gcc -O3 标志导致 -Winline “调用不太可能并且代码大小会增长”警告

Question

我使用的是 Ubuntu 14.04 和 gcc 4.9.3。我遇到了一个奇怪的问题，当我启用 O3 优化时，会弹出一些“不太可能调用并且代码大小会增长 [-Werror=inline]”错误。我的代码中没有 inline 关键字。为什么 gcc 内联会将代码优化到触发它自己的警告的程度？

显然禁用 -Winline 会编译，但有没有更好的方法来解决这个问题？

我正在使用的库是点云库，为了完整起见，代码如下所示。

我的 CMakeLists

cmake_minimum_required(VERSION 2.8)
project(Test)

set(PROJECT_SRCS
${PROJECT_SOURCE_DIR}/Test.cpp
)

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -W -Werror -Winline")

# causes error
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -O3")

find_package( PCL 1.7 REQUIRED )

include_directories(${PCL_INCLUDE_DIRS})

add_executable(${PROJECT_NAME} ${PROJECT_SRCS})

target_link_libraries(${PROJECT_NAME} ${PCL_LIBRARIES})

Test.cpp

#include <string>
#include <vector>

#include "pcl/common/common_headers.h"
#include "pcl/io/obj_io.h"
#include "pcl/io/ply_io.h"
#include "pcl/io/vtk_lib_io.h"
#include "pcl/visualization/pcl_visualizer.h"

int main(){
  pcl::TextureMesh mesh;
  pcl::PointCloud<pcl::PointNormal> xyz;

  pcl::PointNormal point1;
  pcl::PointNormal point2;
  pcl::PointNormal point3;
  point1.x = 0;
  point2.x = 1;
  point3.x = 0;
  point1.y = 0;
  point2.y = 0;
  point3.y = 1;
  point1.z = 2;
  point2.z = 2;
  point3.z = 2;
  xyz.push_back(point1);
  xyz.push_back(point2);
  xyz.push_back(point3);
  pcl::toPCLPointCloud2(xyz, mesh.cloud);

  std::vector<pcl::Vertices> mesh_poly;
  std::vector<Eigen::Vector2f, Eigen::aligned_allocator<Eigen::Vector2f> > mesh_tex;
  pcl::TexMaterial mesh_material;

  pcl::Vertices v;
  v.vertices.push_back(0);
  v.vertices.push_back(1);
  v.vertices.push_back(2);
  mesh_poly.push_back(v);

  Eigen::Vector2f tex1;
  Eigen::Vector2f tex2;
  Eigen::Vector2f tex3;
  tex1(0) = -1.0;
  tex1(1) = 0.0;
  tex2(0) = -1.0;
  tex2(1) = 1.0;
  tex3(0) = 2.0;
  tex3(1) = 0.0;

  mesh_tex.push_back(tex1);
  mesh_tex.push_back(tex2);
  mesh_tex.push_back(tex3);

  mesh_material.tex_file = "lena.png";
  mesh_material.tex_name = "material_0";

  mesh.tex_polygons.push_back(mesh_poly);
  mesh.tex_coordinates.push_back(mesh_tex);
  mesh.tex_materials.push_back(mesh_material);

  pcl::io::saveOBJFile("out.obj", mesh);

  return 0;
}

编辑：更新错误信息

In file included from /usr/local/include/pcl-1.8/pcl/io/obj_io.h:40:0,
                 from /home/david/test/Test.cpp:5:
/usr/local/include/pcl-1.8/pcl/TextureMesh.h: In function ‘int main()’:
/usr/local/include/pcl-1.8/pcl/TextureMesh.h:50:10: error: inlining failed in call to ‘pcl::TexMaterial::~TexMaterial()’: call is unlikely and code size would grow [-Werror=inline]
   struct TexMaterial
          ^
/home/david/test/Test.cpp:37:20: error: called from here [-Werror=inline]
   pcl::TexMaterial mesh_material;
                ^
In file included from /usr/local/include/pcl-1.8/pcl/io/obj_io.h:40:0,
                 from /home/david/test/Test.cpp:5:
/usr/local/include/pcl-1.8/pcl/TextureMesh.h:91:10: error: inlining     failed in call to ‘pcl::TextureMesh::~TextureMesh()’: call is unlikely and code size would grow [-Werror=inline]
   struct TextureMesh
          ^
/home/david/test/Test.cpp:14:20: error: called from here [-Werror=inline]
   pcl::TextureMesh mesh;
                    ^
In file included from /usr/local/include/pcl-1.8/pcl/io/obj_io.h:40:0,
             from /home/david/test/Test.cpp:5:
/usr/local/include/pcl-1.8/pcl/TextureMesh.h:50:10: error: inlining failed in call to ‘pcl::TexMaterial::~TexMaterial()’: call is unlikely and code size would grow [-Werror=inline]
   struct TexMaterial
          ^
/home/david/test/Test.cpp:37:20: error: called from here [-Werror=inline]
   pcl::TexMaterial mesh_material;
                    ^
In file included from /usr/local/include/pcl-1.8/pcl/io/obj_io.h:40:0,
             from /home/david/test/Test.cpp:5:
/usr/local/include/pcl-1.8/pcl/TextureMesh.h:91:10: error: inlining failed in call to ‘pcl::TextureMesh::~TextureMesh()’: call is unlikely and code size would grow [-Werror=inline]
   struct TextureMesh
          ^
/home/david/test/Test.cpp:14:20: error: called from here [-Werror=inline]
   pcl::TextureMesh mesh;
                ^
cc1plus: all warnings being treated as errors
make[2]: *** [CMakeFiles/Test.dir/Test.cpp.o] Error 1
make[1]: *** [CMakeFiles/Test.dir/all] Error 2
make: *** [all] Error 2

Answer 1

使用的类/结构可能有内联成员，即使代码中没有明确说明。

例如，pcl::TextureMesh 结构将具有隐式析构函数，根据 C++ 标准：

隐式声明的析构函数是其类的内联公共成员。

Answer 2

请参阅this 并考虑this answer。

GCC 会开启自动内联，即使-O3 优化级别上没有inline 关键字。所以，正如NathanOliver 所说，PCL 库中可能有不太可能的可调用代码（不幸的是，我不熟悉它）。 我会将优化级别降低到-O2 或使用fno-inline-functions 禁用激进的内联。