/*
* This file is part of the Jikes RVM project (http://jikesrvm.org).
*
* This file is licensed to You under the Eclipse Public License (EPL);
* You may not use this file except in compliance with the License. You
* may obtain a copy of the License at
*
* http://www.opensource.org/licenses/eclipse-1.0.php
*
* See the COPYRIGHT.txt file distributed with this work for information
* regarding copyright ownership.
*/
package org.jikesrvm.compilers.opt.controlflow;
import static org.jikesrvm.compilers.opt.ir.IRTools.CPOS;
import static org.jikesrvm.compilers.opt.ir.Operators.BBEND;
import static org.jikesrvm.compilers.opt.ir.Operators.BOOLEAN_CMP_ADDR;
import static org.jikesrvm.compilers.opt.ir.Operators.BOOLEAN_CMP_INT;
import static org.jikesrvm.compilers.opt.ir.Operators.BOOLEAN_NOT;
import static org.jikesrvm.compilers.opt.ir.Operators.DOUBLE_2FLOAT_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.DOUBLE_ADD_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.DOUBLE_MOVE_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.DOUBLE_MUL_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.DOUBLE_NEG_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.DOUBLE_SUB_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.FLOAT_2DOUBLE_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.FLOAT_ADD_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.FLOAT_MOVE_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.FLOAT_MUL_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.FLOAT_NEG_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.FLOAT_SUB_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.GOTO;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_2BYTE_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_2SHORT_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_2USHORT_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_ADD_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_AND_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_IFCMP;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_IFCMP2;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_MOVE;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_MOVE_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_MUL_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_NEG_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_NOT_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_OR_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_SHL_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_SHR_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_SUB_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_USHR_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.INT_XOR_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_ADD_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_AND_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_IFCMP;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_MOVE_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_NOT_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_OR_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_SHL_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_SHR_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_SUB_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_USHR_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.REF_XOR_opcode;
import static org.jikesrvm.compilers.opt.ir.Operators.RETURN;
import java.util.HashMap;
import java.util.HashSet;
import org.jikesrvm.VM;
import org.jikesrvm.classloader.Atom;
import org.jikesrvm.classloader.TypeReference;
import org.jikesrvm.compilers.opt.OptimizingCompilerException;
import org.jikesrvm.compilers.opt.ir.BasicBlock;
import org.jikesrvm.compilers.opt.ir.BooleanCmp;
import org.jikesrvm.compilers.opt.ir.CondMove;
import org.jikesrvm.compilers.opt.ir.Goto;
import org.jikesrvm.compilers.opt.ir.IR;
import org.jikesrvm.compilers.opt.ir.IRTools;
import org.jikesrvm.compilers.opt.ir.IfCmp;
import org.jikesrvm.compilers.opt.ir.IfCmp2;
import org.jikesrvm.compilers.opt.ir.InlineGuard;
import org.jikesrvm.compilers.opt.ir.Instruction;
import org.jikesrvm.compilers.opt.ir.InstructionEnumeration;
import org.jikesrvm.compilers.opt.ir.Move;
import org.jikesrvm.compilers.opt.ir.OperandEnumeration;
import org.jikesrvm.compilers.opt.ir.Operator;
import org.jikesrvm.compilers.opt.ir.Register;
import org.jikesrvm.compilers.opt.ir.Return;
import org.jikesrvm.compilers.opt.ir.Unary;
import org.jikesrvm.compilers.opt.ir.operand.BranchOperand;
import org.jikesrvm.compilers.opt.ir.operand.BranchProfileOperand;
import org.jikesrvm.compilers.opt.ir.operand.ConditionOperand;
import org.jikesrvm.compilers.opt.ir.operand.IntConstantOperand;
import org.jikesrvm.compilers.opt.ir.operand.Operand;
import org.jikesrvm.compilers.opt.ir.operand.RegisterOperand;
/**
* Perform simple peephole optimizations for branches.
*/
public final class BranchOptimizations extends BranchOptimizationDriver {
/**
* Name of abs method used as a special case in conditional moves
*/
private static final Atom ABS = Atom.findOrCreateAsciiAtom("abs");
/**
* Is branch optimizations allowed to change the code order to
* create fallthrough edges (and thus merge basic blocks)?
* After we run code reordering, we disallow this transformation to avoid
* destroying the desired code order.
*/
private final boolean mayReorderCode;
/**
* Are we allowed to duplication conditional branches?
* Restricted until backedge yieldpoints are inserted to
* avoid creating irreducible control flow by duplicating
* a conditional branch in a loop header into a block outside the
* loop, thus creating two loop entry blocks.
*/
private final boolean mayDuplicateCondBranches;
/**
* @param level the minimum optimization level at which the branch
* optimizations should be performed.
* @param mayReorderCode are we allowed to change the code order?
* @param mayDuplicateCondBranches are we allowed to duplicate conditional branches?
*/
public BranchOptimizations(int level, boolean mayReorderCode, boolean mayDuplicateCondBranches) {
super(level, true);
this.mayReorderCode = mayReorderCode;
this.mayDuplicateCondBranches = mayDuplicateCondBranches;
}
/**
* @param level the minimum optimization level at which the branch
* optimizations should be performed.
* @param mayReorderCode are we allowed to change the code order?
* @param mayDuplicateCondBranches are we allowed to duplicate conditional branches?
* @param simplify simplify prior to optimizing?
*/
public BranchOptimizations(int level, boolean mayReorderCode, boolean mayDuplicateCondBranches,
boolean simplify) {
super(level, simplify);
this.mayReorderCode = mayReorderCode;
this.mayDuplicateCondBranches = mayDuplicateCondBranches;
}
/**
* This method actually does the work of attempting to
* peephole optimize a branch instruction.
* See Muchnick ~p.590
* @param ir the containing IR
* @param s the branch instruction to optimize
* @param bb the containing basic block
* @return true if an optimization was applied, false otherwise
*/
protected boolean optimizeBranchInstruction(IR ir, Instruction s, BasicBlock bb) {
if (Goto.conforms(s)) {
return processGoto(ir, s, bb);
} else if (IfCmp.conforms(s)) {
return processConditionalBranch(ir, s, bb);
} else if (InlineGuard.conforms(s)) {
return processInlineGuard(ir, s, bb);
} else if (IfCmp2.conforms(s)) {
return processTwoTargetConditionalBranch(ir, s, bb);
} else {
return false;
}
}
/**
* Perform optimizations for a Goto.
*
* <p> Patterns:
* <pre>
* 1) GOTO A replaced by GOTO B
* A: GOTO B
*
* 2) GOTO A replaced by IF .. GOTO B
* A: IF .. GOTO B GOTO C
* C: ...
* 3) GOTO next instruction eliminated
* 4) GOTO A replaced by GOTO B
* A: LABEL
* BBEND
* B:
* 5) GOTO BBn where BBn has exactly one in edge
* - move BBn immediately after the GOTO in the code order,
* so that pattern 3) will create a fallthrough
* <pre>
*
* <p> Precondition: Goto.conforms(g)
*
* @param ir governing IR
* @param g the instruction to optimize
* @param bb the basic block holding g
* @return true if made a transformation
*/
private boolean processGoto(IR ir, Instruction g, BasicBlock bb) {
BasicBlock targetBlock = g.getBranchTarget();
// don't optimize jumps to a code motion landing pad
if (targetBlock.getLandingPad()) return false;
Instruction targetLabel = targetBlock.firstInstruction();
// get the first real instruction at the g target
// NOTE: this instruction is not necessarily in targetBlock,
// iff targetBlock has no real instructions
Instruction targetInst = firstRealInstructionFollowing(targetLabel);
if (targetInst == null || targetInst == g) {
return false;
}
Instruction nextLabel = firstLabelFollowing(g);
if (targetLabel == nextLabel) {
// found a GOTO to the next instruction. just remove it.
g.remove();
return true;
}
if (Goto.conforms(targetInst)) {
// unconditional branch to unconditional branch.
// replace g with goto to targetInst's target
Instruction target2 = firstRealInstructionFollowing(targetInst.getBranchTarget().firstInstruction());
if (target2 == targetInst) {
// Avoid an infinite recursion in the following bizarre scenario:
// g: goto L
// ...
// L: goto L
// This happens in jByteMark.EmFloatPnt.denormalize() due to a while(true) {}
return false;
}
Goto.setTarget(g, (BranchOperand) Goto.getTarget(targetInst).copy());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
if (targetBlock.isEmpty()) {
// GOTO an empty basic block. Change target to the
// next block.
BasicBlock nextBlock = targetBlock.getFallThroughBlock();
Goto.setTarget(g, nextBlock.makeJumpTarget());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
if (mayDuplicateCondBranches && IfCmp.conforms(targetInst)) {
// unconditional branch to a conditional branch.
// If the Goto is the only branch instruction in its basic block
// and the IfCmp is the only non-GOTO branch instruction
// in its basic block then replace the goto with a copy of
// targetInst and append another GOTO to the not-taken
// target of targetInst's block.
// We impose these additional restrictions to avoid getting
// multiple conditional branches in a single basic block.
if (!g.prevInstructionInCodeOrder().isBranch() &&
(targetInst.nextInstructionInCodeOrder().operator == BBEND ||
targetInst.nextInstructionInCodeOrder().operator == GOTO)) {
Instruction copy = targetInst.copyWithoutLinks();
g.replace(copy);
Instruction newGoto = targetInst.getBasicBlock().getNotTakenNextBlock().makeGOTO();
copy.insertAfter(newGoto);
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
}
// try to create a fallthrough
if (mayReorderCode && targetBlock.getNumberOfIn() == 1) {
BasicBlock ftBlock = targetBlock.getFallThroughBlock();
if (ftBlock != null) {
BranchOperand ftTarget = ftBlock.makeJumpTarget();
targetBlock.appendInstruction(CPOS(g,Goto.create(GOTO, ftTarget)));
}
ir.cfg.removeFromCodeOrder(targetBlock);
ir.cfg.insertAfterInCodeOrder(bb, targetBlock);
targetBlock.recomputeNormalOut(ir); // fix the CFG
return true;
}
return false;
}
/**
* Perform optimizations for a conditional branch.
*
* <pre>
* 1) IF .. GOTO A replaced by IF .. GOTO B
* ...
* A: GOTO B
* 2) conditional branch to next instruction eliminated
* 3) IF (condition) GOTO A replaced by IF (!condition) GOTO B
* GOTO B A: ...
* A: ...
* 4) special case to generate Boolean compare opcode
* 5) special case to generate conditional move sequence
* 6) IF .. GOTO A replaced by IF .. GOTO B
* A: LABEL
* BBEND
* B:
* 7) fallthrough to a goto: replicate goto to enable other optimizations.
* </pre>
*
* <p> Precondition: IfCmp.conforms(cb)
*
* @param ir the governing IR
* @param cb the instruction to optimize
* @param bb the basic block holding if
* @return true iff made a transformation
*/
private boolean processConditionalBranch(IR ir, Instruction cb, BasicBlock bb) {
BasicBlock targetBlock = cb.getBranchTarget();
// don't optimize jumps to a code motion landing pad
if (targetBlock.getLandingPad()) return false;
Instruction targetLabel = targetBlock.firstInstruction();
// get the first real instruction at the branch target
// NOTE: this instruction is not necessarily in targetBlock,
// iff targetBlock has no real instructions
Instruction targetInst = firstRealInstructionFollowing(targetLabel);
if (targetInst == null || targetInst == cb) {
return false;
}
boolean endsBlock = cb.nextInstructionInCodeOrder().operator() == BBEND;
if (endsBlock) {
Instruction nextLabel = firstLabelFollowing(cb);
if (targetLabel == nextLabel) {
// found a conditional branch to the next instruction. just remove it.
cb.remove();
return true;
}
Instruction nextI = firstRealInstructionFollowing(nextLabel);
if (nextI != null && Goto.conforms(nextI)) {
// Check that the target is not the fall through (the goto itself).
// If we add a goto to the next block, it will be removed by
// processGoto and we will loop indefinitely.
// This can be tripped by (strange) code such as:
// if (condition) while (true);
BasicBlock gotoTarget = nextI.getBranchTarget();
Instruction gotoLabel = gotoTarget.firstInstruction();
Instruction gotoInst = firstRealInstructionFollowing(gotoLabel);
if (gotoInst != nextI) {
// replicate Goto
cb.insertAfter(nextI.copyWithoutLinks());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
}
}
// attempt to generate boolean compare.
if (generateBooleanCompare(ir, bb, cb, targetBlock)) {
// generateBooleanCompare does all necessary CFG fixup.
return true;
}
// attempt to generate a sequence using conditional moves
if (generateCondMove(ir, bb, cb)) {
// generateCondMove does all necessary CFG fixup.
return true;
}
// do we fall through to a block that has only a goto?
BasicBlock fallThrough = bb.getFallThroughBlock();
if (fallThrough != null) {
Instruction fallThroughInstruction = fallThrough.firstRealInstruction();
if ((fallThroughInstruction != null) && Goto.conforms(fallThroughInstruction)) {
// copy goto to bb
bb.appendInstruction(fallThroughInstruction.copyWithoutLinks());
bb.recomputeNormalOut(ir);
}
}
if (Goto.conforms(targetInst)) {
// conditional branch to unconditional branch.
// change conditional branch target to latter's target
Instruction target2 = firstRealInstructionFollowing(targetInst.getBranchTarget().firstInstruction());
if (target2 == targetInst) {
// Avoid an infinite recursion in the following scenario:
// g: if (...) goto L
// ...
// L: goto L
// This happens in GCUtil in some systems due to a while(true) {}
return false;
}
IfCmp.setTarget(cb, (BranchOperand) Goto.getTarget(targetInst).copy());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
if (targetBlock.isEmpty()) {
// branch to an empty block. Change target to the next block.
BasicBlock nextBlock = targetBlock.getFallThroughBlock();
IfCmp.setTarget(cb, nextBlock.makeJumpTarget());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
if (isFlipCandidate(cb, targetInst)) {
flipConditionalBranch(cb);
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
return false;
}
/**
* Perform optimizations for an inline guard.
*
* <p> Precondition: InlineGuard.conforms(cb)
*
* @param ir the governing IR
* @param cb the instruction to optimize
* @param bb the basic block holding if
* @return true iff made a transformation
*/
private boolean processInlineGuard(IR ir, Instruction cb, BasicBlock bb) {
BasicBlock targetBlock = cb.getBranchTarget();
Instruction targetLabel = targetBlock.firstInstruction();
// get the first real instruction at the branch target
// NOTE: this instruction is not necessarily in targetBlock,
// iff targetBlock has no real instructions
Instruction targetInst = firstRealInstructionFollowing(targetLabel);
if (targetInst == null || targetInst == cb) {
return false;
}
boolean endsBlock = cb.nextInstructionInCodeOrder().operator() == BBEND;
if (endsBlock) {
Instruction nextLabel = firstLabelFollowing(cb);
if (targetLabel == nextLabel) {
// found a conditional branch to the next instruction. just remove it.
cb.remove();
return true;
}
Instruction nextI = firstRealInstructionFollowing(nextLabel);
if (nextI != null && Goto.conforms(nextI)) {
// replicate Goto
cb.insertAfter(nextI.copyWithoutLinks());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
}
// do we fall through to a block that has only a goto?
BasicBlock fallThrough = bb.getFallThroughBlock();
if (fallThrough != null) {
Instruction fallThroughInstruction = fallThrough.firstRealInstruction();
if ((fallThroughInstruction != null) && Goto.conforms(fallThroughInstruction)) {
// copy goto to bb
bb.appendInstruction(fallThroughInstruction.copyWithoutLinks());
bb.recomputeNormalOut(ir);
}
}
if (Goto.conforms(targetInst)) {
// conditional branch to unconditional branch.
// change conditional branch target to latter's target
InlineGuard.setTarget(cb, (BranchOperand) Goto.getTarget(targetInst).copy());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
if (targetBlock.isEmpty()) {
// branch to an empty block. Change target to the next block.
BasicBlock nextBlock = targetBlock.getFallThroughBlock();
InlineGuard.setTarget(cb, nextBlock.makeJumpTarget());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
return false;
}
/**
* Perform optimizations for a two way conditional branch.
*
* <p> Precondition: IfCmp2.conforms(cb)
*
* @param ir the governing IR
* @param cb the instruction to optimize
* @param bb the basic block holding if
* @return true iff made a transformation
*/
private boolean processTwoTargetConditionalBranch(IR ir, Instruction cb, BasicBlock bb) {
// First condition/target
Instruction target1Label = IfCmp2.getTarget1(cb).target;
Instruction target1Inst = firstRealInstructionFollowing(target1Label);
Instruction nextLabel = firstLabelFollowing(cb);
boolean endsBlock = cb.nextInstructionInCodeOrder().operator() == BBEND;
if (target1Inst != null && target1Inst != cb) {
if (Goto.conforms(target1Inst)) {
// conditional branch to unconditional branch.
// change conditional branch target to latter's target
IfCmp2.setTarget1(cb, (BranchOperand) Goto.getTarget(target1Inst).copy());
bb.recomputeNormalOut(ir); // fix CFG
return true;
}
BasicBlock target1Block = target1Label.getBasicBlock();
if (target1Block.isEmpty()) {
// branch to an empty block. Change target to the next block.
BasicBlock nextBlock = target1Block.getFallThroughBlock();
IfCmp2.setTarget1(cb, nextBlock.makeJumpTarget());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
}
// Second condition/target
Instruction target2Label = IfCmp2.getTarget2(cb).target;
Instruction target2Inst = firstRealInstructionFollowing(target2Label);
if (target2Inst != null && target2Inst != cb) {
if (Goto.conforms(target2Inst)) {
// conditional branch to unconditional branch.
// change conditional branch target to latter's target
IfCmp2.setTarget2(cb, (BranchOperand) Goto.getTarget(target2Inst).copy());
bb.recomputeNormalOut(ir); // fix CFG
return true;
}
if ((target2Label == nextLabel) && endsBlock) {
// found a conditional branch to the next instruction. Reduce to IfCmp
if (VM.VerifyAssertions) VM._assert(cb.operator() == INT_IFCMP2);
IfCmp.mutate(cb,
INT_IFCMP,
IfCmp2.getGuardResult(cb),
IfCmp2.getVal1(cb),
IfCmp2.getVal2(cb),
IfCmp2.getCond1(cb),
IfCmp2.getTarget1(cb),
IfCmp2.getBranchProfile1(cb));
return true;
}
BasicBlock target2Block = target2Label.getBasicBlock();
if (target2Block.isEmpty()) {
// branch to an empty block. Change target to the next block.
BasicBlock nextBlock = target2Block.getFallThroughBlock();
IfCmp2.setTarget2(cb, nextBlock.makeJumpTarget());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
}
// if fall through to a goto; replicate the goto
if (endsBlock) {
Instruction nextI = firstRealInstructionFollowing(nextLabel);
if (nextI != null && Goto.conforms(nextI)) {
// replicate Goto
cb.insertAfter(nextI.copyWithoutLinks());
bb.recomputeNormalOut(ir); // fix the CFG
return true;
}
}
return false;
}
/**
* Is a conditional branch a candidate to be flipped?
* See comment 3) of processConditionalBranch
*
* <p> Precondition: IfCmp.conforms(cb)
*
* @param cb the conditional branch instruction
* @param target the target instruction (real instruction) of the conditional
* branch
* @return boolean result
*/
private boolean isFlipCandidate(Instruction cb, Instruction target) {
// condition 1: is next instruction a GOTO?
Instruction next = cb.nextInstructionInCodeOrder();
if (!Goto.conforms(next)) {
return false;
}
// condition 2: is the target of the conditional branch the
// next instruction after the GOTO?
next = firstRealInstructionFollowing(next);
if (next != target) {
return false;
}
// got this far. It's a candidate.
return true;
}
/**
* Flip a conditional branch and remove the trailing goto.
* See comment 3) of processConditionalBranch
*
* <p> Precondition isFlipCandidate(cb)
* @param cb the conditional branch instruction
*/
private void flipConditionalBranch(Instruction cb) {
// get the trailing GOTO instruction
Instruction g = cb.nextInstructionInCodeOrder();
BranchOperand gTarget = (BranchOperand) (Goto.getTarget(g).copy());
// now flip the test and set the new target
IfCmp.setCond(cb, IfCmp.getCond(cb).flipCode());
IfCmp.setTarget(cb, gTarget);
// Update the branch probability. It is now the opposite
cb.flipBranchProbability();
// finally, remove the trailing GOTO instruction
g.remove();
}
/**
* Generate a boolean operation opcode
*
* <pre>
* 1) IF br != 0 THEN x=1 ELSE x=0 replaced by INT_MOVE x=br
* IF br == 0 THEN x=0 ELSE x=1
* 2) IF br == 0 THEN x=1 ELSE x=0 replaced by BOOLEAN_NOT x=br
* IF br != 0 THEN x=0 ELSE x=1
* 3) IF v1 ~ v2 THEN x=1 ELSE x=0 replaced by BOOLEAN_CMP x=v1,v2,~
* </pre>
*
*
* @param cb conditional branch instruction
* @param res the operand for result
* @param val1 value being compared
* @param val2 value being compared with
* @param cond comparison condition
*/
private void booleanCompareHelper(Instruction cb, RegisterOperand res, Operand val1, Operand val2,
ConditionOperand cond) {
if ((val1 instanceof RegisterOperand) &&
((RegisterOperand) val1).getType().isBooleanType() &&
(val2 instanceof IntConstantOperand)) {
int value = ((IntConstantOperand) val2).value;
if (VM.VerifyAssertions && (value != 0) && (value != 1)) {
throw new OptimizingCompilerException("Invalid boolean value");
}
int c = cond.evaluate(value, 0);
if (c == ConditionOperand.TRUE) {
Unary.mutate(cb, BOOLEAN_NOT, res, val1);
return;
} else if (c == ConditionOperand.FALSE) {
Move.mutate(cb, INT_MOVE, res, val1);
return;
}
}
BooleanCmp.mutate(cb,
(cb.operator() == REF_IFCMP) ? BOOLEAN_CMP_ADDR : BOOLEAN_CMP_INT,
res,
val1,
val2,
cond,
new BranchProfileOperand());
}
/**
* Attempt to generate a straight-line sequence using conditional move
* instructions, to replace a diamond control flow structure.
*
* <p>Suppose we have the following code, where e{n} is an expression:
* <pre>
* if (a op b) {
* x = e2;
* y = e3;
* } else {
* z = e4;
* x = e5;
* }
* </pre>
* We would transform this to:
* <pre>
* t1 = a;
* t2 = b;
* t3 = e2;
* t4 = e3;
* t5 = e4;
* t6 = e5;
* COND MOVE [if (t1 op t2) x := t3 else x := t6 ];
* COND MOVE [if (t1 op t2) y := t4 else y := y];
* COND MOVE [if (t1 op t2) z := z else z := t5];
* </pre>
*
* <p>Note that we rely on other optimizations (eg. copy propagation) to
* clean up some of this unnecessary mess.
*
* <p>Note that in this example, we've increased the shortest path by 2
* expression evaluations, 2 moves, and 3 cond moves, but eliminated one
* conditional branch.
*
* <p>We apply a cost heuristic to guide this transformation:
* We will eliminate a conditional branch iff it increases the shortest
* path by no more than 'k' operations. Currently, we count each
* instruction (alu, move, or cond move) as 1 evaluation.
* The parameter k is specified by OPT\_Options.COND_MOVE_CUTOFF.
*
* <p> In the example above, since we've increased the shortest path by
* 6 instructions, we will only perform the transformation if k >= 7.
*
* <p> TODO items
* <ul>
* <li> consider smarter cost heuristics
* <li> enhance downstream code generation to avoid redundant evaluation
* of condition codes.
* </ul>
*
* @param ir governing IR
* @param bb basic block of cb
* @param cb conditional branch instruction
* @return true if the transformation succeeds, false otherwise
*/
private boolean generateCondMove(IR ir, BasicBlock bb, Instruction cb) {
final boolean VERBOSE=false;
if (!VM.BuildForIA32) return false;
if (!IfCmp.conforms(cb)) return false;
if (VERBOSE) System.out.println("CondMove: Looking to optimize "+cb);
// Don't generate CMOVs for branches that can be folded.
if (IfCmp.getVal1(cb).isConstant() && IfCmp.getVal2(cb).isConstant()) {
if (VERBOSE) System.out.println("CondMove: fail - could be folded");
return false;
}
// see if bb is the root of an if-then-else.
Diamond diamond = Diamond.buildDiamond(bb);
if (diamond == null) {
if (VERBOSE) System.out.println("CondMove: fail - no diamond");
return false;
}
BasicBlock taken = diamond.getTaken();
BasicBlock notTaken = diamond.getNotTaken();
// do not perform the transformation if either branch of the diamond
// has a taboo instruction (eg., a PEI, store or divide).
if (taken != null && hasCMTaboo(taken)) {
if (VERBOSE) System.out.println("CondMove: fail - taken branch has taboo instruction");
return false;
}
if (notTaken != null && hasCMTaboo(notTaken)) {
if (VERBOSE) System.out.println("CondMove: fail - not taken branch has taboo instruction");
return false;
}
ConditionOperand cond = IfCmp.getCond(cb);
// Do not generate when we don't know the branch probability or
// when branch probability is high. CMOVs reduce performance of
// the out-of-order engine (Intel Optimization Guide -
// Assembly/Compiler Coding Rule 2).
// Ignore in the case of an abs() method as we can create tighter
// instructions.
BranchProfileOperand profile = IfCmp.getBranchProfile(cb);
if ((Math.abs(profile.takenProbability - 0.5) >= ir.options.CONTROL_WELL_PREDICTED_CUTOFF) &&
!(cb.position != null && cb.position.method.getName() == ABS && cond.isFLOATINGPOINT())) {
if (VERBOSE)
System.out.println("CondMove: fail - branch could be well predicted by branch predictor: "+
profile.takenProbability);
return false;
}
// if we must generate FCMP, make sure the condition code is OK
if (cond.isFLOATINGPOINT()) {
if (!fpConditionOK(cond)) {
// Condition not OK, but maybe if we flip the operands
if (!fpConditionOK(cond.flipOperands())) {
// still not ok so flip operands back
cond.flipOperands();
// give up or for SSE2 check if this is a floating point compare
// controlling just floating point moves
if (!VM.BuildForSSE2Full || hasFloatingPointDef(taken, true) || hasFloatingPointDef(notTaken, true)) {
if (VERBOSE) System.out.println("CondMove: fail - fp condition not OK: "+cond);
return false;
}
} else {
// flip operands
Operand val1 = IfCmp.getVal1(cb);
Operand val2 = IfCmp.getVal2(cb);
IfCmp.setVal1(cb, val2);
IfCmp.setVal2(cb, val1);
}
}
}
if (!cond.isFLOATINGPOINT()) {
// Can only generate moves of floating point values for floating point
// compares or for unsigned compares in x87
if (VM.BuildForSSE2Full || !cond.isUNSIGNED()) {
if (hasFloatingPointDef(taken, false) || hasFloatingPointDef(notTaken, false)) {
if (VERBOSE)
System.out.println("CondMove: fail - not allowed integer condition controlling floating conditional move");
return false;
}
}
}
// For now, do not generate CMOVs for longs.
if (hasLongDef(taken) || hasLongDef(notTaken)) {
return false;
}
// count the number of expression evaluations in each side of the
// diamond
int takenCost = 0;
int notTakenCost = 0;
if (taken != null) takenCost = evaluateCost(taken);
if (notTaken != null) notTakenCost = evaluateCost(notTaken);
// evaluate whether it's profitable.
int shortestCost = Math.min(takenCost, notTakenCost);
int xformCost = 2 * (takenCost + notTakenCost);
int k = ir.options.CONTROL_COND_MOVE_CUTOFF;
if (xformCost - shortestCost > k) {
if (VERBOSE) System.out.println("CondMove: fail - cost too high");
return false;
}
// Perform the transformation!
doCondMove(ir, diamond, cb);
return true;
}
/**
* Is a specified condition operand 'safe' to transfer into an FCMP
* instruction?
*/
private boolean fpConditionOK(ConditionOperand c) {
// FCOMI sets ZF, PF, and CF as follows:
// Compare Results ZF PF CF
// left > right 0 0 0
// left < right 0 0 1
// left == right 1 0 0
// UNORDERED 1 1 1
switch (c.value) {
case ConditionOperand.CMPL_EQUAL:
return false; // (ZF == 1) but ordered
case ConditionOperand.CMPL_NOT_EQUAL:
return false; // (ZF == 0) but unordered
case ConditionOperand.CMPG_LESS:
return false; // (CF == 1) but ordered
case ConditionOperand.CMPG_GREATER_EQUAL:
return false; // (CF == 0) but unordered
case ConditionOperand.CMPG_LESS_EQUAL:
return false; // (CF == 1 || ZF == 1) but ordered
case ConditionOperand.CMPG_GREATER:
return false; // (CF == 0 && ZF == 0) but unordered
case ConditionOperand.CMPL_GREATER:
return true; // (CF == 0 && ZF == 0) and ordered
case ConditionOperand.CMPL_LESS_EQUAL:
return true; // (CF == 1 || ZF == 1) and unordered
case ConditionOperand.CMPL_GREATER_EQUAL:
return true; // (CF == 0) and ordered
case ConditionOperand.CMPL_LESS:
return true; // (CF == 1) and unordered
default:
OptimizingCompilerException.UNREACHABLE();
return false; // keep jikes happy
}
}
/**
* Do any of the instructions in a basic block define a floating-point
* register?
*
* @param bb basic block to search
* @param invert invert the sense of the search
*/
private static boolean hasFloatingPointDef(BasicBlock bb, boolean invert) {
if (bb == null) return false;
for (InstructionEnumeration e = bb.forwardRealInstrEnumerator(); e.hasMoreElements();) {
Instruction s = e.nextElement();
for (OperandEnumeration d = s.getDefs(); d.hasMoreElements();) {
Operand def = d.nextElement();
if (def.isRegister()) {
if (def.asRegister().getRegister().isFloatingPoint() != invert) return true;
}
}
}
return false;
}
/**
* Do any of the instructions in a basic block define a long
* register?
*/
private boolean hasLongDef(BasicBlock bb) {
if (bb == null) return false;
for (InstructionEnumeration e = bb.forwardRealInstrEnumerator(); e.hasMoreElements();) {
Instruction s = e.nextElement();
for (OperandEnumeration d = s.getDefs(); d.hasMoreElements();) {
Operand def = d.nextElement();
if (def.isRegister()) {
if (def.asRegister().getRegister().isLong()) return true;
}
}
}
return false;
}
/**
* Do any of the instructions in a basic block preclude eliminating the
* basic block with conditional moves?
*/
private boolean hasCMTaboo(BasicBlock bb) {
if (bb == null) return false;
// Note: it is taboo to assign more than once to any register in the
// block.
HashSet<Register> defined = new HashSet<Register>();
for (InstructionEnumeration e = bb.forwardRealInstrEnumerator(); e.hasMoreElements();) {
Instruction s = e.nextElement();
if (s.isBranch()) continue;
// for now, only the following opcodes are legal.
switch (s.operator.opcode) {
case INT_MOVE_opcode:
case REF_MOVE_opcode:
case DOUBLE_MOVE_opcode:
case FLOAT_MOVE_opcode:
case INT_ADD_opcode:
case REF_ADD_opcode:
case FLOAT_ADD_opcode:
case DOUBLE_ADD_opcode:
case INT_SUB_opcode:
case REF_SUB_opcode:
case FLOAT_SUB_opcode:
case DOUBLE_SUB_opcode:
case INT_MUL_opcode:
case FLOAT_MUL_opcode:
case DOUBLE_MUL_opcode:
case INT_NEG_opcode:
case FLOAT_NEG_opcode:
case DOUBLE_NEG_opcode:
case REF_SHL_opcode:
case INT_SHL_opcode:
case REF_SHR_opcode:
case INT_SHR_opcode:
case REF_USHR_opcode:
case INT_USHR_opcode:
case REF_AND_opcode:
case INT_AND_opcode:
case REF_OR_opcode:
case INT_OR_opcode:
case REF_XOR_opcode:
case INT_XOR_opcode:
case REF_NOT_opcode:
case INT_NOT_opcode:
case INT_2BYTE_opcode:
case INT_2USHORT_opcode:
case INT_2SHORT_opcode:
case FLOAT_2DOUBLE_opcode:
case DOUBLE_2FLOAT_opcode:
// these are OK.
break;
default:
return true;
}
// make sure no register is defined more than once in this block.
for (OperandEnumeration defs = s.getDefs(); defs.hasMoreElements();) {
Operand def = defs.nextElement();
if (VM.VerifyAssertions) VM._assert(def.isRegister());
Register r = def.asRegister().getRegister();
if (defined.contains(r)) return true;
defined.add(r);
}
}
return false;
}
/**
* Evaluate the cost of a basic block, in number of real instructions.
*/
private int evaluateCost(BasicBlock bb) {
int result = 0;
for (InstructionEnumeration e = bb.forwardRealInstrEnumerator(); e.hasMoreElements();) {
Instruction s = e.nextElement();
if (!s.isBranch()) result++;
}
return result;
}
/**
* For each real non-branch instruction s in bb,
* <ul>
* <li> Copy s to s', and store s' in the returned array
* <li> Insert the function s->s' in the map
* </ul>
*/
private Instruction[] copyAndMapInstructions(BasicBlock bb, HashMap<Instruction, Instruction> map) {
if (bb == null) return new Instruction[0];
int count = 0;
// first count the number of instructions
for (InstructionEnumeration e = bb.forwardRealInstrEnumerator(); e.hasMoreElements();) {
Instruction s = e.nextElement();
if (s.isBranch()) continue;
count++;
}
// now copy.
Instruction[] result = new Instruction[count];
int i = 0;
for (InstructionEnumeration e = bb.forwardRealInstrEnumerator(); e.hasMoreElements();) {
Instruction s = e.nextElement();
if (s.isBranch()) continue;
Instruction sprime = s.copyWithoutLinks();
result[i++] = sprime;
map.put(s, sprime);
}
return result;
}
/**
* For each in a set of instructions, rewrite every def to use a new
* temporary register. If a rewritten def is subsequently used, then
* use the new temporary register instead.
*/
private void rewriteWithTemporaries(Instruction[] set, IR ir) {
// Maintain a mapping holding the new name for each register
HashMap<Register, Register> map = new HashMap<Register, Register>();
for (Instruction s : set) {
// rewrite the uses to use the new names
for (OperandEnumeration e = s.getUses(); e.hasMoreElements();) {
Operand use = e.nextElement();
if (use != null && use.isRegister()) {
Register r = use.asRegister().getRegister();
Register temp = map.get(r);
if (temp != null) {
use.asRegister().setRegister(temp);
}
}
}
if (VM.VerifyAssertions) VM._assert(s.getNumberOfDefs() == 1);
Operand def = s.getDefs().nextElement();
RegisterOperand rDef = def.asRegister();
RegisterOperand temp = ir.regpool.makeTemp(rDef);
map.put(rDef.getRegister(), temp.getRegister());
s.replaceOperand(def, temp);
}
}
/**
* Insert each instruction in a list before instruction s
*/
private void insertBefore(Instruction[] list, Instruction s) {
for (Instruction x : list) {
s.insertBefore(x);
}
}
/**
* Perform the transformation to replace conditional branch with a
* sequence using conditional moves.
*
* @param ir governing IR
* @param diamond the IR diamond structure to replace
* @param cb conditional branch instruction at the head of the diamond
*/
private void doCondMove(IR ir, Diamond diamond, Instruction cb) {
BasicBlock taken = diamond.getTaken();
BasicBlock notTaken = diamond.getNotTaken();
// for each non-branch instruction s in the diamond,
// copy s to a new instruction s'
// and store a mapping from s to s'
HashMap<Instruction, Instruction> takenInstructions = new HashMap<Instruction, Instruction>();
Instruction[] takenInstructionList = copyAndMapInstructions(taken, takenInstructions);
HashMap<Instruction, Instruction> notTakenInstructions = new HashMap<Instruction, Instruction>();
Instruction[] notTakenInstructionList = copyAndMapInstructions(notTaken, notTakenInstructions);
// Extract the values and condition from the conditional branch.
Operand val1 = IfCmp.getVal1(cb);
Operand val2 = IfCmp.getVal2(cb);
ConditionOperand cond = IfCmp.getCond(cb);
// Copy val1 and val2 to temporaries, just in case they're defined in
// the diamond. If they're not defined in the diamond, copy prop
// should clean these moves up.
RegisterOperand tempVal1 = ir.regpool.makeTemp(val1);
Operator op = IRTools.getMoveOp(tempVal1.getType());
cb.insertBefore(Move.create(op, tempVal1.copyRO(), val1.copy()));
RegisterOperand tempVal2 = ir.regpool.makeTemp(val2);
op = IRTools.getMoveOp(tempVal2.getType());
cb.insertBefore(Move.create(op, tempVal2.copyRO(), val2.copy()));
// For each instruction in each temporary set, rewrite it to def a new
// temporary, and insert it before the branch.
rewriteWithTemporaries(takenInstructionList, ir);
rewriteWithTemporaries(notTakenInstructionList, ir);
insertBefore(takenInstructionList, cb);
insertBefore(notTakenInstructionList, cb);
// For each register defined in the TAKEN branch, save a mapping to
// the corresponding conditional move.
HashMap<Register, Instruction> takenMap = new HashMap<Register, Instruction>();
// Now insert conditional moves to replace each instruction in the diamond.
// First handle the taken branch.
if (taken != null) {
for (InstructionEnumeration e = taken.forwardRealInstrEnumerator(); e.hasMoreElements();) {
Instruction s = e.nextElement();
if (s.isBranch()) continue;
Operand def = s.getDefs().nextElement();
// if the register does not span a basic block, it is a temporary
// that will now be dead
if (def.asRegister().getRegister().spansBasicBlock()) {
Instruction tempS = takenInstructions.get(s);
RegisterOperand temp = (RegisterOperand) tempS.getDefs().nextElement();
op = IRTools.getCondMoveOp(def.asRegister().getType());
Instruction cmov =
CondMove.create(op,
def.asRegister(),
tempVal1.copy(),
tempVal2.copy(),
cond.copy().asCondition(),
temp.copy(),
def.copy());
takenMap.put(def.asRegister().getRegister(), cmov);
cb.insertBefore(cmov);
}
s.remove();
}
}
// For each register defined in the NOT-TAKEN branch, save a mapping to
// the corresponding conditional move.
HashMap<Register, Instruction> notTakenMap = new HashMap<Register, Instruction>();
// Next handle the not taken branch.
if (notTaken != null) {
for (InstructionEnumeration e = notTaken.forwardRealInstrEnumerator(); e.hasMoreElements();) {
Instruction s = e.nextElement();
if (s.isBranch()) continue;
Operand def = s.getDefs().nextElement();
// if the register does not span a basic block, it is a temporary
// that will now be dead
if (def.asRegister().getRegister().spansBasicBlock()) {
Instruction tempS = notTakenInstructions.get(s);
RegisterOperand temp = (RegisterOperand) tempS.getDefs().nextElement();
Instruction prevCmov = takenMap.get(def.asRegister().getRegister());
if (prevCmov != null) {
// if this register was also defined in the taken branch, change
// the previous cmov with a different 'False' Value
CondMove.setFalseValue(prevCmov, temp.copy());
notTakenMap.put(def.asRegister().getRegister(), prevCmov);
} else {
// create a new cmov instruction
op = IRTools.getCondMoveOp(def.asRegister().getType());
Instruction cmov =
CondMove.create(op,
def.asRegister(),
tempVal1.copy(),
tempVal2.copy(),
cond.copy().asCondition(),
def.copy(),
temp.copy());
cb.insertBefore(cmov);
notTakenMap.put(def.asRegister().getRegister(), cmov);
}
}
s.remove();
}
}
// Mutate the conditional branch into a GOTO.
BranchOperand target = diamond.getBottom().makeJumpTarget();
Goto.mutate(cb, GOTO, target);
// Delete a potential GOTO after cb.
Instruction next = cb.nextInstructionInCodeOrder();
if (next.operator != BBEND) {
next.remove();
}
// Recompute the CFG.
diamond.getTop().recomputeNormalOut(ir); // fix the CFG
}
/**
* Attempt to generate a boolean compare opcode from a conditional branch.
*
* <pre>
* 1) IF .. GOTO A replaced by BOOLEAN_CMP x=..
* x = 0
* GOTO B
* A: x = 1
* B: ...
* </pre>
*
* <p> Precondition: <code>IfCmp.conforms(<i>cb</i>)</code>
*
*
* @param ir governing IR
* @param bb basic block of cb
* @param cb conditional branch instruction
* @return true if the transformation succeeds, false otherwise
*/
private boolean generateBooleanCompare(IR ir, BasicBlock bb, Instruction cb, BasicBlock tb) {
if ((cb.operator() != INT_IFCMP) && (cb.operator() != REF_IFCMP)) {
return false;
}
// make sure this is the last branch in the block
if (cb.nextInstructionInCodeOrder().operator() != BBEND) {
return false;
}
Operand val1 = IfCmp.getVal1(cb);
Operand val2 = IfCmp.getVal2(cb);
ConditionOperand condition = IfCmp.getCond(cb);
// "not taken" path
BasicBlock fb = cb.getBasicBlock().getNotTakenNextBlock();
// make sure it's a diamond
if (tb.getNumberOfNormalOut() != 1) {
return false;
}
if (fb.getNumberOfNormalOut() != 1) {
return false;
}
BasicBlock jb = fb.getNormalOut().next(); // join block
// make sure it's a diamond
if (!tb.pointsOut(jb)) {
return false;
}
Instruction ti = tb.firstRealInstruction();
Instruction fi = fb.firstRealInstruction();
// make sure the instructions in target blocks are either both moves
// or both returns
if (ti == null || fi == null) {
return false;
}
if (ti.operator() != fi.operator()) {
return false;
}
if (ti.operator != RETURN && ti.operator() != INT_MOVE) {
return false;
}
//
// WARNING: This code is currently NOT exercised!
//
if (ti.operator() == RETURN) {
// make sure each of the target blocks contains only one instruction
if (ti != tb.lastRealInstruction()) {
return false;
}
if (fi != fb.lastRealInstruction()) {
return false;
}
Operand tr = Return.getVal(ti);
Operand fr = Return.getVal(fi);
// make sure we're returning constants
if (!(tr instanceof IntConstantOperand) || !(fr instanceof IntConstantOperand)) {
return false;
}
int tv = ((IntConstantOperand) tr).value;
int fv = ((IntConstantOperand) fr).value;
if (!((tv == 1 && fv == 0) || (tv == 1 && fv == 0))) {
return false;
}
RegisterOperand t = ir.regpool.makeTemp(TypeReference.Boolean);
// Cases 1) and 2)
if (tv == 0) {
condition = condition.flipCode();
}
booleanCompareHelper(cb, t, val1.copy(), val2.copy(), condition);
cb.insertAfter(Return.create(RETURN, t.copyD2U()));
} else { // (ti.operator() == INT_MOVE)
// make sure each of the target blocks only does the move
if (ti != tb.lastRealInstruction() && ti.nextInstructionInCodeOrder().operator() != GOTO) {
return false;
}
if (fi != fb.lastRealInstruction() && fi.nextInstructionInCodeOrder().operator() != GOTO) {
return false;
}
RegisterOperand t = Move.getResult(ti);
// make sure both moves are to the same register
if (t.getRegister() != Move.getResult(fi).getRegister()) {
return false;
}
Operand tr = Move.getVal(ti);
Operand fr = Move.getVal(fi);
// make sure we're assigning constants
if (!(tr instanceof IntConstantOperand) || !(fr instanceof IntConstantOperand)) {
return false;
}
int tv = ((IntConstantOperand) tr).value;
int fv = ((IntConstantOperand) fr).value;
if (!((tv == 1 && fv == 0) || (tv == 0 && fv == 1))) {
return false;
}
// Cases 3) and 4)
if (tv == 0) {
condition = condition.flipCode();
}
booleanCompareHelper(cb, t.copyRO(), val1.copy(), val2.copy(), condition);
Instruction next = cb.nextInstructionInCodeOrder();
if (next.operator() == GOTO) {
Goto.setTarget(next, jb.makeJumpTarget());
} else {
cb.insertAfter(jb.makeGOTO());
}
}
// fixup CFG
bb.deleteOut(tb);
bb.deleteOut(fb);
bb.insertOut(jb); // Note: if we processed returns,
// jb is the exit node.
return true;
}
}