tree 1b4b45cf7a5c80b79c331b72b6c138f517a16328
parent 9449c6ad9887ff820891716b4109d19fd2f6e7e1
author Alex Zinenko <zinenko@google.com> 1542811069 -0800
committer jpienaar <jpienaar@google.com> 1553893621 -0700

Lower scalar parts of CFG functions to LLVM IR

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