InstructionSimplify.cpp revision c514c1f5218b8fe7499a0b9a4737860344cf4c43 
1//===- InstructionSimplify.cpp - Fold instruction operands ----------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements routines for folding instructions into simpler forms
11// that do not require creating new instructions.  For example, this does
12// constant folding, and can handle identities like (X&0)->0.
13//
14//===----------------------------------------------------------------------===//
15
16#include "llvm/Analysis/InstructionSimplify.h"
17#include "llvm/Analysis/ConstantFolding.h"
18#include "llvm/Support/ValueHandle.h"
19#include "llvm/Instructions.h"
20#include "llvm/Support/PatternMatch.h"
21using namespace llvm;
22using namespace llvm::PatternMatch;
23
24/// SimplifyAndInst - Given operands for an And, see if we can
25/// fold the result.  If not, this returns null.
26Value *llvm::SimplifyAndInst(Value *Op0, Value *Op1,
27                             const TargetData *TD) {
28  if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
29    if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
30      Constant *Ops[] = { CLHS, CRHS };
31      return ConstantFoldInstOperands(Instruction::And, CLHS->getType(),
32                                      Ops, 2, TD);
33    }
34
35    // Canonicalize the constant to the RHS.
36    std::swap(Op0, Op1);
37  }
38
39  // X & undef -> 0
40  if (isa<UndefValue>(Op1))
41    return Constant::getNullValue(Op0->getType());
42
43  // X & X = X
44  if (Op0 == Op1)
45    return Op0;
46
47  // X & <0,0> = <0,0>
48  if (isa<ConstantAggregateZero>(Op1))
49    return Op1;
50
51  // X & <-1,-1> = X
52  if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
53    if (CP->isAllOnesValue())
54      return Op0;
55
56  if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
57    // X & 0 = 0
58    if (Op1CI->isZero())
59      return Op1CI;
60    // X & -1 = X
61    if (Op1CI->isAllOnesValue())
62      return Op0;
63  }
64
65  // A & ~A  =  ~A & A  =  0
66  Value *A, *B;
67  if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
68      (match(Op1, m_Not(m_Value(A))) && A == Op0))
69    return Constant::getNullValue(Op0->getType());
70
71  // (A | ?) & A = A
72  if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
73      (A == Op1 || B == Op1))
74    return Op1;
75
76  // A & (A | ?) = A
77  if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
78      (A == Op0 || B == Op0))
79    return Op0;
80
81  return 0;
82}
83
84/// SimplifyOrInst - Given operands for an Or, see if we can
85/// fold the result.  If not, this returns null.
86Value *llvm::SimplifyOrInst(Value *Op0, Value *Op1,
87                            const TargetData *TD) {
88  if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
89    if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
90      Constant *Ops[] = { CLHS, CRHS };
91      return ConstantFoldInstOperands(Instruction::Or, CLHS->getType(),
92                                      Ops, 2, TD);
93    }
94
95    // Canonicalize the constant to the RHS.
96    std::swap(Op0, Op1);
97  }
98
99  // X | undef -> -1
100  if (isa<UndefValue>(Op1))
101    return Constant::getAllOnesValue(Op0->getType());
102
103  // X | X = X
104  if (Op0 == Op1)
105    return Op0;
106
107  // X | <0,0> = X
108  if (isa<ConstantAggregateZero>(Op1))
109    return Op0;
110
111  // X | <-1,-1> = <-1,-1>
112  if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
113    if (CP->isAllOnesValue())
114      return Op1;
115
116  if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
117    // X | 0 = X
118    if (Op1CI->isZero())
119      return Op0;
120    // X | -1 = -1
121    if (Op1CI->isAllOnesValue())
122      return Op1CI;
123  }
124
125  // A | ~A  =  ~A | A  =  -1
126  Value *A, *B;
127  if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
128      (match(Op1, m_Not(m_Value(A))) && A == Op0))
129    return Constant::getAllOnesValue(Op0->getType());
130
131  // (A & ?) | A = A
132  if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
133      (A == Op1 || B == Op1))
134    return Op1;
135
136  // A | (A & ?) = A
137  if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
138      (A == Op0 || B == Op0))
139    return Op0;
140
141  return 0;
142}
143
144
145
146
147static const Type *GetCompareTy(Value *Op) {
148  return CmpInst::makeCmpResultType(Op->getType());
149}
150
151
152/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
153/// fold the result.  If not, this returns null.
154Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
155                              const TargetData *TD) {
156  CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
157  assert(CmpInst::isIntPredicate(Pred) && "Not an integer compare!");
158
159  if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
160    if (Constant *CRHS = dyn_cast<Constant>(RHS))
161      return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
162
163    // If we have a constant, make sure it is on the RHS.
164    std::swap(LHS, RHS);
165    Pred = CmpInst::getSwappedPredicate(Pred);
166  }
167
168  // ITy - This is the return type of the compare we're considering.
169  const Type *ITy = GetCompareTy(LHS);
170
171  // icmp X, X -> true/false
172  if (LHS == RHS)
173    return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
174
175  if (isa<UndefValue>(RHS))                  // X icmp undef -> undef
176    return UndefValue::get(ITy);
177
178  // icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
179  // addresses never equal each other!  We already know that Op0 != Op1.
180  if ((isa<GlobalValue>(LHS) || isa<AllocaInst>(LHS) ||
181       isa<ConstantPointerNull>(LHS)) &&
182      (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
183       isa<ConstantPointerNull>(RHS)))
184    return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
185
186  // See if we are doing a comparison with a constant.
187  if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
188    // If we have an icmp le or icmp ge instruction, turn it into the
189    // appropriate icmp lt or icmp gt instruction.  This allows us to rely on
190    // them being folded in the code below.
191    switch (Pred) {
192    default: break;
193    case ICmpInst::ICMP_ULE:
194      if (CI->isMaxValue(false))                 // A <=u MAX -> TRUE
195        return ConstantInt::getTrue(CI->getContext());
196      break;
197    case ICmpInst::ICMP_SLE:
198      if (CI->isMaxValue(true))                  // A <=s MAX -> TRUE
199        return ConstantInt::getTrue(CI->getContext());
200      break;
201    case ICmpInst::ICMP_UGE:
202      if (CI->isMinValue(false))                 // A >=u MIN -> TRUE
203        return ConstantInt::getTrue(CI->getContext());
204      break;
205    case ICmpInst::ICMP_SGE:
206      if (CI->isMinValue(true))                  // A >=s MIN -> TRUE
207        return ConstantInt::getTrue(CI->getContext());
208      break;
209    }
210  }
211
212
213  return 0;
214}
215
216/// SimplifyFCmpInst - Given operands for an FCmpInst, see if we can
217/// fold the result.  If not, this returns null.
218Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
219                              const TargetData *TD) {
220  CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
221  assert(CmpInst::isFPPredicate(Pred) && "Not an FP compare!");
222
223  if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
224    if (Constant *CRHS = dyn_cast<Constant>(RHS))
225      return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
226
227    // If we have a constant, make sure it is on the RHS.
228    std::swap(LHS, RHS);
229    Pred = CmpInst::getSwappedPredicate(Pred);
230  }
231
232  // Fold trivial predicates.
233  if (Pred == FCmpInst::FCMP_FALSE)
234    return ConstantInt::get(GetCompareTy(LHS), 0);
235  if (Pred == FCmpInst::FCMP_TRUE)
236    return ConstantInt::get(GetCompareTy(LHS), 1);
237
238  if (isa<UndefValue>(RHS))                  // fcmp pred X, undef -> undef
239    return UndefValue::get(GetCompareTy(LHS));
240
241  // fcmp x,x -> true/false.  Not all compares are foldable.
242  if (LHS == RHS) {
243    if (CmpInst::isTrueWhenEqual(Pred))
244      return ConstantInt::get(GetCompareTy(LHS), 1);
245    if (CmpInst::isFalseWhenEqual(Pred))
246      return ConstantInt::get(GetCompareTy(LHS), 0);
247  }
248
249  // Handle fcmp with constant RHS
250  if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
251    // If the constant is a nan, see if we can fold the comparison based on it.
252    if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
253      if (CFP->getValueAPF().isNaN()) {
254        if (FCmpInst::isOrdered(Pred))   // True "if ordered and foo"
255          return ConstantInt::getFalse(CFP->getContext());
256        assert(FCmpInst::isUnordered(Pred) &&
257               "Comparison must be either ordered or unordered!");
258        // True if unordered.
259        return ConstantInt::getTrue(CFP->getContext());
260      }
261    }
262  }
263
264  return 0;
265}
266
267/// SimplifyGEPInst - Given operands for an GetElementPtrInst, see if we can
268/// fold the result.  If not, this returns null.
269Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
270                             const TargetData *TD) {
271  // getelementptr P -> P.
272  if (NumOps == 1)
273    return Ops[0];
274
275  // TODO.
276  //if (isa<UndefValue>(Ops[0]))
277  //  return UndefValue::get(GEP.getType());
278
279  // getelementptr P, 0 -> P.
280  if (NumOps == 2)
281    if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
282      if (C->isZero())
283        return Ops[0];
284
285  // Check to see if this is constant foldable.
286  for (unsigned i = 0; i != NumOps; ++i)
287    if (!isa<Constant>(Ops[i]))
288      return 0;
289
290  return ConstantExpr::getGetElementPtr(cast<Constant>(Ops[0]),
291                                        (Constant *const*)Ops+1, NumOps-1);
292}
293
294
295//=== Helper functions for higher up the class hierarchy.
296
297/// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
298/// fold the result.  If not, this returns null.
299Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
300                           const TargetData *TD) {
301  switch (Opcode) {
302  case Instruction::And: return SimplifyAndInst(LHS, RHS, TD);
303  case Instruction::Or:  return SimplifyOrInst(LHS, RHS, TD);
304  default:
305    if (Constant *CLHS = dyn_cast<Constant>(LHS))
306      if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
307        Constant *COps[] = {CLHS, CRHS};
308        return ConstantFoldInstOperands(Opcode, LHS->getType(), COps, 2, TD);
309      }
310    return 0;
311  }
312}
313
314/// SimplifyCmpInst - Given operands for a CmpInst, see if we can
315/// fold the result.
316Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
317                             const TargetData *TD) {
318  if (CmpInst::isIntPredicate((CmpInst::Predicate)Predicate))
319    return SimplifyICmpInst(Predicate, LHS, RHS, TD);
320  return SimplifyFCmpInst(Predicate, LHS, RHS, TD);
321}
322
323
324/// SimplifyInstruction - See if we can compute a simplified version of this
325/// instruction.  If not, this returns null.
326Value *llvm::SimplifyInstruction(Instruction *I, const TargetData *TD) {
327  switch (I->getOpcode()) {
328  default:
329    return ConstantFoldInstruction(I, TD);
330  case Instruction::And:
331    return SimplifyAndInst(I->getOperand(0), I->getOperand(1), TD);
332  case Instruction::Or:
333    return SimplifyOrInst(I->getOperand(0), I->getOperand(1), TD);
334  case Instruction::ICmp:
335    return SimplifyICmpInst(cast<ICmpInst>(I)->getPredicate(),
336                            I->getOperand(0), I->getOperand(1), TD);
337  case Instruction::FCmp:
338    return SimplifyFCmpInst(cast<FCmpInst>(I)->getPredicate(),
339                            I->getOperand(0), I->getOperand(1), TD);
340  case Instruction::GetElementPtr: {
341    SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
342    return SimplifyGEPInst(&Ops[0], Ops.size(), TD);
343  }
344  }
345}
346
347/// ReplaceAndSimplifyAllUses - Perform From->replaceAllUsesWith(To) and then
348/// delete the From instruction.  In addition to a basic RAUW, this does a
349/// recursive simplification of the newly formed instructions.  This catches
350/// things where one simplification exposes other opportunities.  This only
351/// simplifies and deletes scalar operations, it does not change the CFG.
352///
353void llvm::ReplaceAndSimplifyAllUses(Instruction *From, Value *To,
354                                     const TargetData *TD) {
355  assert(From != To && "ReplaceAndSimplifyAllUses(X,X) is not valid!");
356
357  // FromHandle - This keeps a weakvh on the from value so that we can know if
358  // it gets deleted out from under us in a recursive simplification.
359  WeakVH FromHandle(From);
360
361  while (!From->use_empty()) {
362    // Update the instruction to use the new value.
363    Use &U = From->use_begin().getUse();
364    Instruction *User = cast<Instruction>(U.getUser());
365    U = To;
366
367    // See if we can simplify it.
368    if (Value *V = SimplifyInstruction(User, TD)) {
369      // Recursively simplify this.
370      ReplaceAndSimplifyAllUses(User, V, TD);
371
372      // If the recursive simplification ended up revisiting and deleting 'From'
373      // then we're done.
374      if (FromHandle == 0)
375        return;
376    }
377  }
378  From->eraseFromParent();
379}
380
381