[AutoDiff] Fix semantic member accessor linear map structs. (#31745)

Ensure that semantic member accesors have empty linear map structs.
Semantic member accessor VJPs do not accumulate any callee pullbacks.

Resolves SR-12800: SIL verification error.

Author: dan-zheng

lib/SILOptimizer/Differentiation/LinearMapInfo.cpp

@@ -408,6 +408,11 @@ void LinearMapInfo::generateDifferentiationDataStructures(
     linearMapStructEnumFields.insert({linearMapStruct, traceEnumField});
   }
 
+  // Do not add linear map fields for semantic member accessors, which have
+  // special-case pullback generation. Linear map structs should be empty.
+  if (isSemanticMemberAccessor(original))
+    return;
+
   // Add linear map fields to the linear map structs.
   for (auto &origBB : *original) {
     for (auto &inst : origBB) {

test/AutoDiff/SILOptimizer/property_wrappers.swift

@@ -1,4 +1,5 @@
 // RUN: %target-swift-frontend -emit-sil -verify %s %S/Inputs/nontrivial_loadable_type.swift
+// REQUIRES: asserts
 
 // Test property wrapper differentiation coverage for a variety of property
 // types: trivial, non-trivial loadable, and address-only.
@@ -25,17 +26,35 @@ struct Wrapper<Value> {
   }
 }
 
+// `DifferentiableWrapper` conditionally conforms to `Differentiable`.
+@propertyWrapper
+struct DifferentiableWrapper<Value> {
+  private var value: Value
+  var wrappedValue: Value { // computed property
+    get { value }
+    set { value = newValue }
+  }
+
+  init(wrappedValue: Value) {
+    self.value = wrappedValue
+  }
+}
+extension DifferentiableWrapper: Differentiable where Value: Differentiable {}
+
 // MARK: Types with wrapped properties
 
 struct Struct: Differentiable {
   @Wrapper @SimpleWrapper var trivial: Float = 10
   @Wrapper @SimpleWrapper var tracked: Tracked<Float> = 20
   @Wrapper @SimpleWrapper var nontrivial: NontrivialLoadable<Float> = 30
+  // Tests SR-12800: semantic member accessors should have empty linear map structs.
+  @DifferentiableWrapper var differentiableWrapped: Float = 40
 
   static func testGetters() {
     let _: @differentiable (Self) -> Float = { $0.trivial }
     let _: @differentiable (Self) -> Tracked<Float> = { $0.tracked }
     let _: @differentiable (Self) -> NontrivialLoadable<Float> = { $0.nontrivial }
+    let _: @differentiable (Self) -> Float = { $0.differentiableWrapped }
   }
 
   static func testSetters() {
@@ -45,6 +64,8 @@ struct Struct: Differentiable {
       { $0.tracked = $1 }
     let _: @differentiable (inout Self, NontrivialLoadable<Float>) -> Void =
       { $0.nontrivial = $1 }
+    let _: @differentiable (inout Self, Float) -> Void =
+      { $0.differentiableWrapped = $1 }
   }
 }