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[MLIR] Update DRR doc with returnType directive 

Add missing documentation.

Reviewed By: Chia-hungDuan, jpienaar

Differential Revision: https://reviews.llvm.org/D110964
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Mogball 2021-10-01 19:56:38 +00:00 committed by Jeff Niu
parent 72cf8b6044
commit 0210a3de7b
1 changed files with 29 additions and 1 deletions
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mlir/docs/DeclarativeRewrites.md
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@ -714,7 +714,7 @@ string may be specified as an attribute. The following locations are created:
* If no symbol is specified then string must be specified and a NamedLoc is
created instead;
`location` must be used as the last argument to an op creation. For example,
`location` must be used as a trailing argument to an op creation. For example,
```tablegen
def : Pat<(LocSrc1Op:$src1 (LocSrc2Op:$src2 ...),
@ -745,6 +745,34 @@ def : Pat<(Foo $input), (replaceWithValue $input)>;
The above pattern removes the `Foo` and replaces all uses of `Foo` with
`$input`.
### `returnType`
The `returnType` directive allows patterns to directly specify return types for
replacement ops that lack return type inference with op traits or user-defined
builders with return type deduction.
The `returnType` directive must be used as a trailing argument to a node
describing a replacement op. The directive comes in three forms:
* `(returnType $value)`: copy the type of the operand or result bound to
`value`.
* `(returnType "$_builder.getI32Type()")`: a string literal embedding C++. The
embedded snippet is expected to return a `Type` or a `TypeRange`.
* `(returnType (NativeCodeCall<"myFunc($0)"> $value))`: a DAG node with a native
code call that can be passed any bound variables arguments.
Specify multiple return types with a mix of any of the above. Example:
```tablegen
def : Pat<(SourceOp $arg0, $arg1),
(OpA $arg0, (TwoResultOp:$res__1 $arg1,
(returnType $arg1, "$_builder.getI64Type()")))>;
```
Explicitly-specified return types will take precedence over return types
inferred from op traits or user-defined builders. The return types of values
replacing root op results cannot be overridden.
## Debugging Tips
### Run `mlir-tblgen` to see the generated content