When lowering to MLIR(LLVMDialect) we unbox the structs that result
from converting static memrefs, that is, singleton structs
that just contain a raw pointer. This allows us to get rid of all
"extractvalue" instructions in the common case where shapes are fully
known.
PiperOrigin-RevId: 235706021
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 a documentation page on the key points of the conversion to LLVM IR. This
focuses on the aspects of conversion that are relevant for integration of the
LLVM IR dialect (and produced LLVM IR that is mostly a one-to-one translation)
into other projects. In particular, it describes the type conversion rules and
the memref model supporting dynamic sizes.
PiperOrigin-RevId: 235190772
Dimitrios Vytiniotis