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//===--- SimplifyDestructure.swift ----------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
import SIL
extension DestructureTupleInst : OnoneSimplifyable, SILCombineSimplifyable {
func simplify(_ context: SimplifyContext) {
// Eliminate the redundant instruction pair
// ```
// %t = tuple (%0, %1, %2)
// (%3, %4, %5) = destructure_tuple %t
// ```
// and replace the results %3, %4, %5 with %0, %1, %2, respectively
//
if let tuple = self.tuple as? TupleInst {
tryReplaceConstructDestructPair(construct: tuple, destruct: self, context)
}
}
}
extension DestructureStructInst : OnoneSimplifyable, SILCombineSimplifyable {
func simplify(_ context: SimplifyContext) {
switch self.struct {
case let str as StructInst:
// Eliminate the redundant instruction pair
// ```
// %s = struct (%0, %1, %2)
// (%3, %4, %5) = destructure_struct %s
// ```
// and replace the results %3, %4, %5 with %0, %1, %2, respectively
//
tryReplaceConstructDestructPair(construct: str, destruct: self, context)
case let copy as CopyValueInst:
// Similar to the pattern above, but with a copy_value:
// Replace
// ```
// %s = struct (%0, %1, %2)
// %c = copy_value %s // can also be a chain of multiple copies
// (%3, %4, %5) = destructure_struct %c
// ```
// with
// ```
// %c0 = copy_value %0
// %c1 = copy_value %1
// %c2 = copy_value %2
// %s = struct (%0, %1, %2) // keep the original struct
// ```
// and replace the results %3, %4, %5 with %c0, %c1, %c2, respectively.
//
// This transformation has the advantage that we can do it even if the `struct` instruction
// has other uses than the `copy_value`.
//
if copy.uses.singleUse?.instruction == self,
let structInst = copy.fromValue.lookThroughCopy as? StructInst,
structInst.parentBlock == self.parentBlock
{
for (result, operand) in zip(self.results, structInst.operands) {
if operand.value.type.isTrivial(in: parentFunction) {
result.uses.replaceAll(with: operand.value, context)
} else {
let builder = Builder(before: structInst, context)
let copiedOperand = builder.createCopyValue(operand: operand.value)
result.uses.replaceAll(with: copiedOperand, context)
}
}
context.erase(instruction: self)
context.erase(instruction: copy)
}
default:
break
}
}
}
private func tryReplaceConstructDestructPair(construct: SingleValueInstruction,
destruct: MultipleValueInstruction,
_ context: SimplifyContext) {
let singleUse = context.preserveDebugInfo ? construct.uses.singleUse : construct.uses.ignoreDebugUses.singleUse
let canEraseFirst = singleUse?.instruction == destruct
if !canEraseFirst && construct.parentFunction.hasOwnership && construct.ownership == .owned {
// We cannot add more uses to this tuple without inserting a copy.
return
}
for (result, operand) in zip(destruct.results, construct.operands) {
result.uses.replaceAll(with: operand.value, context)
}
if canEraseFirst {
context.erase(instructionIncludingDebugUses: destruct)
}
}
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