Function types are built-in in MLIR and affect the validity of the IR itself.
However, advanced target dialects such as the LLVM IR dialect may include
custom function types. Until now, dialect conversion was expecting function
types not to be converted to the custom type: although the signatures was
allowed to change, the outer type must have been an mlir::FunctionType. This
effectively prevented dialect conversion from creating instructions that
operate on values of the custom function type.
Dissociate function signature conversion from general type conversion.
Function signature conversion must still produce an mlir::FunctionType and is
used in places where built-in types are required to make IR valid. General
type conversion is used for SSA values, including function and block arguments
and function results.
Exercise this behavior in the LLVM IR dialect conversion by converting function
types to LLVM IR function pointer types. The pointer to a function is chosen
to provide consistent lowering of higher-order functions: while it is possible
to have a value of function type, it is not possible to create a function type
accepting a returning another function type.
PiperOrigin-RevId: 234124494
DimOp is converted to a constant LLVM IR dialect operation for static
dimensions and to an access to the dynamic size info stored in the memref
descriptor for the dynamic dimensions. This behavior is consistent with the
existing mlir-translator.
This completes the porting of MLIR -> LLVM lowering to the dialect conversion
infrastructure.
PiperOrigin-RevId: 233665634
Add support for converting `memref_cast` operations into the LLVM IR dialect.
This goes beyond want is currently implemented in the MLIR standard ops to LLVM
IR translation, but follows the general principles of the memref descriptors.
A memref cast creates a new descriptor containing the same buffer pointer but a
potentially different number of dynamic sizes (as many as dynamic dimensions in
the target memref type). The lowering copies the buffer pointer to the new
descriptor and inserts dynamic sizes to it. If the size is static in the
source type, a constant value is inserted as the dynamic size, otherwise a
dynamic value is copied from the source descriptor, taking into account the
difference in dynamic size positions in the descriptor.
PiperOrigin-RevId: 233082035
Implement the lowering of memref load and store standard operations into the
LLVM IR dialect. This largely follows the existing mechanism in
MLIR-to-LLVM-IR translation for the sake of compatibility. A memref value is
transformed into a memref descriptor value which holds the pointer to the
underlying data buffer and the dynamic memref sizes. The data buffer is
contiguous. Accesses to multidimensional memrefs are linearized in row-major
form. In linear address computation, statically known sizes are used as
constants while dynamic sizes are extracted from the memref descriptor.
PiperOrigin-RevId: 233043846
Implement the lowering of memref allocation and deallocation standard
operations into the LLVM IR dialect. This largely follows the existing
mechanism in MLIR-to-LLVM-IR translation for the sake of compatibility.
A memref value is transformed into a memref descriptor value which holds the
pointer to the underlying data buffer and the dynamic memref sizes. The buffer
is allocated using `malloc` and freed using `free`. The lowering inserts
declarations of these functions if necessary. Memref descriptors are values of
the LLVM IR structure type wrapped into an MLIR LLVM dialect type. The pointer
to the buffer and the individual sizes are accessed using `extractvalue` and
`insertvalue` LLVM IR instructions.
PiperOrigin-RevId: 232719419
This commit introduces a generic dialect conversion/lowering/legalization pass
and illustrates it on StandardOps->LLVMIR conversion.
It partially reuses the PatternRewriter infrastructure and adds the following
functionality:
- an actual pass;
- non-default pattern constructors;
- one-to-many rewrites;
- rewriting terminators with successors;
- not applying patterns iteratively (unlike the existing greedy rewrite driver);
- ability to change function signature;
- ability to change basic block argument types.
The latter two things required, given the existing API, to create new functions
in the same module. Eventually, this should converge with the rest of
PatternRewriter. However, we may want to keep two pass versions: "heavy" with
function/block argument conversion and "light" that only touches operations.
This pass creates new functions within a module as a means to change function
signature, then creates new blocks with converted argument types in the new
function. Then, it traverses the CFG in DFS-preorder to make sure defs are
converted before uses in the dominated blocks. The generic pass has a minimal
interface with two hooks: one to fill in the set of patterns, and another one
to convert types for functions and blocks. The patterns are defined as
separate classes that can be table-generated in the future.
The LLVM IR lowering pass partially inherits from the existing LLVM IR
translator, in particular for type conversion. It defines a conversion pattern
template, instantiated for different operations, and is a good candidate for
tablegen. The lowering does not yet support loads and stores and is not
connected to the translator as it would have broken the existing flows. Future
patches will add missing support before switching the translator in a single
patch.
PiperOrigin-RevId: 230951202
