Implement a DDR rewriting for folding the `x[0]` into `*x`, in order
to avoid a useless verbose syntax. Due to concatenation of rewrites, we
will get `&(x[0])` transformed into `x`, which is the rewriting we are
aiming to.
* PrimitiveType is now an interface.
* VoidKind is now VoidType.
* FloatKind is now FloatType.
* The integer kinds are now IntegerType with IntegerKind.
* DecayOp - array or function to pointer decay. Not shown in C.
* BitCastOp - bit-preserving conversion. Emitted as bit_cast if
necessary.
* ExtendOp - zero- or sign-extending conversion from any integer type to
any wider integer type.
* TruncateOp - truncating conversion from any integer type to any
narrower integer type.
* PtrResizeOp - resizes a pointer without changing its pointee type.
The `EmitFieldAccesses` pass transforms `clift` by taking pointer-typed
expressions computed via integerr arithmetic with type-safe field
accesses and array accesses.
The transformation is split in three main phases:
1) `PointerArithmetic` computation.
2) `BestTraversal` computation.
3) `FieldAccess` `clift` rewrite.
The high level driver is implemented in the `EmitFieldAccesses` header
and cpp, while the nested 3 phases are implemented respectively in
`PointerArithmetic`, `BestTraversal` and `FieldAccessReplacement`.
The `computerPointerArithmetic` phase is concerned with taking a
pointer-typed `ExpressionOp`, called `PointerToReplace`, and expressing
it in a `BasePointer+Offset` form.
The `computeBestTraversal` phase is concerned with computing the best
traversal of the type pointed to by `BasePointer`, that can be used to
rewrite the pointer arithmetic in `clift` with just field accesses and
array subscripts.
The `replaceFieldAccess` phase takes the `Traversal` computed at the
previous step, and actually rewrites in `clift` the `PointerToReplace`
in terms of field accesses and array accesses w.r.t. the `BasePointer`.
Contains APIs from upstream LLVM that are not yet present in the current
version, as well as helpers not present in upstream.
See upstream commit 42c31d8302ff8f716601df9c276a5cd9ace6b158.
Roberto Bertolini