* 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.
Introduce the support to decouple the `BaseType` from `BasePointer`
pointee type.
This enable us to wrap pointee typees into an implicit array. This
enables pointer arithmetic rewriting of `*(p + i)` as `p[i]`.
We now don't assume that the `PointerOperand` of a `ptr_add` leads to a
`Address` PA, nor that the `OffsetOperand` leads to a `Numeric` PA.
We now behave as a simple `composeAdd`, keeping the special `Offset`
scaling by the `PointeeSize` of the `PointerOperand`.
Remove the special casing for `composeBitcast`, where we created a
`leaf` PA in case the traversal of the upward tree did only provide a
`Numeric` PA.
This was introduced as a workaround for handling `composePtrAdd` when
the `PointerOperand` was a `Numeric` PA.
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`.
Lauri Vasama