1 //===- llvm/Analysis/TargetTransformInfo.h ----------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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
15 // 3. Codegen-level implementation which uses target-specific hooks.
17 // This file defines #2, which is the interface that IR-level transformations
18 // use for querying the codegen.
20 //===----------------------------------------------------------------------===//
22 #ifndef LLVM_ANALYSIS_TARGETTRANSFORMINFO_H
23 #define LLVM_ANALYSIS_TARGETTRANSFORMINFO_H
25 #include "llvm/IR/Intrinsics.h"
26 #include "llvm/Pass.h"
27 #include "llvm/Support/DataTypes.h"
37 /// TargetTransformInfo - This pass provides access to the codegen
38 /// interfaces that are needed for IR-level transformations.
39 class TargetTransformInfo {
41 /// \brief The TTI instance one level down the stack.
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
46 TargetTransformInfo *PrevTTI;
48 /// \brief The top of the stack of TTI analyses available.
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;
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
60 void pushTTIStack(Pass *P);
62 /// All pass subclasses must call TargetTransformInfo::getAnalysisUsage.
63 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
66 /// This class is intended to be subclassed by real implementations.
67 virtual ~TargetTransformInfo() = 0;
69 /// \name Generic Target Information
72 /// \brief Underlying constants for 'cost' values in this interface.
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.
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.
93 /// \brief Estimate the cost of a specific operation when lowered.
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.
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.
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;
110 /// \brief Estimate the cost of a GEP operation when lowered.
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;
118 /// \brief Estimate the cost of a function call when lowered.
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
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;
129 /// \brief Estimate the cost of calling a specific function when lowered.
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;
135 /// \brief Estimate the cost of calling a specific function when lowered.
137 /// This overload allows specifying a set of candidate argument values.
138 virtual unsigned getCallCost(const Function *F,
139 ArrayRef<const Value *> Arguments) const;
141 /// \brief Estimate the cost of an intrinsic when lowered.
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;
147 /// \brief Estimate the cost of an intrinsic when lowered.
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;
153 /// \brief Estimate the cost of a given IR user when lowered.
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.
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
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;
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
174 virtual bool hasBranchDivergence() const;
176 /// \brief Test whether calls to a function lower to actual program function
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.
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;
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
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
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.
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.
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).
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
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;
234 /// \name Scalar Target Information
237 /// \brief Flags indicating the kind of support for population count.
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 {
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;
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
260 virtual bool isLegalICmpImmediate(int64_t Imm) const;
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;
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;
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;
286 /// \brief Return true if this type is legal.
287 virtual bool isTypeLegal(Type *Ty) const;
289 /// \brief Returns the target's jmp_buf alignment in bytes.
290 virtual unsigned getJumpBufAlignment() const;
292 /// \brief Returns the target's jmp_buf size in bytes.
293 virtual unsigned getJumpBufSize() const;
295 /// \brief Return true if switches should be turned into lookup tables for the
297 virtual bool shouldBuildLookupTables() const;
299 /// \brief Return hardware support for population count.
300 virtual PopcntSupportKind getPopcntSupport(unsigned IntTyWidthInBit) const;
302 /// \brief Return true if the hardware has a fast square-root instruction.
303 virtual bool haveFastSqrt(Type *Ty) const;
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;
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,
314 virtual unsigned getIntImmCost(Intrinsic::ID IID, unsigned Idx,
315 const APInt &Imm, Type *Ty) const;
318 /// \name Vector Target Information
321 /// \brief The various kinds of shuffle patterns for vector queries.
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.
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.
338 /// \brief Additional properties of an operand's values.
339 enum OperandValueProperties { OP_None = 0, OP_PowerOf2 = 1 };
341 /// \return The number of scalar or vector registers that the target has.
342 /// If 'Vectors' is true, it returns the number of vector registers. If it is
343 /// set to false, it returns the number of scalar registers.
344 virtual unsigned getNumberOfRegisters(bool Vector) const;
346 /// \return The width of the largest scalar or vector register type.
347 virtual unsigned getRegisterBitWidth(bool Vector) const;
349 /// \return The maximum unroll factor that the vectorizer should try to
350 /// perform for this target. This number depends on the level of parallelism
351 /// and the number of execution units in the CPU.
352 virtual unsigned getMaximumUnrollFactor() const;
354 /// \return The expected cost of arithmetic ops, such as mul, xor, fsub, etc.
356 getArithmeticInstrCost(unsigned Opcode, Type *Ty,
357 OperandValueKind Opd1Info = OK_AnyValue,
358 OperandValueKind Opd2Info = OK_AnyValue,
359 OperandValueProperties Opd1PropInfo = OP_None,
360 OperandValueProperties Opd2PropInfo = OP_None) const;
362 /// \return The cost of a shuffle instruction of kind Kind and of type Tp.
363 /// The index and subtype parameters are used by the subvector insertion and
364 /// extraction shuffle kinds.
365 virtual unsigned getShuffleCost(ShuffleKind Kind, Type *Tp, int Index = 0,
366 Type *SubTp = nullptr) const;
368 /// \return The expected cost of cast instructions, such as bitcast, trunc,
370 virtual unsigned getCastInstrCost(unsigned Opcode, Type *Dst,
373 /// \return The expected cost of control-flow related instructions such as
375 virtual unsigned getCFInstrCost(unsigned Opcode) const;
377 /// \returns The expected cost of compare and select instructions.
378 virtual unsigned getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
379 Type *CondTy = nullptr) const;
381 /// \return The expected cost of vector Insert and Extract.
382 /// Use -1 to indicate that there is no information on the index value.
383 virtual unsigned getVectorInstrCost(unsigned Opcode, Type *Val,
384 unsigned Index = -1) const;
386 /// \return The cost of Load and Store instructions.
387 virtual unsigned getMemoryOpCost(unsigned Opcode, Type *Src,
389 unsigned AddressSpace) const;
391 /// \brief Calculate the cost of performing a vector reduction.
393 /// This is the cost of reducing the vector value of type \p Ty to a scalar
394 /// value using the operation denoted by \p Opcode. The form of the reduction
395 /// can either be a pairwise reduction or a reduction that splits the vector
396 /// at every reduction level.
400 /// ((v0+v1), (v2, v3), undef, undef)
403 /// ((v0+v2), (v1+v3), undef, undef)
404 virtual unsigned getReductionCost(unsigned Opcode, Type *Ty,
405 bool IsPairwiseForm) const;
407 /// \returns The cost of Intrinsic instructions.
408 virtual unsigned getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
409 ArrayRef<Type *> Tys) const;
411 /// \returns The number of pieces into which the provided type must be
412 /// split during legalization. Zero is returned when the answer is unknown.
413 virtual unsigned getNumberOfParts(Type *Tp) const;
415 /// \returns The cost of the address computation. For most targets this can be
416 /// merged into the instruction indexing mode. Some targets might want to
417 /// distinguish between address computation for memory operations on vector
418 /// types and scalar types. Such targets should override this function.
419 /// The 'IsComplex' parameter is a hint that the address computation is likely
420 /// to involve multiple instructions and as such unlikely to be merged into
421 /// the address indexing mode.
422 virtual unsigned getAddressComputationCost(Type *Ty,
423 bool IsComplex = false) const;
425 /// \returns The cost, if any, of keeping values of the given types alive
428 /// Some types may require the use of register classes that do not have
429 /// any callee-saved registers, so would require a spill and fill.
430 virtual unsigned getCostOfKeepingLiveOverCall(ArrayRef<Type*> Tys) const;
434 /// Analysis group identification.
438 /// \brief Create the base case instance of a pass in the TTI analysis group.
440 /// This class provides the base case for the stack of TTI analyzes. It doesn't
441 /// delegate to anything and uses the STTI and VTTI objects passed in to
442 /// satisfy the queries.
443 ImmutablePass *createNoTargetTransformInfoPass();
445 } // End llvm namespace