Summary:
This sketches out how translation can be approached. It is partially
based on the Sledge code.
For basic blocks, isn't based on the Sledge code, but just my own
thoughts as a starting point. Essentially, we are trying to build up
larger expressions, and so not assigning to temporary registers that
don't live past the end of the block. This does remove sharing, so a
fancier approach could check for multiple uses of end-of-block dead
registers, or look at the sizes of expressions. The approach should be
flexible enough to accommodate such changes.
Fix icmp syntax
Using finite maps is elegant in the semantics, but awkward for writing
the translation function. Refactor the mappings from labels to functions
and from labels to blocks to use association lists instead.
To remove phi nodes, the translation takes every edge in the control
flow graph and makes a new basic block that contains a single parallel
move instruction that corresponds to the action of the phi node of the
target block.
Reviewed By: jberdine
Differential Revision: D16831051
fbshipit-source-id: 005663e26
Summary:
The AST is not complete on expressions, but it should have most of the
important features.
The representation is in some ways very different from the OCaml
implementation, because the OCaml code uses mutation to build the CFG as
an actual pointer graph in memory, and also because the expression
representation is optimised for the backend. For the former, it should
be easy to see that the AST here is isomorphic, representing the CFG
with finite maps from block labels. The correspondence is less clear in
the latter case, but the point here is not to model or verify
implementation optimisations, but to give a semantics to llair as a
language.
Reviewed By: jberdine
Differential Revision: D16807132
fbshipit-source-id: b0f64b3ec
Scott Owens