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marekjm / viuavm

Parallel virtual machine designed to reliably run massively concurrent programs
https://viuavm.org/
GNU General Public License v3.0
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Implement instruction flags #102

Closed marekjm closed 8 years ago

marekjm commented 9 years ago

Instruction flags could be used to implement predicates, e.g. "execute this instruction only if X is true". This would result in an execution speedup since fewer branches will be required to write equivalent code (this is especially true for one- or two-instruction branches).

marekjm commented 9 years ago

Proposed syntax: OP.PRED:RI operand... where OP is opcode name (e.g. iinc), PRED is predicate specification, and RI is register index used to form the predicate.

Example:

; increase 1 only if 4 is true (pp - positive predicate)
iinc.pp:4 1
marekjm commented 8 years ago

The cost of implementing this functionality is too high, given the possible gains. Taking branches is not expensive in Viua, and adding additional complexity in order to avoid branching is not really economical. This could have made sense if the VM supported pipelining, but it doesn't (and there are no plans in the near future to implement such a feature).

Due to above reasons (adding bytecode complexity for no reasonable gains), I'm closing the issue.