1 //===- Expressions.cpp - Expression Analysis Utilities ----------------------=//
3 // This file defines a package of expression analysis utilties:
5 // ClassifyExpression: Analyze an expression to determine the complexity of the
6 // expression, and which other variables it depends on.
8 //===----------------------------------------------------------------------===//
10 #include "llvm/Analysis/Expressions.h"
11 #include "llvm/ConstantHandling.h"
12 #include "llvm/Function.h"
13 #include "llvm/BasicBlock.h"
16 using namespace analysis;
18 ExprType::ExprType(Value *Val) {
20 if (ConstantInt *CPI = dyn_cast<ConstantInt>(Val)) {
28 Var = Val; Offset = 0;
29 ExprTy = Var ? Linear : Constant;
33 ExprType::ExprType(const ConstantInt *scale, Value *var,
34 const ConstantInt *offset) {
35 Scale = var ? scale : 0; Var = var; Offset = offset;
36 ExprTy = Scale ? ScaledLinear : (Var ? Linear : Constant);
37 if (Scale && Scale->equalsInt(0)) { // Simplify 0*Var + const
44 const Type *ExprType::getExprType(const Type *Default) const {
45 if (Offset) return Offset->getType();
46 if (Scale) return Scale->getType();
47 return Var ? Var->getType() : Default;
53 const ConstantInt * const Val;
54 const Type * const Ty;
56 inline DefVal(const ConstantInt *val, const Type *ty) : Val(val), Ty(ty) {}
58 inline const Type *getType() const { return Ty; }
59 inline const ConstantInt *getVal() const { return Val; }
60 inline operator const ConstantInt * () const { return Val; }
61 inline const ConstantInt *operator->() const { return Val; }
64 struct DefZero : public DefVal {
65 inline DefZero(const ConstantInt *val, const Type *ty) : DefVal(val, ty) {}
66 inline DefZero(const ConstantInt *val) : DefVal(val, val->getType()) {}
69 struct DefOne : public DefVal {
70 inline DefOne(const ConstantInt *val, const Type *ty) : DefVal(val, ty) {}
74 // getUnsignedConstant - Return a constant value of the specified type. If the
75 // constant value is not valid for the specified type, return null. This cannot
76 // happen for values in the range of 0 to 127.
78 static ConstantInt *getUnsignedConstant(uint64_t V, const Type *Ty) {
79 if (Ty->isPointerType()) Ty = Type::ULongTy;
81 // If this value is not a valid unsigned value for this type, return null!
82 if (V > 127 && ((int64_t)V < 0 ||
83 !ConstantSInt::isValueValidForType(Ty, (int64_t)V)))
85 return ConstantSInt::get(Ty, V);
87 // If this value is not a valid unsigned value for this type, return null!
88 if (V > 255 && !ConstantUInt::isValueValidForType(Ty, V))
90 return ConstantUInt::get(Ty, V);
94 // Add - Helper function to make later code simpler. Basically it just adds
95 // the two constants together, inserts the result into the constant pool, and
96 // returns it. Of course life is not simple, and this is no exception. Factors
97 // that complicate matters:
98 // 1. Either argument may be null. If this is the case, the null argument is
99 // treated as either 0 (if DefOne = false) or 1 (if DefOne = true)
100 // 2. Types get in the way. We want to do arithmetic operations without
101 // regard for the underlying types. It is assumed that the constants are
102 // integral constants. The new value takes the type of the left argument.
103 // 3. If DefOne is true, a null return value indicates a value of 1, if DefOne
104 // is false, a null return value indicates a value of 0.
106 static const ConstantInt *Add(const ConstantInt *Arg1,
107 const ConstantInt *Arg2, bool DefOne) {
108 assert(Arg1 && Arg2 && "No null arguments should exist now!");
109 assert(Arg1->getType() == Arg2->getType() && "Types must be compatible!");
111 // Actually perform the computation now!
112 Constant *Result = *Arg1 + *Arg2;
113 assert(Result && Result->getType() == Arg1->getType() &&
114 "Couldn't perform addition!");
115 ConstantInt *ResultI = cast<ConstantInt>(Result);
117 // Check to see if the result is one of the special cases that we want to
119 if (ResultI->equalsInt(DefOne ? 1 : 0))
120 return 0; // Yes it is, simply return null.
125 inline const ConstantInt *operator+(const DefZero &L, const DefZero &R) {
126 if (L == 0) return R;
127 if (R == 0) return L;
128 return Add(L, R, false);
131 inline const ConstantInt *operator+(const DefOne &L, const DefOne &R) {
134 return getUnsignedConstant(2, L.getType());
136 return Add(getUnsignedConstant(1, L.getType()), R, true);
138 return Add(L, getUnsignedConstant(1, L.getType()), true);
140 return Add(L, R, true);
144 // Mul - Helper function to make later code simpler. Basically it just
145 // multiplies the two constants together, inserts the result into the constant
146 // pool, and returns it. Of course life is not simple, and this is no
147 // exception. Factors that complicate matters:
148 // 1. Either argument may be null. If this is the case, the null argument is
149 // treated as either 0 (if DefOne = false) or 1 (if DefOne = true)
150 // 2. Types get in the way. We want to do arithmetic operations without
151 // regard for the underlying types. It is assumed that the constants are
152 // integral constants.
153 // 3. If DefOne is true, a null return value indicates a value of 1, if DefOne
154 // is false, a null return value indicates a value of 0.
156 inline const ConstantInt *Mul(const ConstantInt *Arg1,
157 const ConstantInt *Arg2, bool DefOne) {
158 assert(Arg1 && Arg2 && "No null arguments should exist now!");
159 assert(Arg1->getType() == Arg2->getType() && "Types must be compatible!");
161 // Actually perform the computation now!
162 Constant *Result = *Arg1 * *Arg2;
163 assert(Result && Result->getType() == Arg1->getType() &&
164 "Couldn't perform multiplication!");
165 ConstantInt *ResultI = cast<ConstantInt>(Result);
167 // Check to see if the result is one of the special cases that we want to
169 if (ResultI->equalsInt(DefOne ? 1 : 0))
170 return 0; // Yes it is, simply return null.
175 inline const ConstantInt *operator*(const DefZero &L, const DefZero &R) {
176 if (L == 0 || R == 0) return 0;
177 return Mul(L, R, false);
179 inline const ConstantInt *operator*(const DefOne &L, const DefZero &R) {
180 if (R == 0) return getUnsignedConstant(0, L.getType());
181 if (L == 0) return R->equalsInt(1) ? 0 : R.getVal();
182 return Mul(L, R, true);
184 inline const ConstantInt *operator*(const DefZero &L, const DefOne &R) {
185 if (L == 0 || R == 0) return L.getVal();
186 return Mul(R, L, false);
189 // handleAddition - Add two expressions together, creating a new expression that
190 // represents the composite of the two...
192 static ExprType handleAddition(ExprType Left, ExprType Right, Value *V) {
193 const Type *Ty = V->getType();
194 if (Left.ExprTy > Right.ExprTy)
195 std::swap(Left, Right); // Make left be simpler than right
197 switch (Left.ExprTy) {
198 case ExprType::Constant:
199 return ExprType(Right.Scale, Right.Var,
200 DefZero(Right.Offset, Ty) + DefZero(Left.Offset, Ty));
201 case ExprType::Linear: // RHS side must be linear or scaled
202 case ExprType::ScaledLinear: // RHS must be scaled
203 if (Left.Var != Right.Var) // Are they the same variables?
204 return V; // if not, we don't know anything!
206 return ExprType(DefOne(Left.Scale , Ty) + DefOne(Right.Scale , Ty),
208 DefZero(Left.Offset, Ty) + DefZero(Right.Offset, Ty));
210 assert(0 && "Dont' know how to handle this case!");
215 // negate - Negate the value of the specified expression...
217 static inline ExprType negate(const ExprType &E, Value *V) {
218 const Type *Ty = V->getType();
219 ConstantInt *Zero = getUnsignedConstant(0, Ty);
220 ConstantInt *One = getUnsignedConstant(1, Ty);
221 ConstantInt *NegOne = cast<ConstantInt>(*Zero - *One);
222 if (NegOne == 0) return V; // Couldn't subtract values...
224 return ExprType(DefOne (E.Scale , Ty) * NegOne, E.Var,
225 DefZero(E.Offset, Ty) * NegOne);
229 // ClassifyExpression: Analyze an expression to determine the complexity of the
230 // expression, and which other values it depends on.
232 // Note that this analysis cannot get into infinite loops because it treats PHI
233 // nodes as being an unknown linear expression.
235 ExprType analysis::ClassifyExpression(Value *Expr) {
236 assert(Expr != 0 && "Can't classify a null expression!");
237 if (Expr->getType() == Type::FloatTy || Expr->getType() == Type::DoubleTy)
238 return Expr; // FIXME: Can't handle FP expressions
240 switch (Expr->getValueType()) {
241 case Value::InstructionVal: break; // Instruction... hmmm... investigate.
242 case Value::TypeVal: case Value::BasicBlockVal:
243 case Value::FunctionVal: case Value::ModuleVal: default:
244 //assert(0 && "Unexpected expression type to classify!");
245 std::cerr << "Bizarre thing to expr classify: " << Expr << "\n";
247 case Value::GlobalVariableVal: // Global Variable & Function argument:
248 case Value::ArgumentVal: // nothing known, return variable itself
250 case Value::ConstantVal: // Constant value, just return constant
251 Constant *CPV = cast<Constant>(Expr);
252 if (CPV->getType()->isIntegral()) { // It's an integral constant!
253 ConstantInt *CPI = cast<ConstantInt>(Expr);
254 return ExprType(CPI->equalsInt(0) ? 0 : CPI);
259 Instruction *I = cast<Instruction>(Expr);
260 const Type *Ty = I->getType();
262 switch (I->getOpcode()) { // Handle each instruction type seperately
263 case Instruction::Add: {
264 ExprType Left (ClassifyExpression(I->getOperand(0)));
265 ExprType Right(ClassifyExpression(I->getOperand(1)));
266 return handleAddition(Left, Right, I);
267 } // end case Instruction::Add
269 case Instruction::Sub: {
270 ExprType Left (ClassifyExpression(I->getOperand(0)));
271 ExprType Right(ClassifyExpression(I->getOperand(1)));
272 ExprType RightNeg = negate(Right, I);
273 if (RightNeg.Var == I && !RightNeg.Offset && !RightNeg.Scale)
274 return I; // Could not negate value...
275 return handleAddition(Left, RightNeg, I);
276 } // end case Instruction::Sub
278 case Instruction::Shl: {
279 ExprType Right(ClassifyExpression(I->getOperand(1)));
280 if (Right.ExprTy != ExprType::Constant) break;
281 ExprType Left(ClassifyExpression(I->getOperand(0)));
282 if (Right.Offset == 0) return Left; // shl x, 0 = x
283 assert(Right.Offset->getType() == Type::UByteTy &&
284 "Shift amount must always be a unsigned byte!");
285 uint64_t ShiftAmount = ((ConstantUInt*)Right.Offset)->getValue();
286 ConstantInt *Multiplier = getUnsignedConstant(1ULL << ShiftAmount, Ty);
288 // We don't know how to classify it if they are shifting by more than what
289 // is reasonable. In most cases, the result will be zero, but there is one
290 // class of cases where it is not, so we cannot optimize without checking
291 // for it. The case is when you are shifting a signed value by 1 less than
292 // the number of bits in the value. For example:
293 // %X = shl sbyte %Y, ubyte 7
294 // will try to form an sbyte multiplier of 128, which will give a null
295 // multiplier, even though the result is not 0. Until we can check for this
296 // case, be conservative. TODO.
301 return ExprType(DefOne(Left.Scale, Ty) * Multiplier, Left.Var,
302 DefZero(Left.Offset, Ty) * Multiplier);
303 } // end case Instruction::Shl
305 case Instruction::Mul: {
306 ExprType Left (ClassifyExpression(I->getOperand(0)));
307 ExprType Right(ClassifyExpression(I->getOperand(1)));
308 if (Left.ExprTy > Right.ExprTy)
309 std::swap(Left, Right); // Make left be simpler than right
311 if (Left.ExprTy != ExprType::Constant) // RHS must be > constant
312 return I; // Quadratic eqn! :(
314 const ConstantInt *Offs = Left.Offset;
315 if (Offs == 0) return ExprType();
316 return ExprType( DefOne(Right.Scale , Ty) * Offs, Right.Var,
317 DefZero(Right.Offset, Ty) * Offs);
318 } // end case Instruction::Mul
320 case Instruction::Cast: {
321 ExprType Src(ClassifyExpression(I->getOperand(0)));
322 const Type *DestTy = I->getType();
323 if (DestTy->isPointerType())
324 DestTy = Type::ULongTy; // Pointer types are represented as ulong
327 if (!Src.getExprType(0)->isLosslesslyConvertableTo(DestTy)) {
328 if (Src.ExprTy != ExprType::Constant)
329 return I; // Converting cast, and not a constant value...
333 const ConstantInt *Offset = Src.Offset;
334 const ConstantInt *Scale = Src.Scale;
336 const Constant *CPV = ConstantFoldCastInstruction(Offset, DestTy);
338 Offset = cast<ConstantInt>(CPV);
341 const Constant *CPV = ConstantFoldCastInstruction(Scale, DestTy);
343 Scale = cast<ConstantInt>(CPV);
345 return ExprType(Scale, Src.Var, Offset);
346 } // end case Instruction::Cast
347 // TODO: Handle SUB, SHR?
351 // Otherwise, I don't know anything about this value!