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The GraalVM compiler and the Graal-truffle optimizer.
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package org.graalvm.compiler.virtual.phases.ea;

import static org.graalvm.compiler.core.common.GraalOptions.EscapeAnalyzeOnly;

import java.util.Optional;

import org.graalvm.compiler.nodes.GraphState;
import org.graalvm.compiler.nodes.GraphState.StageFlag;
import org.graalvm.compiler.nodes.StructuredGraph;
import org.graalvm.compiler.nodes.StructuredGraph.ScheduleResult;
import org.graalvm.compiler.nodes.cfg.ControlFlowGraph;
import org.graalvm.compiler.nodes.spi.CoreProviders;
import org.graalvm.compiler.phases.common.CanonicalizerPhase;
import org.graalvm.compiler.phases.graph.ReentrantBlockIterator;
import org.graalvm.word.LocationIdentity;

/**
 * This phase performs read and (simple) write elimination on a graph. It operates on multiple
 * granularities, i.e., before and after high-tier lowering. The phase iterates the graph in a
 * reverse-post-order fashion {@linkplain ReentrantBlockIterator} and tracks the currently active
 * value for a specific {@linkplain LocationIdentity}, which allows the removal of subsequent reads
 * if no writes happen in between, etc. if the value read from memory is in a virtual register
 * (node).
 *
 * A trivial example for read elimination can be seen below:
 *
 *  * int i = object.fieldValue;
 * // code not changing object.fieldValue but using i
 * consume(object.fieldValue);
 * 
 *
 * Read elimination will transform this piece of code to the code below and remove the second,
 * unnecessary, memory read of the field:
 *
 *  * int i = object.fieldValue;
 * // code not changing object.fieldValue but using i
 * consume(i);
 * 
 */
public class ReadEliminationPhase extends EffectsPhase {

    protected final boolean considerGuards;

    public ReadEliminationPhase(CanonicalizerPhase canonicalizer) {
        super(1, canonicalizer, true);
        this.considerGuards = true;
    }

    public ReadEliminationPhase(CanonicalizerPhase canonicalizer, boolean considerGuards) {
        super(1, canonicalizer, true);
        this.considerGuards = considerGuards;
    }

    @Override
    public Optional notApplicableTo(GraphState graphState) {
        return NotApplicable.ifAny(
                        super.notApplicableTo(graphState),
                        NotApplicable.when(graphState.isAfterStage(StageFlag.FLOATING_READS) && graphState.isBeforeStage(StageFlag.FIXED_READS),
                                        "This phase must not be applied while reads are floating"));
    }

    @Override
    protected void run(StructuredGraph graph, CoreProviders context) {
        if (VirtualUtil.matches(graph, EscapeAnalyzeOnly.getValue(graph.getOptions()))) {
            runAnalysis(graph, context);
        }
    }

    @Override
    protected Closure createEffectsClosure(CoreProviders context, ScheduleResult schedule, ControlFlowGraph cfg) {
        assert schedule == null;
        return new ReadEliminationClosure(cfg, considerGuards);
    }

    @Override
    public float codeSizeIncrease() {
        return 2f;
    }
}