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/*
* Copyright (C) 2007 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.snapscript.dx.ssa;
import java.util.ArrayList;
import java.util.List;
import org.snapscript.dx.rop.code.Insn;
import org.snapscript.dx.rop.code.PlainCstInsn;
import org.snapscript.dx.rop.code.PlainInsn;
import org.snapscript.dx.rop.code.RegOps;
import org.snapscript.dx.rop.code.RegisterSpec;
import org.snapscript.dx.rop.code.RegisterSpecList;
import org.snapscript.dx.rop.code.Rop;
import org.snapscript.dx.rop.code.Rops;
import org.snapscript.dx.rop.code.TranslationAdvice;
import org.snapscript.dx.rop.cst.Constant;
import org.snapscript.dx.rop.cst.CstLiteralBits;
import org.snapscript.dx.rop.type.Type;
import org.snapscript.dx.rop.type.TypeBearer;
/**
* Upgrades insn to their literal (constant-immediate) equivalent if possible.
* Also switches IF instructions that compare with a constant zero or null
* to be their IF_*Z equivalents.
*/
public class LiteralOpUpgrader {
/** method we're processing */
private final SsaMethod ssaMeth;
/**
* Process a method.
*
* @param ssaMethod {@code non-null;} method to process
*/
public static void process(SsaMethod ssaMethod) {
LiteralOpUpgrader dc;
dc = new LiteralOpUpgrader(ssaMethod);
dc.run();
}
private LiteralOpUpgrader(SsaMethod ssaMethod) {
this.ssaMeth = ssaMethod;
}
/**
* Returns true if the register contains an integer 0 or a known-null
* object reference
*
* @param spec non-null spec
* @return true for 0 or null type bearers
*/
private static boolean isConstIntZeroOrKnownNull(RegisterSpec spec) {
TypeBearer tb = spec.getTypeBearer();
if (tb instanceof CstLiteralBits) {
CstLiteralBits clb = (CstLiteralBits) tb;
return (clb.getLongBits() == 0);
}
return false;
}
/**
* Run the literal op upgrader
*/
private void run() {
final TranslationAdvice advice = Optimizer.getAdvice();
ssaMeth.forEachInsn(new SsaInsn.Visitor() {
public void visitMoveInsn(NormalSsaInsn insn) {
// do nothing
}
public void visitPhiInsn(PhiInsn insn) {
// do nothing
}
public void visitNonMoveInsn(NormalSsaInsn insn) {
Insn originalRopInsn = insn.getOriginalRopInsn();
Rop opcode = originalRopInsn.getOpcode();
RegisterSpecList sources = insn.getSources();
// Replace insns with constant results with const insns
if (tryReplacingWithConstant(insn)) return;
if (sources.size() != 2 ) {
// We're only dealing with two-source insns here.
return;
}
if (opcode.getBranchingness() == Rop.BRANCH_IF) {
/*
* An if instruction can become an if-*z instruction.
*/
if (isConstIntZeroOrKnownNull(sources.get(0))) {
replacePlainInsn(insn, sources.withoutFirst(),
RegOps.flippedIfOpcode(opcode.getOpcode()), null);
} else if (isConstIntZeroOrKnownNull(sources.get(1))) {
replacePlainInsn(insn, sources.withoutLast(),
opcode.getOpcode(), null);
}
} else if (advice.hasConstantOperation(
opcode, sources.get(0), sources.get(1))) {
insn.upgradeToLiteral();
} else if (opcode.isCommutative()
&& advice.hasConstantOperation(
opcode, sources.get(1), sources.get(0))) {
/*
* An instruction can be commuted to a literal operation
*/
insn.setNewSources(
RegisterSpecList.make(
sources.get(1), sources.get(0)));
insn.upgradeToLiteral();
}
}
});
}
/**
* Tries to replace an instruction with a const instruction. The given
* instruction must have a constant result for it to be replaced.
*
* @param insn {@code non-null;} instruction to try to replace
* @return true if the instruction was replaced
*/
private boolean tryReplacingWithConstant(NormalSsaInsn insn) {
Insn originalRopInsn = insn.getOriginalRopInsn();
Rop opcode = originalRopInsn.getOpcode();
RegisterSpec result = insn.getResult();
if (result != null && !ssaMeth.isRegALocal(result) &&
opcode.getOpcode() != RegOps.CONST) {
TypeBearer type = insn.getResult().getTypeBearer();
if (type.isConstant() && type.getBasicType() == Type.BT_INT) {
// Replace the instruction with a constant
replacePlainInsn(insn, RegisterSpecList.EMPTY,
RegOps.CONST, (Constant) type);
// Remove the source as well if this is a move-result-pseudo
if (opcode.getOpcode() == RegOps.MOVE_RESULT_PSEUDO) {
int pred = insn.getBlock().getPredecessors().nextSetBit(0);
ArrayList predInsns =
ssaMeth.getBlocks().get(pred).getInsns();
NormalSsaInsn sourceInsn =
(NormalSsaInsn) predInsns.get(predInsns.size()-1);
replacePlainInsn(sourceInsn, RegisterSpecList.EMPTY,
RegOps.GOTO, null);
}
return true;
}
}
return false;
}
/**
* Replaces an SsaInsn containing a PlainInsn with a new PlainInsn. The
* new PlainInsn is constructed with a new RegOp and new sources.
*
* TODO move this somewhere else.
*
* @param insn {@code non-null;} an SsaInsn containing a PlainInsn
* @param newSources {@code non-null;} new sources list for new insn
* @param newOpcode A RegOp from {@link RegOps}
* @param cst {@code null-ok;} constant for new instruction, if any
*/
private void replacePlainInsn(NormalSsaInsn insn,
RegisterSpecList newSources, int newOpcode, Constant cst) {
Insn originalRopInsn = insn.getOriginalRopInsn();
Rop newRop = Rops.ropFor(newOpcode, insn.getResult(), newSources, cst);
Insn newRopInsn;
if (cst == null) {
newRopInsn = new PlainInsn(newRop, originalRopInsn.getPosition(),
insn.getResult(), newSources);
} else {
newRopInsn = new PlainCstInsn(newRop, originalRopInsn.getPosition(),
insn.getResult(), newSources, cst);
}
NormalSsaInsn newInsn = new NormalSsaInsn(newRopInsn, insn.getBlock());
List insns = insn.getBlock().getInsns();
ssaMeth.onInsnRemoved(insn);
insns.set(insns.lastIndexOf(insn), newInsn);
ssaMeth.onInsnAdded(newInsn);
}
}
