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Loosen tail-call optimization check for functions returning Unit

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Do not check, that all Unit predecessors are POPs. This is safe for the
same reason, as it is safe to allow some of ARETURN sources not be
suspension point results.
To elaborate, before Unit, the stack is empty. This is because if there
are multiple paths to Unit and at least one of them comes from POP after
suspension point (we are interested in this case only - otherwise, the
call is not tail-call), in path from said POP the stack is empty, since
after suspension point the stack contains only one element. Thus, the
stack in other paths leading to Unit has to be empty, otherwise, merge
operation is not possible and ASM will report error during analysis.
Since the stack is empty in all paths, we can hoist Unit and following
ARETURN to predecessors, effectively turning path from suspension point
to tail-call.
This commit is contained in:
Ilmir Usmanov
2021-08-19 05:51:09 +02:00
committed by Space
parent d33b70af1a
commit b5fa129540
8 changed files with 66 additions and 52 deletions
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compiler/backend/src/org/jetbrains/kotlin/codegen/coroutines/TailCallOptimization.kt
+5 -21
View File
@@ -39,7 +39,6 @@ internal class MethodNodeExaminer(
private val popsBeforeSafeUnitInstances = mutableSetOf<AbstractInsnNode>()
private val areturnsAfterSafeUnitInstances = mutableSetOf<AbstractInsnNode>()
private val meaningfulSuccessorsCache = hashMapOf<AbstractInsnNode, List<AbstractInsnNode>>()
private val meaningfulPredecessorsCache = hashMapOf<AbstractInsnNode, List<AbstractInsnNode>>()
init {
if (!disableTailCallOptimizationForFunctionReturningUnit) {
@@ -52,10 +51,8 @@ internal class MethodNodeExaminer(
for (pop in popsBeforeUnitInstances) {
val units = pop.meaningfulSuccessors()
val allUnitsAreSafe = units.all { unit ->
// check no other predecessor exists
unit.meaningfulPredecessors().all { it in popsBeforeUnitInstances } &&
// check they have only returns among successors
unit.meaningfulSuccessors().all { it.opcode == Opcodes.ARETURN }
// check they have only returns among successors
unit.meaningfulSuccessors().all { it.opcode == Opcodes.ARETURN }
}
if (!allUnitsAreSafe) continue
// save them all to the properties
@@ -74,35 +71,22 @@ internal class MethodNodeExaminer(
private fun AbstractInsnNode.isAreturnAfterSafeUnitInstance(): Boolean = this in areturnsAfterSafeUnitInstances
private fun AbstractInsnNode.meaningfulSuccessors(): List<AbstractInsnNode> = meaningfulSuccessorsCache.getOrPut(this) {
meaningfulSuccessorsOrPredecessors(true)
}
private fun AbstractInsnNode.meaningfulPredecessors(): List<AbstractInsnNode> = meaningfulPredecessorsCache.getOrPut(this) {
meaningfulSuccessorsOrPredecessors(false)
}
private fun AbstractInsnNode.meaningfulSuccessorsOrPredecessors(isSuccessors: Boolean): List<AbstractInsnNode> {
fun AbstractInsnNode.isMeaningful() = isMeaningful && opcode != Opcodes.NOP && opcode != Opcodes.GOTO && this !is LineNumberNode
fun AbstractInsnNode.getIndices() =
if (isSuccessors) controlFlowGraph.getSuccessorsIndices(this)
else controlFlowGraph.getPredecessorsIndices(this)
val visited = mutableSetOf<AbstractInsnNode>()
fun dfs(insn: AbstractInsnNode) {
if (insn in visited) return
visited += insn
if (!insn.isMeaningful()) {
for (succIndex in insn.getIndices()) {
for (succIndex in controlFlowGraph.getSuccessorsIndices(insn)) {
dfs(methodNode.instructions[succIndex])
}
}
}
for (succIndex in getIndices()) {
for (succIndex in controlFlowGraph.getSuccessorsIndices(this)) {
dfs(methodNode.instructions[succIndex])
}
return visited.filter { it.isMeaningful() }
visited.filter { it.isMeaningful() }
}
fun replacePopsBeforeSafeUnitInstancesWithCoroutineSuspendedChecks() {