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package jdk.graal.compiler.lir.alloc.lsra.ssa;

import static jdk.graal.compiler.lir.LIRValueUtil.isStackSlotValue;
import static jdk.vm.ci.code.ValueUtil.isRegister;

import jdk.graal.compiler.core.common.cfg.BasicBlock;
import jdk.graal.compiler.debug.Assertions;
import jdk.graal.compiler.debug.DebugContext;
import jdk.graal.compiler.debug.Indent;
import jdk.graal.compiler.lir.LIRInstruction;
import jdk.graal.compiler.lir.StandardOp.LabelOp;
import jdk.graal.compiler.lir.StandardOp.MoveOp;
import jdk.graal.compiler.lir.alloc.lsra.Interval;
import jdk.graal.compiler.lir.alloc.lsra.LinearScan;
import jdk.graal.compiler.lir.alloc.lsra.LinearScanEliminateSpillMovePhase;

public class SSALinearScanEliminateSpillMovePhase extends LinearScanEliminateSpillMovePhase {

    SSALinearScanEliminateSpillMovePhase(LinearScan allocator) {
        super(allocator);
    }

    @Override
    protected int firstInstructionOfInterest() {
        // also look at Labels as they define PHI values
        return 0;
    }

    @Override
    protected boolean canEliminateSpillMove(BasicBlock block, MoveOp move) {
        if (super.canEliminateSpillMove(block, move)) {
            // SSA Linear Scan might introduce moves to stack slots
            Interval curInterval = allocator.intervalFor(move.getResult());
            assert !isRegister(curInterval.location()) && curInterval.alwaysInMemory() : Assertions.errorMessage(curInterval);
            if (!isPhiResolutionMove(block, move, curInterval)) {
                assert isStackSlotValue(curInterval.location()) : "Not a stack slot: " + curInterval.location();
                return true;
            }
        }
        return false;
    }

    @SuppressWarnings("try")
    private boolean isPhiResolutionMove(BasicBlock block, MoveOp move, Interval toInterval) {
        if (!toInterval.isSplitParent()) {
            return false;
        }
        if ((toInterval.from() & 1) == 1) {
            // phi intervals start at even positions.
            return false;
        }
        if (block.getSuccessorCount() != 1) {
            return false;
        }
        LIRInstruction op = allocator.instructionForId(toInterval.from());
        if (!(op instanceof LabelOp)) {
            return false;
        }
        BasicBlock intStartBlock = allocator.blockForId(toInterval.from());
        assert allocator.getLIR().getLIRforBlock(intStartBlock).get(0).equals(op);
        if (!block.getSuccessorAt(0).equals(intStartBlock)) {
            return false;
        }
        DebugContext debug = allocator.getDebug();
        try (Indent indent = debug.indent()) {
            debug.log("Is a move (%s) to phi interval %s", move, toInterval);
        }
        return true;
    }
}