[Bug Fix] Fix CastDataTypeFunctor for low-precision floats to complex types (PaddlePaddle#75934)

这些改动新增了 `CastDataTypeFunctor` 针对 `float8_e5m2`、`float8_e4m3fn`、`float16` 和 `bfloat16` 到 `complex<float>`/`complex<double>` 的专门实现。原本的泛型实现只做 `static_cast<OutType>(in)`，而 `phi::dtype::complex<>` 没有接受这些低精度实数类型的隐式转换，实际调用 `TransDataType` 做类型转换时会缺失对应路径或触发编译/运行错误。现在在转换时先显式转成 `float`/`double` 再构造复数，就能让这些低精度实数张量安全地转换成复数张量，确保在需要复数输出（例如调用复数 kernel）时类型升级可以顺利执行。

Author: youge325

paddle/fluid/framework/data_type_transform.cc

@@ -32,6 +32,78 @@ struct CastDataTypeFunctor {
   }
 };
 
+template <>
+struct CastDataTypeFunctor<::phi::dtype::float8_e5m2,
+                           ::phi::dtype::complex<float>> {
+  HOSTDEVICE ::phi::dtype::complex<float> operator()(
+      ::phi::dtype::float8_e5m2 in) const {
+    return ::phi::dtype::complex<float>(static_cast<float>(in));
+  }
+};
+
+template <>
+struct CastDataTypeFunctor<::phi::dtype::float8_e5m2,
+                           ::phi::dtype::complex<double>> {
+  HOSTDEVICE ::phi::dtype::complex<double> operator()(
+      ::phi::dtype::float8_e5m2 in) const {
+    return ::phi::dtype::complex<double>(static_cast<double>(in));
+  }
+};
+
+template <>
+struct CastDataTypeFunctor<::phi::dtype::float8_e4m3fn,
+                           ::phi::dtype::complex<float>> {
+  HOSTDEVICE ::phi::dtype::complex<float> operator()(
+      ::phi::dtype::float8_e4m3fn in) const {
+    return ::phi::dtype::complex<float>(static_cast<float>(in));
+  }
+};
+
+template <>
+struct CastDataTypeFunctor<::phi::dtype::float8_e4m3fn,
+                           ::phi::dtype::complex<double>> {
+  HOSTDEVICE ::phi::dtype::complex<double> operator()(
+      ::phi::dtype::float8_e4m3fn in) const {
+    return ::phi::dtype::complex<double>(static_cast<double>(in));
+  }
+};
+
+template <>
+struct CastDataTypeFunctor<::phi::dtype::float16,
+                           ::phi::dtype::complex<float>> {
+  HOSTDEVICE ::phi::dtype::complex<float> operator()(
+      ::phi::dtype::float16 in) const {
+    return ::phi::dtype::complex<float>(static_cast<float>(in));
+  }
+};
+
+template <>
+struct CastDataTypeFunctor<::phi::dtype::float16,
+                           ::phi::dtype::complex<double>> {
+  HOSTDEVICE ::phi::dtype::complex<double> operator()(
+      ::phi::dtype::float16 in) const {
+    return ::phi::dtype::complex<double>(static_cast<double>(in));
+  }
+};
+
+template <>
+struct CastDataTypeFunctor<::phi::dtype::bfloat16,
+                           ::phi::dtype::complex<float>> {
+  HOSTDEVICE ::phi::dtype::complex<float> operator()(
+      ::phi::dtype::bfloat16 in) const {
+    return ::phi::dtype::complex<float>(static_cast<float>(in));
+  }
+};
+
+template <>
+struct CastDataTypeFunctor<::phi::dtype::bfloat16,
+                           ::phi::dtype::complex<double>> {
+  HOSTDEVICE ::phi::dtype::complex<double> operator()(
+      ::phi::dtype::bfloat16 in) const {
+    return ::phi::dtype::complex<double>(static_cast<double>(in));
+  }
+};
+
 #if defined(PADDLE_WITH_XPU)
 
 template <typename InType, typename OutType>