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Loop Predication is an optimization in C2. The general idea is to insert a predicate on the entry path to a loop,

and raise a uncommon trap if the check of the condition fails. The condition checks are promoted from inside the

loop body, and thus the checks inside the loop could be eliminated. Currently, loop predication optimization has

been applied to remove array range check, null checks and array checks in loops.

h5.   Loop Predication for Array Range Check Elimination

    Use loop predicate to remove array range checks in a loop.

    Example:

    original loop

&nbsp;&nbsp;&nbsp;&nbsp; for (int i=init, i<limit; i+=stride) {

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ...

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if( scale*i + offset < a.length) { // loop with range check


&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp;&nbsp; ... a\[scale*i + offset\] ...


&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; } else raising_uncommon_trap();

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ...

&nbsp;&nbsp;&nbsp; }

&nbsp;&nbsp;&nbsp; after loop predication

&nbsp;&nbsp;&nbsp; if( scale*imax < a.length) {


&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; for (int i=init, i<limit; i+=stride) {//loop without range check


&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; ...

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp;&nbsp; ... a\[scale*i + offset\] ...


&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }


&nbsp;&nbsp;&nbsp; } else raising_uncommon_trap();