diff options
Diffstat (limited to 'src')
-rw-r--r-- | src/compiler/scala/tools/nsc/backend/jvm/opt/LocalOpt.scala | 281 |
1 files changed, 150 insertions, 131 deletions
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/LocalOpt.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/LocalOpt.scala index c1fdb7eb59..f486bb0cb9 100644 --- a/src/compiler/scala/tools/nsc/backend/jvm/opt/LocalOpt.scala +++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/LocalOpt.scala @@ -771,154 +771,173 @@ object LocalOptImpls { // A set of all exception handlers that guard the current instruction, required for simplifyGotoReturn var activeHandlers = Set.empty[TryCatchBlockNode] - // Instructions that need to be removed. simplifyBranchOverGoto returns an instruction to be - // removed. It cannot remove it itself because the instruction may be the successor of the current - // instruction of the iterator, which is not supported in ASM. - var instructionsToRemove = Set.empty[AbstractInsnNode] + val jumpInsns = mutable.LinkedHashMap.empty[JumpInsnNode, Boolean] - val iterator = method.instructions.iterator() - while (iterator.hasNext) { - val instruction = iterator.next() + for (insn <- method.instructions.iterator().asScala) insn match { + case l: LabelNode => + activeHandlers ++= allHandlers.filter(_.start == l) + activeHandlers = activeHandlers.filter(_.end != l) - instruction match { - case l: LabelNode => - activeHandlers ++= allHandlers.filter(_.start == l) - activeHandlers = activeHandlers.filter(_.end != l) - case _ => + case ji: JumpInsnNode => + jumpInsns(ji) = activeHandlers.nonEmpty + + case _ => + } + + var _jumpTargets: Set[AbstractInsnNode] = null + def jumpTargets = { + if (_jumpTargets == null) { + _jumpTargets = jumpInsns.keysIterator.map(_.label).toSet } + _jumpTargets + } - if (instructionsToRemove(instruction)) { - iterator.remove() - instructionsToRemove -= instruction - } else if (isJumpNonJsr(instruction)) { // fast path - all of the below only treat jumps - var jumpRemoved = simplifyThenElseSameTarget(method, instruction) + def removeJumpFromMap(jump: JumpInsnNode) = { + jumpInsns.remove(jump) + _jumpTargets = null + } - if (!jumpRemoved) { - changed = collapseJumpChains(instruction) || changed - jumpRemoved = removeJumpToSuccessor(method, instruction) + def replaceJumpByPop(jump: JumpInsnNode) = { + removeJumpAndAdjustStack(method, jump) + removeJumpFromMap(jump) + } - if (!jumpRemoved) { - val staleGoto = simplifyBranchOverGoto(method, instruction) - instructionsToRemove ++= staleGoto - changed ||= staleGoto.nonEmpty - changed = simplifyGotoReturn(method, instruction, inTryBlock = activeHandlers.nonEmpty) || changed - } + /** + * Removes a conditional jump if it is followed by a GOTO to the same destination. + * + * CondJump l; [nops]; GOTO l; [...] + * POP*; [nops]; GOTO l; [...] + * + * Introduces 1 or 2 POP instructions, depending on the number of values consumed by the CondJump. + */ + def simplifyThenElseSameTarget(insn: AbstractInsnNode): Boolean = insn match { + case ConditionalJump(jump) => + nextExecutableInstruction(insn) match { + case Some(Goto(elseJump)) if sameTargetExecutableInstruction(jump, elseJump) => + replaceJumpByPop(jump) + true + + case _ => false } - changed ||= jumpRemoved - } + + case _ => false } - assert(instructionsToRemove.isEmpty, "some optimization required removing a previously traversed instruction. add `instructionsToRemove.foreach(method.instructions.remove)`") - changed - } - /** - * Removes a conditional jump if it is followed by a GOTO to the same destination. - * - * CondJump l; [nops]; GOTO l; [...] - * POP*; [nops]; GOTO l; [...] - * - * Introduces 1 or 2 POP instructions, depending on the number of values consumed by the CondJump. - */ - private def simplifyThenElseSameTarget(method: MethodNode, instruction: AbstractInsnNode): Boolean = instruction match { - case ConditionalJump(jump) => - nextExecutableInstruction(instruction) match { - case Some(Goto(elseJump)) if sameTargetExecutableInstruction(jump, elseJump) => - removeJumpAndAdjustStack(method, jump) + /** + * Replace jumps to a sequence of GOTO instructions by a jump to the final destination. + * + * Jump l; [any ops]; l: GOTO m; [any ops]; m: GOTO n; [any ops]; n: NotGOTO; [...] + * => Jump n; [rest unchanged] + * + * If there's a loop of GOTOs, the initial jump is replaced by one of the labels in the loop. + */ + def collapseJumpChains(insn: AbstractInsnNode): Boolean = insn match { + case JumpNonJsr(jump) => + val target = finalJumpTarget(jump) + if (jump.label == target) false else { + jump.label = target + _jumpTargets = null true + } - case _ => false - } - case _ => false - } + case _ => false + } - /** - * Replace jumps to a sequence of GOTO instructions by a jump to the final destination. - * - * Jump l; [any ops]; l: GOTO m; [any ops]; m: GOTO n; [any ops]; n: NotGOTO; [...] - * => Jump n; [rest unchanged] - * - * If there's a loop of GOTOs, the initial jump is replaced by one of the labels in the loop. - */ - private def collapseJumpChains(instruction: AbstractInsnNode): Boolean = instruction match { - case JumpNonJsr(jump) => - val target = finalJumpTarget(jump) - if (jump.label == target) false else { - jump.label = target + /** + * Eliminates unnecessary jump instructions + * + * Jump l; [nops]; l: [...] + * => POP*; [nops]; l: [...] + * + * Introduces 0, 1 or 2 POP instructions, depending on the number of values consumed by the Jump. + */ + def removeJumpToSuccessor(insn: AbstractInsnNode): Boolean = insn match { + case JumpNonJsr(jump) if nextExecutableInstruction(jump, alsoKeep = Set(jump.label)) contains jump.label => + replaceJumpByPop(jump) true - } - case _ => false - } + case _ => false + } - /** - * Eliminates unnecessary jump instructions - * - * Jump l; [nops]; l: [...] - * => POP*; [nops]; l: [...] - * - * Introduces 0, 1 or 2 POP instructions, depending on the number of values consumed by the Jump. - */ - private def removeJumpToSuccessor(method: MethodNode, instruction: AbstractInsnNode) = instruction match { - case JumpNonJsr(jump) if nextExecutableInstruction(jump, alsoKeep = Set(jump.label)) == Some(jump.label) => - removeJumpAndAdjustStack(method, jump) - true - case _ => false - } + /** + * If the "else" part of a conditional branch is a simple GOTO, negates the conditional branch + * and eliminates the GOTO. + * + * CondJump l; [nops, no jump targets]; GOTO m; [nops]; l: [...] + * => NegatedCondJump m; [nops, no jump targets]; [nops]; l: [...] + * + * Note that no jump targets are allowed in the first [nops] section. Otherwise, there could + * be some other jump to the GOTO, and eliminating it would change behavior. + */ + def simplifyBranchOverGoto(insn: AbstractInsnNode, inTryBlock: Boolean): Boolean = insn match { + case ConditionalJump(jump) => + // don't skip over jump targets, see doc comment + nextExecutableInstruction(jump, alsoKeep = jumpTargets) match { + case Some(Goto(goto)) => + if (nextExecutableInstruction(goto, alsoKeep = Set(jump.label)) contains jump.label) { + val newJump = new JumpInsnNode(negateJumpOpcode(jump.getOpcode), goto.label) + method.instructions.set(jump, newJump) + removeJumpFromMap(jump) + jumpInsns(newJump) = inTryBlock + replaceJumpByPop(goto) + true + } else false + + case _ => false + } + case _ => false + } - /** - * If the "else" part of a conditional branch is a simple GOTO, negates the conditional branch - * and eliminates the GOTO. - * - * CondJump l; [nops, no labels]; GOTO m; [nops]; l: [...] - * => NegatedCondJump m; [nops, no labels]; [nops]; l: [...] - * - * Note that no label definitions are allowed in the first [nops] section. Otherwise, there could - * be some other jump to the GOTO, and eliminating it would change behavior. - * - * For technical reasons, we cannot remove the GOTO here (*).Instead this method returns an Option - * containing the GOTO that needs to be eliminated. - * - * (*) The ASM instruction iterator (used in the caller [[simplifyJumps]]) has an undefined - * behavior if the successor of the current instruction is removed, which may be the case here - */ - private def simplifyBranchOverGoto(method: MethodNode, instruction: AbstractInsnNode): Option[JumpInsnNode] = instruction match { - case ConditionalJump(jump) => - // don't skip over labels, see doc comment - nextExecutableInstructionOrLabel(jump) match { - case Some(Goto(goto)) => - if (nextExecutableInstruction(goto, alsoKeep = Set(jump.label)) == Some(jump.label)) { - val newJump = new JumpInsnNode(negateJumpOpcode(jump.getOpcode), goto.label) - method.instructions.set(jump, newJump) - Some(goto) - } else None - - case _ => None - } - case _ => None - } + /** + * Inlines xRETURN and ATHROW + * + * GOTO l; [any ops]; l: xRETURN/ATHROW + * => xRETURN/ATHROW; [any ops]; l: xRETURN/ATHROW + * + * inlining is only done if the GOTO instruction is not part of a try block, otherwise the + * rewrite might change the behavior. For xRETURN, the reason is that return instructions may throw + * an IllegalMonitorStateException, as described here: + * http://docs.oracle.com/javase/specs/jvms/se8/html/jvms-6.html#jvms-6.5.return + */ + def simplifyGotoReturn(instruction: AbstractInsnNode, inTryBlock: Boolean): Boolean = !inTryBlock && (instruction match { + case Goto(jump) => + nextExecutableInstruction(jump.label) match { + case Some(target) => + if (isReturn(target) || target.getOpcode == ATHROW) { + method.instructions.set(jump, target.clone(null)) + removeJumpFromMap(jump) + true + } else false + + case _ => false + } + case _ => false + }) - /** - * Inlines xRETURN and ATHROW - * - * GOTO l; [any ops]; l: xRETURN/ATHROW - * => xRETURN/ATHROW; [any ops]; l: xRETURN/ATHROW - * - * inlining is only done if the GOTO instruction is not part of a try block, otherwise the - * rewrite might change the behavior. For xRETURN, the reason is that return instructions may throw - * an IllegalMonitorStateException, as described here: - * http://docs.oracle.com/javase/specs/jvms/se8/html/jvms-6.html#jvms-6.5.return - */ - private def simplifyGotoReturn(method: MethodNode, instruction: AbstractInsnNode, inTryBlock: Boolean): Boolean = !inTryBlock && (instruction match { - case Goto(jump) => - nextExecutableInstruction(jump.label) match { - case Some(target) => - if (isReturn(target) || target.getOpcode == ATHROW) { - method.instructions.set(jump, target.clone(null)) - true - } else false + def run(): Boolean = { + var changed = false + + // `.toList` because we're modifying the map while iterating over it + for ((jumpInsn, inTryBlock) <- jumpInsns.toList if jumpInsns.contains(jumpInsn) && isJumpNonJsr(jumpInsn)) { + var jumpRemoved = simplifyThenElseSameTarget(jumpInsn) - case _ => false + if (!jumpRemoved) { + changed = collapseJumpChains(jumpInsn) || changed + jumpRemoved = removeJumpToSuccessor(jumpInsn) + + if (!jumpRemoved) { + changed = simplifyBranchOverGoto(jumpInsn, inTryBlock) || changed + changed = simplifyGotoReturn(jumpInsn, inTryBlock) || changed + } + } + + changed ||= jumpRemoved } - case _ => false - }) + + if (changed) run() + changed + } + + run() + } } |