Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

252 Chapter 19
We sum both these quantities and divide by the operation mobility to obtain
Total Excess Load per scheduling time step.
3.2. Speculative mobility
The second component of our ranking function, denoted
is an
indicator of the number of additional time steps made available to the
operation through speculation. It is given by the difference between the
maximum ALAP value over all predecessors of the operation, denoted by
pred(op), before and after speculation. Formally:
3.3. Ranking function
The composite ordering of operations by suitability for speculation, called
Suit(op), is given by:
Suit(op) is computed for each operation that is a candidate for speculation,
and speculation is attempted on the operation with the highest value, as
discussed in the sequel.
4. OPTIMIZATION FRAMEWORK
Figure 19-4 shows the complete iterative optimization flow of OPT-PH.
During the initialization phase, if-conversion is applied to the original CDFG
– control dependences are converted to data dependences by defining the
appropriate predicate define operations and data dependence edges, and an
initial binding is performed using a modified version of the algorithm presented
in [15]. Specifically, the initial phase of this binding algorithm was
implemented in our framework along with some changes specific to the SSA-
PS transformation [9], as outlined below. The original algorithm adds a penalty
for every predecessor of an operation that is bound to a cluster different from
the cluster to which the operation itself is being tentatively bound. In our
version of the algorithm, such penalty is not added if the predecessor is a predicated
move operation. The reason for this modification is the fact that predicated
move operations realizing the reconciliation (i.e. [9]) functions may
themselves be used to perform required (i.e. binding related) data transfers
across clusters and thus may actually not lead to a performance penalty.
After the initialization phase is performed, the algorithm enters an itera-