RedundantBranchElimination (Jikes RVM API)

Overview

Package

Class

Use

Tree

Serialized

Deprecated

Index

Help

PREV CLASS NEXT CLASS

FRAMES NO FRAMES

SUMMARY: NESTED | FIELD | CONSTR | METHOD

DETAIL: FIELD | CONSTR | METHOD

org.jikesrvm.compilers.opt.ssa
Class RedundantBranchElimination

java.lang.Object
  org.jikesrvm.compilers.opt.driver.OptimizationPlanElement
      org.jikesrvm.compilers.opt.driver.OptimizationPlanCompositeElement
          org.jikesrvm.compilers.opt.ssa.RedundantBranchElimination

public final class RedundantBranchElimination
extends OptimizationPlanCompositeElement
extends OptimizationPlanCompositeElement

Redundant branch elimination based on SSA form, global value numbers, and dominance relationships. The following are sufficient conditions for a conditional branch cb1 to be eliminated as redundant

It is equivalent (has the same value number) as another conditional branch cb2
Either (a) the target of the taken branch of cb2 dominates cb1 and said target block has exactly one in edge or (b) the not-taken continuation of cb2 dominates cb1 and said continuation block has exactly one in edge.

NOTE: the check for exactly one in edge is used to rule out situations like the following:

      if (C) goto L2              // cb2
      x = x + 1;
  L2: x = x + 1;
      if (C) goto L3.            // cb1

Consider redundant branch elimination for cb1. Here L2 (the target of cb2) dominates cb1, but it is not correct to eliminate cb1 because it is also reachable (but not dominated) from the continuation block of cb2!

Nested Class Summary
`private static class`	`RedundantBranchElimination.EnsureSSA`
`private static class`	`RedundantBranchElimination.RBE`

Constructor Summary
`RedundantBranchElimination()` Create this phase element as a composite of other elements

Method Summary
`boolean`	`shouldPerform(OptOptions options)` Determine, possibly by consulting the passed options object, if this optimization plan element should be performed.

Methods inherited from class org.jikesrvm.compilers.opt.driver.OptimizationPlanCompositeElement
`compose, elapsedTime, getName, initializeForMeasureCompilation, perform, printingEnabled, reportStats`

Methods inherited from class org.jikesrvm.compilers.opt.driver.OptimizationPlanElement
`prettyPrintTime`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail