ConstantFold.cpp revision a0ae8196a1d2d1291949e268afc1bf932c9f8028 
1//===- ConstantFolding.cpp - LLVM constant folder -------------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by the LLVM research group and is distributed under
6// the University of Illinois Open Source License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements folding of constants for LLVM.  This implements the
11// (internal) ConstantFolding.h interface, which is used by the
12// ConstantExpr::get* methods to automatically fold constants when possible.
13//
14// The current constant folding implementation is implemented in two pieces: the
15// template-based folder for simple primitive constants like ConstantInt, and
16// the special case hackery that we use to symbolically evaluate expressions
17// that use ConstantExprs.
18//
19//===----------------------------------------------------------------------===//
20
21#include "ConstantFolding.h"
22#include "llvm/Constants.h"
23#include "llvm/Instructions.h"
24#include "llvm/DerivedTypes.h"
25#include "llvm/Function.h"
26#include "llvm/Support/GetElementPtrTypeIterator.h"
27#include <cmath>
28using namespace llvm;
29
30namespace {
31  struct ConstRules {
32    ConstRules() {}
33
34    // Binary Operators...
35    virtual Constant *add(const Constant *V1, const Constant *V2) const = 0;
36    virtual Constant *sub(const Constant *V1, const Constant *V2) const = 0;
37    virtual Constant *mul(const Constant *V1, const Constant *V2) const = 0;
38    virtual Constant *div(const Constant *V1, const Constant *V2) const = 0;
39    virtual Constant *rem(const Constant *V1, const Constant *V2) const = 0;
40    virtual Constant *op_and(const Constant *V1, const Constant *V2) const = 0;
41    virtual Constant *op_or (const Constant *V1, const Constant *V2) const = 0;
42    virtual Constant *op_xor(const Constant *V1, const Constant *V2) const = 0;
43    virtual Constant *shl(const Constant *V1, const Constant *V2) const = 0;
44    virtual Constant *shr(const Constant *V1, const Constant *V2) const = 0;
45    virtual Constant *lessthan(const Constant *V1, const Constant *V2) const =0;
46    virtual Constant *equalto(const Constant *V1, const Constant *V2) const = 0;
47
48    // Casting operators.
49    virtual Constant *castToBool  (const Constant *V) const = 0;
50    virtual Constant *castToSByte (const Constant *V) const = 0;
51    virtual Constant *castToUByte (const Constant *V) const = 0;
52    virtual Constant *castToShort (const Constant *V) const = 0;
53    virtual Constant *castToUShort(const Constant *V) const = 0;
54    virtual Constant *castToInt   (const Constant *V) const = 0;
55    virtual Constant *castToUInt  (const Constant *V) const = 0;
56    virtual Constant *castToLong  (const Constant *V) const = 0;
57    virtual Constant *castToULong (const Constant *V) const = 0;
58    virtual Constant *castToFloat (const Constant *V) const = 0;
59    virtual Constant *castToDouble(const Constant *V) const = 0;
60    virtual Constant *castToPointer(const Constant *V,
61                                    const PointerType *Ty) const = 0;
62
63    // ConstRules::get - Return an instance of ConstRules for the specified
64    // constant operands.
65    //
66    static ConstRules &get(const Constant *V1, const Constant *V2);
67  private:
68    ConstRules(const ConstRules &);             // Do not implement
69    ConstRules &operator=(const ConstRules &);  // Do not implement
70  };
71}
72
73
74//===----------------------------------------------------------------------===//
75//                             TemplateRules Class
76//===----------------------------------------------------------------------===//
77//
78// TemplateRules - Implement a subclass of ConstRules that provides all
79// operations as noops.  All other rules classes inherit from this class so
80// that if functionality is needed in the future, it can simply be added here
81// and to ConstRules without changing anything else...
82//
83// This class also provides subclasses with typesafe implementations of methods
84// so that don't have to do type casting.
85//
86template<class ArgType, class SubClassName>
87class TemplateRules : public ConstRules {
88
89  //===--------------------------------------------------------------------===//
90  // Redirecting functions that cast to the appropriate types
91  //===--------------------------------------------------------------------===//
92
93  virtual Constant *add(const Constant *V1, const Constant *V2) const {
94    return SubClassName::Add((const ArgType *)V1, (const ArgType *)V2);
95  }
96  virtual Constant *sub(const Constant *V1, const Constant *V2) const {
97    return SubClassName::Sub((const ArgType *)V1, (const ArgType *)V2);
98  }
99  virtual Constant *mul(const Constant *V1, const Constant *V2) const {
100    return SubClassName::Mul((const ArgType *)V1, (const ArgType *)V2);
101  }
102  virtual Constant *div(const Constant *V1, const Constant *V2) const {
103    return SubClassName::Div((const ArgType *)V1, (const ArgType *)V2);
104  }
105  virtual Constant *rem(const Constant *V1, const Constant *V2) const {
106    return SubClassName::Rem((const ArgType *)V1, (const ArgType *)V2);
107  }
108  virtual Constant *op_and(const Constant *V1, const Constant *V2) const {
109    return SubClassName::And((const ArgType *)V1, (const ArgType *)V2);
110  }
111  virtual Constant *op_or(const Constant *V1, const Constant *V2) const {
112    return SubClassName::Or((const ArgType *)V1, (const ArgType *)V2);
113  }
114  virtual Constant *op_xor(const Constant *V1, const Constant *V2) const {
115    return SubClassName::Xor((const ArgType *)V1, (const ArgType *)V2);
116  }
117  virtual Constant *shl(const Constant *V1, const Constant *V2) const {
118    return SubClassName::Shl((const ArgType *)V1, (const ArgType *)V2);
119  }
120  virtual Constant *shr(const Constant *V1, const Constant *V2) const {
121    return SubClassName::Shr((const ArgType *)V1, (const ArgType *)V2);
122  }
123
124  virtual Constant *lessthan(const Constant *V1, const Constant *V2) const {
125    return SubClassName::LessThan((const ArgType *)V1, (const ArgType *)V2);
126  }
127  virtual Constant *equalto(const Constant *V1, const Constant *V2) const {
128    return SubClassName::EqualTo((const ArgType *)V1, (const ArgType *)V2);
129  }
130
131  // Casting operators.  ick
132  virtual Constant *castToBool(const Constant *V) const {
133    return SubClassName::CastToBool((const ArgType*)V);
134  }
135  virtual Constant *castToSByte(const Constant *V) const {
136    return SubClassName::CastToSByte((const ArgType*)V);
137  }
138  virtual Constant *castToUByte(const Constant *V) const {
139    return SubClassName::CastToUByte((const ArgType*)V);
140  }
141  virtual Constant *castToShort(const Constant *V) const {
142    return SubClassName::CastToShort((const ArgType*)V);
143  }
144  virtual Constant *castToUShort(const Constant *V) const {
145    return SubClassName::CastToUShort((const ArgType*)V);
146  }
147  virtual Constant *castToInt(const Constant *V) const {
148    return SubClassName::CastToInt((const ArgType*)V);
149  }
150  virtual Constant *castToUInt(const Constant *V) const {
151    return SubClassName::CastToUInt((const ArgType*)V);
152  }
153  virtual Constant *castToLong(const Constant *V) const {
154    return SubClassName::CastToLong((const ArgType*)V);
155  }
156  virtual Constant *castToULong(const Constant *V) const {
157    return SubClassName::CastToULong((const ArgType*)V);
158  }
159  virtual Constant *castToFloat(const Constant *V) const {
160    return SubClassName::CastToFloat((const ArgType*)V);
161  }
162  virtual Constant *castToDouble(const Constant *V) const {
163    return SubClassName::CastToDouble((const ArgType*)V);
164  }
165  virtual Constant *castToPointer(const Constant *V,
166                                  const PointerType *Ty) const {
167    return SubClassName::CastToPointer((const ArgType*)V, Ty);
168  }
169
170  //===--------------------------------------------------------------------===//
171  // Default "noop" implementations
172  //===--------------------------------------------------------------------===//
173
174  static Constant *Add(const ArgType *V1, const ArgType *V2) { return 0; }
175  static Constant *Sub(const ArgType *V1, const ArgType *V2) { return 0; }
176  static Constant *Mul(const ArgType *V1, const ArgType *V2) { return 0; }
177  static Constant *Div(const ArgType *V1, const ArgType *V2) { return 0; }
178  static Constant *Rem(const ArgType *V1, const ArgType *V2) { return 0; }
179  static Constant *And(const ArgType *V1, const ArgType *V2) { return 0; }
180  static Constant *Or (const ArgType *V1, const ArgType *V2) { return 0; }
181  static Constant *Xor(const ArgType *V1, const ArgType *V2) { return 0; }
182  static Constant *Shl(const ArgType *V1, const ArgType *V2) { return 0; }
183  static Constant *Shr(const ArgType *V1, const ArgType *V2) { return 0; }
184  static Constant *LessThan(const ArgType *V1, const ArgType *V2) {
185    return 0;
186  }
187  static Constant *EqualTo(const ArgType *V1, const ArgType *V2) {
188    return 0;
189  }
190
191  // Casting operators.  ick
192  static Constant *CastToBool  (const Constant *V) { return 0; }
193  static Constant *CastToSByte (const Constant *V) { return 0; }
194  static Constant *CastToUByte (const Constant *V) { return 0; }
195  static Constant *CastToShort (const Constant *V) { return 0; }
196  static Constant *CastToUShort(const Constant *V) { return 0; }
197  static Constant *CastToInt   (const Constant *V) { return 0; }
198  static Constant *CastToUInt  (const Constant *V) { return 0; }
199  static Constant *CastToLong  (const Constant *V) { return 0; }
200  static Constant *CastToULong (const Constant *V) { return 0; }
201  static Constant *CastToFloat (const Constant *V) { return 0; }
202  static Constant *CastToDouble(const Constant *V) { return 0; }
203  static Constant *CastToPointer(const Constant *,
204                                 const PointerType *) {return 0;}
205};
206
207
208
209//===----------------------------------------------------------------------===//
210//                             EmptyRules Class
211//===----------------------------------------------------------------------===//
212//
213// EmptyRules provides a concrete base class of ConstRules that does nothing
214//
215struct EmptyRules : public TemplateRules<Constant, EmptyRules> {
216  static Constant *EqualTo(const Constant *V1, const Constant *V2) {
217    if (V1 == V2) return ConstantBool::True;
218    return 0;
219  }
220};
221
222
223
224//===----------------------------------------------------------------------===//
225//                              BoolRules Class
226//===----------------------------------------------------------------------===//
227//
228// BoolRules provides a concrete base class of ConstRules for the 'bool' type.
229//
230struct BoolRules : public TemplateRules<ConstantBool, BoolRules> {
231
232  static Constant *LessThan(const ConstantBool *V1, const ConstantBool *V2){
233    return ConstantBool::get(V1->getValue() < V2->getValue());
234  }
235
236  static Constant *EqualTo(const Constant *V1, const Constant *V2) {
237    return ConstantBool::get(V1 == V2);
238  }
239
240  static Constant *And(const ConstantBool *V1, const ConstantBool *V2) {
241    return ConstantBool::get(V1->getValue() & V2->getValue());
242  }
243
244  static Constant *Or(const ConstantBool *V1, const ConstantBool *V2) {
245    return ConstantBool::get(V1->getValue() | V2->getValue());
246  }
247
248  static Constant *Xor(const ConstantBool *V1, const ConstantBool *V2) {
249    return ConstantBool::get(V1->getValue() ^ V2->getValue());
250  }
251
252  // Casting operators.  ick
253#define DEF_CAST(TYPE, CLASS, CTYPE) \
254  static Constant *CastTo##TYPE  (const ConstantBool *V) {    \
255    return CLASS::get(Type::TYPE##Ty, (CTYPE)(bool)V->getValue()); \
256  }
257
258  DEF_CAST(Bool  , ConstantBool, bool)
259  DEF_CAST(SByte , ConstantSInt, signed char)
260  DEF_CAST(UByte , ConstantUInt, unsigned char)
261  DEF_CAST(Short , ConstantSInt, signed short)
262  DEF_CAST(UShort, ConstantUInt, unsigned short)
263  DEF_CAST(Int   , ConstantSInt, signed int)
264  DEF_CAST(UInt  , ConstantUInt, unsigned int)
265  DEF_CAST(Long  , ConstantSInt, int64_t)
266  DEF_CAST(ULong , ConstantUInt, uint64_t)
267  DEF_CAST(Float , ConstantFP  , float)
268  DEF_CAST(Double, ConstantFP  , double)
269#undef DEF_CAST
270};
271
272
273//===----------------------------------------------------------------------===//
274//                            NullPointerRules Class
275//===----------------------------------------------------------------------===//
276//
277// NullPointerRules provides a concrete base class of ConstRules for null
278// pointers.
279//
280struct NullPointerRules : public TemplateRules<ConstantPointerNull,
281                                               NullPointerRules> {
282  static Constant *EqualTo(const Constant *V1, const Constant *V2) {
283    return ConstantBool::True;  // Null pointers are always equal
284  }
285  static Constant *CastToBool(const Constant *V) {
286    return ConstantBool::False;
287  }
288  static Constant *CastToSByte (const Constant *V) {
289    return ConstantSInt::get(Type::SByteTy, 0);
290  }
291  static Constant *CastToUByte (const Constant *V) {
292    return ConstantUInt::get(Type::UByteTy, 0);
293  }
294  static Constant *CastToShort (const Constant *V) {
295    return ConstantSInt::get(Type::ShortTy, 0);
296  }
297  static Constant *CastToUShort(const Constant *V) {
298    return ConstantUInt::get(Type::UShortTy, 0);
299  }
300  static Constant *CastToInt   (const Constant *V) {
301    return ConstantSInt::get(Type::IntTy, 0);
302  }
303  static Constant *CastToUInt  (const Constant *V) {
304    return ConstantUInt::get(Type::UIntTy, 0);
305  }
306  static Constant *CastToLong  (const Constant *V) {
307    return ConstantSInt::get(Type::LongTy, 0);
308  }
309  static Constant *CastToULong (const Constant *V) {
310    return ConstantUInt::get(Type::ULongTy, 0);
311  }
312  static Constant *CastToFloat (const Constant *V) {
313    return ConstantFP::get(Type::FloatTy, 0);
314  }
315  static Constant *CastToDouble(const Constant *V) {
316    return ConstantFP::get(Type::DoubleTy, 0);
317  }
318
319  static Constant *CastToPointer(const ConstantPointerNull *V,
320                                 const PointerType *PTy) {
321    return ConstantPointerNull::get(PTy);
322  }
323};
324
325
326//===----------------------------------------------------------------------===//
327//                             DirectRules Class
328//===----------------------------------------------------------------------===//
329//
330// DirectRules provides a concrete base classes of ConstRules for a variety of
331// different types.  This allows the C++ compiler to automatically generate our
332// constant handling operations in a typesafe and accurate manner.
333//
334template<class ConstantClass, class BuiltinType, Type **Ty, class SuperClass>
335struct DirectRules : public TemplateRules<ConstantClass, SuperClass> {
336  static Constant *Add(const ConstantClass *V1, const ConstantClass *V2) {
337    BuiltinType R = (BuiltinType)V1->getValue() + (BuiltinType)V2->getValue();
338    return ConstantClass::get(*Ty, R);
339  }
340
341  static Constant *Sub(const ConstantClass *V1, const ConstantClass *V2) {
342    BuiltinType R = (BuiltinType)V1->getValue() - (BuiltinType)V2->getValue();
343    return ConstantClass::get(*Ty, R);
344  }
345
346  static Constant *Mul(const ConstantClass *V1, const ConstantClass *V2) {
347    BuiltinType R = (BuiltinType)V1->getValue() * (BuiltinType)V2->getValue();
348    return ConstantClass::get(*Ty, R);
349  }
350
351  static Constant *Div(const ConstantClass *V1, const ConstantClass *V2) {
352    if (V2->isNullValue()) return 0;
353    BuiltinType R = (BuiltinType)V1->getValue() / (BuiltinType)V2->getValue();
354    return ConstantClass::get(*Ty, R);
355  }
356
357  static Constant *LessThan(const ConstantClass *V1, const ConstantClass *V2) {
358    bool R = (BuiltinType)V1->getValue() < (BuiltinType)V2->getValue();
359    return ConstantBool::get(R);
360  }
361
362  static Constant *EqualTo(const ConstantClass *V1, const ConstantClass *V2) {
363    bool R = (BuiltinType)V1->getValue() == (BuiltinType)V2->getValue();
364    return ConstantBool::get(R);
365  }
366
367  static Constant *CastToPointer(const ConstantClass *V,
368                                 const PointerType *PTy) {
369    if (V->isNullValue())    // Is it a FP or Integral null value?
370      return ConstantPointerNull::get(PTy);
371    return 0;  // Can't const prop other types of pointers
372  }
373
374  // Casting operators.  ick
375#define DEF_CAST(TYPE, CLASS, CTYPE) \
376  static Constant *CastTo##TYPE  (const ConstantClass *V) {    \
377    return CLASS::get(Type::TYPE##Ty, (CTYPE)(BuiltinType)V->getValue()); \
378  }
379
380  DEF_CAST(Bool  , ConstantBool, bool)
381  DEF_CAST(SByte , ConstantSInt, signed char)
382  DEF_CAST(UByte , ConstantUInt, unsigned char)
383  DEF_CAST(Short , ConstantSInt, signed short)
384  DEF_CAST(UShort, ConstantUInt, unsigned short)
385  DEF_CAST(Int   , ConstantSInt, signed int)
386  DEF_CAST(UInt  , ConstantUInt, unsigned int)
387  DEF_CAST(Long  , ConstantSInt, int64_t)
388  DEF_CAST(ULong , ConstantUInt, uint64_t)
389  DEF_CAST(Float , ConstantFP  , float)
390  DEF_CAST(Double, ConstantFP  , double)
391#undef DEF_CAST
392};
393
394
395//===----------------------------------------------------------------------===//
396//                           DirectIntRules Class
397//===----------------------------------------------------------------------===//
398//
399// DirectIntRules provides implementations of functions that are valid on
400// integer types, but not all types in general.
401//
402template <class ConstantClass, class BuiltinType, Type **Ty>
403struct DirectIntRules
404  : public DirectRules<ConstantClass, BuiltinType, Ty,
405                       DirectIntRules<ConstantClass, BuiltinType, Ty> > {
406
407  static Constant *Div(const ConstantClass *V1, const ConstantClass *V2) {
408    if (V2->isNullValue()) return 0;
409    if (V2->isAllOnesValue() &&              // MIN_INT / -1
410        (BuiltinType)V1->getValue() == -(BuiltinType)V1->getValue())
411      return 0;
412    BuiltinType R = (BuiltinType)V1->getValue() / (BuiltinType)V2->getValue();
413    return ConstantClass::get(*Ty, R);
414  }
415
416  static Constant *Rem(const ConstantClass *V1,
417                       const ConstantClass *V2) {
418    if (V2->isNullValue()) return 0;         // X / 0
419    if (V2->isAllOnesValue() &&              // MIN_INT / -1
420        (BuiltinType)V1->getValue() == -(BuiltinType)V1->getValue())
421      return 0;
422    BuiltinType R = (BuiltinType)V1->getValue() % (BuiltinType)V2->getValue();
423    return ConstantClass::get(*Ty, R);
424  }
425
426  static Constant *And(const ConstantClass *V1, const ConstantClass *V2) {
427    BuiltinType R = (BuiltinType)V1->getValue() & (BuiltinType)V2->getValue();
428    return ConstantClass::get(*Ty, R);
429  }
430  static Constant *Or(const ConstantClass *V1, const ConstantClass *V2) {
431    BuiltinType R = (BuiltinType)V1->getValue() | (BuiltinType)V2->getValue();
432    return ConstantClass::get(*Ty, R);
433  }
434  static Constant *Xor(const ConstantClass *V1, const ConstantClass *V2) {
435    BuiltinType R = (BuiltinType)V1->getValue() ^ (BuiltinType)V2->getValue();
436    return ConstantClass::get(*Ty, R);
437  }
438
439  static Constant *Shl(const ConstantClass *V1, const ConstantClass *V2) {
440    BuiltinType R = (BuiltinType)V1->getValue() << (BuiltinType)V2->getValue();
441    return ConstantClass::get(*Ty, R);
442  }
443
444  static Constant *Shr(const ConstantClass *V1, const ConstantClass *V2) {
445    BuiltinType R = (BuiltinType)V1->getValue() >> (BuiltinType)V2->getValue();
446    return ConstantClass::get(*Ty, R);
447  }
448};
449
450
451//===----------------------------------------------------------------------===//
452//                           DirectFPRules Class
453//===----------------------------------------------------------------------===//
454//
455/// DirectFPRules provides implementations of functions that are valid on
456/// floating point types, but not all types in general.
457///
458template <class ConstantClass, class BuiltinType, Type **Ty>
459struct DirectFPRules
460  : public DirectRules<ConstantClass, BuiltinType, Ty,
461                       DirectFPRules<ConstantClass, BuiltinType, Ty> > {
462  static Constant *Rem(const ConstantClass *V1, const ConstantClass *V2) {
463    if (V2->isNullValue()) return 0;
464    BuiltinType Result = std::fmod((BuiltinType)V1->getValue(),
465                                   (BuiltinType)V2->getValue());
466    return ConstantClass::get(*Ty, Result);
467  }
468};
469
470
471/// ConstRules::get - This method returns the constant rules implementation that
472/// implements the semantics of the two specified constants.
473ConstRules &ConstRules::get(const Constant *V1, const Constant *V2) {
474  static EmptyRules       EmptyR;
475  static BoolRules        BoolR;
476  static NullPointerRules NullPointerR;
477  static DirectIntRules<ConstantSInt,   signed char , &Type::SByteTy>  SByteR;
478  static DirectIntRules<ConstantUInt, unsigned char , &Type::UByteTy>  UByteR;
479  static DirectIntRules<ConstantSInt,   signed short, &Type::ShortTy>  ShortR;
480  static DirectIntRules<ConstantUInt, unsigned short, &Type::UShortTy> UShortR;
481  static DirectIntRules<ConstantSInt,   signed int  , &Type::IntTy>    IntR;
482  static DirectIntRules<ConstantUInt, unsigned int  , &Type::UIntTy>   UIntR;
483  static DirectIntRules<ConstantSInt,  int64_t      , &Type::LongTy>   LongR;
484  static DirectIntRules<ConstantUInt, uint64_t      , &Type::ULongTy>  ULongR;
485  static DirectFPRules <ConstantFP  , float         , &Type::FloatTy>  FloatR;
486  static DirectFPRules <ConstantFP  , double        , &Type::DoubleTy> DoubleR;
487
488  if (isa<ConstantExpr>(V1) || isa<ConstantExpr>(V2) ||
489      isa<ConstantPointerRef>(V1) || isa<ConstantPointerRef>(V2))
490    return EmptyR;
491
492  switch (V1->getType()->getPrimitiveID()) {
493  default: assert(0 && "Unknown value type for constant folding!");
494  case Type::BoolTyID:    return BoolR;
495  case Type::PointerTyID: return NullPointerR;
496  case Type::SByteTyID:   return SByteR;
497  case Type::UByteTyID:   return UByteR;
498  case Type::ShortTyID:   return ShortR;
499  case Type::UShortTyID:  return UShortR;
500  case Type::IntTyID:     return IntR;
501  case Type::UIntTyID:    return UIntR;
502  case Type::LongTyID:    return LongR;
503  case Type::ULongTyID:   return ULongR;
504  case Type::FloatTyID:   return FloatR;
505  case Type::DoubleTyID:  return DoubleR;
506  }
507}
508
509
510//===----------------------------------------------------------------------===//
511//                ConstantFold*Instruction Implementations
512//===----------------------------------------------------------------------===//
513//
514// These methods contain the special case hackery required to symbolically
515// evaluate some constant expression cases, and use the ConstantRules class to
516// evaluate normal constants.
517//
518static unsigned getSize(const Type *Ty) {
519  unsigned S = Ty->getPrimitiveSize();
520  return S ? S : 8;  // Treat pointers at 8 bytes
521}
522
523Constant *llvm::ConstantFoldCastInstruction(const Constant *V,
524                                            const Type *DestTy) {
525  if (V->getType() == DestTy) return (Constant*)V;
526
527  // Cast of a global address to boolean is always true.
528  if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V))
529    if (DestTy == Type::BoolTy)
530      // FIXME: When we support 'external weak' references, we have to prevent
531      // this transformation from happening.  In the meantime we avoid folding
532      // any cast of an external symbol.
533      if (!CPR->getValue()->isExternal())
534        return ConstantBool::True;
535
536  if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
537    if (CE->getOpcode() == Instruction::Cast) {
538      Constant *Op = const_cast<Constant*>(CE->getOperand(0));
539      // Try to not produce a cast of a cast, which is almost always redundant.
540      if (!Op->getType()->isFloatingPoint() &&
541          !CE->getType()->isFloatingPoint() &&
542          !DestTy->getType()->isFloatingPoint()) {
543        unsigned S1 = getSize(Op->getType()), S2 = getSize(CE->getType());
544        unsigned S3 = getSize(DestTy);
545        if (Op->getType() == DestTy && S3 >= S2)
546          return Op;
547        if (S1 >= S2 && S2 >= S3)
548          return ConstantExpr::getCast(Op, DestTy);
549        if (S1 <= S2 && S2 >= S3 && S1 <= S3)
550          return ConstantExpr::getCast(Op, DestTy);
551      }
552    } else if (CE->getOpcode() == Instruction::GetElementPtr) {
553      // If all of the indexes in the GEP are null values, there is no pointer
554      // adjustment going on.  We might as well cast the source pointer.
555      bool isAllNull = true;
556      for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
557        if (!CE->getOperand(i)->isNullValue()) {
558          isAllNull = false;
559          break;
560        }
561      if (isAllNull)
562        return ConstantExpr::getCast(CE->getOperand(0), DestTy);
563    }
564
565  ConstRules &Rules = ConstRules::get(V, V);
566
567  switch (DestTy->getPrimitiveID()) {
568  case Type::BoolTyID:    return Rules.castToBool(V);
569  case Type::UByteTyID:   return Rules.castToUByte(V);
570  case Type::SByteTyID:   return Rules.castToSByte(V);
571  case Type::UShortTyID:  return Rules.castToUShort(V);
572  case Type::ShortTyID:   return Rules.castToShort(V);
573  case Type::UIntTyID:    return Rules.castToUInt(V);
574  case Type::IntTyID:     return Rules.castToInt(V);
575  case Type::ULongTyID:   return Rules.castToULong(V);
576  case Type::LongTyID:    return Rules.castToLong(V);
577  case Type::FloatTyID:   return Rules.castToFloat(V);
578  case Type::DoubleTyID:  return Rules.castToDouble(V);
579  case Type::PointerTyID:
580    return Rules.castToPointer(V, cast<PointerType>(DestTy));
581  default: return 0;
582  }
583}
584
585Constant *llvm::ConstantFoldSelectInstruction(const Constant *Cond,
586                                              const Constant *V1,
587                                              const Constant *V2) {
588  if (Cond == ConstantBool::True)
589    return const_cast<Constant*>(V1);
590  else if (Cond == ConstantBool::False)
591    return const_cast<Constant*>(V2);
592  return 0;
593}
594
595
596/// IdxCompare - Compare the two constants as though they were getelementptr
597/// indices.  This allows coersion of the types to be the same thing.
598///
599/// If the two constants are the "same" (after coersion), return 0.  If the
600/// first is less than the second, return -1, if the second is less than the
601/// first, return 1.  If the constants are not integral, return -2.
602///
603static int IdxCompare(Constant *C1, Constant *C2) {
604  if (C1 == C2) return 0;
605
606  // Ok, we found a different index.  Are either of the operands
607  // ConstantExprs?  If so, we can't do anything with them.
608  if (!isa<ConstantInt>(C1) || !isa<ConstantInt>(C2))
609    return -2; // don't know!
610
611  // Ok, we have two differing integer indices.  Sign extend them to be the same
612  // type.  Long is always big enough, so we use it.
613  C1 = ConstantExpr::getSignExtend(C1, Type::LongTy);
614  C2 = ConstantExpr::getSignExtend(C2, Type::LongTy);
615  if (C1 == C2) return 0;  // Are they just differing types?
616
617  // If they are really different, now that they are the same type, then we
618  // found a difference!
619  if (cast<ConstantSInt>(C1)->getValue() < cast<ConstantSInt>(C2)->getValue())
620    return -1;
621  else
622    return 1;
623}
624
625/// evaluateRelation - This function determines if there is anything we can
626/// decide about the two constants provided.  This doesn't need to handle simple
627/// things like integer comparisons, but should instead handle ConstantExpr's
628/// and ConstantPointerRef's.  If we can determine that the two constants have a
629/// particular relation to each other, we should return the corresponding SetCC
630/// code, otherwise return Instruction::BinaryOpsEnd.
631///
632/// To simplify this code we canonicalize the relation so that the first
633/// operand is always the most "complex" of the two.  We consider simple
634/// constants (like ConstantInt) to be the simplest, followed by
635/// ConstantPointerRef's, followed by ConstantExpr's (the most complex).
636///
637static Instruction::BinaryOps evaluateRelation(const Constant *V1,
638                                               const Constant *V2) {
639  assert(V1->getType() == V2->getType() &&
640         "Cannot compare different types of values!");
641  if (V1 == V2) return Instruction::SetEQ;
642
643  if (!isa<ConstantExpr>(V1) && !isa<ConstantPointerRef>(V1)) {
644    // If the first operand is simple, swap operands.
645    assert((isa<ConstantPointerRef>(V2) || isa<ConstantExpr>(V2)) &&
646           "Simple cases should have been handled by caller!");
647    Instruction::BinaryOps SwappedRelation = evaluateRelation(V2, V1);
648    if (SwappedRelation != Instruction::BinaryOpsEnd)
649      return SetCondInst::getSwappedCondition(SwappedRelation);
650
651  } else if (const ConstantPointerRef *CPR1 = dyn_cast<ConstantPointerRef>(V1)){
652    if (isa<ConstantExpr>(V2)) {  // Swap as necessary.
653    Instruction::BinaryOps SwappedRelation = evaluateRelation(V2, V1);
654    if (SwappedRelation != Instruction::BinaryOpsEnd)
655      return SetCondInst::getSwappedCondition(SwappedRelation);
656    else
657      return Instruction::BinaryOpsEnd;
658    }
659
660    // Now we know that the RHS is a ConstantPointerRef or simple constant,
661    // which (since the types must match) means that it's a ConstantPointerNull.
662    if (const ConstantPointerRef *CPR2 = dyn_cast<ConstantPointerRef>(V2)) {
663      assert(CPR1->getValue() != CPR2->getValue() &&
664             "CPRs for the same value exist at different addresses??");
665      // FIXME: If both globals are external weak, they might both be null!
666      return Instruction::SetNE;
667    } else {
668      assert(isa<ConstantPointerNull>(V2) && "Canonicalization guarantee!");
669      // Global can never be null.  FIXME: if we implement external weak
670      // linkage, this is not necessarily true!
671      return Instruction::SetNE;
672    }
673
674  } else {
675    // Ok, the LHS is known to be a constantexpr.  The RHS can be any of a
676    // constantexpr, a CPR, or a simple constant.
677    const ConstantExpr *CE1 = cast<ConstantExpr>(V1);
678    Constant *CE1Op0 = CE1->getOperand(0);
679
680    switch (CE1->getOpcode()) {
681    case Instruction::Cast:
682      // If the cast is not actually changing bits, and the second operand is a
683      // null pointer, do the comparison with the pre-casted value.
684      if (V2->isNullValue() &&
685          CE1->getType()->isLosslesslyConvertibleTo(CE1Op0->getType()))
686        return evaluateRelation(CE1Op0,
687                                Constant::getNullValue(CE1Op0->getType()));
688      break;
689
690    case Instruction::GetElementPtr:
691      // Ok, since this is a getelementptr, we know that the constant has a
692      // pointer type.  Check the various cases.
693      if (isa<ConstantPointerNull>(V2)) {
694        // If we are comparing a GEP to a null pointer, check to see if the base
695        // of the GEP equals the null pointer.
696        if (isa<ConstantPointerRef>(CE1Op0)) {
697          // FIXME: this is not true when we have external weak references!
698          // No offset can go from a global to a null pointer.
699          return Instruction::SetGT;
700        } else if (isa<ConstantPointerNull>(CE1Op0)) {
701          // If we are indexing from a null pointer, check to see if we have any
702          // non-zero indices.
703          for (unsigned i = 1, e = CE1->getNumOperands(); i != e; ++i)
704            if (!CE1->getOperand(i)->isNullValue())
705              // Offsetting from null, must not be equal.
706              return Instruction::SetGT;
707          // Only zero indexes from null, must still be zero.
708          return Instruction::SetEQ;
709        }
710        // Otherwise, we can't really say if the first operand is null or not.
711      } else if (const ConstantPointerRef *CPR2 =
712                                             dyn_cast<ConstantPointerRef>(V2)) {
713        if (isa<ConstantPointerNull>(CE1Op0)) {
714          // FIXME: This is not true with external weak references.
715          return Instruction::SetLT;
716        } else if (const ConstantPointerRef *CPR1 =
717                   dyn_cast<ConstantPointerRef>(CE1Op0)) {
718          if (CPR1 == CPR2) {
719            // If this is a getelementptr of the same global, then it must be
720            // different.  Because the types must match, the getelementptr could
721            // only have at most one index, and because we fold getelementptr's
722            // with a single zero index, it must be nonzero.
723            assert(CE1->getNumOperands() == 2 &&
724                   !CE1->getOperand(1)->isNullValue() &&
725                   "Suprising getelementptr!");
726            return Instruction::SetGT;
727          } else {
728            // If they are different globals, we don't know what the value is,
729            // but they can't be equal.
730            return Instruction::SetNE;
731          }
732        }
733      } else {
734        const ConstantExpr *CE2 = cast<ConstantExpr>(V2);
735        const Constant *CE2Op0 = CE2->getOperand(0);
736
737        // There are MANY other foldings that we could perform here.  They will
738        // probably be added on demand, as they seem needed.
739        switch (CE2->getOpcode()) {
740        default: break;
741        case Instruction::GetElementPtr:
742          // By far the most common case to handle is when the base pointers are
743          // obviously to the same or different globals.
744          if (isa<ConstantPointerRef>(CE1Op0) &&
745              isa<ConstantPointerRef>(CE2Op0)) {
746            if (CE1Op0 != CE2Op0) // Don't know relative ordering, but not equal
747              return Instruction::SetNE;
748            // Ok, we know that both getelementptr instructions are based on the
749            // same global.  From this, we can precisely determine the relative
750            // ordering of the resultant pointers.
751            unsigned i = 1;
752
753            // Compare all of the operands the GEP's have in common.
754            for (;i != CE1->getNumOperands() && i != CE2->getNumOperands(); ++i)
755              switch (IdxCompare(CE1->getOperand(i), CE2->getOperand(i))) {
756              case -1: return Instruction::SetLT;
757              case 1:  return Instruction::SetGT;
758              case -2: return Instruction::BinaryOpsEnd;
759              }
760
761            // Ok, we ran out of things they have in common.  If any leftovers
762            // are non-zero then we have a difference, otherwise we are equal.
763            for (; i < CE1->getNumOperands(); ++i)
764              if (!CE1->getOperand(i)->isNullValue())
765                return Instruction::SetGT;
766            for (; i < CE2->getNumOperands(); ++i)
767              if (!CE2->getOperand(i)->isNullValue())
768                return Instruction::SetLT;
769            return Instruction::SetEQ;
770          }
771        }
772      }
773
774    default:
775      break;
776    }
777  }
778
779  return Instruction::BinaryOpsEnd;
780}
781
782Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
783                                              const Constant *V1,
784                                              const Constant *V2) {
785  Constant *C = 0;
786  switch (Opcode) {
787  default:                   break;
788  case Instruction::Add:     C = ConstRules::get(V1, V2).add(V1, V2); break;
789  case Instruction::Sub:     C = ConstRules::get(V1, V2).sub(V1, V2); break;
790  case Instruction::Mul:     C = ConstRules::get(V1, V2).mul(V1, V2); break;
791  case Instruction::Div:     C = ConstRules::get(V1, V2).div(V1, V2); break;
792  case Instruction::Rem:     C = ConstRules::get(V1, V2).rem(V1, V2); break;
793  case Instruction::And:     C = ConstRules::get(V1, V2).op_and(V1, V2); break;
794  case Instruction::Or:      C = ConstRules::get(V1, V2).op_or (V1, V2); break;
795  case Instruction::Xor:     C = ConstRules::get(V1, V2).op_xor(V1, V2); break;
796  case Instruction::Shl:     C = ConstRules::get(V1, V2).shl(V1, V2); break;
797  case Instruction::Shr:     C = ConstRules::get(V1, V2).shr(V1, V2); break;
798  case Instruction::SetEQ:   C = ConstRules::get(V1, V2).equalto(V1, V2); break;
799  case Instruction::SetLT:   C = ConstRules::get(V1, V2).lessthan(V1, V2);break;
800  case Instruction::SetGT:   C = ConstRules::get(V1, V2).lessthan(V2, V1);break;
801  case Instruction::SetNE:   // V1 != V2  ===  !(V1 == V2)
802    C = ConstRules::get(V1, V2).equalto(V1, V2);
803    if (C) return ConstantExpr::get(Instruction::Xor, C, ConstantBool::True);
804    break;
805  case Instruction::SetLE:   // V1 <= V2  ===  !(V2 < V1)
806    C = ConstRules::get(V1, V2).lessthan(V2, V1);
807    if (C) return ConstantExpr::get(Instruction::Xor, C, ConstantBool::True);
808    break;
809  case Instruction::SetGE:   // V1 >= V2  ===  !(V1 < V2)
810    C = ConstRules::get(V1, V2).lessthan(V1, V2);
811    if (C) return ConstantExpr::get(Instruction::Xor, C, ConstantBool::True);
812    break;
813  }
814
815  // If we successfully folded the expression, return it now.
816  if (C) return C;
817
818  if (SetCondInst::isRelational(Opcode))
819    switch (evaluateRelation(V1, V2)) {
820    default: assert(0 && "Unknown relational!");
821    case Instruction::BinaryOpsEnd:
822      break;  // Couldn't determine anything about these constants.
823    case Instruction::SetEQ:   // We know the constants are equal!
824      // If we know the constants are equal, we can decide the result of this
825      // computation precisely.
826      return ConstantBool::get(Opcode == Instruction::SetEQ ||
827                               Opcode == Instruction::SetLE ||
828                               Opcode == Instruction::SetGE);
829    case Instruction::SetLT:
830      // If we know that V1 < V2, we can decide the result of this computation
831      // precisely.
832      return ConstantBool::get(Opcode == Instruction::SetLT ||
833                               Opcode == Instruction::SetNE ||
834                               Opcode == Instruction::SetLE);
835    case Instruction::SetGT:
836      // If we know that V1 > V2, we can decide the result of this computation
837      // precisely.
838      return ConstantBool::get(Opcode == Instruction::SetGT ||
839                               Opcode == Instruction::SetNE ||
840                               Opcode == Instruction::SetGE);
841    case Instruction::SetLE:
842      // If we know that V1 <= V2, we can only partially decide this relation.
843      if (Opcode == Instruction::SetGT) return ConstantBool::False;
844      if (Opcode == Instruction::SetLT) return ConstantBool::True;
845      break;
846
847    case Instruction::SetGE:
848      // If we know that V1 >= V2, we can only partially decide this relation.
849      if (Opcode == Instruction::SetLT) return ConstantBool::False;
850      if (Opcode == Instruction::SetGT) return ConstantBool::True;
851      break;
852
853    case Instruction::SetNE:
854      // If we know that V1 != V2, we can only partially decide this relation.
855      if (Opcode == Instruction::SetEQ) return ConstantBool::False;
856      if (Opcode == Instruction::SetNE) return ConstantBool::True;
857      break;
858    }
859
860  if (const ConstantExpr *CE1 = dyn_cast<ConstantExpr>(V1)) {
861    if (const ConstantExpr *CE2 = dyn_cast<ConstantExpr>(V2)) {
862      // There are many possible foldings we could do here.  We should probably
863      // at least fold add of a pointer with an integer into the appropriate
864      // getelementptr.  This will improve alias analysis a bit.
865
866
867
868
869    } else {
870      // Just implement a couple of simple identities.
871      switch (Opcode) {
872      case Instruction::Add:
873        if (V2->isNullValue()) return const_cast<Constant*>(V1);  // X + 0 == X
874        break;
875      case Instruction::Sub:
876        if (V2->isNullValue()) return const_cast<Constant*>(V1);  // X - 0 == X
877        break;
878      case Instruction::Mul:
879        if (V2->isNullValue()) return const_cast<Constant*>(V2);  // X * 0 == 0
880        if (const ConstantInt *CI = dyn_cast<ConstantInt>(V2))
881          if (CI->getRawValue() == 1)
882            return const_cast<Constant*>(V1);                     // X * 1 == X
883        break;
884      case Instruction::Div:
885        if (const ConstantInt *CI = dyn_cast<ConstantInt>(V2))
886          if (CI->getRawValue() == 1)
887            return const_cast<Constant*>(V1);                     // X / 1 == X
888        break;
889      case Instruction::Rem:
890        if (const ConstantInt *CI = dyn_cast<ConstantInt>(V2))
891          if (CI->getRawValue() == 1)
892            return Constant::getNullValue(CI->getType()); // X % 1 == 0
893        break;
894      case Instruction::And:
895        if (cast<ConstantIntegral>(V2)->isAllOnesValue())
896          return const_cast<Constant*>(V1);                       // X & -1 == X
897        if (V2->isNullValue()) return const_cast<Constant*>(V2);  // X & 0 == 0
898        if (CE1->getOpcode() == Instruction::Cast &&
899            isa<ConstantPointerRef>(CE1->getOperand(0))) {
900          ConstantPointerRef *CPR =cast<ConstantPointerRef>(CE1->getOperand(0));
901
902          // Functions are at least 4-byte aligned.  If and'ing the address of a
903          // function with a constant < 4, fold it to zero.
904          if (const ConstantInt *CI = dyn_cast<ConstantInt>(V2))
905            if (CI->getRawValue() < 4 && isa<Function>(CPR->getValue()))
906              return Constant::getNullValue(CI->getType());
907        }
908        break;
909      case Instruction::Or:
910        if (V2->isNullValue()) return const_cast<Constant*>(V1);  // X | 0 == X
911        if (cast<ConstantIntegral>(V2)->isAllOnesValue())
912          return const_cast<Constant*>(V2);  // X | -1 == -1
913        break;
914      case Instruction::Xor:
915        if (V2->isNullValue()) return const_cast<Constant*>(V1);  // X ^ 0 == X
916        break;
917      }
918    }
919
920  } else if (const ConstantExpr *CE2 = dyn_cast<ConstantExpr>(V2)) {
921    // If V2 is a constant expr and V1 isn't, flop them around and fold the
922    // other way if possible.
923    switch (Opcode) {
924    case Instruction::Add:
925    case Instruction::Mul:
926    case Instruction::And:
927    case Instruction::Or:
928    case Instruction::Xor:
929    case Instruction::SetEQ:
930    case Instruction::SetNE:
931      // No change of opcode required.
932      return ConstantFoldBinaryInstruction(Opcode, V2, V1);
933
934    case Instruction::SetLT:
935    case Instruction::SetGT:
936    case Instruction::SetLE:
937    case Instruction::SetGE:
938      // Change the opcode as necessary to swap the operands.
939      Opcode = SetCondInst::getSwappedCondition((Instruction::BinaryOps)Opcode);
940      return ConstantFoldBinaryInstruction(Opcode, V2, V1);
941
942    case Instruction::Shl:
943    case Instruction::Shr:
944    case Instruction::Sub:
945    case Instruction::Div:
946    case Instruction::Rem:
947    default:  // These instructions cannot be flopped around.
948      break;
949    }
950  }
951  return 0;
952}
953
954Constant *llvm::ConstantFoldGetElementPtr(const Constant *C,
955                                        const std::vector<Constant*> &IdxList) {
956  if (IdxList.size() == 0 ||
957      (IdxList.size() == 1 && IdxList[0]->isNullValue()))
958    return const_cast<Constant*>(C);
959
960  if (C->isNullValue()) {
961    bool isNull = true;
962    for (unsigned i = 0, e = IdxList.size(); i != e; ++i)
963      if (!IdxList[i]->isNullValue()) {
964        isNull = false;
965        break;
966      }
967    if (isNull) {
968      std::vector<Value*> VIdxList(IdxList.begin(), IdxList.end());
969      const Type *Ty = GetElementPtrInst::getIndexedType(C->getType(), VIdxList,
970                                                         true);
971      assert(Ty != 0 && "Invalid indices for GEP!");
972      return ConstantPointerNull::get(PointerType::get(Ty));
973    }
974  }
975
976  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(const_cast<Constant*>(C))) {
977    // Combine Indices - If the source pointer to this getelementptr instruction
978    // is a getelementptr instruction, combine the indices of the two
979    // getelementptr instructions into a single instruction.
980    //
981    if (CE->getOpcode() == Instruction::GetElementPtr) {
982      const Type *LastTy = 0;
983      for (gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
984           I != E; ++I)
985        LastTy = *I;
986
987      if ((LastTy && isa<ArrayType>(LastTy)) || IdxList[0]->isNullValue()) {
988        std::vector<Constant*> NewIndices;
989        NewIndices.reserve(IdxList.size() + CE->getNumOperands());
990        for (unsigned i = 1, e = CE->getNumOperands()-1; i != e; ++i)
991          NewIndices.push_back(cast<Constant>(CE->getOperand(i)));
992
993        // Add the last index of the source with the first index of the new GEP.
994        // Make sure to handle the case when they are actually different types.
995        Constant *Combined = CE->getOperand(CE->getNumOperands()-1);
996        if (!IdxList[0]->isNullValue())   // Otherwise it must be an array
997          Combined =
998            ConstantExpr::get(Instruction::Add,
999                              ConstantExpr::getCast(IdxList[0], Type::LongTy),
1000                              ConstantExpr::getCast(Combined, Type::LongTy));
1001
1002        NewIndices.push_back(Combined);
1003        NewIndices.insert(NewIndices.end(), IdxList.begin()+1, IdxList.end());
1004        return ConstantExpr::getGetElementPtr(CE->getOperand(0), NewIndices);
1005      }
1006    }
1007
1008    // Implement folding of:
1009    //    int* getelementptr ([2 x int]* cast ([3 x int]* %X to [2 x int]*),
1010    //                        long 0, long 0)
1011    // To: int* getelementptr ([3 x int]* %X, long 0, long 0)
1012    //
1013    if (CE->getOpcode() == Instruction::Cast && IdxList.size() > 1 &&
1014        IdxList[0]->isNullValue())
1015      if (const PointerType *SPT =
1016          dyn_cast<PointerType>(CE->getOperand(0)->getType()))
1017        if (const ArrayType *SAT = dyn_cast<ArrayType>(SPT->getElementType()))
1018          if (const ArrayType *CAT =
1019              dyn_cast<ArrayType>(cast<PointerType>(C->getType())->getElementType()))
1020            if (CAT->getElementType() == SAT->getElementType())
1021              return ConstantExpr::getGetElementPtr(
1022                      (Constant*)CE->getOperand(0), IdxList);
1023  }
1024  return 0;
1025}
1026
1027