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author Shinji KONO <kono@ie.u-ryukyu.ac.jp>
date Mon, 25 May 2020 11:55:54 +0900
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1 # Introduction to MLIR Operation Traits 1 # Operation Traits
2 2
3 [TOC] 3 [TOC]
4 4
5 MLIR allows for a truly open operation ecosystem, as any dialect may define 5 MLIR allows for a truly open operation ecosystem, as any dialect may define
6 operations that suit a specific level of abstraction. `Traits` are a mechanism 6 operations that suit a specific level of abstraction. `Traits` are a mechanism
7 in which to abstract implementation details and properties that are common 7 which abstracts implementation details and properties that are common
8 across many different operations. `Traits` may be used to specify special 8 across many different operations. `Traits` may be used to specify special
9 properties and constraints of the operation, including whether the operation has 9 properties and constraints of the operation, including whether the operation has
10 side effects or whether its output has the same type as the input. Some examples 10 side effects or whether its output has the same type as the input. Some examples
11 of traits are `Commutative`, `SingleResult`, `Terminator`, etc. See the more 11 of traits are `Commutative`, `SingleResult`, `Terminator`, etc. See the more
12 [comprehensive list](#traits) below for more examples of what is possible. 12 [comprehensive list](#traits) below for more examples of what is possible.
132 may be used directly by any dialect. The format of the header for each trait 132 may be used directly by any dialect. The format of the header for each trait
133 section goes as follows: 133 section goes as follows:
134 134
135 * `Header` 135 * `Header`
136 - (`C++ class` -- `ODS class`(if applicable)) 136 - (`C++ class` -- `ODS class`(if applicable))
137
138 ### AffineScope
139
140 * `OpTrait::AffineScope` -- `AffineScope`
141
142 This trait is carried by region holding operations that define a new scope for
143 the purposes of polyhedral optimization and the affine dialect in particular.
144 Any SSA values of 'index' type that either dominate such operations, or are
145 defined at the top-level of such operations, or appear as region arguments for
146 such operations automatically become valid symbols for the polyhedral scope
147 defined by that operation. As a result, such SSA values could be used as the
148 operands or index operands of various affine dialect operations like affine.for,
149 affine.load, and affine.store. The polyhedral scope defined by an operation
150 with this trait includes all operations in its region excluding operations that
151 are nested inside of other operations that themselves have this trait.
152
153 ### AutomaticAllocationScope
154
155 * `OpTrait::AutomaticAllocationScope` -- `AutomaticAllocationScope`
156
157 This trait is carried by region holding operations that define a new scope for
158 automatic allocation. Such allocations are automatically freed when control is
159 transferred back from the regions of such operations. As an example, allocations
160 performed by [`std.alloca`](Dialects/Standard.md#stdalloca-allocaop) are
161 automatically freed when control leaves the region of its closest surrounding op
162 that has the trait AutomaticAllocationScope.
137 163
138 ### Broadcastable 164 ### Broadcastable
139 165
140 * `OpTrait::ResultsBroadcastableShape` -- `ResultsBroadcastableShape` 166 * `OpTrait::ResultsBroadcastableShape` -- `ResultsBroadcastableShape`
141 167
204 foo.yield %result : i32 230 foo.yield %result : i32
205 } 231 }
206 ``` 232 ```
207 233
208 This trait is an important structural property of the IR, and enables operations 234 This trait is an important structural property of the IR, and enables operations
209 to have [passes](WritingAPass.md) scheduled under them. 235 to have [passes](PassManagement.md) scheduled under them.
210
211 ### NoSideEffect
212
213 * `OpTrait::HasNoSideEffect` -- `NoSideEffect`
214
215 This trait signifies that the operation is pure and has no visible side effects.
216 236
217 ### Single Block with Implicit Terminator 237 ### Single Block with Implicit Terminator
218 238
219 * `OpTrait::SingleBlockImplicitTerminator<typename TerminatorOpType>` : 239 * `OpTrait::SingleBlockImplicitTerminator<typename TerminatorOpType>` :
220 `SingleBlockImplicitTerminator<string op>` 240 `SingleBlockImplicitTerminator<string op>`