/*
 * Copyright (c) 2015, 2015, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package com.oracle.graal.lir.alloc.lsra;

import static com.oracle.graal.api.code.ValueUtil.*;
import static com.oracle.graal.lir.LIRValueUtil.*;

import com.oracle.graal.compiler.common.cfg.*;
import com.oracle.graal.debug.*;
import com.oracle.graal.debug.Debug.*;
import com.oracle.graal.lir.*;
import com.oracle.graal.lir.StandardOp.*;
import com.oracle.graal.lir.ssa.*;

public class SSAEliminateSpillMove extends EliminateSpillMove {

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

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

    @Override
    protected void beforeSpillMoveElimination() {
        /*
         * PHI Ins are needed for the RegisterVerifier, otherwise PHIs where the Out and In value
         * matches (ie. there is no resolution move) are falsely detected as errors.
         */
        try (Scope s1 = Debug.scope("Remove Phi In")) {
            for (AbstractBlockBase<?> toBlock : allocator.sortedBlocks) {
                if (toBlock.getPredecessorCount() > 1) {
                    SSAUtils.removePhiIn(allocator.ir, toBlock);
                }
            }
        }
    }

    @Override
    protected boolean canEliminateSpillMove(AbstractBlockBase<?> block, MoveOp move) {
        // SSA Linear Scan might introduce moves to stack slots
        assert isVariable(move.getResult()) || LinearScanPhase.SSA_LSRA.getValue() : "Move should not be produced in a non-SSA compilation: " + move;

        Interval curInterval = allocator.intervalFor(move.getResult());

        if (!isRegister(curInterval.location()) && curInterval.alwaysInMemory() && !isPhiResolutionMove(block, move, curInterval)) {
            assert isStackSlotValue(curInterval.location()) : "Not a stack slot: " + curInterval.location();
            return true;
        }
        return false;
    }

    private boolean isPhiResolutionMove(AbstractBlockBase<?> block, MoveOp move, Interval toInterval) {
        if (!LinearScanPhase.SSA_LSRA.getValue()) {
            return false;
        }
        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;
        }
        AbstractBlockBase<?> intStartBlock = allocator.blockForId(toInterval.from());
        assert allocator.ir.getLIRforBlock(intStartBlock).get(0).equals(op);
        if (!block.getSuccessors().get(0).equals(intStartBlock)) {
            return false;
        }
        try (Indent indet = Debug.indent()) {
            Debug.log("Is a move (%s) to phi interval %s", move, toInterval);
        }
        return true;
    }
}