Commit Graph

1426 Commits

Author SHA1 Message Date
River Riddle 0c7890c844 [mlir] Convert NamedAttribute to be a class
NamedAttribute is currently represented as an std::pair, but this
creates an extremely clunky .first/.second API. This commit
converts it to a class, with better accessors (getName/getValue)
and also opens the door for more convenient API in the future.

Differential Revision: https://reviews.llvm.org/D113956
2021-11-18 05:39:29 +00:00
River Riddle edc6c0ecb9 [mlir] Refactor AbstractOperation and OperationName
The current implementation is quite clunky; OperationName stores either an Identifier
or an AbstractOperation that corresponds to an operation. This has several problems:

* OperationNames created before and after an operation are registered are different
* Accessing the identifier name/dialect/etc. from an OperationName are overly branchy
  - they need to dyn_cast a PointerUnion to check the state

This commit refactors this such that we create a single information struct for every
operation name, even operations that aren't registered yet. When an OperationName is
created for an unregistered operation, we only populate the name field. When the
operation is registered, we populate the remaining fields. With this we now have two
new classes: OperationName and RegisteredOperationName. These both point to the
same underlying operation information struct, but only RegisteredOperationName can
assume that the operation is actually registered. This leads to a much cleaner API, and
we can also move some AbstractOperation functionality directly to OperationName.

Differential Revision: https://reviews.llvm.org/D114049
2021-11-17 22:29:57 +00:00
Michal Terepeta ddf2d62c7d [mlir][Vector] First step for 0D vector type
There seems to be a consensus that we should allow 0D vectors:
https://llvm.discourse.group/t/should-we-have-0-d-vectors/3097

This commit is only the first step: it changes the verifier and the parser to
allow vectors like `vector<f32>` (but does not allow explicit 0 dimensions,
i.e., `vector<0xf32>` is not allowed).

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D114086
2021-11-17 14:58:24 +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
Arnab Dutta 1402299271 [MLIR] Simplify semi-affine expressions using flattening
For the semi affine expressions, whenever rhs of a floordiv, ceildiv, mod
or product expression is a symbolic expression, we introduce a local variable
representing the result, and store the floordiv/ceildiv, mod or product
affine expression in LocalExprs. In this way the expression is flattened,
and trivial addition and subtraction related simplifications are performed.
Also rule based matching for detecting and transforming "expr - q * (expr floordiv q)"
to "expr mod q", where q is a symbolic exxpression, in simplifyAdd function.

Differential Revision: https://reviews.llvm.org/D112808
2021-11-16 15:42:22 +05:30
River Riddle 6de6131f02 [mlir] Optimize usage of llvm::mapped_iterator
mapped_iterator is a useful abstraction for applying a
map function over an existing iterator, but our current
usage ends up allocating storage/making indirect calls
even with the map function is a known function, which
is horribly inefficient. This commit refactors the usage
of mapped_iterator to avoid this, and allows for directly
referencing the map function when dereferencing.

Fixes PR52319

Differential Revision: https://reviews.llvm.org/D113511
2021-11-11 03:26:29 +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
River Riddle ae40d62541 [mlir] Refactor ElementsAttr's value access API
There are several aspects of the API that either aren't easy to use, or are
deceptively easy to do the wrong thing. The main change of this commit
is to remove all of the `getValue<T>`/`getFlatValue<T>` from ElementsAttr
and instead provide operator[] methods on the ranges returned by
`getValues<T>`. This provides a much more convenient API for the value
ranges. It also removes the easy-to-be-inefficient nature of
getValue/getFlatValue, which under the hood would construct a new range for
the type `T`. Constructing a range is not necessarily cheap in all cases, and
could lead to very poor performance if used within a loop; i.e. if you were to
naively write something like:

```
DenseElementsAttr attr = ...;
for (int i = 0; i < size; ++i) {
  // We are internally rebuilding the APFloat value range on each iteration!!
  APFloat it = attr.getFlatValue<APFloat>(i);
}
```

Differential Revision: https://reviews.llvm.org/D113229
2021-11-09 00:15:08 +00:00
Christian Sigg fce529fc6e Fix `insertFunctionArguments()` block argument order.
Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D113171
2021-11-05 10:08:20 +01:00
Mogball 2125eb3446 [mlir][core] Slightly improved attribute lookup
- String binary search does 1 less string comparison
- Identifier linear scan on large attribute list is switched to string binary search

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D112970
2021-11-04 21:48:58 +00:00
Chia-hung Duan 64ce74a6c8 [mlir] Handle StringAttr in SparseElementsAttr::getZeroAttr.
Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D111203
2021-11-04 18:18:20 +00:00
River Riddle 7f312f6d79 [mlir] Avoid folding in OpBuilder::tryFold when types change
This was missed when tightening fold restrictions in https://reviews.llvm.org/D95991.

Differential Revision: https://reviews.llvm.org/D113138
2021-11-03 20:35:46 +00:00
River Riddle a039113446 [mlir] Move the Operation OperandStorage to the first trailing object
The main benefits of this change are faster access to operands
(no need to compute the offset, as it is now right after the
operation), simpler code(no need to manage a lot of the "is the
operand storage trailing" logic we had to before). The major
downside to this though, is that operand holding operations now
grow in size by 1 word (as no matter how we do this change, there
will need to be some additional book keeping).

Differential Revision: https://reviews.llvm.org/D111695
2021-11-03 18:34:31 +00:00
Alex Zinenko feec2d901c [mlir] return the updated symbol table after inserting into SymbolTable
Inserting a symbol into a SymbolTable may lead to the name of the symbol being
changed in order to ensure uniqueness of symbol names in the table. Return this
new name to spare the caller the need to extract it from the symbol operation.

Depends On D112700

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D112886
2021-11-02 14:22:57 +01:00
Mehdi Amini 19ced834cc Check if an attribute is in the builtin dialect before going through all the possible combinations (NFC)
This is just a "micro-optimization" noticed through code review.

Differential Revision: https://reviews.llvm.org/D112984
2021-11-02 05:57:40 +00:00
Alex Zinenko 24685aaeb7 [mlir][python] allow for detaching operations from a block
Provide support for removing an operation from the block that contains it and
moving it back to detached state. This allows for the operation to be moved to
a different block, a common IR manipulation for, e.g., module merging.

Also fix a potential one-past-end iterator dereference in Operation::moveAfter
discovered in the process.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D112700
2021-10-31 09:42:15 +01:00
Markus Böck 10a80c4413 [mlir] Implement replacement of SymbolRefAttrs in Dialect attributes using SubElementAttr interface
This patch extends the SubElementAttr interface to allow replacing a contained sub attribute. The attribute that should be replaced is identified by an index which denotes the n-th element returned by the accompanying walkImmediateSubElements method.

Using this addition the patch implements replacing SymbolRefAttrs contained within any dialect attributes.

Differential Revision: https://reviews.llvm.org/D111357
2021-10-28 19:08:20 +02:00
Kazu Hirata a88867a085 [IR] Fix a warning
This patch fixes:

  mlir/lib/IR/BuiltinAttributes.cpp:876:39: error: unused function
  'isComplexOfIntType' [-Werror,-Wunused-function]

in a release build.
2021-10-28 09:38:25 -07:00
River Riddle 015192c634 [mlir:DialectConversion] Restructure how argument/target materializations get invoked
The current implementation invokes materializations
whenever an input operand does not have a mapping for the
desired type, i.e. it requires materialization at the earliest possible
point. This conflicts with goal of dialect conversion (and also the
current documentation) which states that a materialization is only
required if the materialization is supposed to persist after the
conversion process has finished.

This revision refactors this such that whenever a target
materialization "might" be necessary, we insert an
unrealized_conversion_cast to act as a temporary materialization.
This allows for deferring the invocation of the user
materialization hooks until the end of the conversion process,
where we actually have a better sense if it's actually
necessary. This has several benefits:

* In some cases a target materialization hook is no longer
   necessary
When performing a full conversion, there are some situations
where a temporary materialization is necessary. Moving forward,
these users won't need to provide any target materializations,
as the temporary materializations do not require the user to
provide materialization hooks.

* getRemappedValue can now handle values that haven't been
   converted yet
Before this commit, it wasn't well supported to get the remapped
value of a value that hadn't been converted yet (making it
difficult/impossible to convert multiple operations in many
situations). This commit updates getRemappedValue to properly
handle this case by inserting temporary materializations when
necessary.

Another code-health related benefit is that with this change we
can move a majority of the complexity related to materializations
to the end of the conversion process, instead of handling adhoc
while conversion is happening.

Differential Revision: https://reviews.llvm.org/D111620
2021-10-27 02:09:04 +00:00
Uday Bondhugula 41a8b46007 [MLIR] Fix AffineExpr getLargestKnownDivisor for ceildiv and floordiv
Fix AffineExpr `getLargestKnownDivisor` for ceil/floor div cases.
In these cases, nothing can be inferred on the divisor of the
result.

Add test case for `mod` as well.

Differential Revision: https://reviews.llvm.org/D112523
2021-10-26 16:21:29 +05:30
Kazu Hirata 4ba9d9c84f Use StringRef::contains (NFC) 2021-10-23 20:41:46 -07:00
Vladislav Vinogradov e41ebbecf9 [mlir][RFC] Refactor layout representation in MemRefType
The change is based on the proposal from the following discussion:
https://llvm.discourse.group/t/rfc-memreftype-affine-maps-list-vs-single-item/3968

* Introduce `MemRefLayoutAttr` interface to get `AffineMap` from an `Attribute`
  (`AffineMapAttr` implements this interface).
* Store layout as a single generic `MemRefLayoutAttr`.

This change removes the affine map composition feature and related API.
Actually, while the `MemRefType` itself supported it, almost none of the upstream
can work with more than 1 affine map in `MemRefType`.

The introduced `MemRefLayoutAttr` allows to re-implement this feature
in a more stable way - via separate attribute class.

Also the interface allows to use different layout representations rather than affine maps.
For example, the described "stride + offset" form, which is currently supported in ASM parser only,
can now be expressed as separate attribute.

Reviewed By: ftynse, bondhugula

Differential Revision: https://reviews.llvm.org/D111553
2021-10-19 12:31:15 +03:00
Mogball 21bb463e96 [mlir] fix bugs with NamedAttrList
- `assign` with ArrayRef was calling `append`
- `assign` with empty ArrayRef was not clearing storage

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D112043
2021-10-19 01:30:00 +00:00
River Riddle a77cd55dea [mlir] Add support for specifying printing flags when adding an op to a Diagnostic
This removes edge cases where the default flags we want to use
during printing (e.g. local scope, eliding attributes, etc.)
get missed/dropped.

Differential Revision: https://reviews.llvm.org/D111761
2021-10-18 15:07:55 +00:00
Andrew Young 844706701e
[MLIR] Add `KeywordOrString` handling to AsmParser
This adds a new parser and printer for text which may be a keyword or a
string. When printing, it will attempt to print the text as a keyword,
but if it has any special or non-printable characters, it will be
printed as an escaped string.  When parsing, it will parse either a
valid keyword or a potentially escaped string. The printer allows for an
empty string, in which case it prints `""`.

This new function is used for printing the name in NamedAttributes, and
for printing the symbol name after the `@`. In CIRCT we are using this
to print module port names, which are conceptually similar to named
function arguments.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D111683
2021-10-15 00:08:34 -07:00
Uday Bondhugula 05fb26062c [MLIR] Fix assert crash when an unregistered dialect op is encountered
Fix assert crash when an unregistered dialect op is encountered during
parsing and `-allow-unregistered-dialect' isn't on. Instead, emit an
error.

While on this, clean up "registered" vs "loaded" on `getDialect()` and
local clang-tidy warnings.

https://llvm.discourse.group/t/assert-behavior-on-unregistered-dialect-ops/4402

Differential Revision: https://reviews.llvm.org/D111628
2021-10-14 15:43:53 +05:30
Diego Caballero 5c1d356c18 [mlir][Linalg] Enable vectorization of explicit broadcasts
This patch teaches `isProjectedPermutation` and `inverseAndBroadcastProjectedPermutation`
utilities to deal with maps representing an explicit broadcast, e.g., (d0, d1) -> (d0, 0).
This extension is needed to enable vectorization of such explicit broadcast in Linalg.

Reviewed By: pifon2a, nicolasvasilache

Differential Revision: https://reviews.llvm.org/D111563
2021-10-12 21:08:22 +00:00
Vladislav Vinogradov c6390f19f2 [mlir] Fix AsmPrinter for types with sub elements
Call `printType(subElemType)` instead of `os << subElemType` for them.
It allows to handle type aliases inside complex types.

As a side effect, fixed `test.int` parsing.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D111536
2021-10-12 12:08:16 +03:00
Stella Laurenzo 5d6d30edf8 [mlir] Extend C and Python API to support bulk loading of DenseElementsAttr.
* This already half existed in terms of reading the raw buffer backing a DenseElementsAttr.
* Documented the precise expectations of the buffer layout.
* Extended the Python API to support construction from bitcasted buffers, allowing construction of all primitive element types (even those that lack a compatible representation in Python).
* Specifically, the Python API can now load all integer types at all bit widths and all floating point types (f16, f32, f64, bf16).

Differential Revision: https://reviews.llvm.org/D111284
2021-10-07 08:42:12 -07:00
Geoffrey Martin-Noble b096ac9092 [MLIR] Improve debug messages in BuiltinTypes
It's nice for users to have more information when debugging failures and
these are only triggered in a failure path.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D107676
2021-10-06 09:42:13 -07:00
Mehdi Amini 00b7d95182 Stop stripping the `std.` prefix when printing operations in a region with a defined default dialect
This fixes round-trip / ambiguity when an operation in the standard dialect would
have the same name as an operation in the default dialect.

Differential Revision: https://reviews.llvm.org/D111204
2021-10-06 02:36:14 +00:00
Nicolas Vasilache fab634b4e2 [mlir] Tighten strided layout specification.
Clarify that the strided layout specification is represented by a single semi-affine map.

Differential Revision: https://reviews.llvm.org/D110921
2021-10-04 10:37:05 +00:00
Mehdi Amini 9312cb6f20 Fix Undefined Behavior in MLIR Diagnostic: don't call memcpy with a nullptr source
This happens when streaming an empty Twine as part of a diagnostic.

Differential Revision: https://reviews.llvm.org/D111002
2021-10-02 21:32:20 +00:00
Chris Lattner 33f4315324 [AsmParser] move AsmParser::getContext to IR library.
This is (perhaps unintuitively) where the other AsmParser method
implementations are, which means that dialects don't generally need
to depend on MLIRParser directly.  This should fix a build failure
building .so files on the mlir-nvidia builder.
2021-09-29 22:07:00 -07:00
Diego Caballero 2a876a711d [mlir] Create a generic reduction detection utility
This patch introduces a generic reduction detection utility that works
across different dialecs. It is mostly a generalization of the reduction
detection algorithm in Affine. The reduction detection logic in Affine,
Linalg and SCFToOpenMP have been replaced with this new generic utility.

The utility takes some basic components of the potential reduction and
returns: 1) the reduced value, and 2) a list with the combiner operations.
The logic to match reductions involving multiple combiner operations disabled
until we can properly test it.

Reviewed By: ftynse, bondhugula, nicolasvasilache, pifon2a

Differential Revision: https://reviews.llvm.org/D110303
2021-09-24 20:45:59 +00:00
River Riddle 531206310a [mlir:OpAsm] Factor out the common bits of (Op/Dialect)Asm(Parser/Printer)
This has a few benefits:
* It allows for defining parsers/printer code blocks that
  can be shared between operations and attribute/types.
* It removes the weird duplication of generic parser/printer hooks,
  which means that newly added hooks only require touching one class.

Differential Revision: https://reviews.llvm.org/D110375
2021-09-24 20:12:19 +00:00
Chris Lattner da93829b44 [DialectAsmPrinter] Add missing 'printAttributeWithoutType' member.
DialectAsmParser has a `parseAttribute` member that takes a
contextual type, but DialectAsmPrinter doesn't have the corresponding
member to take advantage of it.  As such, custom attribute
implementations can't really use it.  This adds the obvious missing
method which fills this hole.

Differential Revision: https://reviews.llvm.org/D110211
2021-09-21 18:45:24 -07:00
River Riddle d80d3a358f [mlir] Refactor ElementsAttr into an AttrInterface
This revision refactors ElementsAttr into an Attribute Interface.
This enables a common interface with which to interact with
element attributes, without needing to modify the builtin
dialect. It also removes a majority (if not all?) of the need for
the current OpaqueElementsAttr, which was originally intended as
a way to opaquely represent data that was not representable by
the other builtin constructs.

The new ElementsAttr interface not only allows for users to
natively represent their data in the way that best suits them,
it also allows for efficient opaque access and iteration of the
underlying data. Attributes using the ElementsAttr interface
can directly expose support for interacting with the held
elements using any C++ data type they claim to support. For
example, DenseIntOrFpElementsAttr supports iteration using
various native C++ integer/float data types, as well as
APInt/APFloat, and more. ElementsAttr instances that refer to
DenseIntOrFpElementsAttr can use all of these data types for
iteration:

```c++
DenseIntOrFpElementsAttr intElementsAttr = ...;

ElementsAttr attr = intElementsAttr;
for (uint64_t value : attr.getValues<uint64_t>())
  ...;
for (APInt value : attr.getValues<APInt>())
  ...;
for (IntegerAttr value : attr.getValues<IntegerAttr>())
  ...;
```

ElementsAttr also supports failable range/iterator access,
allowing for selective code paths depending on data type
support:

```c++
ElementsAttr attr = ...;
if (auto range = attr.tryGetValues<uint64_t>()) {
  for (uint64_t value : *range)
    ...;
}
```

Differential Revision: https://reviews.llvm.org/D109190
2021-09-21 01:57:43 +00:00
River Riddle 0cb5d7fc7f [mlir] Add value_begin/value_end methods to DenseElementsAttr
Currently DenseElementsAttr only exposes the ability to get the full range of values for a given type T, but there are many situations where we just want the beginning/end iterator. This revision adds proper value_begin/value_end methods for all of the supported T types, and also cleans up a bit of the interface.

Differential Revision: https://reviews.llvm.org/D104173
2021-09-21 01:57:43 +00:00
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
Krzysztof Drewniak 121aab84d1 [MLIR][Affine] Simplify nested modulo operations when able
It is the case that, for all positive a and b such that b divides a
(e mod (a * b)) mod b = e mod b. For example, ((d0 mod 35) mod 5) can
be simplified to (d0 mod 5), but ((d0 mod 35) mod 4) cannot be simplified
further (x = 36 is a counterexample).

This change enables more complex simplifications. For example,
((d0 * 72 + d1) mod 144) mod 9 can now simplify to (d0 * 72 + d1) mod 9
and thus to d1 mod 9. Expressions with chained modulus operators are
reasonably common in tensor applications, and this change _should_
improve code generation for such expressions.

Reviewed By: nicolasvasilache

Differential Revision: https://reviews.llvm.org/D109930
2021-09-17 19:06:00 +00:00
Mehdi Amini a32300a68f Make the --mlir-disable-threading command line option overrides the C++ API usage
This seems in-line with the intent and how we build tools around it.
Update the description for the flag accordingly.
Also use an injected thread pool in MLIROptMain, now we will create
threads up-front and reuse them across split buffers.

Differential Revision: https://reviews.llvm.org/D109802
2021-09-15 03:20:48 +00:00
Mehdi Amini 1a406cd5f2 Remove unused llvm/Support/Parallel.h from MLIR (NFC)
This header aren't needed anymore: MLIR is using a thread pool
injected in the context instead of a global one.
2021-09-14 23:30:42 +00:00
Uday Bondhugula a91cfd1990 [MLIR] Improve op parse error message for AtLeastNOperands trait
Improve parse error message for "at least N operands" op trait.

Differential Revision: https://reviews.llvm.org/D109747
2021-09-14 15:01:51 +05:30
Chris Lattner 735f46715d [APInt] Normalize naming on keep constructors / predicate methods.
This renames the primary methods for creating a zero value to `getZero`
instead of `getNullValue` and renames predicates like `isAllOnesValue`
to simply `isAllOnes`.  This achieves two things:

1) This starts standardizing predicates across the LLVM codebase,
   following (in this case) ConstantInt.  The word "Value" doesn't
   convey anything of merit, and is missing in some of the other things.

2) Calling an integer "null" doesn't make any sense.  The original sin
   here is mine and I've regretted it for years.  This moves us to calling
   it "zero" instead, which is correct!

APInt is widely used and I don't think anyone is keen to take massive source
breakage on anything so core, at least not all in one go.  As such, this
doesn't actually delete any entrypoints, it "soft deprecates" them with a
comment.

Included in this patch are changes to a bunch of the codebase, but there are
more.  We should normalize SelectionDAG and other APIs as well, which would
make the API change more mechanical.

Differential Revision: https://reviews.llvm.org/D109483
2021-09-09 09:50:24 -07:00
Mehdi Amini 387f95541b Add a new interface allowing to set a default dialect to be used for printing/parsing regions
Currently the builtin dialect is the default namespace used for parsing
and printing. As such module and func don't need to be prefixed.
In the case of some dialects that defines new regions for their own
purpose (like SpirV modules for example), it can be beneficial to
change the default dialect in order to improve readability.

Differential Revision: https://reviews.llvm.org/D107236
2021-08-31 17:52:40 +00:00
Mehdi Amini c41b16c26b Change ASM Op printer to print the operation name in the framework instead of leaving it up to each individual operation
This aligns the printer with the parser contract: the operation isn't part of the user-controllable part of the syntax.

Differential Revision: https://reviews.llvm.org/D108804
2021-08-31 17:52:40 +00:00
Mehdi Amini fd87963eee Change dialect `printOperation()` hook to `getOperationPrinter()`
This makes the hook return a printer if available, instead of using LogicalResult  to
indicate if a printer was available (and invoked). This allows the caller to detect that
the dialect has a printer for a given operation without actually invoking the printer.
It'll be leveraged in a future revision to move printing the op name itself under control
of the ASMPrinter.

Differential Revision: https://reviews.llvm.org/D108803
2021-08-31 17:52:39 +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
Chris Lattner 41d4aa7de6 [SymbolRefAttr] Revise SymbolRefAttr to hold a StringAttr.
SymbolRefAttr is fundamentally a base string plus a sequence
of nested references.  Instead of storing the string data as
a copies StringRef, store it as an already-uniqued StringAttr.

This makes a lot of things simpler and more efficient because:
1) references to the symbol are already stored as StringAttr's:
   there is no need to copy the string data into MLIRContext
   multiple times.
2) This allows pointer comparisons instead of string
   comparisons (or redundant uniquing) within SymbolTable.cpp.
3) This allows SymbolTable to hold a DenseMap instead of a
   StringMap (which again copies the string data and slows
   lookup).

This is a moderately invasive patch, so I kept a lot of
compatibility APIs around.  It would be nice to explore changing
getName() to return a StringAttr for example (right now you have
to use getNameAttr()), and eliminate things like the StringRef
version of getSymbol.

Differential Revision: https://reviews.llvm.org/D108899
2021-08-29 21:54:47 -07:00