[AutoDiff] Fix pullback subset thunk generation crash.

lib/SILOptimizer/Differentiation/Thunk.cpp

@@ -768,7 +768,8 @@ getOrCreateSubsetParametersThunkForLinearMap(
     if (!paramInfo.isIndirectMutating())
       continue;
     auto inoutArg = *std::next(ai->getInoutArguments().begin(), inoutArgIdx++);
-    allResults.insert(allResults.begin() + paramIdx, inoutArg);
+    unsigned mappedParamIdx = mapOriginalParameterIndex(paramIdx);
+    allResults.insert(allResults.begin() + mappedParamIdx, inoutArg);
   }
   assert(allResults.size() == actualIndices.parameters->getNumIndices() &&
          "Number of pullback results should match number of differentiability "

test/AutoDiff/compiler_crashers_fixed/tf1315-pullback-subset-parameter-thunk-generation.swift

@@ -0,0 +1,27 @@
+// RUN: %target-swift-frontend -emit-sil %s
+// REQUIRES: asserts
+
+// TF-1315: Pullback subset thunk generation crash due to unmapped parameter
+// index for `inout` differentiability parameters.
+
+import _Differentiation
+
+func foo(_ x: Int, _ y: Float, _ z: inout Float) {}
+
+@derivative(of: foo, wrt: (y, z))
+func vjpFoo(_ x: Int, _ y: Float, _ z: inout Float) -> (
+  value: Void, pullback: (inout Float) -> Float
+) {
+  fatalError()
+}
+
+@differentiable
+func TF_1315(_ x: Float) -> Float {
+  var x = x
+  // The call to `foo` below triggers pullback subset parameter thunk generation.
+  // `foo` original function type: `(Int, Float, inout Float) -> ()`
+  //     Actual parameter indices: 1, 2
+  //    Desired parameter indices: 2
+  foo(1, 2, &x)
+  return x
+}