making the IR dumps much nicer.
This is part 2/3 of the path to making dialect types more nice. Part 3/3 will
slightly generalize the set of characters allowed in pretty types and make it
more principled.
--
PiperOrigin-RevId: 242249955
Historically, the LLVM IR dialect has been using the generic form of MLIR
operation syntax. It is verbose and often redundant. Introduce the custom
printing and parsing for all existing operations in the LLVM IR dialect.
Update the relevant documentation and tests.
--
PiperOrigin-RevId: 241617393
When the LLVM IR dialect was implemented, TableGen operation definition scheme
did not support operations with variadic results. Therefore, the `call`
instruction was split into `call` and `call0` for the single- and zero-result
calls (LLVM does not support multi-result operations). Unify `call` and
`call0` using the recently added TableGen support for operations with Variadic
results. Explicitly verify that the new operation has 0 or 1 results. As a
side effect, this change enables clean-ups in the conversion to the LLVM IR
dialect that no longer needs to rely on wrapped LLVM IR void types when
constructing zero-result calls.
PiperOrigin-RevId: 236119197
Since the goal of the LLVM IR dialect is to reflect LLVM IR in MLIR, the
dialect and the conversion procedure must account for the differences betweeen
block arguments and LLVM IR PHI nodes. In particular, LLVM IR disallows PHI
nodes with different values coming from the same source. Therefore, the LLVM IR
dialect now disallows `cond_br` operations that have identical successors
accepting arguments, which would lead to invalid PHI nodes. The conversion
process resolves the potential PHI source ambiguity by injecting dummy blocks
if the same block is used more than once as a successor in an instruction.
These dummy blocks branch unconditionally to the original successors, pass them
the original operands (available in the dummy block because it is dominated by
the original block) and are used instead of them in the original terminator
operation.
PiperOrigin-RevId: 235682798
Add support for lowering DivF and RemF to LLVM::FDiv and LLMV::FRem
respectively. The lowering is a trivial one-to-one transformation.
The corresponding operations already existed in the LLVM IR dialect and can be
lowered to the LLVM IR proper. Add the necessary tests for scalar and vector
forms.
PiperOrigin-RevId: 234984608
Add support for converting MLIR `call_indirect` instructions to the LLVM IR
dialect. In LLVM IR, the same instruction is used for direct and indirect
calls. In the dialect, we have `llvm.call` and `llvm.call0` to work around the
absence of the void type in MLIR. For direct calls, the callee is stored as
instruction attribute. Use the same pair of instructions for indirect calls by
omitting the callee attribute. In the MLIR to LLVM IR translator, check the
presence of attribute to decide whether to construct a direct or an indirect
call using different LLVM IR Builder functions.
Add support for converting constants of function type to the LLVM IR dialect
and for translating them to the LLVM IR proper. The `llvm.constant` operation
works similarly to other types: its attribute has MLIR function type but the
value it produces has LLVM IR function type wrapped in the dialect type. While
lowering, look up the pointer to the converted function in the corresponding
mapping.
PiperOrigin-RevId: 234132351
Original implementation of the translation from MLIR to LLVM IR operated on the
Standard+BuiltIn dialect, with a later addition of the SuperVector dialect.
This required the translation to be aware of a potetially large number of other
dialects as the infrastructure extended. With the recent introduction of the
LLVM IR dialect into MLIR, the translation can be switched to only translate
the LLVM IR dialect, and the translation of the operations becomes largely
mechanical.
The reimplementation of the translator follows the lines of the original
translator in function and basic block conversion. In particular, block
arguments are converted to LLVM IR PHI nodes, which are connected to their
sources after all blocks of a function had been converted. Thanks to LLVM IR
types being wrapped in the MLIR LLVM dialect type, type conversion is
simplified to only convert function types, all other types are simply
unwrapped. Individual instructions are constructed using the LLVM IRBuilder,
which has a great potential for being table-generated from the LLVM IR dialect
operation definitions.
The input of the test/Target/llvmir.mlir is updated to use the MLIR LLVM IR
dialect. While it is now redundant with the dialect conversion test, the point
of the exercise is to guarantee exactly the same LLVM IR is emitted. (Only the
name of the allocation function is changed from `__mlir_alloc` to `alloc` in
the CHECK lines.) It will be simplified in a follow-up commit.
PiperOrigin-RevId: 233842306
These operations trivially map to LLVM IR counterparts for operands of scalar
and (one-dimensional) vector type. Multi-dimensional vector and tensor type
operands would fail type conversion before the operation conversion takes
place. Add tests for scalar and vector cases. Also add a test for vector
`select` instruction for consistency with other tests.
PiperOrigin-RevId: 228077564
The entire compiler now looks at structural properties of the function (e.g.
does it have one block, does it contain an if/for stmt, etc) so the only thing
holding up this difference is round tripping through the parser/printer syntax.
Removing this shrinks the compile by ~140LOC.
This is step 31/n towards merging instructions and statements. The last step
is updating the docs, which I will do as a separate patch in order to split it
from this mostly mechanical patch.
PiperOrigin-RevId: 227540453
This commit adds support for the "select" operation that lowers directly into
its LLVM IR counterpart. A simple test is included.
PiperOrigin-RevId: 227527893
printing the entry block in a CFG function's argument line. Since I'm touching
all of the testcases anyway, change the argument list from printing as
"%arg : type" to "%arg: type" which is more consistent with bb arguments.
In addition to being more consistent, this is a much nicer look for cfg functions.
PiperOrigin-RevId: 227240069
The binary subtraction operations were not supported by the lowering because
they were not essential for the testing flow. Add support for these
operations.
PiperOrigin-RevId: 226941463
Introduce initial support for 1D vector operations. LLVM does not support
higher-dimensional vectors so the caller must make sure they don't appear in
the input MLIR. Handle the presence of higher-dimensional vectors by failing
gracefully.
Introduce the type conversion for 1D vector types and hook it up with the rest
of the type convresion system. Support "splat" constants for vector types. As
a side effect, this refactors constant operation emission by separating out
scalar integer constants into a separate case and by extracting out the helper
function for scalar float construction. Existing binary operations apply to
vectors transparently.
PiperOrigin-RevId: 225172349
Unlike MLIR, LLVM IR does not support functions that return multiple values.
Simulate this by packing values into the LLVM structure type in the same order
as they appear in the MLIR return. If the function returns only a single
value, return it directly without packing.
PiperOrigin-RevId: 223964886
Add support for translating 'dim' opreation on MemRefs to LLVM IR. For a
static size, this operation merely defines an LLVM IR constant value that may
not appear in the output IR if not used (and had not been removed before by
DCE). For a dynamic size, this operation is translated into an access to the
MemRef descriptor that contains the dynamic size.
PiperOrigin-RevId: 223160774
Introduce initial support for MemRef types, including type conversion,
allocation and deallocation, read and write element-wise access, passing
MemRefs to and returning from functions. Affine map compositions and
non-default memory spaces are NOT YET supported.
Lowered code needs to handle potentially dynamic sizes of the MemRef. To do
so, it replaces a MemRef-typed value with a special MemRef descriptor that
carries the data and the dynamic sizes together. A MemRef type is converted to
LLVM's first-class structure type with the first element being the pointer to
the data buffer with data layed out linearly, followed by as many integer-typed
elements as MemRef has dynamic sizes. The type of these elements is that of
MLIR index lowered to LLVM. For example, `memref<?x42x?xf32>` is converted to
`{ f32*, i64, i64 }` provided `index` is lowered to `i64`. While it is
possible to convert MemRefs with fully static sizes to simple pointers to their
elemental types, we opted for consistency and convert them to the
single-element structure. This makes the conversion code simpler and the
calling convention of the generated LLVM IR functions consistent.
Loads from and stores to a MemRef element are lowered to a sequence of LLVM
instructions that, first, computes the linearized index of the element in the
data buffer using the access indices and combining the static sizes with the
dynamic sizes stored in the descriptor, and then loads from or stores to the
buffer element indexed by the linearized subscript. While some of the index
computations may be redundant (i.e., consecutive load and store to the same
location in the same scope could reuse the linearized index), we emit them for
every operation. A subsequent optimization pass may eliminate them if
necessary.
MemRef allocation and deallocation is performed using external functions
`__mlir_alloc(index) -> i8*` and `__mlir_free(i8*)` that must be implemented by
the caller. These functions behave similarly to `malloc` and `free`, but can
be extended to support different memory spaces in future. Allocation and
deallocation instructions take care of casting the pointers. Prior to calling
the allocation function, the emitted code creates an SSA Value for the
descriptor and uses it to store the dynamic sizes of the MemRef passed to the
allocation operation. It further emits instructions that compute the dynamic
amount of memory to allocate in bytes. Finally, the allocation stores the
result of calling the `__mlir_alloc` in the MemRef descriptor. Deallocation
extracts the pointer to the allocated memory from the descriptor and calls
`__mlir_free` on it. The descriptor itself is not modified and, being
stack-allocated, ceases to exist when it goes out of scope.
MLIR functions that access MemRef values as arguments or return them are
converted to LLVM IR functions that accept MemRef descriptors as LLVM IR
structure types by value. This significantly simplifies the calling convention
at the LLVM IR level and avoids handling descriptors in the dynamic memory,
however is not always comaptible with LLVM IR functions emitted from C code
with similar signatures. A separate LLVM pass may be introduced in the future
to provide C-compatible calling conventions for LLVM IR functions generated
from MLIR.
PiperOrigin-RevId: 223134883
Initial restricted implementaiton of the MLIR to LLVM IR translation.
Introduce a new flow into the mlir-translate tool taking an MLIR module
containing CFG functions only and producing and LLVM IR module. The MLIR
features supported by the translator are as follows:
- primitive and function types;
- integer constants;
- cfg and ext functions with 0 or 1 return values;
- calls to these functions;
- basic block conversion translation of arguments to phi nodes;
- conversion between arguments of the first basic block and function arguments;
- (conditional) branches;
- integer addition and comparison operations.
Are NOT supported:
- vector and tensor types and operations on them;
- memrefs and operations on them;
- allocations;
- functions returning multiple values;
- LLVM Module triple and data layout (index type is hardcoded to i64).
Create a new MLIR library and place it under lib/Target/LLVMIR. The "Target"
library group is similar to the one present in LLVM and is intended to contain
all future public MLIR translation targets.
The general flow of MLIR to LLVM IR convresion will include several lowering
and simplification passes on the MLIR itself in order to make the translation
as simple as possible. In particular, ML functions should be transformed to
CFG functions by the recently introduced pass, operations on structured types
will be converted to sequences of operations on primitive types, complex
operations such as affine_apply will be converted into sequence of primitive
operations, primitive operations themselves may eventually be converted to an
LLVM dialect that uses LLVM-like operations.
Introduce the first translation test so that further changes make sure the
basic translation functionality is not broken.
PiperOrigin-RevId: 222400112
Chris Lattner