Commit Graph

59 Commits

Author SHA1 Message Date
Jeff Niu b7f93c2809 [mlir] (NFC) run clang-format on all files 2022-07-14 13:32:13 -07:00
Kazu Hirata c27d815249 [mlir] Use value instead of getValue (NFC) 2022-07-14 00:19:59 -07:00
Kazu Hirata 491d27013d [mlir] Use has_value instead of hasValue (NFC) 2022-07-13 00:57:02 -07:00
Adrian Kuegel aabfaf901b [mlir] Allow empty lists for DenseArrayAttr.
Differential Revision: https://reviews.llvm.org/D129552
2022-07-13 09:16:09 +02:00
River Riddle fe4f512be7 [mlir:LSP] Add support for code completing attributes and types
This required changing a bit of how attributes/types are parsed. A new
`KeywordSwitch` class was added to AsmParser that provides a StringSwitch
like API for parsing keywords with a set of potential matches. It intends to
both provide a cleaner API, and enable injection for code completion. This
required changing the API of `generated(Attr|Type)Parser` to handle the
parsing of the keyword, instead of having the user do it. Most upstream
dialects use the autogenerated handling and didn't require a direct update.

Differential Revision: https://reviews.llvm.org/D129267
2022-07-08 16:24:55 -07:00
Mehdi Amini 7faf75bb3e Introduce a new Dense Array attribute
This attribute is similar to DenseElementsAttr but does not support
splat. As such it has a much simpler API and does not need any smart
iterator: it exposes direct ArrayRef access.

A new syntax is introduced so that the generic printing/parsing looks
like:

  [:i64 1, -2, 3]

This attribute beings like an ArrayAttr but has a `:` token after the
opening square brace to introduce the element type (supported are I8,
I16, I32, I64, F32, F64) and the comma separated list for the data.

This is particularly convenient for attributes intended to be small,
like those referring to shapes.
For example a `transpose` operation with a `dims` attribute could be
defined as such:

  let arguments = (ins AnyTensor:$input, DenseI64ArrayAttr:$dims);
  let assemblyFormat = "$input `dims` `=` $dims attr-dict : type($input)";

And printed this way (the element type is elided in this case):

  transpose %input dims = [0, 2, 1] : tensor<2x3x4xf32>

The C++ API for dims would just directly return an ArrayRef<int64>

RFC: https://discourse.llvm.org/t/rfc-introduce-a-new-dense-array-attribute/63279

Recommit with a custom DenseArrayBaseAttrStorage class to ensure
over-alignment of the storage to the largest type.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D123774
2022-06-28 13:28:06 +00:00
Mehdi Amini 744d06e4f2 Revert "Introduce a new Dense Array attribute"
This reverts commit 508eb41d82.

UBSAN indicates some pointer mis-alignment I need to investigate
2022-06-28 12:47:15 +00:00
Mehdi Amini 508eb41d82 Introduce a new Dense Array attribute
This attribute is similar to DenseElementsAttr but does not support
splat. As such it has a much simpler API and does not need any smart
iterator: it exposes direct ArrayRef access.

A new syntax is introduced so that the generic printing/parsing looks
like:

  [:i64 1, -2, 3]

This attribute beings like an ArrayAttr but has a `:` token after the
opening square brace to introduce the element type (supported are I8,
I16, I32, I64, F32, F64) and the comma separated list for the data.

This is particularly convenient for attributes intended to be small,
like those referring to shapes.
For example a `transpose` operation with a `dims` attribute could be
defined as such:

  let arguments = (ins AnyTensor:$input, DenseI64ArrayAttr:$dims);
  let assemblyFormat = "$input `dims` `=` $dims attr-dict : type($input)";

And printed this way (the element type is elided in this case):

  transpose %input dims = [0, 2, 1] : tensor<2x3x4xf32>

The C++ API for dims would just directly return an ArrayRef<int64>

RFC: https://discourse.llvm.org/t/rfc-introduce-a-new-dense-array-attribute/63279

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D123774
2022-06-28 12:08:25 +00:00
Kazu Hirata 3b7c3a654c Revert "Don't use Optional::hasValue (NFC)"
This reverts commit aa8feeefd3.
2022-06-25 11:56:50 -07:00
Kazu Hirata aa8feeefd3 Don't use Optional::hasValue (NFC) 2022-06-25 11:55:57 -07:00
Kazu Hirata 6d5fc1e3d5 [mlir] Don't use Optional::getValue (NFC) 2022-06-20 23:20:25 -07:00
Kazu Hirata 037f09959a [mlir] Don't use Optional::hasValue (NFC) 2022-06-20 11:22:37 -07:00
Chris Lattner f21896f2c6 [DenseElementAttr] Simplify the public API for creating these.
Instead of requiring the client to compute the "isSplat" bit,
compute it internally.  This makes the logic more consistent
and defines away a lot of "elements.size()==1" in the clients.

This addresses Issue #55185

Differential Revision: https://reviews.llvm.org/D125447
2022-05-12 16:18:23 +01:00
Chris Lattner 86445e8c63 [AsmParser] Adopt emitWrongTokenError more, improving QoI
This is a full audit of emitError calls, I took the opportunity
to remove extranous parens and fix a couple cases where we'd
generate multiple diagnostics for the same error.

Differential Revision: https://reviews.llvm.org/D125355
2022-05-11 20:41:12 +01:00
River Riddle 6609c1cc59 [mlir] Add a better error message when failing to parse an attribute
The fallback attribute parse path is parsing a Type attribute, but this results
in a really unintuitive error message: `expected non-function type`, which
doesn't really hint at tall that we were trying to parse an attribute. This
commit fixes this by trying to optionally parse a type, and on failure
emitting an error that we were expecting an attribute.

Differential Revision: https://reviews.llvm.org/D124870
2022-05-05 15:06:11 -07:00
Chris Lattner d85eb4e2d6 [AsmParser] Introduce a new "Argument" abstraction + supporting logic
MLIR has a common pattern for "arguments" that uses syntax
like `%x : i32 {attrs} loc("sourceloc")` which is implemented
in adhoc ways throughout the codebase.  The approach this uses
is verbose (because it is implemented with parallel arrays) and
inconsistent (e.g. lots of things drop source location info).

Solve this by introducing OpAsmParser::Argument and make addRegion
(which sets up BlockArguments for the region) take it.  Convert the
world to propagating this down.  This means that we correctly
capture and propagate source location information in a lot more
cases (e.g. see the affine.for testcase example), and it also
simplifies much code.

Differential Revision: https://reviews.llvm.org/D124649
2022-04-29 12:19:34 -07:00
Jacques Pienaar f4085c57dd [mlir] Fix two AttributeParser aborts
Reproducers that resulted in triggering the following asserts

mlir::NamedAttribute::NamedAttribute(mlir::StringAttr, mlir::Attribute)
mlir/lib/IR/Attributes.cpp:29:3
consumeToken
mlir/lib/Parser/Parser.h:126

Differential Revision: https://reviews.llvm.org/D122240
2022-04-18 09:30:35 -07:00
Siddharth Bhat e83c6aa91e [MLIR] [LangRef] Clarify parsing of dense<...>
dense<...> expects ... to be a tensor-literal.
Define this in the grammar in BuiltinAttributes.td,
and reflect this in the reference grammar written in
AttributeParser.cpp.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D121048
2022-03-16 22:25:52 +05:30
River Riddle 6842ec42f6 [mlir][NFC] Add a using for llvm::SMLoc/llvm::SMRange to LLVM.h
These are used pervasively during parsing.

Differential Revision: https://reviews.llvm.org/D118291
2022-01-26 21:37:23 -08:00
Mehdi Amini 4b12f4b2b1 Fix crash in MLIR opaque attribute parser
An assertion is triggered when the dialect is malformed.

Differential Revision: https://reviews.llvm.org/D117709
2022-01-19 23:35:48 +00:00
Stella Laurenzo 5cd0b817e2 [mlir] Allow IntegerAttr to parse zero width integers.
https://reviews.llvm.org/D109555 added support to APInt for this, so the special case to disable it is no longer valid. It is in fact legal to construct these programmatically today, and they print properly but do not parse.

Justification: zero bit integers arise naturally in various bit reduction optimization problems, and having them defined for MLIR reduces special casing.

I think there is a solid case for i0 and ui0 being supported. I'm less convinced about si0 and opted to just allow the parser to round-trip values that already verify. The counter argument is that the proper singular value for an si0 is -1. But the counter to this counter is that the sign bit is N-1, which does not exist for si0 and it is not unreasonable to consider this non-existent bit to be 0. Various sources consider it having the singular value "0" to be the least surprising.

Reviewed By: lattner

Differential Revision: https://reviews.llvm.org/D116413
2021-12-30 20:33:00 -08:00
Mehdi Amini e5639b3fa4 Fix more clang-tidy cleanups in mlir/ (NFC) 2021-12-22 20:53:11 +00:00
Mehdi Amini be0a7e9f27 Adjust "end namespace" comment in MLIR to match new agree'd coding style
See D115115 and this mailing list discussion:
https://lists.llvm.org/pipermail/llvm-dev/2021-December/154199.html

Differential Revision: https://reviews.llvm.org/D115309
2021-12-08 06:05:26 +00:00
River Riddle 195730a650 [mlir][NFC] Replace references to Identifier with StringAttr
This is part of the replacement of Identifier with StringAttr.

Differential Revision: https://reviews.llvm.org/D113953
2021-11-16 17:36:26 +00:00
River Riddle 120591e126 [mlir] Replace usages of Identifier with StringAttr
Identifier and StringAttr essentially serve the same purpose, i.e. to hold a string value. Keeping these seemingly identical pieces of functionality separate has caused problems in certain situations:

* Identifier has nice accessors that StringAttr doesn't
* Identifier can't be used as an Attribute, meaning strings are often duplicated between Identifier/StringAttr (e.g. in PDL)

The only thing that Identifier has that StringAttr doesn't is support for caching a dialect that is referenced by the string (e.g. dialect.foo). This functionality is added to StringAttr, as this is useful for StringAttr in generally the same ways it was useful for Identifier.

Differential Revision: https://reviews.llvm.org/D113536
2021-11-11 02:02:24 +00:00
Stella Laurenzo a201829a20 Fix parsing of hex-format index dense tensor attributes.
TensorLiteralParser::getHexAttr does a isIntOrIndexOrFloat check and properly handles index elements, but TensorLiteralParser::getAttr that calls into it has a mismatched check. This just makes the checks match so that index element attrs can parse when of type tensor.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D111374
2021-10-08 15:44:02 +00:00
Chris Lattner 58abc8c34b [OpAsmParser] Add a parseCommaSeparatedList helper and beef up Delimeter.
Lots of custom ops have hand-rolled comma-delimited parsing loops, as does
the MLIR parser itself.  Provides a standard interface for doing this that
is less error prone and less boilerplate.

While here, extend Delimiter to support <> and {} delimited sequences as
well (I have a use for <> in CIRCT specifically).

Differential Revision: https://reviews.llvm.org/D110122
2021-09-20 20:59:11 -07:00
River Riddle 4f21152af1 [mlir] Tighten verification of SparseElementsAttr
SparseElementsAttr currently does not perform any verfication on construction, with the only verification existing within the parser. This revision moves the parser verification to SparseElementsAttr, and also adds additional verification for when a sparse index is not valid.

Differential Revision: https://reviews.llvm.org/D109189
2021-09-21 01:57:42 +00:00
Chris Lattner faf1c22408 [Builder] Eliminate the StringRef/StringAttr forms of getSymbolRefAttr.
The StringAttr version doesn't need a context, so we can just use the
existing `SymbolRefAttr::get` form.  The StringRef version isn't preferred
so we want to encourage people to use StringAttr.

There is an additional form of getSymbolRefAttr that takes a (SymbolTrait
implementing) operation.  This should also be moved, but I'll do that as
a separate patch.

Differential Revision: https://reviews.llvm.org/D108922
2021-08-30 16:05:36 -07:00
River Riddle d6af89beb2 [mlir-lsp-server] Add support for tracking the use/def chains of symbols
This revision adds assembly state tracking for uses of symbols, allowing for go-to-definition and references support for SymbolRefAttrs.

Differential Revision: https://reviews.llvm.org/D103585
2021-06-03 16:12:27 -07:00
River Riddle d70185ec48 [mlir][IR] Support parsing hex float values in the DialectSymbolParser
This has been a TODO for a while, and prevents breakages for attributes/types that contain floats that can't roundtrip outside of the hex format.

Differential Revision: https://reviews.llvm.org/D98808
2021-03-17 13:52:32 -07:00
River Riddle caa7038a89 [mlir][IR] Move the remaining builtin attributes to ODS.
With this revision, all builtin attributes and types will have been moved to the ODS generator.

Differential Revision: https://reviews.llvm.org/D98474
2021-03-16 16:31:53 -07:00
Tres Popp c2c83e97c3 Revert "Revert "Reorder MLIRContext location in BuiltinAttributes.h""
This reverts commit 511dd4f438 along with
a couple fixes.

Original message:
Now the context is the first, rather than the last input.

This better matches the rest of the infrastructure and makes
it easier to move these types to being declaratively specified.

Phabricator: https://reviews.llvm.org/D96111
2021-02-08 10:39:58 +01:00
Tres Popp 511dd4f438 Revert "Reorder MLIRContext location in BuiltinAttributes.h"
This reverts commit 7827753f98.
2021-02-08 09:32:42 +01:00
Tres Popp 7827753f98 Reorder MLIRContext location in BuiltinAttributes.h
Now the context is the first, rather than the last input.

This better matches the rest of the infrastructure and makes
it easier to move these types to being declaratively specified.

Differential Revision: https://reviews.llvm.org/D96111
2021-02-08 09:28:09 +01:00
Chris Lattner dcac2da106 [IR Parser] Fix a crash handling zero width integer attributes.
llvm::APInt cannot hold zero bit values, therefore we shouldn't try
to form them.

Differential Revision: https://reviews.llvm.org/D94384
2021-01-10 21:18:01 -08:00
River Riddle 75eca67c1c [mlir][Parser] Fix crash in DenseElementsAttr parser when no elements are parsed
This fixes a crash when no elements are parsed, but the type expects at least one.

Fixes PR#47763

Differential Revision: https://reviews.llvm.org/D92982
2020-12-10 12:48:37 -08:00
River Riddle 09f7a55fad [mlir][Types][NFC] Move all of the builtin Type classes to BuiltinTypes.h
This is part of a larger refactoring the better congregates the builtin structures under the BuiltinDialect. This also removes the problematic "standard" naming that clashes with the "standard" dialect, which is not defined within IR/. A temporary forward is placed in StandardTypes.h to allow time for downstream users to replaced references.

Differential Revision: https://reviews.llvm.org/D92435
2020-12-03 18:02:10 -08:00
River Riddle 892605b449 [mlir][Asm] Add support for using an alias for trailing operation locations
Locations often get very long and clutter up operations when printed inline with them. This revision adds support for using aliases with trailing operation locations, and makes printing with aliases the default behavior. Aliases in the trailing location take the form `loc(<alias>)`, such as `loc(#loc0)`. As with all aliases, using `mlir-print-local-scope` can be used to disable them and get the inline behavior.

Differential Revision: https://reviews.llvm.org/D90652
2020-11-09 21:54:47 -08:00
Rahul Joshi c298824f9c [MLIR] Check for duplicate entries in attribute dictionary during custom parsing
- Verify that attributes parsed using a custom parser do not have duplicates.
- If there are duplicated in the attribute dictionary in the input, they get caught during the
  dictionary parsing.
- This check verifies that there is no duplication between the parsed dictionary and any
  attributes that might be added by the custom parser (or when the custom parsing code
  adds duplicate attributes).
- Fixes https://bugs.llvm.org/show_bug.cgi?id=48025

Differential Revision: https://reviews.llvm.org/D90502
2020-11-03 16:40:46 -08:00
Rahul Joshi c254b0bb69 [MLIR] Introduce std.global_memref and std.get_global_memref operations.
- Add standard dialect operations to define global variables with memref types and to
  retrieve the memref for to a named global variable
- Extend unit tests to test verification for these operations.

Differential Revision: https://reviews.llvm.org/D90337
2020-11-02 13:43:04 -08:00
Haruki Imai a66e334ceb [mlir] Convert raw data in dense element attributes for big-endian machines.
This patch fixes a bug [[ https://bugs.llvm.org/show_bug.cgi?id=46091 | 46091 ]]

Raw data for the `dense-element attribute` is written in little endian (LE) format.
This commit converts the format to big endian (BE) in ʻAttribute Parser` on the
 BE machine. Also, when outputting on a BE machine, the BE format is converted
 to LE in "AsmPrinter".

Differential Revision: https://reviews.llvm.org/D80695
2020-10-28 17:06:16 -07:00
River Riddle bf0440be91 [mlir] Optimize the parsing of ElementsAttr hex strings
This revision optimizes the parsing of hex strings by using the checked variant of llvm::fromHex, and adding a specialized method to Token for extracting hex strings. This leads a large decrease in compile time when parsing large hex constants (one example: 2.6 seconds -> 370 miliseconds)

Differential Revision: https://reviews.llvm.org/D90266
2020-10-28 16:58:06 -07:00
River Riddle eaeadce9bd [mlir][OpFormatGen] Add initial support for regions in the custom op assembly format
This adds some initial support for regions and does not support formatting the specific arguments of a region. For now this can be achieved by using a custom directive that formats the arguments and then parses the region.

Differential Revision: https://reviews.llvm.org/D86760
2020-08-31 13:26:24 -07:00
River Riddle d289a97f91 [mlir][PDL] Add a PDL Interpreter Dialect
The PDL Interpreter dialect provides a lower level abstraction compared to the PDL dialect, and is targeted towards low level optimization and interpreter code generation. The dialect operations encapsulates low-level pattern match and rewrite "primitives", such as navigating the IR (Operation::getOperand), creating new operations (OpBuilder::create), etc. Many of the operations within this dialect also fuse branching control flow with some form of a predicate comparison operation. This type of fusion reduces the amount of work that an interpreter must do when executing.

An example of this representation is shown below:

```mlir
// The following high level PDL pattern:
pdl.pattern : benefit(1) {
  %resultType = pdl.type
  %inputOperand = pdl.input
  %root, %results = pdl.operation "foo.op"(%inputOperand) -> %resultType
  pdl.rewrite %root {
    pdl.replace %root with (%inputOperand)
  }
}

// May be represented in the interpreter dialect as follows:
module {
  func @matcher(%arg0: !pdl.operation) {
    pdl_interp.check_operation_name of %arg0 is "foo.op" -> ^bb2, ^bb1
  ^bb1:
    pdl_interp.return
  ^bb2:
    pdl_interp.check_operand_count of %arg0 is 1 -> ^bb3, ^bb1
  ^bb3:
    pdl_interp.check_result_count of %arg0 is 1 -> ^bb4, ^bb1
  ^bb4:
    %0 = pdl_interp.get_operand 0 of %arg0
    pdl_interp.is_not_null %0 : !pdl.value -> ^bb5, ^bb1
  ^bb5:
    %1 = pdl_interp.get_result 0 of %arg0
    pdl_interp.is_not_null %1 : !pdl.value -> ^bb6, ^bb1
  ^bb6:
    pdl_interp.record_match @rewriters::@rewriter(%0, %arg0 : !pdl.value, !pdl.operation) : benefit(1), loc([%arg0]), root("foo.op") -> ^bb1
  }
  module @rewriters {
    func @rewriter(%arg0: !pdl.value, %arg1: !pdl.operation) {
      pdl_interp.replace %arg1 with(%arg0)
      pdl_interp.return
    }
  }
}
```

Differential Revision: https://reviews.llvm.org/D84579
2020-08-26 05:22:27 -07:00
Mehdi Amini f9dc2b7079 Separate the Registration from Loading dialects in the Context
This changes the behavior of constructing MLIRContext to no longer load globally
registered dialects on construction. Instead Dialects are only loaded explicitly
on demand:
- the Parser is lazily loading Dialects in the context as it encounters them
during parsing. This is the only purpose for registering dialects and not load
them in the context.
- Passes are expected to declare the dialects they will create entity from
(Operations, Attributes, or Types), and the PassManager is loading Dialects into
the Context when starting a pipeline.

This changes simplifies the configuration of the registration: a compiler only
need to load the dialect for the IR it will emit, and the optimizer is
self-contained and load the required Dialects. For example in the Toy tutorial,
the compiler only needs to load the Toy dialect in the Context, all the others
(linalg, affine, std, LLVM, ...) are automatically loaded depending on the
optimization pipeline enabled.

To adjust to this change, stop using the existing dialect registration: the
global registry will be removed soon.

1) For passes, you need to override the method:

virtual void getDependentDialects(DialectRegistry &registry) const {}

and registery on the provided registry any dialect that this pass can produce.
Passes defined in TableGen can provide this list in the dependentDialects list
field.

2) For dialects, on construction you can register dependent dialects using the
provided MLIRContext: `context.getOrLoadDialect<DialectName>()`
This is useful if a dialect may canonicalize or have interfaces involving
another dialect.

3) For loading IR, dialect that can be in the input file must be explicitly
registered with the context. `MlirOptMain()` is taking an explicit registry for
this purpose. See how the standalone-opt.cpp example is setup:

  mlir::DialectRegistry registry;
  registry.insert<mlir::standalone::StandaloneDialect>();
  registry.insert<mlir::StandardOpsDialect>();

Only operations from these two dialects can be in the input file. To include all
of the dialects in MLIR Core, you can populate the registry this way:

  mlir::registerAllDialects(registry);

4) For `mlir-translate` callback, as well as frontend, Dialects can be loaded in
the context before emitting the IR: context.getOrLoadDialect<ToyDialect>()

Differential Revision: https://reviews.llvm.org/D85622
2020-08-19 01:19:03 +00:00
Mehdi Amini e75bc5c791 Revert "Separate the Registration from Loading dialects in the Context"
This reverts commit d14cf45735.
The build is broken with GCC-5.
2020-08-19 01:19:03 +00:00
Mehdi Amini d14cf45735 Separate the Registration from Loading dialects in the Context
This changes the behavior of constructing MLIRContext to no longer load globally
registered dialects on construction. Instead Dialects are only loaded explicitly
on demand:
- the Parser is lazily loading Dialects in the context as it encounters them
during parsing. This is the only purpose for registering dialects and not load
them in the context.
- Passes are expected to declare the dialects they will create entity from
(Operations, Attributes, or Types), and the PassManager is loading Dialects into
the Context when starting a pipeline.

This changes simplifies the configuration of the registration: a compiler only
need to load the dialect for the IR it will emit, and the optimizer is
self-contained and load the required Dialects. For example in the Toy tutorial,
the compiler only needs to load the Toy dialect in the Context, all the others
(linalg, affine, std, LLVM, ...) are automatically loaded depending on the
optimization pipeline enabled.

To adjust to this change, stop using the existing dialect registration: the
global registry will be removed soon.

1) For passes, you need to override the method:

virtual void getDependentDialects(DialectRegistry &registry) const {}

and registery on the provided registry any dialect that this pass can produce.
Passes defined in TableGen can provide this list in the dependentDialects list
field.

2) For dialects, on construction you can register dependent dialects using the
provided MLIRContext: `context.getOrLoadDialect<DialectName>()`
This is useful if a dialect may canonicalize or have interfaces involving
another dialect.

3) For loading IR, dialect that can be in the input file must be explicitly
registered with the context. `MlirOptMain()` is taking an explicit registry for
this purpose. See how the standalone-opt.cpp example is setup:

  mlir::DialectRegistry registry;
  registry.insert<mlir::standalone::StandaloneDialect>();
  registry.insert<mlir::StandardOpsDialect>();

Only operations from these two dialects can be in the input file. To include all
of the dialects in MLIR Core, you can populate the registry this way:

  mlir::registerAllDialects(registry);

4) For `mlir-translate` callback, as well as frontend, Dialects can be loaded in
the context before emitting the IR: context.getOrLoadDialect<ToyDialect>()

Differential Revision: https://reviews.llvm.org/D85622
2020-08-18 23:23:56 +00:00
Mehdi Amini d84fe55e0d Revert "Separate the Registration from Loading dialects in the Context"
This reverts commit e1de2b7550.
Broke a build bot.
2020-08-18 22:16:34 +00:00
Mehdi Amini e1de2b7550 Separate the Registration from Loading dialects in the Context
This changes the behavior of constructing MLIRContext to no longer load globally
registered dialects on construction. Instead Dialects are only loaded explicitly
on demand:
- the Parser is lazily loading Dialects in the context as it encounters them
during parsing. This is the only purpose for registering dialects and not load
them in the context.
- Passes are expected to declare the dialects they will create entity from
(Operations, Attributes, or Types), and the PassManager is loading Dialects into
the Context when starting a pipeline.

This changes simplifies the configuration of the registration: a compiler only
need to load the dialect for the IR it will emit, and the optimizer is
self-contained and load the required Dialects. For example in the Toy tutorial,
the compiler only needs to load the Toy dialect in the Context, all the others
(linalg, affine, std, LLVM, ...) are automatically loaded depending on the
optimization pipeline enabled.

To adjust to this change, stop using the existing dialect registration: the
global registry will be removed soon.

1) For passes, you need to override the method:

virtual void getDependentDialects(DialectRegistry &registry) const {}

and registery on the provided registry any dialect that this pass can produce.
Passes defined in TableGen can provide this list in the dependentDialects list
field.

2) For dialects, on construction you can register dependent dialects using the
provided MLIRContext: `context.getOrLoadDialect<DialectName>()`
This is useful if a dialect may canonicalize or have interfaces involving
another dialect.

3) For loading IR, dialect that can be in the input file must be explicitly
registered with the context. `MlirOptMain()` is taking an explicit registry for
this purpose. See how the standalone-opt.cpp example is setup:

  mlir::DialectRegistry registry;
  mlir::registerDialect<mlir::standalone::StandaloneDialect>();
  mlir::registerDialect<mlir::StandardOpsDialect>();

Only operations from these two dialects can be in the input file. To include all
of the dialects in MLIR Core, you can populate the registry this way:

  mlir::registerAllDialects(registry);

4) For `mlir-translate` callback, as well as frontend, Dialects can be loaded in
the context before emitting the IR: context.getOrLoadDialect<ToyDialect>()
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