Add TF-1232 negative test: proper mangling for AutoDiff-generated declarations.

IRGenDebugInfo crash due to lack of proper mangling for AutoDiff-generated
declarations: linear map structs and branching trace enums.

Author: dan-zheng

test/AutoDiff/compiler_crashers/tf1232-autodiff-generated-declaration-mangling.swift

@@ -0,0 +1,34 @@
+// RUN: not %target-build-swift -g %s
+// REQUIRES: asserts
+
+// TF-1232: IRGenDebugInfo crash due to lack of proper mangling for
+// AutoDiff-generated declarations: linear map structs and branching trace
+// enums.
+
+import _Differentiation
+
+extension Float {
+  @_silgen_name("add")
+  static func add(_ x: Float, _ y: Float) -> Float {
+    return x + y
+  }
+
+  @derivative(of: add)
+  static func addVJP(_ x: Float, _ y: Float) -> (
+    value: Float, pullback: (Float) -> (Float, Float)
+  ) {
+    return (add(x, y), { v in (v, v) })
+  }
+}
+
+@differentiable
+func foo(_ x: Float) -> Float {
+  let y = Float.add(x, x)
+  return y
+}
+
+// Failed to reconstruct type for $s4main42_AD__$s4main3fooyS2fF_bb0__PB__src_0_wrt_0VmD
+// Original type:
+// (metatype_type
+//   (struct_type decl=main.(file)._AD__$s4main3fooyS2fF_bb0__PB__src_0_wrt_0))
+// Assertion failed: (isa<X>(Val) && "cast<Ty>() argument of incompatible type!"), function cast, file /Users/danielzheng/swift-merge/llvm-project/llvm/include/llvm/Support/Casting.h, line 264.