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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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
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 *
 * 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.
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package org.graalvm.compiler.lir.aarch64;

import static jdk.vm.ci.code.ValueUtil.asStackSlot;
import static jdk.vm.ci.code.ValueUtil.isStackSlot;
import static org.graalvm.compiler.lir.LIRInstruction.OperandFlag.STACK;

import java.util.Arrays;

import jdk.internal.vm.compiler.collections.EconomicSet;
import org.graalvm.compiler.asm.aarch64.AArch64MacroAssembler;
import org.graalvm.compiler.lir.LIRInstructionClass;
import org.graalvm.compiler.lir.LIRValueUtil;
import org.graalvm.compiler.lir.Opcode;
import org.graalvm.compiler.lir.StandardOp.SaveRegistersOp;
import org.graalvm.compiler.lir.asm.CompilationResultBuilder;
import org.graalvm.compiler.lir.framemap.FrameMap;

import jdk.vm.ci.code.Register;
import jdk.vm.ci.code.RegisterSaveLayout;
import jdk.vm.ci.code.StackSlot;
import jdk.vm.ci.meta.AllocatableValue;

/**
 * Saves registers to stack slots.
 */
@Opcode("SAVE_REGISTER")
public class AArch64SaveRegistersOp extends AArch64LIRInstruction implements SaveRegistersOp {
    public static final LIRInstructionClass<AArch64SaveRegistersOp> TYPE = LIRInstructionClass.create(AArch64SaveRegistersOp.class);

    /**
     * The registers (potentially) saved by this operation.
     */
    protected final Register[] savedRegisters;

    /**
     * The slots to which the registers are saved.
     */
    @Def(STACK) protected final AllocatableValue[] slots;

    /**
     * Specifies if {@link #remove(EconomicSet)} should have an effect.
     */
    protected final boolean supportsRemove;

    /**
     *
     * @param savedRegisters the registers saved by this operation which may be subject to
     *            {@linkplain #remove(EconomicSet) pruning}
     * @param savedRegisterLocations the slots to which the registers are saved
     * @param supportsRemove determines if registers can be {@linkplain #remove(EconomicSet) pruned}
     */
    public AArch64SaveRegistersOp(Register[] savedRegisters, AllocatableValue[] savedRegisterLocations, boolean supportsRemove) {
        this(TYPE, savedRegisters, savedRegisterLocations, supportsRemove);
    }

    public AArch64SaveRegistersOp(LIRInstructionClass<? extends AArch64SaveRegistersOp> c, Register[] savedRegisters, AllocatableValue[] savedRegisterLocations, boolean supportsRemove) {
        super(c);
        assert Arrays.asList(savedRegisterLocations).stream().allMatch(LIRValueUtil::isVirtualStackSlot);
        this.savedRegisters = savedRegisters;
        this.slots = savedRegisterLocations;
        this.supportsRemove = supportsRemove;
    }

    protected void saveRegister(CompilationResultBuilder crb, AArch64MacroAssembler masm, StackSlot result, Register input) {
        AArch64Move.reg2stack(crb, masm, result, input.asValue());
    }

    @Override
    public void emitCode(CompilationResultBuilder crb, AArch64MacroAssembler masm) {
        for (int i = 0; i < savedRegisters.length; i++) {
            if (savedRegisters[i] != null) {
                assert isStackSlot(slots[i]) : "not a StackSlot: " + slots[i];
                saveRegister(crb, masm, asStackSlot(slots[i]), savedRegisters[i]);
            }
        }
    }

    public AllocatableValue[] getSlots() {
        return slots;
    }

    @Override
    public boolean supportsRemove() {
        return supportsRemove;
    }

    @Override
    public int remove(EconomicSet<Register> doNotSave) {
        if (!supportsRemove) {
            throw new UnsupportedOperationException();
        }
        return prune(doNotSave, savedRegisters);
    }

    static int prune(EconomicSet<Register> toRemove, Register[] registers) {
        int pruned = 0;
        for (int i = 0; i < registers.length; i++) {
            if (registers[i] != null) {
                if (toRemove.contains(registers[i])) {
                    registers[i] = null;
                    pruned++;
                }
            }
        }
        return pruned;
    }

    @Override
    public RegisterSaveLayout getMap(FrameMap frameMap) {
        int total = 0;
        for (int i = 0; i < savedRegisters.length; i++) {
            if (savedRegisters[i] != null) {
                total++;
            }
        }
        Register[] keys = new Register[total];
        int[] values = new int[total];
        if (total != 0) {
            int mapIndex = 0;
            for (int i = 0; i < savedRegisters.length; i++) {
                if (savedRegisters[i] != null) {
                    keys[mapIndex] = savedRegisters[i];
                    assert isStackSlot(slots[i]) : "not a StackSlot: " + slots[i];
                    StackSlot slot = asStackSlot(slots[i]);
                    values[mapIndex] = indexForStackSlot(frameMap, slot);
                    mapIndex++;
                }
            }
            assert mapIndex == total;
        }
        return new RegisterSaveLayout(keys, values);
    }

    /**
     * Computes the index of a stack slot relative to slot 0. This is also the bit index of stack
     * slots in the reference map.
     *
     * @param slot a stack slot
     * @return the index of the stack slot
     */
    private static int indexForStackSlot(FrameMap frameMap, StackSlot slot) {
        assert frameMap.offsetForStackSlot(slot) % frameMap.getTarget().wordSize == 0;
        int value = frameMap.offsetForStackSlot(slot) / frameMap.getTarget().wordSize;
        return value;
    }
}
