Merge pull request #82831 from atrick/reassign-immortal

Fix LifetimeDependenceDiagnostics: allow inout assignment to Void.

Author: atrick

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/LifetimeDependenceDiagnostics.swift

@@ -110,6 +110,20 @@ private func analyze(dependence: LifetimeDependence, _ context: FunctionPassCont
     }
   }
 
+  // Check for immortal dependence.
+  switch dependence.scope {
+  case .global:
+    log("Immortal global dependence.")
+    return true
+  case let .unknown(value):
+    if value.type.isVoid {
+      log("Immortal void dependence.")
+      return true
+    }
+  default:
+    break
+  }
+
   // Compute this dependence scope.
   var range = dependence.computeRange(context)
   defer { range?.deinitialize() }
@@ -200,6 +214,9 @@ private struct DiagnoseDependence {
       return .continueWalk
     }
     // Check for immortal lifetime.
+    //
+    // FIXME: remove this immortal check. It should be redundant with the earlier check that bypasses dependence
+    // diagnostics.
     switch dependence.scope {
     case .global:
       return .continueWalk

test/SILOptimizer/lifetime_dependence/verify_diagnostics.swift

@@ -305,6 +305,16 @@ func testSpanMayThrow(buffer: inout [Int]) {
   try! mutableSpanMayThrow(bufferSpan)
 }
 
+// =============================================================================
+// inout
+// =============================================================================
+
+@available(Span 0.1, *)
+func inoutToImmortal(_ s: inout RawSpan) {
+  let tmp = RawSpan(_unsafeBytes: UnsafeRawBufferPointer(start: nil, count: 0))
+  s = _overrideLifetime(tmp, borrowing: ())
+}
+
 // =============================================================================
 // Dependence on non-Copyable values
 // =============================================================================