Today we continue to discuss the WRL research report on Swift Java compiler.
We were discussing pattern based peephole optimizer. The graph rewriting order is as follows An SSA value is processed before all of its inputs. There is an exception when there are cycles in the value graphs. For each value, rules are applied in the order specified by the rules file until one matches and mutates a value. The rewriting then proceeds to the next value. Each pass changes the value. Consequently the passes are iterated through the entire SSA graph until there are no more changes. The ordering of rules is somewhat important in ensuring that optimizations are applied in the most effective order.
Many of the machine independent peephole optimization apply simple algebraic or boolean identifies. When placing the length of a new array, it is replaced by an allocated size of an array. Similarly a get_field operation can be replaced by the value from the previous put_field operation. Other optimizations include dead code elimination by way of repeated passés, This is done via mark and sweep. The live values in a Swift SSA graph are the control values and all inputs of live values. All the unmarked values are removed as dead code. Swift also does pass for conditional constant propagation and simultaneous elimination of impossible control flow
We were discussing pattern based peephole optimizer. The graph rewriting order is as follows An SSA value is processed before all of its inputs. There is an exception when there are cycles in the value graphs. For each value, rules are applied in the order specified by the rules file until one matches and mutates a value. The rewriting then proceeds to the next value. Each pass changes the value. Consequently the passes are iterated through the entire SSA graph until there are no more changes. The ordering of rules is somewhat important in ensuring that optimizations are applied in the most effective order.
Many of the machine independent peephole optimization apply simple algebraic or boolean identifies. When placing the length of a new array, it is replaced by an allocated size of an array. Similarly a get_field operation can be replaced by the value from the previous put_field operation. Other optimizations include dead code elimination by way of repeated passés, This is done via mark and sweep. The live values in a Swift SSA graph are the control values and all inputs of live values. All the unmarked values are removed as dead code. Swift also does pass for conditional constant propagation and simultaneous elimination of impossible control flow
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