
1020 if (Instruction *Result = visit(*I)) {
1022 // Should we replace the old instruction with a new one?
1024 // Instructions can end up on the worklist more than once. Make sure
1025 // we do not process an instruction that has been deleted.
1026 removeFromWorkList(I);
1027 ReplaceInstWithInst(I, Result);
1029 BasicBlock::iterator II = I;
1031 // If the instruction was modified, it's possible that it is now dead.
1032 // if so, remove it.
1033 if (dceInstruction(II)) {
1034 // Instructions may end up in the worklist more than once. Erase them
1036 removeFromWorkList(I);
1042 WorkList.push_back(Result);
1043 AddUsesToWorkList(*Result);
1052 Pass *createInstructionCombiningPass() {
1053 return new InstCombiner();