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");
112 // getComplexity: Assign a complexity or rank value to LLVM Values...
113 // 0 -> Constant, 1 -> Other, 2 -> Argument, 2 -> Unary, 3 -> OtherInst
114 static unsigned getComplexity(Value *V) {
115 if (isa<Instruction>(V)) {
116 if (BinaryOperator::isNeg(V) || BinaryOperator::isNot(V))
120 if (isa<Argument>(V)) return 2;
121 return isa<Constant>(V) ? 0 : 1;
124 // SimplifyCommutative - This performs a few simplifications for commutative
127 // 1. Order operands such that they are listed from right (least complex) to
128 // left (most complex). This puts constants before unary operators before
131 // 2. Handle the case of (op (op V, C1), C2), changing it to:
132 // (op V, (op C1, C2))
134 static bool SimplifyCommutative(BinaryOperator &I) {
135 bool Changed = false;
136 if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1)))
137 Changed = !I.swapOperands();
139 if (!I.isAssociative()) return Changed;
140 Instruction::BinaryOps Opcode = I.getOpcode();
141 if (BinaryOperator *Op = dyn_cast<BinaryOperator>(I.getOperand(0))) {
142 if (Op->getOpcode() == Opcode && isa<Constant>(I.getOperand(1)) &&
143 isa<Constant>(Op->getOperand(1))) {
144 Instruction *New = BinaryOperator::create(I.getOpcode(), I.getOperand(1),
146 Constant *Folded = ConstantFoldInstruction(New);
148 assert(Folded && "Couldn't constant fold commutative operand?");
149 I.setOperand(0, Op->getOperand(0));
150 I.setOperand(1, Folded);
157 // dyn_castNegVal - Given a 'sub' instruction, return the RHS of the instruction
158 // if the LHS is a constant zero (which is the 'negate' form).
160 static inline Value *dyn_castNegVal(Value *V) {
161 if (BinaryOperator::isNeg(V))
162 return BinaryOperator::getNegArgument(cast<BinaryOperator>(V));
164 // Constants can be considered to be negated values...
165 if (Constant *C = dyn_cast<Constant>(V)) {
166 Constant *NC = *Constant::getNullValue(V->getType()) - *C;
167 assert(NC && "Couldn't constant fold a subtract!");
173 static inline Value *dyn_castNotVal(Value *V) {
174 if (BinaryOperator::isNot(V))
175 return BinaryOperator::getNotArgument(cast<BinaryOperator>(V));
177 // Constants can be considered to be not'ed values...
178 if (ConstantIntegral *C = dyn_cast<ConstantIntegral>(V)) {
179 Constant *NC = *ConstantIntegral::getAllOnesValue(C->getType()) ^ *C;
180 assert(NC && "Couldn't constant fold an exclusive or!");
186 static bool isOnlyUse(Value *V) {
187 return V->use_size() == 1 || isa<Constant>(V);
191 // Log2 - Calculate the log base 2 for the specified value if it is exactly a
193 static unsigned Log2(uint64_t Val) {
194 assert(Val > 1 && "Values 0 and 1 should be handled elsewhere!");
197 if (Val & 1) return 0; // Multiple bits set?
204 static inline Value *dyn_castFoldableMul(Value *V) {
205 if (V->use_size() == 1 && V->getType()->isInteger())
206 if (Instruction *I = dyn_cast<Instruction>(V))
207 if (I->getOpcode() == Instruction::Mul)
208 if (isa<Constant>(I->getOperand(1)))
209 return I->getOperand(0);
214 Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
215 bool Changed = SimplifyCommutative(I);
216 Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
218 // Eliminate 'add int %X, 0'
219 if (RHS == Constant::getNullValue(I.getType()))
220 return ReplaceInstUsesWith(I, LHS);
223 if (Value *V = dyn_castNegVal(LHS))
224 return BinaryOperator::create(Instruction::Sub, RHS, V);
227 if (!isa<Constant>(RHS))
228 if (Value *V = dyn_castNegVal(RHS))
229 return BinaryOperator::create(Instruction::Sub, LHS, V);
231 // X*C + X --> X * (C+1)
232 if (dyn_castFoldableMul(LHS) == RHS) {
233 Constant *CP1 = *cast<Constant>(cast<Instruction>(LHS)->getOperand(1)) +
234 *ConstantInt::get(I.getType(), 1);
235 assert(CP1 && "Couldn't constant fold C + 1?");
236 return BinaryOperator::create(Instruction::Mul, RHS, CP1);
239 // X + X*C --> X * (C+1)
240 if (dyn_castFoldableMul(RHS) == LHS) {
241 Constant *CP1 = *cast<Constant>(cast<Instruction>(RHS)->getOperand(1)) +
242 *ConstantInt::get(I.getType(), 1);
243 assert(CP1 && "Couldn't constant fold C + 1?");
244 return BinaryOperator::create(Instruction::Mul, LHS, CP1);
247 return Changed ? &I : 0;
250 Instruction *InstCombiner::visitSub(BinaryOperator &I) {
251 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
253 if (Op0 == Op1) // sub X, X -> 0
254 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
256 // If this is a 'B = x-(-A)', change to B = x+A...
257 if (Value *V = dyn_castNegVal(Op1))
258 return BinaryOperator::create(Instruction::Add, Op0, V);
260 // Replace (-1 - A) with (~A)...
261 if (ConstantInt *C = dyn_cast<ConstantInt>(Op0))
262 if (C->isAllOnesValue())
263 return BinaryOperator::createNot(Op1);
265 if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1))
266 if (Op1I->use_size() == 1) {
267 // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression
268 // is not used by anyone else...
270 if (Op1I->getOpcode() == Instruction::Sub) {
271 // Swap the two operands of the subexpr...
272 Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
273 Op1I->setOperand(0, IIOp1);
274 Op1I->setOperand(1, IIOp0);
276 // Create the new top level add instruction...
277 return BinaryOperator::create(Instruction::Add, Op0, Op1);
280 // Replace (A - (A & B)) with (A & ~B) if this is the only use of (A&B)...
282 if (Op1I->getOpcode() == Instruction::And &&
283 (Op1I->getOperand(0) == Op0 || Op1I->getOperand(1) == Op0)) {
284 Value *OtherOp = Op1I->getOperand(Op1I->getOperand(0) == Op0);
286 Instruction *NewNot = BinaryOperator::createNot(OtherOp, "B.not", &I);
287 return BinaryOperator::create(Instruction::And, Op0, NewNot);
290 // X - X*C --> X * (1-C)
291 if (dyn_castFoldableMul(Op1I) == Op0) {
292 Constant *CP1 = *ConstantInt::get(I.getType(), 1) -
293 *cast<Constant>(cast<Instruction>(Op1)->getOperand(1));
294 assert(CP1 && "Couldn't constant fold 1-C?");
295 return BinaryOperator::create(Instruction::Mul, Op0, CP1);
299 // X*C - X --> X * (C-1)
300 if (dyn_castFoldableMul(Op0) == Op1) {
301 Constant *CP1 = *cast<Constant>(cast<Instruction>(Op0)->getOperand(1)) -
302 *ConstantInt::get(I.getType(), 1);
303 assert(CP1 && "Couldn't constant fold C - 1?");
304 return BinaryOperator::create(Instruction::Mul, Op1, CP1);
310 Instruction *InstCombiner::visitMul(BinaryOperator &I) {
311 bool Changed = SimplifyCommutative(I);
312 Value *Op0 = I.getOperand(0);
314 // Simplify mul instructions with a constant RHS...
315 if (Constant *Op1 = dyn_cast<Constant>(I.getOperand(1))) {
316 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
317 const Type *Ty = CI->getType();
318 uint64_t Val = Ty->isSigned() ?
319 (uint64_t)cast<ConstantSInt>(CI)->getValue() :
320 cast<ConstantUInt>(CI)->getValue();
323 return ReplaceInstUsesWith(I, Op1); // Eliminate 'mul double %X, 0'
325 return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul int %X, 1'
326 case 2: // Convert 'mul int %X, 2' to 'add int %X, %X'
327 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
330 if (uint64_t C = Log2(Val)) // Replace X*(2^C) with X << C
331 return new ShiftInst(Instruction::Shl, Op0,
332 ConstantUInt::get(Type::UByteTy, C));
334 ConstantFP *Op1F = cast<ConstantFP>(Op1);
335 if (Op1F->isNullValue())
336 return ReplaceInstUsesWith(I, Op1);
338 // "In IEEE floating point, x*1 is not equivalent to x for nans. However,
339 // ANSI says we can drop signals, so we can do this anyway." (from GCC)
340 if (Op1F->getValue() == 1.0)
341 return ReplaceInstUsesWith(I, Op0); // Eliminate 'mul double %X, 1.0'
345 return Changed ? &I : 0;
348 Instruction *InstCombiner::visitDiv(BinaryOperator &I) {
350 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) {
351 if (RHS->equalsInt(1))
352 return ReplaceInstUsesWith(I, I.getOperand(0));
354 // Check to see if this is an unsigned division with an exact power of 2,
355 // if so, convert to a right shift.
356 if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
357 if (uint64_t Val = C->getValue()) // Don't break X / 0
358 if (uint64_t C = Log2(Val))
359 return new ShiftInst(Instruction::Shr, I.getOperand(0),
360 ConstantUInt::get(Type::UByteTy, C));
363 // 0 / X == 0, we don't need to preserve faults!
364 if (ConstantInt *LHS = dyn_cast<ConstantInt>(I.getOperand(0)))
365 if (LHS->equalsInt(0))
366 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
372 Instruction *InstCombiner::visitRem(BinaryOperator &I) {
373 if (ConstantInt *RHS = dyn_cast<ConstantInt>(I.getOperand(1))) {
374 if (RHS->equalsInt(1)) // X % 1 == 0
375 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
377 // Check to see if this is an unsigned remainder with an exact power of 2,
378 // if so, convert to a bitwise and.
379 if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
380 if (uint64_t Val = C->getValue()) // Don't break X % 0 (divide by zero)
382 return BinaryOperator::create(Instruction::And, I.getOperand(0),
383 ConstantUInt::get(I.getType(), Val-1));
386 // 0 % X == 0, we don't need to preserve faults!
387 if (ConstantInt *LHS = dyn_cast<ConstantInt>(I.getOperand(0)))
388 if (LHS->equalsInt(0))
389 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
394 // isMaxValueMinusOne - return true if this is Max-1
395 static bool isMaxValueMinusOne(const ConstantInt *C) {
396 if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C)) {
397 // Calculate -1 casted to the right type...
398 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
399 uint64_t Val = ~0ULL; // All ones
400 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
401 return CU->getValue() == Val-1;
404 const ConstantSInt *CS = cast<ConstantSInt>(C);
406 // Calculate 0111111111..11111
407 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
408 int64_t Val = INT64_MAX; // All ones
409 Val >>= 64-TypeBits; // Shift out unwanted 1 bits...
410 return CS->getValue() == Val-1;
413 // isMinValuePlusOne - return true if this is Min+1
414 static bool isMinValuePlusOne(const ConstantInt *C) {
415 if (const ConstantUInt *CU = dyn_cast<ConstantUInt>(C))
416 return CU->getValue() == 1;
418 const ConstantSInt *CS = cast<ConstantSInt>(C);
420 // Calculate 1111111111000000000000
421 unsigned TypeBits = C->getType()->getPrimitiveSize()*8;
422 int64_t Val = -1; // All ones
423 Val <<= TypeBits-1; // Shift over to the right spot
424 return CS->getValue() == Val+1;
428 Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
429 bool Changed = SimplifyCommutative(I);
430 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
432 // and X, X = X and X, 0 == 0
433 if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
434 return ReplaceInstUsesWith(I, Op1);
437 if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
438 if (RHS->isAllOnesValue())
439 return ReplaceInstUsesWith(I, Op0);
441 Value *Op0NotVal = dyn_castNotVal(Op0);
442 Value *Op1NotVal = dyn_castNotVal(Op1);
444 // (~A & ~B) == (~(A | B)) - Demorgan's Law
445 if (Op0NotVal && Op1NotVal && isOnlyUse(Op0) && isOnlyUse(Op1)) {
446 Instruction *Or = BinaryOperator::create(Instruction::Or, Op0NotVal,
447 Op1NotVal,I.getName()+".demorgan",
449 return BinaryOperator::createNot(Or);
452 if (Op0NotVal == Op1 || Op1NotVal == Op0) // A & ~A == ~A & A == 0
453 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
455 return Changed ? &I : 0;
460 Instruction *InstCombiner::visitOr(BinaryOperator &I) {
461 bool Changed = SimplifyCommutative(I);
462 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
464 // or X, X = X or X, 0 == X
465 if (Op0 == Op1 || Op1 == Constant::getNullValue(I.getType()))
466 return ReplaceInstUsesWith(I, Op0);
469 if (ConstantIntegral *RHS = dyn_cast<ConstantIntegral>(Op1))
470 if (RHS->isAllOnesValue())
471 return ReplaceInstUsesWith(I, Op1);
473 if (Value *X = dyn_castNotVal(Op0)) // ~A | A == -1
475 return ReplaceInstUsesWith(I,
476 ConstantIntegral::getAllOnesValue(I.getType()));
478 if (Value *X = dyn_castNotVal(Op1)) // A | ~A == -1
480 return ReplaceInstUsesWith(I,
481 ConstantIntegral::getAllOnesValue(I.getType()));
483 return Changed ? &I : 0;
488 Instruction *InstCombiner::visitXor(BinaryOperator &I) {
489 bool Changed = SimplifyCommutative(I);
490 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
494 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
496 if (ConstantIntegral *Op1C = dyn_cast<ConstantIntegral>(Op1)) {
498 if (Op1C->isNullValue())
499 return ReplaceInstUsesWith(I, Op0);
501 // Is this a "NOT" instruction?
502 if (Op1C->isAllOnesValue()) {
503 // xor (xor X, -1), -1 = not (not X) = X
504 if (Value *X = dyn_castNotVal(Op0))
505 return ReplaceInstUsesWith(I, X);
507 // xor (setcc A, B), true = not (setcc A, B) = setncc A, B
508 if (SetCondInst *SCI = dyn_cast<SetCondInst>(Op0))
509 if (SCI->use_size() == 1)
510 return new SetCondInst(SCI->getInverseCondition(),
511 SCI->getOperand(0), SCI->getOperand(1));
515 if (Value *X = dyn_castNotVal(Op0)) // ~A ^ A == -1
517 return ReplaceInstUsesWith(I,
518 ConstantIntegral::getAllOnesValue(I.getType()));
520 if (Value *X = dyn_castNotVal(Op1)) // A ^ ~A == -1
522 return ReplaceInstUsesWith(I,
523 ConstantIntegral::getAllOnesValue(I.getType()));
527 if (Instruction *Op1I = dyn_cast<Instruction>(Op1))
528 if (Op1I->getOpcode() == Instruction::Or)
529 if (Op1I->getOperand(0) == Op0) { // B^(B|A) == (A|B)^B
530 cast<BinaryOperator>(Op1I)->swapOperands();
533 } else if (Op1I->getOperand(1) == Op0) { // B^(A|B) == (A|B)^B
538 if (Instruction *Op0I = dyn_cast<Instruction>(Op0))
539 if (Op0I->getOpcode() == Instruction::Or && Op0I->use_size() == 1) {
540 if (Op0I->getOperand(0) == Op1) // (B|A)^B == (A|B)^B
541 cast<BinaryOperator>(Op0I)->swapOperands();
542 if (Op0I->getOperand(1) == Op1) { // (A|B)^B == A & ~B
543 Value *NotB = BinaryOperator::createNot(Op1, Op1->getName()+".not", &I);
544 WorkList.push_back(cast<Instruction>(NotB));
545 return BinaryOperator::create(Instruction::And, Op0I->getOperand(0),
550 return Changed ? &I : 0;
553 // AddOne, SubOne - Add or subtract a constant one from an integer constant...
554 static Constant *AddOne(ConstantInt *C) {
555 Constant *Result = *C + *ConstantInt::get(C->getType(), 1);
556 assert(Result && "Constant folding integer addition failed!");
559 static Constant *SubOne(ConstantInt *C) {
560 Constant *Result = *C - *ConstantInt::get(C->getType(), 1);
561 assert(Result && "Constant folding integer addition failed!");
565 // isTrueWhenEqual - Return true if the specified setcondinst instruction is
566 // true when both operands are equal...
568 static bool isTrueWhenEqual(Instruction &I) {
569 return I.getOpcode() == Instruction::SetEQ ||
570 I.getOpcode() == Instruction::SetGE ||
571 I.getOpcode() == Instruction::SetLE;
574 Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
575 bool Changed = SimplifyCommutative(I);
576 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
577 const Type *Ty = Op0->getType();
581 return ReplaceInstUsesWith(I, ConstantBool::get(isTrueWhenEqual(I)));
583 // setcc <global*>, 0 - Global value addresses are never null!
584 if (isa<GlobalValue>(Op0) && isa<ConstantPointerNull>(Op1))
585 return ReplaceInstUsesWith(I, ConstantBool::get(!isTrueWhenEqual(I)));
587 // setcc's with boolean values can always be turned into bitwise operations
588 if (Ty == Type::BoolTy) {
589 // If this is <, >, or !=, we can change this into a simple xor instruction
590 if (!isTrueWhenEqual(I))
591 return BinaryOperator::create(Instruction::Xor, Op0, Op1, I.getName());
593 // Otherwise we need to make a temporary intermediate instruction and insert
594 // it into the instruction stream. This is what we are after:
596 // seteq bool %A, %B -> ~(A^B)
597 // setle bool %A, %B -> ~A | B
598 // setge bool %A, %B -> A | ~B
600 if (I.getOpcode() == Instruction::SetEQ) { // seteq case
601 Instruction *Xor = BinaryOperator::create(Instruction::Xor, Op0, Op1,
603 InsertNewInstBefore(Xor, I);
604 return BinaryOperator::createNot(Xor, I.getName());
607 // Handle the setXe cases...
608 assert(I.getOpcode() == Instruction::SetGE ||
609 I.getOpcode() == Instruction::SetLE);
611 if (I.getOpcode() == Instruction::SetGE)
612 std::swap(Op0, Op1); // Change setge -> setle
614 // Now we just have the SetLE case.
615 Instruction *Not = BinaryOperator::createNot(Op0, I.getName()+"tmp");
616 InsertNewInstBefore(Not, I);
617 return BinaryOperator::create(Instruction::Or, Not, Op1, I.getName());
620 // Check to see if we are doing one of many comparisons against constant
621 // integers at the end of their ranges...
623 if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
624 // Check to see if we are comparing against the minimum or maximum value...
625 if (CI->isMinValue()) {
626 if (I.getOpcode() == Instruction::SetLT) // A < MIN -> FALSE
627 return ReplaceInstUsesWith(I, ConstantBool::False);
628 if (I.getOpcode() == Instruction::SetGE) // A >= MIN -> TRUE
629 return ReplaceInstUsesWith(I, ConstantBool::True);
630 if (I.getOpcode() == Instruction::SetLE) // A <= MIN -> A == MIN
631 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
632 if (I.getOpcode() == Instruction::SetGT) // A > MIN -> A != MIN
633 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
635 } else if (CI->isMaxValue()) {
636 if (I.getOpcode() == Instruction::SetGT) // A > MAX -> FALSE
637 return ReplaceInstUsesWith(I, ConstantBool::False);
638 if (I.getOpcode() == Instruction::SetLE) // A <= MAX -> TRUE
639 return ReplaceInstUsesWith(I, ConstantBool::True);
640 if (I.getOpcode() == Instruction::SetGE) // A >= MAX -> A == MAX
641 return BinaryOperator::create(Instruction::SetEQ, Op0,Op1, I.getName());
642 if (I.getOpcode() == Instruction::SetLT) // A < MAX -> A != MAX
643 return BinaryOperator::create(Instruction::SetNE, Op0,Op1, I.getName());
645 // Comparing against a value really close to min or max?
646 } else if (isMinValuePlusOne(CI)) {
647 if (I.getOpcode() == Instruction::SetLT) // A < MIN+1 -> A == MIN
648 return BinaryOperator::create(Instruction::SetEQ, Op0,
649 SubOne(CI), I.getName());
650 if (I.getOpcode() == Instruction::SetGE) // A >= MIN-1 -> A != MIN
651 return BinaryOperator::create(Instruction::SetNE, Op0,
652 SubOne(CI), I.getName());
654 } else if (isMaxValueMinusOne(CI)) {
655 if (I.getOpcode() == Instruction::SetGT) // A > MAX-1 -> A == MAX
656 return BinaryOperator::create(Instruction::SetEQ, Op0,
657 AddOne(CI), I.getName());
658 if (I.getOpcode() == Instruction::SetLE) // A <= MAX-1 -> A != MAX
659 return BinaryOperator::create(Instruction::SetNE, Op0,
660 AddOne(CI), I.getName());
664 return Changed ? &I : 0;
669 Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
670 assert(I.getOperand(1)->getType() == Type::UByteTy);
671 Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
673 // shl X, 0 == X and shr X, 0 == X
674 // shl 0, X == 0 and shr 0, X == 0
675 if (Op1 == Constant::getNullValue(Type::UByteTy) ||
676 Op0 == Constant::getNullValue(Op0->getType()))
677 return ReplaceInstUsesWith(I, Op0);
679 // If this is a shift of a shift, see if we can fold the two together...
680 if (ShiftInst *Op0SI = dyn_cast<ShiftInst>(Op0)) {
681 if (isa<Constant>(Op1) && isa<Constant>(Op0SI->getOperand(1))) {
682 ConstantUInt *ShiftAmt1C = cast<ConstantUInt>(Op0SI->getOperand(1));
683 unsigned ShiftAmt1 = ShiftAmt1C->getValue();
684 unsigned ShiftAmt2 = cast<ConstantUInt>(Op1)->getValue();
686 // Check for (A << c1) << c2 and (A >> c1) >> c2
687 if (I.getOpcode() == Op0SI->getOpcode()) {
688 unsigned Amt = ShiftAmt1+ShiftAmt2; // Fold into one big shift...
689 return new ShiftInst(I.getOpcode(), Op0SI->getOperand(0),
690 ConstantUInt::get(Type::UByteTy, Amt));
693 if (I.getType()->isUnsigned()) { // Check for (A << c1) >> c2 or visaversa
694 // Calculate bitmask for what gets shifted off the edge...
695 Constant *C = ConstantIntegral::getAllOnesValue(I.getType());
696 if (I.getOpcode() == Instruction::Shr)
697 C = *C >> *ShiftAmt1C;
699 C = *C << *ShiftAmt1C;
700 assert(C && "Couldn't constant fold shift expression?");
703 BinaryOperator::create(Instruction::And, Op0SI->getOperand(0),
704 C, Op0SI->getOperand(0)->getName()+".mask",&I);
705 WorkList.push_back(Mask);
707 // Figure out what flavor of shift we should use...
708 if (ShiftAmt1 == ShiftAmt2)
709 return ReplaceInstUsesWith(I, Mask); // (A << c) >> c === A & c2
710 else if (ShiftAmt1 < ShiftAmt2) {
711 return new ShiftInst(I.getOpcode(), Mask,
712 ConstantUInt::get(Type::UByteTy, ShiftAmt2-ShiftAmt1));
714 return new ShiftInst(Op0SI->getOpcode(), Mask,
715 ConstantUInt::get(Type::UByteTy, ShiftAmt1-ShiftAmt2));
721 // shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr of
724 if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
725 unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
726 if (CUI->getValue() >= TypeBits &&
727 (!Op0->getType()->isSigned() || I.getOpcode() == Instruction::Shl))
728 return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
730 // Check to see if we are shifting left by 1. If so, turn it into an add
732 if (I.getOpcode() == Instruction::Shl && CUI->equalsInt(1))
733 // Convert 'shl int %X, 1' to 'add int %X, %X'
734 return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
738 // shr int -1, X = -1 (for any arithmetic shift rights of ~0)
739 if (ConstantSInt *CSI = dyn_cast<ConstantSInt>(Op0))
740 if (I.getOpcode() == Instruction::Shr && CSI->isAllOnesValue())
741 return ReplaceInstUsesWith(I, CSI);
747 // isEliminableCastOfCast - Return true if it is valid to eliminate the CI
750 static inline bool isEliminableCastOfCast(const CastInst &CI,
751 const CastInst *CSrc) {
752 assert(CI.getOperand(0) == CSrc);
753 const Type *SrcTy = CSrc->getOperand(0)->getType();
754 const Type *MidTy = CSrc->getType();
755 const Type *DstTy = CI.getType();
757 // It is legal to eliminate the instruction if casting A->B->A if the sizes
758 // are identical and the bits don't get reinterpreted (for example
759 // int->float->int would not be allowed)
760 if (SrcTy == DstTy && SrcTy->isLosslesslyConvertableTo(MidTy))
763 // Allow free casting and conversion of sizes as long as the sign doesn't
765 if (SrcTy->isIntegral() && MidTy->isIntegral() && DstTy->isIntegral()) {
766 unsigned SrcSize = SrcTy->getPrimitiveSize();
767 unsigned MidSize = MidTy->getPrimitiveSize();
768 unsigned DstSize = DstTy->getPrimitiveSize();
770 // Cases where we are monotonically decreasing the size of the type are
771 // always ok, regardless of what sign changes are going on.
773 if (SrcSize >= MidSize && MidSize >= DstSize)
776 // Cases where the source and destination type are the same, but the middle
777 // type is bigger are noops.
779 if (SrcSize == DstSize && MidSize > SrcSize)
782 // If we are monotonically growing, things are more complex.
784 if (SrcSize <= MidSize && MidSize <= DstSize) {
785 // We have eight combinations of signedness to worry about. Here's the
787 static const int SignTable[8] = {
788 // CODE, SrcSigned, MidSigned, DstSigned, Comment
789 1, // U U U Always ok
790 1, // U U S Always ok
791 3, // U S U Ok iff SrcSize != MidSize
792 3, // U S S Ok iff SrcSize != MidSize
794 2, // S U S Ok iff MidSize == DstSize
795 1, // S S U Always ok
796 1, // S S S Always ok
799 // Choose an action based on the current entry of the signtable that this
800 // cast of cast refers to...
801 unsigned Row = SrcTy->isSigned()*4+MidTy->isSigned()*2+DstTy->isSigned();
802 switch (SignTable[Row]) {
803 case 0: return false; // Never ok
804 case 1: return true; // Always ok
805 case 2: return MidSize == DstSize; // Ok iff MidSize == DstSize
806 case 3: // Ok iff SrcSize != MidSize
807 return SrcSize != MidSize || SrcTy == Type::BoolTy;
808 default: assert(0 && "Bad entry in sign table!");
813 // Otherwise, we cannot succeed. Specifically we do not want to allow things
814 // like: short -> ushort -> uint, because this can create wrong results if
815 // the input short is negative!
821 // CastInst simplification
823 Instruction *InstCombiner::visitCastInst(CastInst &CI) {
824 // If the user is casting a value to the same type, eliminate this cast
826 if (CI.getType() == CI.getOperand(0)->getType())
827 return ReplaceInstUsesWith(CI, CI.getOperand(0));
829 // If casting the result of another cast instruction, try to eliminate this
832 if (CastInst *CSrc = dyn_cast<CastInst>(CI.getOperand(0))) {
833 if (isEliminableCastOfCast(CI, CSrc)) {
834 // This instruction now refers directly to the cast's src operand. This
835 // has a good chance of making CSrc dead.
836 CI.setOperand(0, CSrc->getOperand(0));
840 // If this is an A->B->A cast, and we are dealing with integral types, try
841 // to convert this into a logical 'and' instruction.
843 if (CSrc->getOperand(0)->getType() == CI.getType() &&
844 CI.getType()->isInteger() && CSrc->getType()->isInteger() &&
845 CI.getType()->isUnsigned() && CSrc->getType()->isUnsigned() &&
846 CSrc->getType()->getPrimitiveSize() < CI.getType()->getPrimitiveSize()){
847 assert(CSrc->getType() != Type::ULongTy &&
848 "Cannot have type bigger than ulong!");
849 unsigned AndValue = (1U << CSrc->getType()->getPrimitiveSize()*8)-1;
850 Constant *AndOp = ConstantUInt::get(CI.getType(), AndValue);
851 return BinaryOperator::create(Instruction::And, CSrc->getOperand(0),
860 // PHINode simplification
862 Instruction *InstCombiner::visitPHINode(PHINode &PN) {
863 // If the PHI node only has one incoming value, eliminate the PHI node...
864 if (PN.getNumIncomingValues() == 1)
865 return ReplaceInstUsesWith(PN, PN.getIncomingValue(0));
867 // Otherwise if all of the incoming values are the same for the PHI, replace
868 // the PHI node with the incoming value.
871 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
872 if (PN.getIncomingValue(i) != &PN) // Not the PHI node itself...
873 if (InVal && PN.getIncomingValue(i) != InVal)
874 return 0; // Not the same, bail out.
876 InVal = PN.getIncomingValue(i);
878 // The only case that could cause InVal to be null is if we have a PHI node
879 // that only has entries for itself. In this case, there is no entry into the
880 // loop, so kill the PHI.
882 if (InVal == 0) InVal = Constant::getNullValue(PN.getType());
884 // All of the incoming values are the same, replace the PHI node now.
885 return ReplaceInstUsesWith(PN, InVal);
889 Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
890 // Is it 'getelementptr %P, uint 0' or 'getelementptr %P'
891 // If so, eliminate the noop.
892 if ((GEP.getNumOperands() == 2 &&
893 GEP.getOperand(1) == Constant::getNullValue(Type::LongTy)) ||
894 GEP.getNumOperands() == 1)
895 return ReplaceInstUsesWith(GEP, GEP.getOperand(0));
897 // Combine Indices - If the source pointer to this getelementptr instruction
898 // is a getelementptr instruction, combine the indices of the two
899 // getelementptr instructions into a single instruction.
901 if (GetElementPtrInst *Src = dyn_cast<GetElementPtrInst>(GEP.getOperand(0))) {
902 std::vector<Value *> Indices;
904 // Can we combine the two pointer arithmetics offsets?
905 if (Src->getNumOperands() == 2 && isa<Constant>(Src->getOperand(1)) &&
906 isa<Constant>(GEP.getOperand(1))) {
907 // Replace: gep (gep %P, long C1), long C2, ...
908 // With: gep %P, long (C1+C2), ...
909 Value *Sum = *cast<Constant>(Src->getOperand(1)) +
910 *cast<Constant>(GEP.getOperand(1));
911 assert(Sum && "Constant folding of longs failed!?");
912 GEP.setOperand(0, Src->getOperand(0));
913 GEP.setOperand(1, Sum);
914 AddUsesToWorkList(*Src); // Reduce use count of Src
916 } else if (Src->getNumOperands() == 2 && Src->use_size() == 1) {
917 // Replace: gep (gep %P, long B), long A, ...
918 // With: T = long A+B; gep %P, T, ...
920 Value *Sum = BinaryOperator::create(Instruction::Add, Src->getOperand(1),
922 Src->getName()+".sum", &GEP);
923 GEP.setOperand(0, Src->getOperand(0));
924 GEP.setOperand(1, Sum);
925 WorkList.push_back(cast<Instruction>(Sum));
927 } else if (*GEP.idx_begin() == Constant::getNullValue(Type::LongTy) &&
928 Src->getNumOperands() != 1) {
929 // Otherwise we can do the fold if the first index of the GEP is a zero
930 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end());
931 Indices.insert(Indices.end(), GEP.idx_begin()+1, GEP.idx_end());
932 } else if (Src->getOperand(Src->getNumOperands()-1) ==
933 Constant::getNullValue(Type::LongTy)) {
934 // If the src gep ends with a constant array index, merge this get into
935 // it, even if we have a non-zero array index.
936 Indices.insert(Indices.end(), Src->idx_begin(), Src->idx_end()-1);
937 Indices.insert(Indices.end(), GEP.idx_begin(), GEP.idx_end());
940 if (!Indices.empty())
941 return new GetElementPtrInst(Src->getOperand(0), Indices, GEP.getName());
943 } else if (GlobalValue *GV = dyn_cast<GlobalValue>(GEP.getOperand(0))) {
944 // GEP of global variable. If all of the indices for this GEP are
945 // constants, we can promote this to a constexpr instead of an instruction.
947 // Scan for nonconstants...
948 std::vector<Constant*> Indices;
949 User::op_iterator I = GEP.idx_begin(), E = GEP.idx_end();
950 for (; I != E && isa<Constant>(*I); ++I)
951 Indices.push_back(cast<Constant>(*I));
953 if (I == E) { // If they are all constants...
955 ConstantExpr::getGetElementPtr(ConstantPointerRef::get(GV), Indices);
957 // Replace all uses of the GEP with the new constexpr...
958 return ReplaceInstUsesWith(GEP, CE);
965 Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
966 // Convert: malloc Ty, C - where C is a constant != 1 into: malloc [C x Ty], 1
967 if (AI.isArrayAllocation()) // Check C != 1
968 if (const ConstantUInt *C = dyn_cast<ConstantUInt>(AI.getArraySize())) {
969 const Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getValue());
970 AllocationInst *New = 0;
972 // Create and insert the replacement instruction...
973 if (isa<MallocInst>(AI))
974 New = new MallocInst(NewTy, 0, AI.getName(), &AI);
976 assert(isa<AllocaInst>(AI) && "Unknown type of allocation inst!");
977 New = new AllocaInst(NewTy, 0, AI.getName(), &AI);
980 // Scan to the end of the allocation instructions, to skip over a block of
981 // allocas if possible...
983 BasicBlock::iterator It = New;
984 while (isa<AllocationInst>(*It)) ++It;
986 // Now that I is pointing to the first non-allocation-inst in the block,
987 // insert our getelementptr instruction...
989 std::vector<Value*> Idx(2, Constant::getNullValue(Type::LongTy));
990 Value *V = new GetElementPtrInst(New, Idx, New->getName()+".sub", It);
992 // Now make everything use the getelementptr instead of the original
994 ReplaceInstUsesWith(AI, V);
1002 void InstCombiner::removeFromWorkList(Instruction *I) {
1003 WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),
1007 bool InstCombiner::runOnFunction(Function &F) {
1008 bool Changed = false;
1010 WorkList.insert(WorkList.end(), inst_begin(F), inst_end(F));
1012 while (!WorkList.empty()) {
1013 Instruction *I = WorkList.back(); // Get an instruction from the worklist
1014 WorkList.pop_back();
1016 // Check to see if we can DCE or ConstantPropagate the instruction...
1017 // Check to see if we can DIE the instruction...
1018 if (isInstructionTriviallyDead(I)) {
1019 // Add operands to the worklist...
1020 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1021 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
1022 WorkList.push_back(Op);
1025 BasicBlock::iterator BBI = I;
1026 if (dceInstruction(BBI)) {
1027 removeFromWorkList(I);
1032 // Instruction isn't dead, see if we can constant propagate it...
1033 if (Constant *C = ConstantFoldInstruction(I)) {
1034 // Add operands to the worklist...
1035 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
1036 if (Instruction *Op = dyn_cast<Instruction>(I->getOperand(i)))
1037 WorkList.push_back(Op);
1038 ReplaceInstUsesWith(*I, C);
1041 BasicBlock::iterator BBI = I;
1042 if (dceInstruction(BBI)) {
1043 removeFromWorkList(I);
1048 // Now that we have an instruction, try combining it to simplify it...
1049 if (Instruction *Result = visit(*I)) {
1051 // Should we replace the old instruction with a new one?
1053 // Instructions can end up on the worklist more than once. Make sure
1054 // we do not process an instruction that has been deleted.
1055 removeFromWorkList(I);
1056 ReplaceInstWithInst(I, Result);
1058 BasicBlock::iterator II = I;
1060 // If the instruction was modified, it's possible that it is now dead.
1061 // if so, remove it.
1062 if (dceInstruction(II)) {
1063 // Instructions may end up in the worklist more than once. Erase them
1065 removeFromWorkList(I);
1071 WorkList.push_back(Result);
1072 AddUsesToWorkList(*Result);
1081 Pass *createInstructionCombiningPass() {
1082 return new InstCombiner();