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//===--- SimplificationPasses.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
/// Removes redundant `debug_step` instructions.
/// If a `debug_step` has the same debug location as a previous or succeeding instruction
/// it is removed. It's just important that there is at least one instruction for a
/// certain debug location so that single stepping on that location will work.
let cleanupDebugStepsPass = FunctionPass(name: "cleanup-debug-steps") {
(function: Function, context: FunctionPassContext) in
for block in function.blocks {
cleanupDebugSteps(in: block, context)
}
}
private func cleanupDebugSteps(in block: BasicBlock, _ context: FunctionPassContext) {
var lastInstWithSameLocation: Instruction?
for inst in block.instructions {
if !inst.location.isDebugSteppable {
if inst is DebugStepInst && !inst.location.isDebugSteppable {
// First case: the instruction which is replaced by the debug_step didn't have a valid
// location itself. Then we don't need the debug_step either.
context.erase(instruction: inst)
}
continue
}
if let li = lastInstWithSameLocation,
!inst.location.hasSameSourceLocation(as: li.location) {
lastInstWithSameLocation = nil
}
// Only instructions which are really compiled down to some machine instructions can be
// single stepped on.
if !inst.producesMachineCode {
continue
}
if let li = lastInstWithSameLocation {
if inst is DebugStepInst {
// Second case:
// %li = some_instruction, loc "l"
// debug_step, loc "l" // current inst -> erase
context.erase(instruction: inst)
continue
} else if li is DebugStepInst {
// Third case:
// debug_step, loc "l" // li -> erase
// %inst = some_instruction, loc "l" // current inst
context.erase(instruction: li)
}
}
lastInstWithSameLocation = inst
}
}
private extension Instruction {
var producesMachineCode: Bool {
switch self {
// We could include more instructions here.
// In worst case a debug_step instruction remains in the code although it's not needed.
// This is harmless.
case is DebugStepInst, is ApplySite, is LoadInst, is StoreInst, is TermInst:
return location.isDebugSteppable
default:
return false
}
}
}
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