[Framework] Support custom allocator

[shentanyue]

PR devices

Framework

PR types

New features

PR changes

API

Description

新增外部 API 用于设置 Allocator，其中 PaddleLite 框架传入默认 alignment 值为64，用于Byte alignment，用户可自定义。

使用方法：

void* allocfunc(size_t size, size_t alignment) {
  size_t offset = sizeof(void*) + alignment - 1;
  char* p = static_cast<char*>(std::malloc(offset + size));
  // Byte alignment
  void* r = reinterpret_cast<void*>(reinterpret_cast<size_t>(p + offset) &
                                    (~(alignment - 1)));
  static_cast<void**>(r)[-1] = p;
  return r;
}

void freefunc(void* ptr) {
  if (ptr) {
    std::free(static_cast<void**>(ptr)[-1]);
  }
}

paddle::lite_api::MobileConfig mobile_config;
paddle::lite_api::CustomAllocator custom_allocator;
custom_allocator.alloc = allocfunc;
custom_allocator.free = freefunc;
mobile_config.set_custom_allocator(TARGET(kHost), custom_allocator);

[paddle-bot]

Thanks for your contribution!

[hong19860320]

是否有必要进行初始化？

[shentanyue]

不需要初始化，用的Lazy Singleton，实际使用的时候才初始化。

[shentanyue]

CustomAllocator本身也已经初始化

struct LITE_API CustomAllocator {
  void* (*alloc)(size_t size, size_t alignment) = nullptr;
  void (*free)(void* ptr) = nullptr;
};

[hong19860320]

LGTM