Commit Graph

415 Commits

Author SHA1 Message Date
Alex Zinenko 559e816f3f Add OpTraits for operand types: IntegerLike and SameType.
Introduce new OpTraits verifying relation between operands of an Operation,
similarly to its results.  Arithmetic operations are defined separately for
integer and floating point types.  While we are currently leveraging the
equality of result and operand types to make sure the right arithmetic
operations are used for the right types, we may eventually want to verify
operand types directly.  Furthermore, for upcoming comparison operations, the
type of the result differs from those of the operands so we need to verify the
operand types directly.  Similarly, we will want to restrict comparisons (and
potentially binary arithmetic operations) to operands of the same type.

PiperOrigin-RevId: 220365629
2019-03-29 13:49:19 -07:00
Uday Bondhugula 6cd5d5c544 Introduce loop tiling code generation (hyper-rectangular case)
- simple perfectly nested band tiling with fixed tile sizes.
- only the hyper-rectangular case is handled, with other limitations of
  getIndexSet applying (constant loop bounds, etc.);  once
  the latter utility is extended, tiled code generation should become more
  general.
- Add FlatAffineConstraints::isHyperRectangular()

PiperOrigin-RevId: 220324933
2019-03-29 13:49:05 -07:00
Jacques Pienaar 5e01000d46 Start TFLite legalizer pass
Start of TFLite legalizer pass. Currently focussed on macro expanding ops, limited to what is registered directly in a separate pass (this should instead be a general pass), no querying of what gets produced, the matching is string based instead of using the ops proper (the matching TF ops should be defined) etc. This is a step to enable prototyping. In addition to the above shortcomings, the legalizer is very verbose in this form and should instead be driven by autogenerated patterns (same is true for the op builders too). But this starts from the explicit form and extracting out commonality in follow up.

Add definition for tfl.relu for basic selection of fused relu add.

PiperOrigin-RevId: 220287087
2019-03-29 13:48:50 -07:00
Uday Bondhugula 4269a01863 Clean up memref dep check utilities; update FlatAffineConstraints API, add
simple utility methods.

- clean up some of the analysis utilities used by memref dep checking
- add additional asserts / comments at places in analysis utilities
- add additional simple methods to the FlatAffineConstraints API.

PiperOrigin-RevId: 220124523
2019-03-29 13:48:35 -07:00
Jacques Pienaar 9a62178372 Rename OpRegistration to DialectRegistration. NFC.
The op registration files now are registering dialects instead, mechanical update names to reflect the change.

PiperOrigin-RevId: 219825547
2019-03-29 13:48:20 -07:00
MLIR Team 239e328913 Adds MemRefDependenceCheck analysis pass, plus multiple dependence check tests.
Adds equality constraints to dependence constraint system for accesses using dims/symbols where the defining operation of the dim/symbol is a constant.

PiperOrigin-RevId: 219814740
2019-03-29 13:48:05 -07:00
Alex Zinenko 4aeb0a872c Uniformize MemRefType well-formedness checks.
Introduce a new public static member function, MemRefType::getChecked, intended
for the users that want detailed error messages to be emitted during MemRefType
construction and can gracefully handle these errors.  This function takes a
Location of the "MemRef" token if known.  The parser is one user of getChecked
that has location information, it outputs errors as compiler diagnostics.
Other users may pass in an instance of UnknownLoc and still have error messages
emitted.  Compiler-internal users not expecting the MemRefType construction to
fail should call MemRefType::get, which now aborts on failure with a generic
message.

Both "getChecked" and "get" call to a static free function that does actual
construction with well-formedness checks, optionally emits errors and returns
nullptr on failure.

The location information passed to getChecked has voluntarily coarse precision.
The error messages are intended for compiler engineers and do not justify
heavier API than a single location.  The text of the messages can be written so
that it pinpoints the actual location of the error within a MemRef declaration.

PiperOrigin-RevId: 219765902
2019-03-29 13:47:49 -07:00
Uday Bondhugula 74c62c8ce0 Complete memref bound checker for arbitrary affine expressions. Handle local
variables from mod's and div's when converting to flat form.

- propagate mod, floordiv, ceildiv / local variables constraint information
  when flattening affine expressions and converting them into flat affine
  constraints; resolve multiple TODOs.
- enables memref bound checker to work with arbitrary affine expressions
- update FlatAffineConstraints API with several new methods
- test/exercise functionality mostly through -memref-bound-check
- other analyses such as dependence tests, etc. should now be able to work in the
  presence of any affine composition of add, mul, floor, ceil, mod.

PiperOrigin-RevId: 219711806
2019-03-29 13:47:29 -07:00
MLIR Team f28e4df666 Adds a dependence check to test whether two accesses to the same memref access the same element.
- Builds access functions and iterations domains for each access.
- Builds dependence polyhedron constraint system which has equality constraints for equated access functions and inequality constraints for iteration domain loop bounds.
- Runs elimination on the dependence polyhedron to test if no dependence exists between the accesses.
- Adds a trivial LoopFusion transformation pass with a simple test policy to test dependence between accesses to the same memref in adjacent loops.
- The LoopFusion pass will be extended in subsequent CLs.

PiperOrigin-RevId: 219630898
2019-03-29 13:47:13 -07:00
Nicolas Vasilache 21638dcda9 [MLIR] Extend vectorization to 2+-D patterns
This CL adds support for vectorization using more interesting 2-D and 3-D
patterns. Note in particular the fact that we match some pretty complex
imperfectly nested 2-D patterns with a quite minimal change to the
implementation: we just add a bit of recursion to traverse the matched
patterns and actually vectorize the loops.

For instance, vectorizing the following loop by 128:
```
for %i3 = 0 to %0 {
  %7 = affine_apply (d0) -> (d0)(%i3)
  %8 = load %arg0[%c0_0, %7] : memref<?x?xf32>
}
```

Currently generates:
```
#map0 = ()[s0] -> (s0 + 127)
#map1 = (d0) -> (d0)
for %i3 = 0 to #map0()[%0] step 128 {
  %9 = affine_apply #map1(%i3)
  %10 = alloc() : memref<1xvector<128xf32>>
  %11 = "n_d_unaligned_load"(%arg0, %c0_0, %9, %10, %c0) :
    (memref<?x?xf32>, index, index, memref<1xvector<128xf32>>, index) ->
    (memref<?x?xf32>, index, index, memref<1xvector<128xf32>>, index)
   %12 = load %10[%c0] : memref<1xvector<128xf32>>
}
```

The above is subject to evolution.

PiperOrigin-RevId: 219629745
2019-03-29 13:46:58 -07:00
MLIR Team 710b20aeb1 Fix formatting of mlir snippet.
PiperOrigin-RevId: 219535523
2019-03-29 13:46:36 -07:00
Jacques Pienaar e1f9e65b9a Enable constructing a FuncBuilder using a Operation*.
FuncBuilder is useful to build a operation to replace an existing operation, so change the constructor to allow constructing it with an existing operation. Change FuncBuilder to contain (effectively) a tagged union of CFGFuncBuilder and MLFuncBuilder (as these should be cheap to copy and avoid allocating/deletion when created via a operation).

PiperOrigin-RevId: 219532952
2019-03-29 13:46:22 -07:00
Uday Bondhugula 8201e19e3d Introduce memref bound checking.
Introduce analysis to check memref accesses (in MLFunctions) for out of bound
ones. It works as follows:

$ mlir-opt -memref-bound-check test/Transforms/memref-bound-check.mlir

/tmp/single.mlir:10:12: error: 'load' op memref out of upper bound access along dimension tensorflow/mlir#1
      %x = load %A[%idxtensorflow/mlir#0, %idxtensorflow/mlir#1] : memref<9 x 9 x i32>
           ^
/tmp/single.mlir:10:12: error: 'load' op memref out of lower bound access along dimension tensorflow/mlir#1
      %x = load %A[%idxtensorflow/mlir#0, %idxtensorflow/mlir#1] : memref<9 x 9 x i32>
           ^
/tmp/single.mlir:10:12: error: 'load' op memref out of upper bound access along dimension tensorflow/mlir#2
      %x = load %A[%idxtensorflow/mlir#0, %idxtensorflow/mlir#1] : memref<9 x 9 x i32>
           ^
/tmp/single.mlir:10:12: error: 'load' op memref out of lower bound access along dimension tensorflow/mlir#2
      %x = load %A[%idxtensorflow/mlir#0, %idxtensorflow/mlir#1] : memref<9 x 9 x i32>
           ^
/tmp/single.mlir:12:12: error: 'load' op memref out of upper bound access along dimension tensorflow/mlir#1
      %y = load %B[%idy] : memref<128 x i32>
           ^
/tmp/single.mlir:12:12: error: 'load' op memref out of lower bound access along dimension tensorflow/mlir#1
      %y = load %B[%idy] : memref<128 x i32>
           ^
#map0 = (d0, d1) -> (d0, d1)
#map1 = (d0, d1) -> (d0 * 128 - d1)
mlfunc @test() {
  %0 = alloc() : memref<9x9xi32>
  %1 = alloc() : memref<128xi32>
  for %i0 = -1 to 9 {
    for %i1 = -1 to 9 {
      %2 = affine_apply #map0(%i0, %i1)
      %3 = load %0[%2tensorflow/mlir#0, %2tensorflow/mlir#1] : memref<9x9xi32>
      %4 = affine_apply #map1(%i0, %i1)
      %5 = load %1[%4] : memref<128xi32>
    }
  }
  return
}

- Improves productivity while manually / semi-automatically developing MLIR for
  testing / prototyping; also provides an indirect way to catch errors in
  transformations.

- This pass is an easy way to test the underlying affine analysis
  machinery including low level routines.

Some code (in getMemoryRegion()) borrowed from @andydavis cl/218263256.

While on this:

- create mlir/Analysis/Passes.h; move Pass.h up from mlir/Transforms/ to mlir/

- fix a bug in AffineAnalysis.cpp::toAffineExpr

TODO: extend to non-constant loop bounds (straightforward). Will transparently
work for all accesses once floordiv, mod, ceildiv are supported in the
AffineMap -> FlatAffineConstraints conversion.
PiperOrigin-RevId: 219397961
2019-03-29 13:46:08 -07:00
River Riddle 4c465a181d Implement value type abstraction for types.
This is done by changing Type to be a POD interface around an underlying pointer storage and adding in-class support for isa/dyn_cast/cast.

PiperOrigin-RevId: 219372163
2019-03-29 13:45:54 -07:00
Jacques Pienaar 75376b8e33 Change Attr to have a storage and return type.
Separate the storage and return type more explicitly. This is in preparation for, among others, allowing supporting enum attributes where the return type is a enum class. NFC.

PiperOrigin-RevId: 219368487
2019-03-29 13:45:38 -07:00
Uday Bondhugula c5128e152a FlatAffineConstraints API update - additional methods
- add methods addConstantLowerBound, addConstantUpperBound, setIdToConstant,
  addDimsForMap
- update coefficient storage to use numReservedCols * rows instead of numCols *
  rows (makes the code simpler/natural; reduces movement of data when new
  columns are added, eliminates movement of data when columns are added to the
  end).

(addDimsForMap is tested in the child CL on memref bound checking: cl/219000460)

PiperOrigin-RevId: 219358376
2019-03-29 13:45:14 -07:00
Lei Zhang 5ffb211bff Rename mlir::match to mlir::matchPattern and add m_Op()
- We already have Pattern::match(). Using mlir::match() in Pattern::match()
  confuses the compiler.
- Created m_Op() to avoid using detailed matcher implementation in
  StandardOps.cpp.

PiperOrigin-RevId: 219328823
2019-03-29 13:44:47 -07:00
Nicolas Vasilache af7f56fdf8 [MLIR] Implement 1-D vectorization for fastest varying load/stores
This CL is a first in a series that implements early vectorization of
increasingly complex patterns. In particular, early vectorization will support
arbitrary loop nesting patterns (both perfectly and imperfectly nested), at
arbitrary depths in the loop tree.

This first CL builds the minimal support for applying 1-D patterns.
It relies on an unaligned load/store op abstraction that can be inplemented
differently on different HW.
Future CLs will support higher dimensional patterns, but 1-D patterns already
exhibit interesting properties.
In particular, we want to separate pattern matching (i.e. legality both
structural and dependency analysis based), from profitability analysis, from
application of the transformation.
As a consequence patterns may intersect and we need to verify that a pattern
can still apply by the time we get to applying it.

A non-greedy analysis on profitability that takes into account pattern
intersection is left for future work.

Additionally the CL makes the following cleanups:
1. the matches method now returns a value, not a reference;
2. added comments about the MLFunctionMatcher and MLFunctionMatches usage by
value;
3. added size and empty methods to matches;
4. added a negative vectorization test with a conditional, this exhibited a
but in the iterators. Iterators now return nullptr if the underlying storage
is nullpt.

PiperOrigin-RevId: 219299489
2019-03-29 13:44:26 -07:00
Alex Zinenko 19f14b72bb Drop unbounded identity map from MemRef affine map composition.
Unbounded identity maps do not affect the accesses through MemRefs in any way.
A previous CL dropped such maps only if they were alone in the composition.  Go
further and drop such maps everywhere they appear in the composition.

Update the parser test to check for unique'd hoisted map to be present but
without assuming any particular order.  Because some of the hoisted identity
maps still apear due to the nested "for" statements, we need to check for them.
However, they no longer appear above the non-identity maps because they are no
longer necessary for the extfunc memref declarations that are textually first
in the test file.  This order may change further as map simplification is
improved, there is no reason to assume a particular order.

PiperOrigin-RevId: 219287280
2019-03-29 13:44:13 -07:00
Uday Bondhugula bdfd6193b8 Add getMemRefType() accessors to LoadOp/StoreOp.
- There are several places where we are casting the type of the memref obtained
  from the load/store op to a memref type, and this will become even more
  common (some upcoming CLs this week). Add a getMemRefType and use it at
  several places where the cast was being used.

PiperOrigin-RevId: 219164326
2019-03-29 13:43:58 -07:00
Lei Zhang 582b0761c6 Use matcher sugars for cannonicalization pattern matching
- Added a mechanism for specifying pattern matching more concisely like LLVM.
- Added support for canonicalization of addi/muli over vector/tensor splat
- Added ValueType to Attribute class hierarchy
- Allowed creating constant splat

PiperOrigin-RevId: 219149621
2019-03-29 13:43:44 -07:00
Uday Bondhugula 1ec77cecf2 FourierMotzkinEliminate trivial bug fix
PiperOrigin-RevId: 219148982
2019-03-29 13:43:30 -07:00
Alex Zinenko d45e193680 [trivial] fix MLIRContext::registerDiagnosticHandler documentation
The documentation for MLIRContext::registerDiagnosticHandler describing the
arguments of the diagnostic handler is inconsistent with the code.  It also
mentions LLVM context rather than MLIR context, likely a typo.  Fix both
issues.

PiperOrigin-RevId: 219120954
2019-03-29 13:43:16 -07:00
Chris Lattner 085b687fbd Add support for walking the use list of an SSAValue and converting owners to
Operation*'s, simplifying some code in GreedyPatternRewriteDriver.cpp.

Also add print/dump methods on Operation.

PiperOrigin-RevId: 219045764
2019-03-29 13:43:01 -07:00
Jacques Pienaar f8dee9ee05 Split off op_base from ops.
Mostly a mechanical change to make it easier to try reuse the same core definitions. Added additional string members summary/description, that mirrors OpDef's documentation (thinking about document generation :))

PiperOrigin-RevId: 219044183
2019-03-29 13:42:46 -07:00
Chris Lattner a10cd107de Introduce a common base class (IROperandOwner) between Instruction and
Statement, which paves the way to make SSAValue's have a useful owner
available, which will allow subsequent patches to improve their use/def
chains.

While I'm poking at this, shrink sizeof(Instruction) and sizeof(Statement) by a
word by packing the kind and location together into a single PointerIntPair.

NFC.

PiperOrigin-RevId: 218959651
2019-03-29 13:42:32 -07:00
Uday Bondhugula 2eb9550f68 Internal cleanup - update doc/comments for DMA ops.
PiperOrigin-RevId: 218908334
2019-03-29 13:42:17 -07:00
Lei Zhang 60b5184c8b Canonicalize muli(x, 1) into x
PiperOrigin-RevId: 218885877
2019-03-29 13:42:01 -07:00
Alex Zinenko aae372ecb8 Drop trivial identity affine mappings in MemRef construction.
As per MLIR spec, the absence of affine maps in MemRef type is interpreted as
an implicit identity affine map.  Therefore, MemRef types declared with
explicit or implicit identity map should be considered equal at the MemRefType
level.  During MemRefType construction, drop trivial identity affine map
compositions.  A trivial identity composition consists of a single unbounded
identity map.  It is unclear whether affine maps should be composed in-place to
a single map during MemRef type construction, so non-trivial compositions that
could have been simplified to an identity are NOT removed.  We chose to drop
the trivial identity map rather than inject it in places that assume its
present implicitly because it makes the code simpler by reducing boilerplate;
identity mappings are obvious defaults.

Update tests that were checking for the presence of trivial identity map
compositions in the outputs.

PiperOrigin-RevId: 218862454
2019-03-29 13:41:47 -07:00
Alex Zinenko 87c5145a5d Perform the MemRef layout map dimensionality check in the Parser.
This check was being performed in AllocOp::verify.  However it is not specific
to AllocOp and should apply to all MemRef type declarations.  At the same time,
the unique *Type factory functions in MLIRContext do not have access to
location information necessary to properly emit diagnostics.  Emit the error in
Parser where the location information is available.  Keep the error emission in
AllocOp for the cases of programmatically-constructed, e.g. through Builders,
IR with a note.  Once we decided on the diagnostic infrastructure in type
construction system, the type-related checks should be removed from specific
Ops.

Correct several parser test cases that have been using affine maps of
mismatching dimensionality.

This CL prepares for an upcoming change that will drop trivial identity affine
map compositions during MemRefType construction.  In that case, the
dimensionality mismatch error must be emitted before dropping the identity map,
i.e. during the type construction at the latest and before "verify" being
called.

PiperOrigin-RevId: 218844127
2019-03-29 13:41:33 -07:00
Lei Zhang 5c7667b5bd Fix comment typos and formatting
PiperOrigin-RevId: 218836217
2019-03-29 13:41:19 -07:00
River Riddle 6e6e40ae79 Move AffineMap.h/IntegerSet.h from Attributes.h to AttributeDetail.h where they belong.
PiperOrigin-RevId: 218806426
2019-03-29 13:41:05 -07:00
Uday Bondhugula ea65c695b9 Introduce integer set attribute
- add IntegerSetAttr to Attributes; add parsing and other support for it
  (builder, etc.).

PiperOrigin-RevId: 218804579
2019-03-29 13:40:50 -07:00
Chris Lattner 967d934180 Fix two issues:
1) We incorrectly reassociated non-reassociative operations like subi, causing
    miscompilations.
 2) When constant folding, we didn't add users of the new constant back to the
    worklist for reprocessing, causing us to miss some cases (pointed out by
    Uday).

The code for tensorflow/mlir#2 is gross, but I'll add the new APIs in a followup patch.

PiperOrigin-RevId: 218803984
2019-03-29 13:40:35 -07:00
Uday Bondhugula 988ce3387f Change sigil for integer set: @@ -> #
PiperOrigin-RevId: 218786684
2019-03-29 13:40:21 -07:00
Chris Lattner adbba70d82 Simplify FunctionPass to eliminate the CFGFunctionPass/MLFunctionPass
distinction.  FunctionPasses can now choose to get called on all functions, or
have the driver split CFG/ML Functions up for them.  NFC.

PiperOrigin-RevId: 218775885
2019-03-29 13:40:05 -07:00
Chris Lattner 7de0da9594 Refactor all of the canonicalization patterns out of the Canonicalize pass, and
make operations provide a list of canonicalizations that can be applied to
them.  This allows canonicalization to be general to any IR definition.

As part of this, sink PatternMatch.h/cpp down to the IR library to fix a
layering problem.

PiperOrigin-RevId: 218773981
2019-03-29 13:39:49 -07:00
MLIR Team 13f6cc0187 Run GCD test before elimination. Adds test case with rational solutions, but no integer solutions.
PiperOrigin-RevId: 218772332
2019-03-29 13:39:34 -07:00
River Riddle 792d1c25e4 Implement value type abstraction for attributes.
This is done by changing Attribute to be a POD interface around an underlying pointer storage and adding in-class support for isa/dyn_cast/cast.

PiperOrigin-RevId: 218764173
2019-03-29 13:39:19 -07:00
Chris Lattner 64d52014bd Move transform utilities out to their own TransformUtils library, instead of
just having the pattern matcher in its own library.  At this point,
lib/Transforms/*.cpp are all actually passes themselves (and will probably
eventually be themselves move to a new subdirectory as we accrete more).

PiperOrigin-RevId: 218745193
2019-03-29 13:39:06 -07:00
Chris Lattner 92285814e2 Refactor the bulk of the worklist driver out of the canonicalizer into its own
helper function, in preparation for it being used by other passes.

There is still a lot of room for improvement in its design, this patch is
intended as an NFC refactoring, and the improvements will continue after this
lands.

PiperOrigin-RevId: 218737116
2019-03-29 13:38:52 -07:00
Chris Lattner 144795e35c Add a doc explaining our approach to canonicalization, which is more of a
framework than a useful doc at this point.

PiperOrigin-RevId: 218737032
2019-03-29 13:38:38 -07:00
Uday Bondhugula 80610c2f49 Introduce Fourier-Motzkin variable elimination + other cleanup/support
- Introduce Fourier-Motzkin variable elimination to eliminate a dimension from
  a system of linear equalities/inequalities. Update isEmpty to use this.
  Since FM is only exact on rational/real spaces, an emptiness check based on
  this is guaranteed to be exact whenever it says the underlying set is empty;
  if it says, it's not empty, there may still be no integer points in it.
  Also, supports a version that computes "dark shadows".

- Test this by checking for "always false" conditionals in if statements.

- Unique IntegerSet's that are small (few constraints, few variables). This
  basically means the canonical empty set and other small sets that are
  likely commonly used get uniqued; allows checking for the canonical empty set
  by pointer. IntegerSet::kUniquingThreshold gives the threshold constraint size
  for uniqui'ing.

- rename simplify-affine-expr -> simplify-affine-structures

Other cleanup

- IntegerSet::numConstraints, AffineMap::numResults are no longer needed;
  remove them.
- add copy assignment operators for AffineMap, IntegerSet.
- rename Invalid() -> Null() on AffineExpr, AffineMap, IntegerSet
- Misc cleanup for FlatAffineConstraints API

PiperOrigin-RevId: 218690456
2019-03-29 13:38:24 -07:00
MLIR Team 5413239350 Adds Gaussian Elimination to FlatAffineConstraints.
- Adds FlatAffineConstraints::isEmpty method to test if there are no solutions to the system.
- Adds GCD test check if equality constraints have no solution.
- Adds unit test cases.

PiperOrigin-RevId: 218546319
2019-03-29 13:38:10 -07:00
Lei Zhang 52a0e58bdb Change typedef to using to be consistent across the codebase
Google C++ style guide also prefers using to typedef.

PiperOrigin-RevId: 218541849
2019-03-29 13:37:55 -07:00
Alex Zinenko e8d254b909 Rename shape_cast to tensor_cast.
"shape_cast" only applies to tensors, and there are other operations that
actually affect shape, for example "reshape".  Rename "shape_cast" to
"tensor_cast" in both the code and the documentation.

PiperOrigin-RevId: 218528122
2019-03-29 13:37:41 -07:00
Alex Zinenko c1b0918617 Add MLIR Rationale converted to g3doc.
This CL only converts the document to the g3doc format and does some minor
typesetting, e.g. removing unicode ellipsis and mdash symbols, replace single
quotes with backticks to trigger tt-type dispay, etc.  The original document
is located at
https://docs.google.com/document/d/1KoVYgp-m-dgAyKwqRne2c72j0FoxpsdNgfa9DTfWGgw/view
Links to the sections of the same document are updated to point to the anchors
in the converted document whereas links to external documents are kept as is.
Cross-links between LangRef.md and Rationale.md are updated to point to the
relevant anchors in the g3doc files.

PiperOrigin-RevId: 218527560
2019-03-29 13:37:27 -07:00
Alex Zinenko 1321f6affd Add MLIR specification.
PiperOrigin-RevId: 218527452
2019-03-29 13:37:13 -07:00
Chris Lattner bd01f9541f Teach canonicalize pass to unique and hoist constants to the entry block. This
is a straight-forward change, but required adding missing moveBefore() methods
on operations (requiring moving some traits around to make C++ happy).  This
also fixes a constness issue with the getBlock/getFunction() methods on
Instruction, and adds a missing getFunction() method on MLFuncBuilder.

PiperOrigin-RevId: 218523905
2019-03-29 13:36:59 -07:00
Feng Liu 3d7ab2d265 Add support to opaque elements attributes
For some of the constant vector / tesor, if the compiler doesn't need to
interpret their elements content, they can be stored in this class to save the
serialize / deserialize cost.

syntax:

`opaque<` tensor-type `,` opaque-string `>`

opaque-string ::= `0x` [0-9a-fA-F]*
PiperOrigin-RevId: 218399426
2019-03-29 13:36:45 -07:00