1 //===- llvm/Analysis/TargetTransformInfo.h ----------------------*- C++ -*-===// 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 pass exposes codegen information to IR-level passes. Every 11 // transformation that uses codegen information is broken into three parts: 12 // 1. The IR-level analysis pass. 13 // 2. The IR-level transformation interface which provides the needed 14 // information. 15 // 3. Codegen-level implementation which uses target-specific hooks. 16 // 17 // This file defines #2, which is the interface that IR-level transformations 18 // use for querying the codegen. 19 // 20 //===----------------------------------------------------------------------===// 21 22 #ifndef LLVM_ANALYSIS_TARGETTRANSFORMINFO_H 23 #define LLVM_ANALYSIS_TARGETTRANSFORMINFO_H 24 25 #include "llvm/IR/Intrinsics.h" 26 #include "llvm/Pass.h" 27 #include "llvm/Support/DataTypes.h" 28 29 namespace llvm { 30 31 class GlobalValue; 32 class Loop; 33 class Type; 34 class User; 35 class Value; 36 37 /// TargetTransformInfo - This pass provides access to the codegen 38 /// interfaces that are needed for IR-level transformations. 39 class TargetTransformInfo { 40 protected: 41 /// \brief The TTI instance one level down the stack. 42 /// 43 /// This is used to implement the default behavior all of the methods which 44 /// is to delegate up through the stack of TTIs until one can answer the 45 /// query. 46 TargetTransformInfo *PrevTTI; 47 48 /// \brief The top of the stack of TTI analyses available. 49 /// 50 /// This is a convenience routine maintained as TTI analyses become available 51 /// that complements the PrevTTI delegation chain. When one part of an 52 /// analysis pass wants to query another part of the analysis pass it can use 53 /// this to start back at the top of the stack. 54 TargetTransformInfo *TopTTI; 55 56 /// All pass subclasses must in their initializePass routine call 57 /// pushTTIStack with themselves to update the pointers tracking the previous 58 /// TTI instance in the analysis group's stack, and the top of the analysis 59 /// group's stack. 60 void pushTTIStack(Pass *P); 61 62 /// All pass subclasses must call TargetTransformInfo::getAnalysisUsage. 63 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 64 65 public: 66 /// This class is intended to be subclassed by real implementations. 67 virtual ~TargetTransformInfo() = 0; 68 69 /// \name Generic Target Information 70 /// @{ 71 72 /// \brief Underlying constants for 'cost' values in this interface. 73 /// 74 /// Many APIs in this interface return a cost. This enum defines the 75 /// fundamental values that should be used to interpret (and produce) those 76 /// costs. The costs are returned as an unsigned rather than a member of this 77 /// enumeration because it is expected that the cost of one IR instruction 78 /// may have a multiplicative factor to it or otherwise won't fit directly 79 /// into the enum. Moreover, it is common to sum or average costs which works 80 /// better as simple integral values. Thus this enum only provides constants. 81 /// 82 /// Note that these costs should usually reflect the intersection of code-size 83 /// cost and execution cost. A free instruction is typically one that folds 84 /// into another instruction. For example, reg-to-reg moves can often be 85 /// skipped by renaming the registers in the CPU, but they still are encoded 86 /// and thus wouldn't be considered 'free' here. 87 enum TargetCostConstants { 88 TCC_Free = 0, ///< Expected to fold away in lowering. 89 TCC_Basic = 1, ///< The cost of a typical 'add' instruction. 90 TCC_Expensive = 4 ///< The cost of a 'div' instruction on x86. 91 }; 92 93 /// \brief Estimate the cost of a specific operation when lowered. 94 /// 95 /// Note that this is designed to work on an arbitrary synthetic opcode, and 96 /// thus work for hypothetical queries before an instruction has even been 97 /// formed. However, this does *not* work for GEPs, and must not be called 98 /// for a GEP instruction. Instead, use the dedicated getGEPCost interface as 99 /// analyzing a GEP's cost required more information. 100 /// 101 /// Typically only the result type is required, and the operand type can be 102 /// omitted. However, if the opcode is one of the cast instructions, the 103 /// operand type is required. 104 /// 105 /// The returned cost is defined in terms of \c TargetCostConstants, see its 106 /// comments for a detailed explanation of the cost values. 107 virtual unsigned getOperationCost(unsigned Opcode, Type *Ty, 108 Type *OpTy = nullptr) const; 109 110 /// \brief Estimate the cost of a GEP operation when lowered. 111 /// 112 /// The contract for this function is the same as \c getOperationCost except 113 /// that it supports an interface that provides extra information specific to 114 /// the GEP operation. 115 virtual unsigned getGEPCost(const Value *Ptr, 116 ArrayRef<const Value *> Operands) const; 117 118 /// \brief Estimate the cost of a function call when lowered. 119 /// 120 /// The contract for this is the same as \c getOperationCost except that it 121 /// supports an interface that provides extra information specific to call 122 /// instructions. 123 /// 124 /// This is the most basic query for estimating call cost: it only knows the 125 /// function type and (potentially) the number of arguments at the call site. 126 /// The latter is only interesting for varargs function types. 127 virtual unsigned getCallCost(FunctionType *FTy, int NumArgs = -1) const; 128 129 /// \brief Estimate the cost of calling a specific function when lowered. 130 /// 131 /// This overload adds the ability to reason about the particular function 132 /// being called in the event it is a library call with special lowering. 133 virtual unsigned getCallCost(const Function *F, int NumArgs = -1) const; 134 135 /// \brief Estimate the cost of calling a specific function when lowered. 136 /// 137 /// This overload allows specifying a set of candidate argument values. 138 virtual unsigned getCallCost(const Function *F, 139 ArrayRef<const Value *> Arguments) const; 140 141 /// \brief Estimate the cost of an intrinsic when lowered. 142 /// 143 /// Mirrors the \c getCallCost method but uses an intrinsic identifier. 144 virtual unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy, 145 ArrayRef<Type *> ParamTys) const; 146 147 /// \brief Estimate the cost of an intrinsic when lowered. 148 /// 149 /// Mirrors the \c getCallCost method but uses an intrinsic identifier. 150 virtual unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy, 151 ArrayRef<const Value *> Arguments) const; 152 153 /// \brief Estimate the cost of a given IR user when lowered. 154 /// 155 /// This can estimate the cost of either a ConstantExpr or Instruction when 156 /// lowered. It has two primary advantages over the \c getOperationCost and 157 /// \c getGEPCost above, and one significant disadvantage: it can only be 158 /// used when the IR construct has already been formed. 159 /// 160 /// The advantages are that it can inspect the SSA use graph to reason more 161 /// accurately about the cost. For example, all-constant-GEPs can often be 162 /// folded into a load or other instruction, but if they are used in some 163 /// other context they may not be folded. This routine can distinguish such 164 /// cases. 165 /// 166 /// The returned cost is defined in terms of \c TargetCostConstants, see its 167 /// comments for a detailed explanation of the cost values. 168 virtual unsigned getUserCost(const User *U) const; 169 170 /// \brief hasBranchDivergence - Return true if branch divergence exists. 171 /// Branch divergence has a significantly negative impact on GPU performance 172 /// when threads in the same wavefront take different paths due to conditional 173 /// branches. 174 virtual bool hasBranchDivergence() const; 175 176 /// \brief Test whether calls to a function lower to actual program function 177 /// calls. 178 /// 179 /// The idea is to test whether the program is likely to require a 'call' 180 /// instruction or equivalent in order to call the given function. 181 /// 182 /// FIXME: It's not clear that this is a good or useful query API. Client's 183 /// should probably move to simpler cost metrics using the above. 184 /// Alternatively, we could split the cost interface into distinct code-size 185 /// and execution-speed costs. This would allow modelling the core of this 186 /// query more accurately as the a call is a single small instruction, but 187 /// incurs significant execution cost. 188 virtual bool isLoweredToCall(const Function *F) const; 189 190 /// Parameters that control the generic loop unrolling transformation. 191 struct UnrollingPreferences { 192 /// The cost threshold for the unrolled loop, compared to 193 /// CodeMetrics.NumInsts aggregated over all basic blocks in the loop body. 194 /// The unrolling factor is set such that the unrolled loop body does not 195 /// exceed this cost. Set this to UINT_MAX to disable the loop body cost 196 /// restriction. 197 unsigned Threshold; 198 /// The cost threshold for the unrolled loop when optimizing for size (set 199 /// to UINT_MAX to disable). 200 unsigned OptSizeThreshold; 201 /// The cost threshold for the unrolled loop, like Threshold, but used 202 /// for partial/runtime unrolling (set to UINT_MAX to disable). 203 unsigned PartialThreshold; 204 /// The cost threshold for the unrolled loop when optimizing for size, like 205 /// OptSizeThreshold, but used for partial/runtime unrolling (set to UINT_MAX 206 /// to disable). 207 unsigned PartialOptSizeThreshold; 208 /// A forced unrolling factor (the number of concatenated bodies of the 209 /// original loop in the unrolled loop body). When set to 0, the unrolling 210 /// transformation will select an unrolling factor based on the current cost 211 /// threshold and other factors. 212 unsigned Count; 213 // Set the maximum unrolling factor. The unrolling factor may be selected 214 // using the appropriate cost threshold, but may not exceed this number 215 // (set to UINT_MAX to disable). This does not apply in cases where the 216 // loop is being fully unrolled. 217 unsigned MaxCount; 218 /// Allow partial unrolling (unrolling of loops to expand the size of the 219 /// loop body, not only to eliminate small constant-trip-count loops). 220 bool Partial; 221 /// Allow runtime unrolling (unrolling of loops to expand the size of the 222 /// loop body even when the number of loop iterations is not known at compile 223 /// time). 224 bool Runtime; 225 }; 226 227 /// \brief Get target-customized preferences for the generic loop unrolling 228 /// transformation. The caller will initialize UP with the current 229 /// target-independent defaults. 230 virtual void getUnrollingPreferences(Loop *L, UnrollingPreferences &UP) const; 231 232 /// @} 233 234 /// \name Scalar Target Information 235 /// @{ 236 237 /// \brief Flags indicating the kind of support for population count. 238 /// 239 /// Compared to the SW implementation, HW support is supposed to 240 /// significantly boost the performance when the population is dense, and it 241 /// may or may not degrade performance if the population is sparse. A HW 242 /// support is considered as "Fast" if it can outperform, or is on a par 243 /// with, SW implementation when the population is sparse; otherwise, it is 244 /// considered as "Slow". 245 enum PopcntSupportKind { 246 PSK_Software, 247 PSK_SlowHardware, 248 PSK_FastHardware 249 }; 250 251 /// \brief Return true if the specified immediate is legal add immediate, that 252 /// is the target has add instructions which can add a register with the 253 /// immediate without having to materialize the immediate into a register. 254 virtual bool isLegalAddImmediate(int64_t Imm) const; 255 256 /// \brief Return true if the specified immediate is legal icmp immediate, 257 /// that is the target has icmp instructions which can compare a register 258 /// against the immediate without having to materialize the immediate into a 259 /// register. 260 virtual bool isLegalICmpImmediate(int64_t Imm) const; 261 262 /// \brief Return true if the addressing mode represented by AM is legal for 263 /// this target, for a load/store of the specified type. 264 /// The type may be VoidTy, in which case only return true if the addressing 265 /// mode is legal for a load/store of any legal type. 266 /// TODO: Handle pre/postinc as well. 267 virtual bool isLegalAddressingMode(Type *Ty, GlobalValue *BaseGV, 268 int64_t BaseOffset, bool HasBaseReg, 269 int64_t Scale) const; 270 271 /// \brief Return the cost of the scaling factor used in the addressing 272 /// mode represented by AM for this target, for a load/store 273 /// of the specified type. 274 /// If the AM is supported, the return value must be >= 0. 275 /// If the AM is not supported, it returns a negative value. 276 /// TODO: Handle pre/postinc as well. 277 virtual int getScalingFactorCost(Type *Ty, GlobalValue *BaseGV, 278 int64_t BaseOffset, bool HasBaseReg, 279 int64_t Scale) const; 280 281 /// \brief Return true if it's free to truncate a value of type Ty1 to type 282 /// Ty2. e.g. On x86 it's free to truncate a i32 value in register EAX to i16 283 /// by referencing its sub-register AX. 284 virtual bool isTruncateFree(Type *Ty1, Type *Ty2) const; 285 286 /// \brief Return true if this type is legal. 287 virtual bool isTypeLegal(Type *Ty) const; 288 289 /// \brief Returns the target's jmp_buf alignment in bytes. 290 virtual unsigned getJumpBufAlignment() const; 291 292 /// \brief Returns the target's jmp_buf size in bytes. 293 virtual unsigned getJumpBufSize() const; 294 295 /// \brief Return true if switches should be turned into lookup tables for the 296 /// target. 297 virtual bool shouldBuildLookupTables() const; 298 299 /// \brief Return hardware support for population count. 300 virtual PopcntSupportKind getPopcntSupport(unsigned IntTyWidthInBit) const; 301 302 /// \brief Return true if the hardware has a fast square-root instruction. 303 virtual bool haveFastSqrt(Type *Ty) const; 304 305 /// \brief Return the expected cost of materializing for the given integer 306 /// immediate of the specified type. 307 virtual unsigned getIntImmCost(const APInt &Imm, Type *Ty) const; 308 309 /// \brief Return the expected cost of materialization for the given integer 310 /// immediate of the specified type for a given instruction. The cost can be 311 /// zero if the immediate can be folded into the specified instruction. 312 virtual unsigned getIntImmCost(unsigned Opc, unsigned Idx, const APInt &Imm, 313 Type *Ty) const; 314 virtual unsigned getIntImmCost(Intrinsic::ID IID, unsigned Idx, 315 const APInt &Imm, Type *Ty) const; 316 /// @} 317 318 /// \name Vector Target Information 319 /// @{ 320 321 /// \brief The various kinds of shuffle patterns for vector queries. 322 enum ShuffleKind { 323 SK_Broadcast, ///< Broadcast element 0 to all other elements. 324 SK_Reverse, ///< Reverse the order of the vector. 325 SK_Alternate, ///< Choose alternate elements from vector. 326 SK_InsertSubvector, ///< InsertSubvector. Index indicates start offset. 327 SK_ExtractSubvector ///< ExtractSubvector Index indicates start offset. 328 }; 329 330 /// \brief Additional information about an operand's possible values. 331 enum OperandValueKind { 332 OK_AnyValue, // Operand can have any value. 333 OK_UniformValue, // Operand is uniform (splat of a value). 334 OK_UniformConstantValue, // Operand is uniform constant. 335 OK_NonUniformConstantValue // Operand is a non uniform constant value. 336 }; 337 338 /// \return The number of scalar or vector registers that the target has. 339 /// If 'Vectors' is true, it returns the number of vector registers. If it is 340 /// set to false, it returns the number of scalar registers. 341 virtual unsigned getNumberOfRegisters(bool Vector) const; 342 343 /// \return The width of the largest scalar or vector register type. 344 virtual unsigned getRegisterBitWidth(bool Vector) const; 345 346 /// \return The maximum unroll factor that the vectorizer should try to 347 /// perform for this target. This number depends on the level of parallelism 348 /// and the number of execution units in the CPU. 349 virtual unsigned getMaximumUnrollFactor() const; 350 351 /// \return The expected cost of arithmetic ops, such as mul, xor, fsub, etc. 352 virtual unsigned getArithmeticInstrCost(unsigned Opcode, Type *Ty, 353 OperandValueKind Opd1Info = OK_AnyValue, 354 OperandValueKind Opd2Info = OK_AnyValue) const; 355 356 /// \return The cost of a shuffle instruction of kind Kind and of type Tp. 357 /// The index and subtype parameters are used by the subvector insertion and 358 /// extraction shuffle kinds. 359 virtual unsigned getShuffleCost(ShuffleKind Kind, Type *Tp, int Index = 0, 360 Type *SubTp = nullptr) const; 361 362 /// \return The expected cost of cast instructions, such as bitcast, trunc, 363 /// zext, etc. 364 virtual unsigned getCastInstrCost(unsigned Opcode, Type *Dst, 365 Type *Src) const; 366 367 /// \return The expected cost of control-flow related instructions such as 368 /// Phi, Ret, Br. 369 virtual unsigned getCFInstrCost(unsigned Opcode) const; 370 371 /// \returns The expected cost of compare and select instructions. 372 virtual unsigned getCmpSelInstrCost(unsigned Opcode, Type *ValTy, 373 Type *CondTy = nullptr) const; 374 375 /// \return The expected cost of vector Insert and Extract. 376 /// Use -1 to indicate that there is no information on the index value. 377 virtual unsigned getVectorInstrCost(unsigned Opcode, Type *Val, 378 unsigned Index = -1) const; 379 380 /// \return The cost of Load and Store instructions. 381 virtual unsigned getMemoryOpCost(unsigned Opcode, Type *Src, 382 unsigned Alignment, 383 unsigned AddressSpace) const; 384 385 /// \brief Calculate the cost of performing a vector reduction. 386 /// 387 /// This is the cost of reducing the vector value of type \p Ty to a scalar 388 /// value using the operation denoted by \p Opcode. The form of the reduction 389 /// can either be a pairwise reduction or a reduction that splits the vector 390 /// at every reduction level. 391 /// 392 /// Pairwise: 393 /// (v0, v1, v2, v3) 394 /// ((v0+v1), (v2, v3), undef, undef) 395 /// Split: 396 /// (v0, v1, v2, v3) 397 /// ((v0+v2), (v1+v3), undef, undef) 398 virtual unsigned getReductionCost(unsigned Opcode, Type *Ty, 399 bool IsPairwiseForm) const; 400 401 /// \returns The cost of Intrinsic instructions. 402 virtual unsigned getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy, 403 ArrayRef<Type *> Tys) const; 404 405 /// \returns The number of pieces into which the provided type must be 406 /// split during legalization. Zero is returned when the answer is unknown. 407 virtual unsigned getNumberOfParts(Type *Tp) const; 408 409 /// \returns The cost of the address computation. For most targets this can be 410 /// merged into the instruction indexing mode. Some targets might want to 411 /// distinguish between address computation for memory operations on vector 412 /// types and scalar types. Such targets should override this function. 413 /// The 'IsComplex' parameter is a hint that the address computation is likely 414 /// to involve multiple instructions and as such unlikely to be merged into 415 /// the address indexing mode. 416 virtual unsigned getAddressComputationCost(Type *Ty, 417 bool IsComplex = false) const; 418 419 /// @} 420 421 /// Analysis group identification. 422 static char ID; 423 }; 424 425 /// \brief Create the base case instance of a pass in the TTI analysis group. 426 /// 427 /// This class provides the base case for the stack of TTI analyzes. It doesn't 428 /// delegate to anything and uses the STTI and VTTI objects passed in to 429 /// satisfy the queries. 430 ImmutablePass *createNoTargetTransformInfoPass(); 431 432 } // End llvm namespace 433 434 #endif 435
