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"
22 ExprType::ExprType(Value *Val) {
24 if (ConstantInt *CPI = dyn_cast<ConstantInt>(Val)) {
32 Var = Val; Offset = 0;
33 ExprTy = Var ? Linear : Constant;
37 ExprType::ExprType(const ConstantInt *scale, Value *var,
38 const ConstantInt *offset) {
39 Scale = var ? scale : 0; Var = var; Offset = offset;
40 ExprTy = Scale ? ScaledLinear : (Var ? Linear : Constant);
41 if (Scale && Scale->isNullValue()) { // Simplify 0*Var + const
48 const Type *ExprType::getExprType(const Type *Default) const {
49 if (Offset) return Offset->getType();
50 if (Scale) return Scale->getType();
51 return Var ? Var->getType() : Default;
57 const ConstantInt * const Val;
58 const Type * const Ty;
60 inline DefVal(const ConstantInt *val, const Type *ty) : Val(val), Ty(ty) {}
62 inline const Type *getType() const { return Ty; }
63 inline const ConstantInt *getVal() const { return Val; }
64 inline operator const ConstantInt * () const { return Val; }
65 inline const ConstantInt *operator->() const { return Val; }
68 struct DefZero : public DefVal {
69 inline DefZero(const ConstantInt *val, const Type *ty) : DefVal(val, ty) {}
70 inline DefZero(const ConstantInt *val) : DefVal(val, val->getType()) {}
73 struct DefOne : public DefVal {
74 inline DefOne(const ConstantInt *val, const Type *ty) : DefVal(val, ty) {}
79 // getUnsignedConstant - Return a constant value of the specified type. If the
80 // constant value is not valid for the specified type, return null. This cannot
81 // happen for values in the range of 0 to 127.
83 static ConstantInt *getUnsignedConstant(uint64_t V, const Type *Ty) {
84 if (isa<PointerType>(Ty)) Ty = Type::ULongTy;
86 // If this value is not a valid unsigned value for this type, return null!
87 if (V > 127 && ((int64_t)V < 0 ||
88 !ConstantSInt::isValueValidForType(Ty, (int64_t)V)))
90 return ConstantSInt::get(Ty, V);
92 // If this value is not a valid unsigned value for this type, return null!
93 if (V > 255 && !ConstantUInt::isValueValidForType(Ty, V))
95 return ConstantUInt::get(Ty, V);
99 // Add - Helper function to make later code simpler. Basically it just adds
100 // the two constants together, inserts the result into the constant pool, and
101 // returns it. Of course life is not simple, and this is no exception. Factors
102 // that complicate matters:
103 // 1. Either argument may be null. If this is the case, the null argument is
104 // treated as either 0 (if DefOne = false) or 1 (if DefOne = true)
105 // 2. Types get in the way. We want to do arithmetic operations without
106 // regard for the underlying types. It is assumed that the constants are
107 // integral constants. The new value takes the type of the left argument.
108 // 3. If DefOne is true, a null return value indicates a value of 1, if DefOne
109 // is false, a null return value indicates a value of 0.
111 static const ConstantInt *Add(const ConstantInt *Arg1,
112 const ConstantInt *Arg2, bool DefOne) {
113 assert(Arg1 && Arg2 && "No null arguments should exist now!");
114 assert(Arg1->getType() == Arg2->getType() && "Types must be compatible!");
116 // Actually perform the computation now!
117 Constant *Result = *Arg1 + *Arg2;
118 assert(Result && Result->getType() == Arg1->getType() &&
119 "Couldn't perform addition!");
120 ConstantInt *ResultI = cast<ConstantInt>(Result);
122 // Check to see if the result is one of the special cases that we want to
124 if (ResultI->equalsInt(DefOne ? 1 : 0))
125 return 0; // Yes it is, simply return null.
130 static inline const ConstantInt *operator+(const DefZero &L, const DefZero &R) {
131 if (L == 0) return R;
132 if (R == 0) return L;
133 return Add(L, R, false);
136 static inline const ConstantInt *operator+(const DefOne &L, const DefOne &R) {
139 return getUnsignedConstant(2, L.getType());
141 return Add(getUnsignedConstant(1, L.getType()), R, true);
143 return Add(L, getUnsignedConstant(1, L.getType()), true);
145 return Add(L, R, true);
149 // Mul - Helper function to make later code simpler. Basically it just
150 // multiplies the two constants together, inserts the result into the constant
151 // pool, and returns it. Of course life is not simple, and this is no
152 // exception. Factors that complicate matters:
153 // 1. Either argument may be null. If this is the case, the null argument is
154 // treated as either 0 (if DefOne = false) or 1 (if DefOne = true)
155 // 2. Types get in the way. We want to do arithmetic operations without
156 // regard for the underlying types. It is assumed that the constants are
157 // integral constants.
158 // 3. If DefOne is true, a null return value indicates a value of 1, if DefOne
159 // is false, a null return value indicates a value of 0.
161 static inline const ConstantInt *Mul(const ConstantInt *Arg1,
162 const ConstantInt *Arg2, bool DefOne) {
163 assert(Arg1 && Arg2 && "No null arguments should exist now!");
164 assert(Arg1->getType() == Arg2->getType() && "Types must be compatible!");
166 // Actually perform the computation now!
167 Constant *Result = *Arg1 * *Arg2;
168 assert(Result && Result->getType() == Arg1->getType() &&
169 "Couldn't perform multiplication!");
170 ConstantInt *ResultI = cast<ConstantInt>(Result);
172 // Check to see if the result is one of the special cases that we want to
174 if (ResultI->equalsInt(DefOne ? 1 : 0))
175 return 0; // Yes it is, simply return null.
181 inline const ConstantInt *operator*(const DefZero &L, const DefZero &R) {
182 if (L == 0 || R == 0) return 0;
183 return Mul(L, R, false);
185 inline const ConstantInt *operator*(const DefOne &L, const DefZero &R) {
186 if (R == 0) return getUnsignedConstant(0, L.getType());
187 if (L == 0) return R->equalsInt(1) ? 0 : R.getVal();
188 return Mul(L, R, true);
190 inline const ConstantInt *operator*(const DefZero &L, const DefOne &R) {
191 if (L == 0 || R == 0) return L.getVal();
192 return Mul(R, L, false);
196 // handleAddition - Add two expressions together, creating a new expression that
197 // represents the composite of the two...
199 static ExprType handleAddition(ExprType Left, ExprType Right, Value *V) {
200 const Type *Ty = V->getType();
201 if (Left.ExprTy > Right.ExprTy)
202 std::swap(Left, Right); // Make left be simpler than right
204 switch (Left.ExprTy) {
205 case ExprType::Constant:
206 return ExprType(Right.Scale, Right.Var,
207 DefZero(Right.Offset, Ty) + DefZero(Left.Offset, Ty));
208 case ExprType::Linear: // RHS side must be linear or scaled
209 case ExprType::ScaledLinear: // RHS must be scaled
210 if (Left.Var != Right.Var) // Are they the same variables?
211 return V; // if not, we don't know anything!
213 return ExprType(DefOne(Left.Scale , Ty) + DefOne(Right.Scale , Ty),
215 DefZero(Left.Offset, Ty) + DefZero(Right.Offset, Ty));
217 assert(0 && "Dont' know how to handle this case!");
222 // negate - Negate the value of the specified expression...
224 static inline ExprType negate(const ExprType &E, Value *V) {
225 const Type *Ty = V->getType();
226 ConstantInt *Zero = getUnsignedConstant(0, Ty);
227 ConstantInt *One = getUnsignedConstant(1, Ty);
228 ConstantInt *NegOne = cast<ConstantInt>(*Zero - *One);
229 if (NegOne == 0) return V; // Couldn't subtract values...
231 return ExprType(DefOne (E.Scale , Ty) * NegOne, E.Var,
232 DefZero(E.Offset, Ty) * NegOne);
236 // ClassifyExpr: Analyze an expression to determine the complexity of the
237 // expression, and which other values it depends on.
239 // Note that this analysis cannot get into infinite loops because it treats PHI
240 // nodes as being an unknown linear expression.
242 ExprType llvm::ClassifyExpr(Value *Expr) {
243 assert(Expr != 0 && "Can't classify a null expression!");
244 if (Expr->getType() == Type::FloatTy || Expr->getType() == Type::DoubleTy)
245 return Expr; // FIXME: Can't handle FP expressions
247 switch (Expr->getValueType()) {
248 case Value::InstructionVal: break; // Instruction... hmmm... investigate.
249 case Value::TypeVal: case Value::BasicBlockVal:
250 case Value::FunctionVal: default:
251 //assert(0 && "Unexpected expression type to classify!");
252 std::cerr << "Bizarre thing to expr classify: " << Expr << "\n";
254 case Value::GlobalVariableVal: // Global Variable & Function argument:
255 case Value::ArgumentVal: // nothing known, return variable itself
257 case Value::ConstantVal: // Constant value, just return constant
258 if (ConstantInt *CPI = dyn_cast<ConstantInt>(cast<Constant>(Expr)))
259 // It's an integral constant!
260 return ExprType(CPI->isNullValue() ? 0 : CPI);
264 Instruction *I = cast<Instruction>(Expr);
265 const Type *Ty = I->getType();
267 switch (I->getOpcode()) { // Handle each instruction type separately
268 case Instruction::Add: {
269 ExprType Left (ClassifyExpr(I->getOperand(0)));
270 ExprType Right(ClassifyExpr(I->getOperand(1)));
271 return handleAddition(Left, Right, I);
272 } // end case Instruction::Add
274 case Instruction::Sub: {
275 ExprType Left (ClassifyExpr(I->getOperand(0)));
276 ExprType Right(ClassifyExpr(I->getOperand(1)));
277 ExprType RightNeg = negate(Right, I);
278 if (RightNeg.Var == I && !RightNeg.Offset && !RightNeg.Scale)
279 return I; // Could not negate value...
280 return handleAddition(Left, RightNeg, I);
281 } // end case Instruction::Sub
283 case Instruction::Shl: {
284 ExprType Right(ClassifyExpr(I->getOperand(1)));
285 if (Right.ExprTy != ExprType::Constant) break;
286 ExprType Left(ClassifyExpr(I->getOperand(0)));
287 if (Right.Offset == 0) return Left; // shl x, 0 = x
288 assert(Right.Offset->getType() == Type::UByteTy &&
289 "Shift amount must always be a unsigned byte!");
290 uint64_t ShiftAmount = cast<ConstantUInt>(Right.Offset)->getValue();
291 ConstantInt *Multiplier = getUnsignedConstant(1ULL << ShiftAmount, Ty);
293 // We don't know how to classify it if they are shifting by more than what
294 // is reasonable. In most cases, the result will be zero, but there is one
295 // class of cases where it is not, so we cannot optimize without checking
296 // for it. The case is when you are shifting a signed value by 1 less than
297 // the number of bits in the value. For example:
298 // %X = shl sbyte %Y, ubyte 7
299 // will try to form an sbyte multiplier of 128, which will give a null
300 // multiplier, even though the result is not 0. Until we can check for this
301 // case, be conservative. TODO.
306 return ExprType(DefOne(Left.Scale, Ty) * Multiplier, Left.Var,
307 DefZero(Left.Offset, Ty) * Multiplier);
308 } // end case Instruction::Shl
310 case Instruction::Mul: {
311 ExprType Left (ClassifyExpr(I->getOperand(0)));
312 ExprType Right(ClassifyExpr(I->getOperand(1)));
313 if (Left.ExprTy > Right.ExprTy)
314 std::swap(Left, Right); // Make left be simpler than right
316 if (Left.ExprTy != ExprType::Constant) // RHS must be > constant
317 return I; // Quadratic eqn! :(
319 const ConstantInt *Offs = Left.Offset;
320 if (Offs == 0) return ExprType();
321 return ExprType( DefOne(Right.Scale , Ty) * Offs, Right.Var,
322 DefZero(Right.Offset, Ty) * Offs);
323 } // end case Instruction::Mul
325 case Instruction::Cast: {
326 ExprType Src(ClassifyExpr(I->getOperand(0)));
327 const Type *DestTy = I->getType();
328 if (isa<PointerType>(DestTy))
329 DestTy = Type::ULongTy; // Pointer types are represented as ulong
331 const Type *SrcValTy = Src.getExprType(0);
332 if (!SrcValTy) return I;
333 if (!SrcValTy->isLosslesslyConvertibleTo(DestTy)) {
334 if (Src.ExprTy != ExprType::Constant)
335 return I; // Converting cast, and not a constant value...
338 const ConstantInt *Offset = Src.Offset;
339 const ConstantInt *Scale = Src.Scale;
341 const Constant *CPV = ConstantFoldCastInstruction(Offset, DestTy);
343 Offset = cast<ConstantInt>(CPV);
346 const Constant *CPV = ConstantFoldCastInstruction(Scale, DestTy);
348 Scale = cast<ConstantInt>(CPV);
350 return ExprType(Scale, Src.Var, Offset);
351 } // end case Instruction::Cast
352 // TODO: Handle SUB, SHR?
356 // Otherwise, I don't know anything about this value!