1 //===- Expressions.cpp - Expression Analysis Utilities --------------------===//
3 // The LLVM Compiler Infrastructure
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.
8 //===----------------------------------------------------------------------===//
10 // This file defines a package of expression analysis utilties:
12 // ClassifyExpression: Analyze an expression to determine the complexity of the
13 // expression, and which other variables it depends on.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Analysis/Expressions.h"
18 #include "llvm/ConstantHandling.h"
19 #include "llvm/Function.h"
21 ExprType::ExprType(Value *Val) {
23 if (ConstantInt *CPI = dyn_cast<ConstantInt>(Val)) {
31 Var = Val; Offset = 0;
32 ExprTy = Var ? Linear : Constant;
36 ExprType::ExprType(const ConstantInt *scale, Value *var,
37 const ConstantInt *offset) {
38 Scale = var ? scale : 0; Var = var; Offset = offset;
39 ExprTy = Scale ? ScaledLinear : (Var ? Linear : Constant);
40 if (Scale && Scale->isNullValue()) { // Simplify 0*Var + const
47 const Type *ExprType::getExprType(const Type *Default) const {
48 if (Offset) return Offset->getType();
49 if (Scale) return Scale->getType();
50 return Var ? Var->getType() : Default;
56 const ConstantInt * const Val;
57 const Type * const Ty;
59 inline DefVal(const ConstantInt *val, const Type *ty) : Val(val), Ty(ty) {}
61 inline const Type *getType() const { return Ty; }
62 inline const ConstantInt *getVal() const { return Val; }
63 inline operator const ConstantInt * () const { return Val; }
64 inline const ConstantInt *operator->() const { return Val; }
67 struct DefZero : public DefVal {
68 inline DefZero(const ConstantInt *val, const Type *ty) : DefVal(val, ty) {}
69 inline DefZero(const ConstantInt *val) : DefVal(val, val->getType()) {}
72 struct DefOne : public DefVal {
73 inline DefOne(const ConstantInt *val, const Type *ty) : DefVal(val, ty) {}
77 // getUnsignedConstant - Return a constant value of the specified type. If the
78 // constant value is not valid for the specified type, return null. This cannot
79 // happen for values in the range of 0 to 127.
81 static ConstantInt *getUnsignedConstant(uint64_t V, const Type *Ty) {
82 if (isa<PointerType>(Ty)) Ty = Type::ULongTy;
84 // If this value is not a valid unsigned value for this type, return null!
85 if (V > 127 && ((int64_t)V < 0 ||
86 !ConstantSInt::isValueValidForType(Ty, (int64_t)V)))
88 return ConstantSInt::get(Ty, V);
90 // If this value is not a valid unsigned value for this type, return null!
91 if (V > 255 && !ConstantUInt::isValueValidForType(Ty, V))
93 return ConstantUInt::get(Ty, V);
97 // Add - Helper function to make later code simpler. Basically it just adds
98 // the two constants together, inserts the result into the constant pool, and
99 // returns it. Of course life is not simple, and this is no exception. Factors
100 // that complicate matters:
101 // 1. Either argument may be null. If this is the case, the null argument is
102 // treated as either 0 (if DefOne = false) or 1 (if DefOne = true)
103 // 2. Types get in the way. We want to do arithmetic operations without
104 // regard for the underlying types. It is assumed that the constants are
105 // integral constants. The new value takes the type of the left argument.
106 // 3. If DefOne is true, a null return value indicates a value of 1, if DefOne
107 // is false, a null return value indicates a value of 0.
109 static const ConstantInt *Add(const ConstantInt *Arg1,
110 const ConstantInt *Arg2, bool DefOne) {
111 assert(Arg1 && Arg2 && "No null arguments should exist now!");
112 assert(Arg1->getType() == Arg2->getType() && "Types must be compatible!");
114 // Actually perform the computation now!
115 Constant *Result = *Arg1 + *Arg2;
116 assert(Result && Result->getType() == Arg1->getType() &&
117 "Couldn't perform addition!");
118 ConstantInt *ResultI = cast<ConstantInt>(Result);
120 // Check to see if the result is one of the special cases that we want to
122 if (ResultI->equalsInt(DefOne ? 1 : 0))
123 return 0; // Yes it is, simply return null.
128 inline const ConstantInt *operator+(const DefZero &L, const DefZero &R) {
129 if (L == 0) return R;
130 if (R == 0) return L;
131 return Add(L, R, false);
134 inline const ConstantInt *operator+(const DefOne &L, const DefOne &R) {
137 return getUnsignedConstant(2, L.getType());
139 return Add(getUnsignedConstant(1, L.getType()), R, true);
141 return Add(L, getUnsignedConstant(1, L.getType()), true);
143 return Add(L, R, true);
147 // Mul - Helper function to make later code simpler. Basically it just
148 // multiplies the two constants together, inserts the result into the constant
149 // pool, and returns it. Of course life is not simple, and this is no
150 // exception. Factors that complicate matters:
151 // 1. Either argument may be null. If this is the case, the null argument is
152 // treated as either 0 (if DefOne = false) or 1 (if DefOne = true)
153 // 2. Types get in the way. We want to do arithmetic operations without
154 // regard for the underlying types. It is assumed that the constants are
155 // integral constants.
156 // 3. If DefOne is true, a null return value indicates a value of 1, if DefOne
157 // is false, a null return value indicates a value of 0.
159 inline const ConstantInt *Mul(const ConstantInt *Arg1,
160 const ConstantInt *Arg2, bool DefOne) {
161 assert(Arg1 && Arg2 && "No null arguments should exist now!");
162 assert(Arg1->getType() == Arg2->getType() && "Types must be compatible!");
164 // Actually perform the computation now!
165 Constant *Result = *Arg1 * *Arg2;
166 assert(Result && Result->getType() == Arg1->getType() &&
167 "Couldn't perform multiplication!");
168 ConstantInt *ResultI = cast<ConstantInt>(Result);
170 // Check to see if the result is one of the special cases that we want to
172 if (ResultI->equalsInt(DefOne ? 1 : 0))
173 return 0; // Yes it is, simply return null.
178 inline const ConstantInt *operator*(const DefZero &L, const DefZero &R) {
179 if (L == 0 || R == 0) return 0;
180 return Mul(L, R, false);
182 inline const ConstantInt *operator*(const DefOne &L, const DefZero &R) {
183 if (R == 0) return getUnsignedConstant(0, L.getType());
184 if (L == 0) return R->equalsInt(1) ? 0 : R.getVal();
185 return Mul(L, R, true);
187 inline const ConstantInt *operator*(const DefZero &L, const DefOne &R) {
188 if (L == 0 || R == 0) return L.getVal();
189 return Mul(R, L, false);
192 // handleAddition - Add two expressions together, creating a new expression that
193 // represents the composite of the two...
195 static ExprType handleAddition(ExprType Left, ExprType Right, Value *V) {
196 const Type *Ty = V->getType();
197 if (Left.ExprTy > Right.ExprTy)
198 std::swap(Left, Right); // Make left be simpler than right
200 switch (Left.ExprTy) {
201 case ExprType::Constant:
202 return ExprType(Right.Scale, Right.Var,
203 DefZero(Right.Offset, Ty) + DefZero(Left.Offset, Ty));
204 case ExprType::Linear: // RHS side must be linear or scaled
205 case ExprType::ScaledLinear: // RHS must be scaled
206 if (Left.Var != Right.Var) // Are they the same variables?
207 return V; // if not, we don't know anything!
209 return ExprType(DefOne(Left.Scale , Ty) + DefOne(Right.Scale , Ty),
211 DefZero(Left.Offset, Ty) + DefZero(Right.Offset, Ty));
213 assert(0 && "Dont' know how to handle this case!");
218 // negate - Negate the value of the specified expression...
220 static inline ExprType negate(const ExprType &E, Value *V) {
221 const Type *Ty = V->getType();
222 ConstantInt *Zero = getUnsignedConstant(0, Ty);
223 ConstantInt *One = getUnsignedConstant(1, Ty);
224 ConstantInt *NegOne = cast<ConstantInt>(*Zero - *One);
225 if (NegOne == 0) return V; // Couldn't subtract values...
227 return ExprType(DefOne (E.Scale , Ty) * NegOne, E.Var,
228 DefZero(E.Offset, Ty) * NegOne);
232 // ClassifyExpression: Analyze an expression to determine the complexity of the
233 // expression, and which other values it depends on.
235 // Note that this analysis cannot get into infinite loops because it treats PHI
236 // nodes as being an unknown linear expression.
238 ExprType ClassifyExpression(Value *Expr) {
239 assert(Expr != 0 && "Can't classify a null expression!");
240 if (Expr->getType() == Type::FloatTy || Expr->getType() == Type::DoubleTy)
241 return Expr; // FIXME: Can't handle FP expressions
243 switch (Expr->getValueType()) {
244 case Value::InstructionVal: break; // Instruction... hmmm... investigate.
245 case Value::TypeVal: case Value::BasicBlockVal:
246 case Value::FunctionVal: default:
247 //assert(0 && "Unexpected expression type to classify!");
248 std::cerr << "Bizarre thing to expr classify: " << Expr << "\n";
250 case Value::GlobalVariableVal: // Global Variable & Function argument:
251 case Value::ArgumentVal: // nothing known, return variable itself
253 case Value::ConstantVal: // Constant value, just return constant
254 if (ConstantInt *CPI = dyn_cast<ConstantInt>(cast<Constant>(Expr)))
255 // It's an integral constant!
256 return ExprType(CPI->isNullValue() ? 0 : CPI);
260 Instruction *I = cast<Instruction>(Expr);
261 const Type *Ty = I->getType();
263 switch (I->getOpcode()) { // Handle each instruction type separately
264 case Instruction::Add: {
265 ExprType Left (ClassifyExpression(I->getOperand(0)));
266 ExprType Right(ClassifyExpression(I->getOperand(1)));
267 return handleAddition(Left, Right, I);
268 } // end case Instruction::Add
270 case Instruction::Sub: {
271 ExprType Left (ClassifyExpression(I->getOperand(0)));
272 ExprType Right(ClassifyExpression(I->getOperand(1)));
273 ExprType RightNeg = negate(Right, I);
274 if (RightNeg.Var == I && !RightNeg.Offset && !RightNeg.Scale)
275 return I; // Could not negate value...
276 return handleAddition(Left, RightNeg, I);
277 } // end case Instruction::Sub
279 case Instruction::Shl: {
280 ExprType Right(ClassifyExpression(I->getOperand(1)));
281 if (Right.ExprTy != ExprType::Constant) break;
282 ExprType Left(ClassifyExpression(I->getOperand(0)));
283 if (Right.Offset == 0) return Left; // shl x, 0 = x
284 assert(Right.Offset->getType() == Type::UByteTy &&
285 "Shift amount must always be a unsigned byte!");
286 uint64_t ShiftAmount = cast<ConstantUInt>(Right.Offset)->getValue();
287 ConstantInt *Multiplier = getUnsignedConstant(1ULL << ShiftAmount, Ty);
289 // We don't know how to classify it if they are shifting by more than what
290 // is reasonable. In most cases, the result will be zero, but there is one
291 // class of cases where it is not, so we cannot optimize without checking
292 // for it. The case is when you are shifting a signed value by 1 less than
293 // the number of bits in the value. For example:
294 // %X = shl sbyte %Y, ubyte 7
295 // will try to form an sbyte multiplier of 128, which will give a null
296 // multiplier, even though the result is not 0. Until we can check for this
297 // case, be conservative. TODO.
302 return ExprType(DefOne(Left.Scale, Ty) * Multiplier, Left.Var,
303 DefZero(Left.Offset, Ty) * Multiplier);
304 } // end case Instruction::Shl
306 case Instruction::Mul: {
307 ExprType Left (ClassifyExpression(I->getOperand(0)));
308 ExprType Right(ClassifyExpression(I->getOperand(1)));
309 if (Left.ExprTy > Right.ExprTy)
310 std::swap(Left, Right); // Make left be simpler than right
312 if (Left.ExprTy != ExprType::Constant) // RHS must be > constant
313 return I; // Quadratic eqn! :(
315 const ConstantInt *Offs = Left.Offset;
316 if (Offs == 0) return ExprType();
317 return ExprType( DefOne(Right.Scale , Ty) * Offs, Right.Var,
318 DefZero(Right.Offset, Ty) * Offs);
319 } // end case Instruction::Mul
321 case Instruction::Cast: {
322 ExprType Src(ClassifyExpression(I->getOperand(0)));
323 const Type *DestTy = I->getType();
324 if (isa<PointerType>(DestTy))
325 DestTy = Type::ULongTy; // Pointer types are represented as ulong
327 const Type *SrcValTy = Src.getExprType(0);
328 if (!SrcValTy) return I;
329 if (!SrcValTy->isLosslesslyConvertibleTo(DestTy)) {
330 if (Src.ExprTy != ExprType::Constant)
331 return I; // Converting cast, and not a constant value...
334 const ConstantInt *Offset = Src.Offset;
335 const ConstantInt *Scale = Src.Scale;
337 const Constant *CPV = ConstantFoldCastInstruction(Offset, DestTy);
339 Offset = cast<ConstantInt>(CPV);
342 const Constant *CPV = ConstantFoldCastInstruction(Scale, DestTy);
344 Scale = cast<ConstantInt>(CPV);
346 return ExprType(Scale, Src.Var, Offset);
347 } // end case Instruction::Cast
348 // TODO: Handle SUB, SHR?
352 // Otherwise, I don't know anything about this value!