Expose values and variables in the IR

[ulysseB]

Data flow is currently implicit in our representation. This causes some problems:

• we can't measure the register pressure
• it is hard to measure the size of memory blocks. This leads to a O(n^3) search space representation.
• we don't know when to introduce broadcasts
• reductions are hard to manipulate and we cannot represent parallel reductions
• we do not know when to privatise shared memory

Bellow is the modifications necessary to implement the new value system:

• Allow accessing the value produce by an instruction with a Value object. This lays out the ground work for the rest of the modifications. WIP: Expose data-flow information in Telamon #63
  - Define a Value struct, along with accessors.
  - Allow to store the result of an instruction in a value
• Expose values in code generation
  - Expose a specified value struct
  - Name values
• Expose values in the .exh file
• Add a new operand kind to read a value
  - Expose the points where a value is created and used
  - Enforce ordering constraints from the exh.
• Make the performance model value-aware
  - Take dependencies between values uses and defs into account.
• Handle the last operator
• Handle dimensions mapping
• Handle the fby operator
• Update the builder to use values and remove inst and reduce operands.
• Handle Lowering
• Remove the old operand system.
  • remove instruction type